23 files changed, 4615 insertions, 0 deletions

diff --git a/crates/ide_diagnostics/Cargo.toml b/crates/ide_diagnostics/Cargo.toml
new file mode 100644
index 000000000..fa2adf212
--- /dev/null
+++ b/crates/ide_diagnostics/Cargo.toml
@@ -0,0 +1,29 @@
+[package]
+name = "ide_diagnostics"
+version = "0.0.0"
+description = "TBD"
+license = "MIT OR Apache-2.0"
+authors = ["rust-analyzer developers"]
+edition = "2018"
+
+[lib]
+doctest = false
+
+[dependencies]
+cov-mark = "2.0.0-pre.1"
+itertools = "0.10.0"
+rustc-hash = "1.1.0"
+either = "1.5.3"
+
+profile = { path = "../profile", version = "0.0.0" }
+stdx = { path = "../stdx", version = "0.0.0" }
+syntax = { path = "../syntax", version = "0.0.0" }
+text_edit = { path = "../text_edit", version = "0.0.0" }
+cfg = { path = "../cfg", version = "0.0.0" }
+hir = { path = "../hir", version = "0.0.0" }
+ide_db = { path = "../ide_db", version = "0.0.0" }
+
+[dev-dependencies]
+expect-test = "1.1"
+
+test_utils = { path = "../test_utils" }
diff --git a/crates/ide_diagnostics/src/handlers/break_outside_of_loop.rs b/crates/ide_diagnostics/src/handlers/break_outside_of_loop.rs
new file mode 100644
index 000000000..d12594a4c
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/break_outside_of_loop.rs
@@ -0,0 +1,30 @@
+use crate::{Diagnostic, DiagnosticsContext};
+
+// Diagnostic: break-outside-of-loop
+//
+// This diagnostic is triggered if the `break` keyword is used outside of a loop.
+pub(crate) fn break_outside_of_loop(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::BreakOutsideOfLoop,
+) -> Diagnostic {
+    Diagnostic::new(
+        "break-outside-of-loop",
+        "break outside of loop",
+        ctx.sema.diagnostics_display_range(d.expr.clone().map(|it| it.into())).range,
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    #[test]
+    fn break_outside_of_loop() {
+        check_diagnostics(
+            r#"
+fn foo() { break; }
+         //^^^^^ error: break outside of loop
+"#,
+        );
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/field_shorthand.rs b/crates/ide_diagnostics/src/handlers/field_shorthand.rs
new file mode 100644
index 000000000..33152e284
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/field_shorthand.rs
@@ -0,0 +1,203 @@
+//! Suggests shortening `Foo { field: field }` to `Foo { field }` in both
+//! expressions and patterns.
+
+use ide_db::{base_db::FileId, source_change::SourceChange};
+use syntax::{ast, match_ast, AstNode, SyntaxNode};
+use text_edit::TextEdit;
+
+use crate::{fix, Diagnostic, Severity};
+
+pub(crate) fn field_shorthand(acc: &mut Vec<Diagnostic>, file_id: FileId, node: &SyntaxNode) {
+    match_ast! {
+        match node {
+            ast::RecordExpr(it) => check_expr_field_shorthand(acc, file_id, it),
+            ast::RecordPat(it) => check_pat_field_shorthand(acc, file_id, it),
+            _ => ()
+        }
+    };
+}
+
+fn check_expr_field_shorthand(
+    acc: &mut Vec<Diagnostic>,
+    file_id: FileId,
+    record_expr: ast::RecordExpr,
+) {
+    let record_field_list = match record_expr.record_expr_field_list() {
+        Some(it) => it,
+        None => return,
+    };
+    for record_field in record_field_list.fields() {
+        let (name_ref, expr) = match record_field.name_ref().zip(record_field.expr()) {
+            Some(it) => it,
+            None => continue,
+        };
+
+        let field_name = name_ref.syntax().text().to_string();
+        let field_expr = expr.syntax().text().to_string();
+        let field_name_is_tup_index = name_ref.as_tuple_field().is_some();
+        if field_name != field_expr || field_name_is_tup_index {
+            continue;
+        }
+
+        let mut edit_builder = TextEdit::builder();
+        edit_builder.delete(record_field.syntax().text_range());
+        edit_builder.insert(record_field.syntax().text_range().start(), field_name);
+        let edit = edit_builder.finish();
+
+        let field_range = record_field.syntax().text_range();
+        acc.push(
+            Diagnostic::new("use-field-shorthand", "Shorthand struct initialization", field_range)
+                .severity(Severity::WeakWarning)
+                .with_fixes(Some(vec![fix(
+                    "use_expr_field_shorthand",
+                    "Use struct shorthand initialization",
+                    SourceChange::from_text_edit(file_id, edit),
+                    field_range,
+                )])),
+        );
+    }
+}
+
+fn check_pat_field_shorthand(
+    acc: &mut Vec<Diagnostic>,
+    file_id: FileId,
+    record_pat: ast::RecordPat,
+) {
+    let record_pat_field_list = match record_pat.record_pat_field_list() {
+        Some(it) => it,
+        None => return,
+    };
+    for record_pat_field in record_pat_field_list.fields() {
+        let (name_ref, pat) = match record_pat_field.name_ref().zip(record_pat_field.pat()) {
+            Some(it) => it,
+            None => continue,
+        };
+
+        let field_name = name_ref.syntax().text().to_string();
+        let field_pat = pat.syntax().text().to_string();
+        let field_name_is_tup_index = name_ref.as_tuple_field().is_some();
+        if field_name != field_pat || field_name_is_tup_index {
+            continue;
+        }
+
+        let mut edit_builder = TextEdit::builder();
+        edit_builder.delete(record_pat_field.syntax().text_range());
+        edit_builder.insert(record_pat_field.syntax().text_range().start(), field_name);
+        let edit = edit_builder.finish();
+
+        let field_range = record_pat_field.syntax().text_range();
+        acc.push(
+            Diagnostic::new("use-field-shorthand", "Shorthand struct pattern", field_range)
+                .severity(Severity::WeakWarning)
+                .with_fixes(Some(vec![fix(
+                    "use_pat_field_shorthand",
+                    "Use struct field shorthand",
+                    SourceChange::from_text_edit(file_id, edit),
+                    field_range,
+                )])),
+        );
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_diagnostics, check_fix};
+
+    #[test]
+    fn test_check_expr_field_shorthand() {
+        check_diagnostics(
+            r#"
+struct A { a: &'static str }
+fn main() { A { a: "hello" } }
+"#,
+        );
+        check_diagnostics(
+            r#"
+struct A(usize);
+fn main() { A { 0: 0 } }
+"#,
+        );
+
+        check_fix(
+            r#"
+struct A { a: &'static str }
+fn main() {
+    let a = "haha";
+    A { a$0: a }
+}
+"#,
+            r#"
+struct A { a: &'static str }
+fn main() {
+    let a = "haha";
+    A { a }
+}
+"#,
+        );
+
+        check_fix(
+            r#"
+struct A { a: &'static str, b: &'static str }
+fn main() {
+    let a = "haha";
+    let b = "bb";
+    A { a$0: a, b }
+}
+"#,
+            r#"
+struct A { a: &'static str, b: &'static str }
+fn main() {
+    let a = "haha";
+    let b = "bb";
+    A { a, b }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_check_pat_field_shorthand() {
+        check_diagnostics(
+            r#"
+struct A { a: &'static str }
+fn f(a: A) { let A { a: hello } = a; }
+"#,
+        );
+        check_diagnostics(
+            r#"
+struct A(usize);
+fn f(a: A) { let A { 0: 0 } = a; }
+"#,
+        );
+
+        check_fix(
+            r#"
+struct A { a: &'static str }
+fn f(a: A) {
+    let A { a$0: a } = a;
+}
+"#,
+            r#"
+struct A { a: &'static str }
+fn f(a: A) {
+    let A { a } = a;
+}
+"#,
+        );
+
+        check_fix(
+            r#"
+struct A { a: &'static str, b: &'static str }
+fn f(a: A) {
+    let A { a$0: a, b } = a;
+}
+"#,
+            r#"
+struct A { a: &'static str, b: &'static str }
+fn f(a: A) {
+    let A { a, b } = a;
+}
+"#,
+        );
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/inactive_code.rs b/crates/ide_diagnostics/src/handlers/inactive_code.rs
new file mode 100644
index 000000000..dfd0e3351
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/inactive_code.rs
@@ -0,0 +1,116 @@
+use cfg::DnfExpr;
+use stdx::format_to;
+
+use crate::{Diagnostic, DiagnosticsContext, Severity};
+
+// Diagnostic: inactive-code
+//
+// This diagnostic is shown for code with inactive `#[cfg]` attributes.
+pub(crate) fn inactive_code(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::InactiveCode,
+) -> Option<Diagnostic> {
+    // If there's inactive code somewhere in a macro, don't propagate to the call-site.
+    if d.node.file_id.expansion_info(ctx.sema.db).is_some() {
+        return None;
+    }
+
+    let inactive = DnfExpr::new(d.cfg.clone()).why_inactive(&d.opts);
+    let mut message = "code is inactive due to #[cfg] directives".to_string();
+
+    if let Some(inactive) = inactive {
+        format_to!(message, ": {}", inactive);
+    }
+
+    let res = Diagnostic::new(
+        "inactive-code",
+        message,
+        ctx.sema.diagnostics_display_range(d.node.clone()).range,
+    )
+    .severity(Severity::WeakWarning)
+    .with_unused(true);
+    Some(res)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{tests::check_diagnostics_with_config, DiagnosticsConfig};
+
+    pub(crate) fn check(ra_fixture: &str) {
+        let config = DiagnosticsConfig::default();
+        check_diagnostics_with_config(config, ra_fixture)
+    }
+
+    #[test]
+    fn cfg_diagnostics() {
+        check(
+            r#"
+fn f() {
+    // The three g̶e̶n̶d̶e̶r̶s̶ statements:
+
+    #[cfg(a)] fn f() {}  // Item statement
+  //^^^^^^^^^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: a is disabled
+    #[cfg(a)] {}         // Expression statement
+  //^^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: a is disabled
+    #[cfg(a)] let x = 0; // let statement
+  //^^^^^^^^^^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: a is disabled
+
+    abc(#[cfg(a)] 0);
+      //^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: a is disabled
+    let x = Struct {
+        #[cfg(a)] f: 0,
+      //^^^^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: a is disabled
+    };
+    match () {
+        () => (),
+        #[cfg(a)] () => (),
+      //^^^^^^^^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: a is disabled
+    }
+
+    #[cfg(a)] 0          // Trailing expression of block
+  //^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: a is disabled
+}
+        "#,
+        );
+    }
+
+    #[test]
+    fn inactive_item() {
+        // Additional tests in `cfg` crate. This only tests disabled cfgs.
+
+        check(
+            r#"
+    #[cfg(no)] pub fn f() {}
+  //^^^^^^^^^^^^^^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: no is disabled
+
+    #[cfg(no)] #[cfg(no2)] mod m;
+  //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: no and no2 are disabled
+
+    #[cfg(all(not(a), b))] enum E {}
+  //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: b is disabled
+
+    #[cfg(feature = "std")] use std;
+  //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: feature = "std" is disabled
+"#,
+        );
+    }
+
+    /// Tests that `cfg` attributes behind `cfg_attr` is handled properly.
+    #[test]
+    fn inactive_via_cfg_attr() {
+        cov_mark::check!(cfg_attr_active);
+        check(
+            r#"
+    #[cfg_attr(not(never), cfg(no))] fn f() {}
+  //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: no is disabled
+
+    #[cfg_attr(not(never), cfg(not(no)))] fn f() {}
+
+    #[cfg_attr(never, cfg(no))] fn g() {}
+
+    #[cfg_attr(not(never), inline, cfg(no))] fn h() {}
+  //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: no is disabled
+"#,
+        );
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/incorrect_case.rs b/crates/ide_diagnostics/src/handlers/incorrect_case.rs
new file mode 100644
index 000000000..68f25f284
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/incorrect_case.rs
@@ -0,0 +1,459 @@
+use hir::{db::AstDatabase, InFile};
+use ide_db::{assists::Assist, defs::NameClass};
+use syntax::AstNode;
+
+use crate::{
+    // references::rename::rename_with_semantics,
+    unresolved_fix,
+    Diagnostic,
+    DiagnosticsContext,
+    Severity,
+};
+
+// Diagnostic: incorrect-ident-case
+//
+// This diagnostic is triggered if an item name doesn't follow https://doc.rust-lang.org/1.0.0/style/style/naming/README.html[Rust naming convention].
+pub(crate) fn incorrect_case(ctx: &DiagnosticsContext<'_>, d: &hir::IncorrectCase) -> Diagnostic {
+    Diagnostic::new(
+        "incorrect-ident-case",
+        format!(
+            "{} `{}` should have {} name, e.g. `{}`",
+            d.ident_type, d.ident_text, d.expected_case, d.suggested_text
+        ),
+        ctx.sema.diagnostics_display_range(InFile::new(d.file, d.ident.clone().into())).range,
+    )
+    .severity(Severity::WeakWarning)
+    .with_fixes(fixes(ctx, d))
+}
+
+fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::IncorrectCase) -> Option<Vec<Assist>> {
+    let root = ctx.sema.db.parse_or_expand(d.file)?;
+    let name_node = d.ident.to_node(&root);
+    let def = NameClass::classify(&ctx.sema, &name_node)?.defined(ctx.sema.db)?;
+
+    let name_node = InFile::new(d.file, name_node.syntax());
+    let frange = name_node.original_file_range(ctx.sema.db);
+
+    let label = format!("Rename to {}", d.suggested_text);
+    let mut res = unresolved_fix("change_case", &label, frange.range);
+    if ctx.resolve.should_resolve(&res.id) {
+        let source_change = def.rename(&ctx.sema, &d.suggested_text);
+        res.source_change = Some(source_change.ok().unwrap_or_default());
+    }
+
+    Some(vec![res])
+}
+
+#[cfg(test)]
+mod change_case {
+    use crate::tests::{check_diagnostics, check_fix};
+
+    #[test]
+    fn test_rename_incorrect_case() {
+        check_fix(
+            r#"
+pub struct test_struct$0 { one: i32 }
+
+pub fn some_fn(val: test_struct) -> test_struct {
+    test_struct { one: val.one + 1 }
+}
+"#,
+            r#"
+pub struct TestStruct { one: i32 }
+
+pub fn some_fn(val: TestStruct) -> TestStruct {
+    TestStruct { one: val.one + 1 }
+}
+"#,
+        );
+
+        check_fix(
+            r#"
+pub fn some_fn(NonSnakeCase$0: u8) -> u8 {
+    NonSnakeCase
+}
+"#,
+            r#"
+pub fn some_fn(non_snake_case: u8) -> u8 {
+    non_snake_case
+}
+"#,
+        );
+
+        check_fix(
+            r#"
+pub fn SomeFn$0(val: u8) -> u8 {
+    if val != 0 { SomeFn(val - 1) } else { val }
+}
+"#,
+            r#"
+pub fn some_fn(val: u8) -> u8 {
+    if val != 0 { some_fn(val - 1) } else { val }
+}
+"#,
+        );
+
+        check_fix(
+            r#"
+fn some_fn() {
+    let whatAWeird_Formatting$0 = 10;
+    another_func(whatAWeird_Formatting);
+}
+"#,
+            r#"
+fn some_fn() {
+    let what_a_weird_formatting = 10;
+    another_func(what_a_weird_formatting);
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_uppercase_const_no_diagnostics() {
+        check_diagnostics(
+            r#"
+fn foo() {
+    const ANOTHER_ITEM: &str = "some_item";
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_rename_incorrect_case_struct_method() {
+        check_fix(
+            r#"
+pub struct TestStruct;
+
+impl TestStruct {
+    pub fn SomeFn$0() -> TestStruct {
+        TestStruct
+    }
+}
+"#,
+            r#"
+pub struct TestStruct;
+
+impl TestStruct {
+    pub fn some_fn() -> TestStruct {
+        TestStruct
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_single_incorrect_case_diagnostic_in_function_name_issue_6970() {
+        check_diagnostics(
+            r#"
+fn FOO() {}
+// ^^^ 💡 weak: Function `FOO` should have snake_case name, e.g. `foo`
+"#,
+        );
+        check_fix(r#"fn FOO$0() {}"#, r#"fn foo() {}"#);
+    }
+
+    #[test]
+    fn incorrect_function_name() {
+        check_diagnostics(
+            r#"
+fn NonSnakeCaseName() {}
+// ^^^^^^^^^^^^^^^^ 💡 weak: Function `NonSnakeCaseName` should have snake_case name, e.g. `non_snake_case_name`
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_function_params() {
+        check_diagnostics(
+            r#"
+fn foo(SomeParam: u8) {}
+    // ^^^^^^^^^ 💡 weak: Parameter `SomeParam` should have snake_case name, e.g. `some_param`
+
+fn foo2(ok_param: &str, CAPS_PARAM: u8) {}
+                     // ^^^^^^^^^^ 💡 weak: Parameter `CAPS_PARAM` should have snake_case name, e.g. `caps_param`
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_variable_names() {
+        check_diagnostics(
+            r#"
+fn foo() {
+    let SOME_VALUE = 10;
+     // ^^^^^^^^^^ 💡 weak: Variable `SOME_VALUE` should have snake_case name, e.g. `some_value`
+    let AnotherValue = 20;
+     // ^^^^^^^^^^^^ 💡 weak: Variable `AnotherValue` should have snake_case name, e.g. `another_value`
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_struct_names() {
+        check_diagnostics(
+            r#"
+struct non_camel_case_name {}
+    // ^^^^^^^^^^^^^^^^^^^ 💡 weak: Structure `non_camel_case_name` should have CamelCase name, e.g. `NonCamelCaseName`
+
+struct SCREAMING_CASE {}
+    // ^^^^^^^^^^^^^^ 💡 weak: Structure `SCREAMING_CASE` should have CamelCase name, e.g. `ScreamingCase`
+"#,
+        );
+    }
+
+    #[test]
+    fn no_diagnostic_for_camel_cased_acronyms_in_struct_name() {
+        check_diagnostics(
+            r#"
+struct AABB {}
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_struct_field() {
+        check_diagnostics(
+            r#"
+struct SomeStruct { SomeField: u8 }
+                 // ^^^^^^^^^ 💡 weak: Field `SomeField` should have snake_case name, e.g. `some_field`
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_enum_names() {
+        check_diagnostics(
+            r#"
+enum some_enum { Val(u8) }
+  // ^^^^^^^^^ 💡 weak: Enum `some_enum` should have CamelCase name, e.g. `SomeEnum`
+
+enum SOME_ENUM {}
+  // ^^^^^^^^^ 💡 weak: Enum `SOME_ENUM` should have CamelCase name, e.g. `SomeEnum`
+"#,
+        );
+    }
+
+    #[test]
+    fn no_diagnostic_for_camel_cased_acronyms_in_enum_name() {
+        check_diagnostics(
+            r#"
+enum AABB {}
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_enum_variant_name() {
+        check_diagnostics(
+            r#"
+enum SomeEnum { SOME_VARIANT(u8) }
+             // ^^^^^^^^^^^^ 💡 weak: Variant `SOME_VARIANT` should have CamelCase name, e.g. `SomeVariant`
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_const_name() {
+        check_diagnostics(
+            r#"
+const some_weird_const: u8 = 10;
+   // ^^^^^^^^^^^^^^^^ 💡 weak: Constant `some_weird_const` should have UPPER_SNAKE_CASE name, e.g. `SOME_WEIRD_CONST`
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_static_name() {
+        check_diagnostics(
+            r#"
+static some_weird_const: u8 = 10;
+    // ^^^^^^^^^^^^^^^^ 💡 weak: Static variable `some_weird_const` should have UPPER_SNAKE_CASE name, e.g. `SOME_WEIRD_CONST`
+"#,
+        );
+    }
+
+    #[test]
+    fn fn_inside_impl_struct() {
+        check_diagnostics(
+            r#"
+struct someStruct;
+    // ^^^^^^^^^^ 💡 weak: Structure `someStruct` should have CamelCase name, e.g. `SomeStruct`
+
+impl someStruct {
+    fn SomeFunc(&self) {
+    // ^^^^^^^^ 💡 weak: Function `SomeFunc` should have snake_case name, e.g. `some_func`
+        let WHY_VAR_IS_CAPS = 10;
+         // ^^^^^^^^^^^^^^^ 💡 weak: Variable `WHY_VAR_IS_CAPS` should have snake_case name, e.g. `why_var_is_caps`
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn no_diagnostic_for_enum_varinats() {
+        check_diagnostics(
+            r#"
+enum Option { Some, None }
+
+fn main() {
+    match Option::None {
+        None => (),
+        Some => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn non_let_bind() {
+        check_diagnostics(
+            r#"
+enum Option { Some, None }
+
+fn main() {
+    match Option::None {
+        SOME_VAR @ None => (),
+     // ^^^^^^^^ 💡 weak: Variable `SOME_VAR` should have snake_case name, e.g. `some_var`
+        Some => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn allow_attributes_crate_attr() {
+        check_diagnostics(
+            r#"
+#![allow(non_snake_case)]
+
+mod F {
+    fn CheckItWorksWithCrateAttr(BAD_NAME_HI: u8) {}
+}
+    "#,
+        );
+    }
+
+    #[test]
+    fn complex_ignore() {
+        // FIXME: this should trigger errors for the second case.
+        check_diagnostics(
+            r#"
+trait T { fn a(); }
+struct U {}
+impl T for U {
+    fn a() {
+        #[allow(non_snake_case)]
+        trait __BitFlagsOk {
+            const HiImAlsoBad: u8 = 2;
+            fn Dirty(&self) -> bool { false }
+        }
+
+        trait __BitFlagsBad {
+            const HiImAlsoBad: u8 = 2;
+            fn Dirty(&self) -> bool { false }
+        }
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn infinite_loop_inner_items() {
+        check_diagnostics(
+            r#"
+fn qualify() {
+    mod foo {
+        use super::*;
+    }
+}
+            "#,
+        )
+    }
+
+    #[test] // Issue #8809.
+    fn parenthesized_parameter() {
+        check_diagnostics(r#"fn f((O): _) {}"#)
+    }
+
+    #[test]
+    fn ignores_extern_items() {
+        cov_mark::check!(extern_func_incorrect_case_ignored);
+        cov_mark::check!(extern_static_incorrect_case_ignored);
+        check_diagnostics(
+            r#"
+extern {
+    fn NonSnakeCaseName(SOME_VAR: u8) -> u8;
+    pub static SomeStatic: u8 = 10;
+}
+            "#,
+        );
+    }
+
+    #[test]
+    fn bug_traits_arent_checked() {
+        // FIXME: Traits and functions in traits aren't currently checked by
+        // r-a, even though rustc will complain about them.
+        check_diagnostics(
+            r#"
+trait BAD_TRAIT {
+    fn BAD_FUNCTION();
+    fn BadFunction();
+}
+    "#,
+        );
+    }
+
+    #[test]
+    fn allow_attributes() {
+        check_diagnostics(
+            r#"
+#[allow(non_snake_case)]
+fn NonSnakeCaseName(SOME_VAR: u8) -> u8{
+    // cov_flags generated output from elsewhere in this file
+    extern "C" {
+        #[no_mangle]
+        static lower_case: u8;
+    }
+
+    let OtherVar = SOME_VAR + 1;
+    OtherVar
+}
+
+#[allow(nonstandard_style)]
+mod CheckNonstandardStyle {
+    fn HiImABadFnName() {}
+}
+
+#[allow(bad_style)]
+mod CheckBadStyle {
+    fn HiImABadFnName() {}
+}
+
+mod F {
+    #![allow(non_snake_case)]
+    fn CheckItWorksWithModAttr(BAD_NAME_HI: u8) {}
+}
+
+#[allow(non_snake_case, non_camel_case_types)]
+pub struct some_type {
+    SOME_FIELD: u8,
+    SomeField: u16,
+}
+
+#[allow(non_upper_case_globals)]
+pub const some_const: u8 = 10;
+
+#[allow(non_upper_case_globals)]
+pub static SomeStatic: u8 = 10;
+    "#,
+        );
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/macro_error.rs b/crates/ide_diagnostics/src/handlers/macro_error.rs
new file mode 100644
index 000000000..356f089b2
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/macro_error.rs
@@ -0,0 +1,173 @@
+use crate::{Diagnostic, DiagnosticsContext};
+
+// Diagnostic: macro-error
+//
+// This diagnostic is shown for macro expansion errors.
+pub(crate) fn macro_error(ctx: &DiagnosticsContext<'_>, d: &hir::MacroError) -> Diagnostic {
+    Diagnostic::new(
+        "macro-error",
+        d.message.clone(),
+        ctx.sema.diagnostics_display_range(d.node.clone()).range,
+    )
+    .experimental()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        tests::{check_diagnostics, check_diagnostics_with_config},
+        DiagnosticsConfig,
+    };
+
+    #[test]
+    fn builtin_macro_fails_expansion() {
+        check_diagnostics(
+            r#"
+#[rustc_builtin_macro]
+macro_rules! include { () => {} }
+
+  include!("doesntexist");
+//^^^^^^^^^^^^^^^^^^^^^^^^ error: failed to load file `doesntexist`
+            "#,
+        );
+    }
+
+    #[test]
+    fn include_macro_should_allow_empty_content() {
+        let mut config = DiagnosticsConfig::default();
+
+        // FIXME: This is a false-positive, the file is actually linked in via
+        // `include!` macro
+        config.disabled.insert("unlinked-file".to_string());
+
+        check_diagnostics_with_config(
+            config,
+            r#"
+//- /lib.rs
+#[rustc_builtin_macro]
+macro_rules! include { () => {} }
+
+include!("foo/bar.rs");
+//- /foo/bar.rs
+// empty
+"#,
+        );
+    }
+
+    #[test]
+    fn good_out_dir_diagnostic() {
+        check_diagnostics(
+            r#"
+#[rustc_builtin_macro]
+macro_rules! include { () => {} }
+#[rustc_builtin_macro]
+macro_rules! env { () => {} }
+#[rustc_builtin_macro]
+macro_rules! concat { () => {} }
+
+  include!(concat!(env!("OUT_DIR"), "/out.rs"));
+//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: `OUT_DIR` not set, enable "run build scripts" to fix
+"#,
+        );
+    }
+
+    #[test]
+    fn register_attr_and_tool() {
+        cov_mark::check!(register_attr);
+        cov_mark::check!(register_tool);
+        check_diagnostics(
+            r#"
+#![register_tool(tool)]
+#![register_attr(attr)]
+
+#[tool::path]
+#[attr]
+struct S;
+"#,
+        );
+        // NB: we don't currently emit diagnostics here
+    }
+
+    #[test]
+    fn macro_diag_builtin() {
+        check_diagnostics(
+            r#"
+#[rustc_builtin_macro]
+macro_rules! env {}
+
+#[rustc_builtin_macro]
+macro_rules! include {}
+
+#[rustc_builtin_macro]
+macro_rules! compile_error {}
+
+#[rustc_builtin_macro]
+macro_rules! format_args { () => {} }
+
+fn main() {
+    // Test a handful of built-in (eager) macros:
+
+    include!(invalid);
+  //^^^^^^^^^^^^^^^^^ error: could not convert tokens
+    include!("does not exist");
+  //^^^^^^^^^^^^^^^^^^^^^^^^^^ error: failed to load file `does not exist`
+
+    env!(invalid);
+  //^^^^^^^^^^^^^ error: could not convert tokens
+
+    env!("OUT_DIR");
+  //^^^^^^^^^^^^^^^ error: `OUT_DIR` not set, enable "run build scripts" to fix
+
+    compile_error!("compile_error works");
+  //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: compile_error works
+
+    // Lazy:
+
+    format_args!();
+  //^^^^^^^^^^^^^^ error: no rule matches input tokens
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn macro_rules_diag() {
+        check_diagnostics(
+            r#"
+macro_rules! m {
+    () => {};
+}
+fn f() {
+    m!();
+
+    m!(hi);
+  //^^^^^^ error: leftover tokens
+}
+      "#,
+        );
+    }
+    #[test]
+    fn dollar_crate_in_builtin_macro() {
+        check_diagnostics(
+            r#"
+#[macro_export]
+#[rustc_builtin_macro]
+macro_rules! format_args {}
+
+#[macro_export]
+macro_rules! arg { () => {} }
+
+#[macro_export]
+macro_rules! outer {
+    () => {
+        $crate::format_args!( "", $crate::arg!(1) )
+    };
+}
+
+fn f() {
+    outer!();
+} //^^^^^^^^ error: leftover tokens
+"#,
+        )
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/mismatched_arg_count.rs b/crates/ide_diagnostics/src/handlers/mismatched_arg_count.rs
new file mode 100644
index 000000000..a9b6d3870
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/mismatched_arg_count.rs
@@ -0,0 +1,272 @@
+use crate::{Diagnostic, DiagnosticsContext};
+
+// Diagnostic: mismatched-arg-count
+//
+// This diagnostic is triggered if a function is invoked with an incorrect amount of arguments.
+pub(crate) fn mismatched_arg_count(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::MismatchedArgCount,
+) -> Diagnostic {
+    let s = if d.expected == 1 { "" } else { "s" };
+    let message = format!("expected {} argument{}, found {}", d.expected, s, d.found);
+    Diagnostic::new(
+        "mismatched-arg-count",
+        message,
+        ctx.sema.diagnostics_display_range(d.call_expr.clone().map(|it| it.into())).range,
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    #[test]
+    fn simple_free_fn_zero() {
+        check_diagnostics(
+            r#"
+fn zero() {}
+fn f() { zero(1); }
+       //^^^^^^^ error: expected 0 arguments, found 1
+"#,
+        );
+
+        check_diagnostics(
+            r#"
+fn zero() {}
+fn f() { zero(); }
+"#,
+        );
+    }
+
+    #[test]
+    fn simple_free_fn_one() {
+        check_diagnostics(
+            r#"
+fn one(arg: u8) {}
+fn f() { one(); }
+       //^^^^^ error: expected 1 argument, found 0
+"#,
+        );
+
+        check_diagnostics(
+            r#"
+fn one(arg: u8) {}
+fn f() { one(1); }
+"#,
+        );
+    }
+
+    #[test]
+    fn method_as_fn() {
+        check_diagnostics(
+            r#"
+struct S;
+impl S { fn method(&self) {} }
+
+fn f() {
+    S::method();
+} //^^^^^^^^^^^ error: expected 1 argument, found 0
+"#,
+        );
+
+        check_diagnostics(
+            r#"
+struct S;
+impl S { fn method(&self) {} }
+
+fn f() {
+    S::method(&S);
+    S.method();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn method_with_arg() {
+        check_diagnostics(
+            r#"
+struct S;
+impl S { fn method(&self, arg: u8) {} }
+
+            fn f() {
+                S.method();
+            } //^^^^^^^^^^ error: expected 1 argument, found 0
+            "#,
+        );
+
+        check_diagnostics(
+            r#"
+struct S;
+impl S { fn method(&self, arg: u8) {} }
+
+fn f() {
+    S::method(&S, 0);
+    S.method(1);
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn method_unknown_receiver() {
+        // note: this is incorrect code, so there might be errors on this in the
+        // future, but we shouldn't emit an argument count diagnostic here
+        check_diagnostics(
+            r#"
+trait Foo { fn method(&self, arg: usize) {} }
+
+fn f() {
+    let x;
+    x.method();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn tuple_struct() {
+        check_diagnostics(
+            r#"
+struct Tup(u8, u16);
+fn f() {
+    Tup(0);
+} //^^^^^^ error: expected 2 arguments, found 1
+"#,
+        )
+    }
+
+    #[test]
+    fn enum_variant() {
+        check_diagnostics(
+            r#"
+enum En { Variant(u8, u16), }
+fn f() {
+    En::Variant(0);
+} //^^^^^^^^^^^^^^ error: expected 2 arguments, found 1
+"#,
+        )
+    }
+
+    #[test]
+    fn enum_variant_type_macro() {
+        check_diagnostics(
+            r#"
+macro_rules! Type {
+    () => { u32 };
+}
+enum Foo {
+    Bar(Type![])
+}
+impl Foo {
+    fn new() {
+        Foo::Bar(0);
+        Foo::Bar(0, 1);
+      //^^^^^^^^^^^^^^ error: expected 1 argument, found 2
+        Foo::Bar();
+      //^^^^^^^^^^ error: expected 1 argument, found 0
+    }
+}
+        "#,
+        );
+    }
+
+    #[test]
+    fn varargs() {
+        check_diagnostics(
+            r#"
+extern "C" {
+    fn fixed(fixed: u8);
+    fn varargs(fixed: u8, ...);
+    fn varargs2(...);
+}
+
+fn f() {
+    unsafe {
+        fixed(0);
+        fixed(0, 1);
+      //^^^^^^^^^^^ error: expected 1 argument, found 2
+        varargs(0);
+        varargs(0, 1);
+        varargs2();
+        varargs2(0);
+        varargs2(0, 1);
+    }
+}
+        "#,
+        )
+    }
+
+    #[test]
+    fn arg_count_lambda() {
+        check_diagnostics(
+            r#"
+fn main() {
+    let f = |()| ();
+    f();
+  //^^^ error: expected 1 argument, found 0
+    f(());
+    f((), ());
+  //^^^^^^^^^ error: expected 1 argument, found 2
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn cfgd_out_call_arguments() {
+        check_diagnostics(
+            r#"
+struct C(#[cfg(FALSE)] ());
+impl C {
+    fn new() -> Self {
+        Self(
+            #[cfg(FALSE)]
+            (),
+        )
+    }
+
+    fn method(&self) {}
+}
+
+fn main() {
+    C::new().method(#[cfg(FALSE)] 0);
+}
+            "#,
+        );
+    }
+
+    #[test]
+    fn cfgd_out_fn_params() {
+        check_diagnostics(
+            r#"
+fn foo(#[cfg(NEVER)] x: ()) {}
+
+struct S;
+
+impl S {
+    fn method(#[cfg(NEVER)] self) {}
+    fn method2(#[cfg(NEVER)] self, arg: u8) {}
+    fn method3(self, #[cfg(NEVER)] arg: u8) {}
+}
+
+extern "C" {
+    fn fixed(fixed: u8, #[cfg(NEVER)] ...);
+    fn varargs(#[cfg(not(NEVER))] ...);
+}
+
+fn main() {
+    foo();
+    S::method();
+    S::method2(0);
+    S::method3(S);
+    S.method3();
+    unsafe {
+        fixed(0);
+        varargs(1, 2, 3);
+    }
+}
+            "#,
+        )
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/missing_fields.rs b/crates/ide_diagnostics/src/handlers/missing_fields.rs
new file mode 100644
index 000000000..bc56e0342
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/missing_fields.rs
@@ -0,0 +1,355 @@
+use either::Either;
+use hir::{db::AstDatabase, InFile};
+use ide_db::{assists::Assist, source_change::SourceChange};
+use stdx::format_to;
+use syntax::{algo, ast::make, AstNode, SyntaxNodePtr};
+use text_edit::TextEdit;
+
+use crate::{fix, Diagnostic, DiagnosticsContext};
+
+// Diagnostic: missing-fields
+//
+// This diagnostic is triggered if record lacks some fields that exist in the corresponding structure.
+//
+// Example:
+//
+// ```rust
+// struct A { a: u8, b: u8 }
+//
+// let a = A { a: 10 };
+// ```
+pub(crate) fn missing_fields(ctx: &DiagnosticsContext<'_>, d: &hir::MissingFields) -> Diagnostic {
+    let mut message = String::from("missing structure fields:\n");
+    for field in &d.missed_fields {
+        format_to!(message, "- {}\n", field);
+    }
+
+    let ptr = InFile::new(
+        d.file,
+        d.field_list_parent_path
+            .clone()
+            .map(SyntaxNodePtr::from)
+            .unwrap_or_else(|| d.field_list_parent.clone().either(|it| it.into(), |it| it.into())),
+    );
+
+    Diagnostic::new("missing-fields", message, ctx.sema.diagnostics_display_range(ptr).range)
+        .with_fixes(fixes(ctx, d))
+}
+
+fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::MissingFields) -> Option<Vec<Assist>> {
+    // Note that although we could add a diagnostics to
+    // fill the missing tuple field, e.g :
+    // `struct A(usize);`
+    // `let a = A { 0: () }`
+    // but it is uncommon usage and it should not be encouraged.
+    if d.missed_fields.iter().any(|it| it.as_tuple_index().is_some()) {
+        return None;
+    }
+
+    let root = ctx.sema.db.parse_or_expand(d.file)?;
+    let field_list_parent = match &d.field_list_parent {
+        Either::Left(record_expr) => record_expr.to_node(&root),
+        // FIXE: patterns should be fixable as well.
+        Either::Right(_) => return None,
+    };
+    let old_field_list = field_list_parent.record_expr_field_list()?;
+    let new_field_list = old_field_list.clone_for_update();
+    for f in d.missed_fields.iter() {
+        let field =
+            make::record_expr_field(make::name_ref(&f.to_string()), Some(make::expr_unit()))
+                .clone_for_update();
+        new_field_list.add_field(field);
+    }
+
+    let edit = {
+        let mut builder = TextEdit::builder();
+        algo::diff(old_field_list.syntax(), new_field_list.syntax()).into_text_edit(&mut builder);
+        builder.finish()
+    };
+    Some(vec![fix(
+        "fill_missing_fields",
+        "Fill struct fields",
+        SourceChange::from_text_edit(d.file.original_file(ctx.sema.db), edit),
+        ctx.sema.original_range(field_list_parent.syntax()).range,
+    )])
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_diagnostics, check_fix};
+
+    #[test]
+    fn missing_record_pat_field_diagnostic() {
+        check_diagnostics(
+            r#"
+struct S { foo: i32, bar: () }
+fn baz(s: S) {
+    let S { foo: _ } = s;
+      //^ error: missing structure fields:
+      //| - bar
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn missing_record_pat_field_no_diagnostic_if_not_exhaustive() {
+        check_diagnostics(
+            r"
+struct S { foo: i32, bar: () }
+fn baz(s: S) -> i32 {
+    match s {
+        S { foo, .. } => foo,
+    }
+}
+",
+        )
+    }
+
+    #[test]
+    fn missing_record_pat_field_box() {
+        check_diagnostics(
+            r"
+struct S { s: Box<u32> }
+fn x(a: S) {
+    let S { box s } = a;
+}
+",
+        )
+    }
+
+    #[test]
+    fn missing_record_pat_field_ref() {
+        check_diagnostics(
+            r"
+struct S { s: u32 }
+fn x(a: S) {
+    let S { ref s } = a;
+}
+",
+        )
+    }
+
+    #[test]
+    fn range_mapping_out_of_macros() {
+        // FIXME: this is very wrong, but somewhat tricky to fix.
+        check_fix(
+            r#"
+fn some() {}
+fn items() {}
+fn here() {}
+
+macro_rules! id { ($($tt:tt)*) => { $($tt)*}; }
+
+fn main() {
+    let _x = id![Foo { a: $042 }];
+}
+
+pub struct Foo { pub a: i32, pub b: i32 }
+"#,
+            r#"
+fn some(, b: () ) {}
+fn items() {}
+fn here() {}
+
+macro_rules! id { ($($tt:tt)*) => { $($tt)*}; }
+
+fn main() {
+    let _x = id![Foo { a: 42 }];
+}
+
+pub struct Foo { pub a: i32, pub b: i32 }
+"#,
+        );
+    }
+
+    #[test]
+    fn test_fill_struct_fields_empty() {
+        check_fix(
+            r#"
+struct TestStruct { one: i32, two: i64 }
+
+fn test_fn() {
+    let s = TestStruct {$0};
+}
+"#,
+            r#"
+struct TestStruct { one: i32, two: i64 }
+
+fn test_fn() {
+    let s = TestStruct { one: (), two: () };
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_fill_struct_fields_self() {
+        check_fix(
+            r#"
+struct TestStruct { one: i32 }
+
+impl TestStruct {
+    fn test_fn() { let s = Self {$0}; }
+}
+"#,
+            r#"
+struct TestStruct { one: i32 }
+
+impl TestStruct {
+    fn test_fn() { let s = Self { one: () }; }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_fill_struct_fields_enum() {
+        check_fix(
+            r#"
+enum Expr {
+    Bin { lhs: Box<Expr>, rhs: Box<Expr> }
+}
+
+impl Expr {
+    fn new_bin(lhs: Box<Expr>, rhs: Box<Expr>) -> Expr {
+        Expr::Bin {$0 }
+    }
+}
+"#,
+            r#"
+enum Expr {
+    Bin { lhs: Box<Expr>, rhs: Box<Expr> }
+}
+
+impl Expr {
+    fn new_bin(lhs: Box<Expr>, rhs: Box<Expr>) -> Expr {
+        Expr::Bin { lhs: (), rhs: () }
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_fill_struct_fields_partial() {
+        check_fix(
+            r#"
+struct TestStruct { one: i32, two: i64 }
+
+fn test_fn() {
+    let s = TestStruct{ two: 2$0 };
+}
+"#,
+            r"
+struct TestStruct { one: i32, two: i64 }
+
+fn test_fn() {
+    let s = TestStruct{ two: 2, one: () };
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_fill_struct_fields_raw_ident() {
+        check_fix(
+            r#"
+struct TestStruct { r#type: u8 }
+
+fn test_fn() {
+    TestStruct { $0 };
+}
+"#,
+            r"
+struct TestStruct { r#type: u8 }
+
+fn test_fn() {
+    TestStruct { r#type: ()  };
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_fill_struct_fields_no_diagnostic() {
+        check_diagnostics(
+            r#"
+struct TestStruct { one: i32, two: i64 }
+
+fn test_fn() {
+    let one = 1;
+    let s = TestStruct{ one, two: 2 };
+}
+        "#,
+        );
+    }
+
+    #[test]
+    fn test_fill_struct_fields_no_diagnostic_on_spread() {
+        check_diagnostics(
+            r#"
+struct TestStruct { one: i32, two: i64 }
+
+fn test_fn() {
+    let one = 1;
+    let s = TestStruct{ ..a };
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_fill_struct_fields_blank_line() {
+        check_fix(
+            r#"
+struct S { a: (), b: () }
+
+fn f() {
+    S {
+        $0
+    };
+}
+"#,
+            r#"
+struct S { a: (), b: () }
+
+fn f() {
+    S {
+        a: (),
+        b: (),
+    };
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn import_extern_crate_clash_with_inner_item() {
+        // This is more of a resolver test, but doesn't really work with the hir_def testsuite.
+
+        check_diagnostics(
+            r#"
+//- /lib.rs crate:lib deps:jwt
+mod permissions;
+
+use permissions::jwt;
+
+fn f() {
+    fn inner() {}
+    jwt::Claims {}; // should resolve to the local one with 0 fields, and not get a diagnostic
+}
+
+//- /permissions.rs
+pub mod jwt  {
+    pub struct Claims {}
+}
+
+//- /jwt/lib.rs crate:jwt
+pub struct Claims {
+    field: u8,
+}
+        "#,
+        );
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/missing_match_arms.rs b/crates/ide_diagnostics/src/handlers/missing_match_arms.rs
new file mode 100644
index 000000000..947b0f2e2
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/missing_match_arms.rs
@@ -0,0 +1,929 @@
+use hir::InFile;
+
+use crate::{Diagnostic, DiagnosticsContext};
+
+// Diagnostic: missing-match-arm
+//
+// This diagnostic is triggered if `match` block is missing one or more match arms.
+pub(crate) fn missing_match_arms(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::MissingMatchArms,
+) -> Diagnostic {
+    Diagnostic::new(
+        "missing-match-arm",
+        "missing match arm",
+        ctx.sema.diagnostics_display_range(InFile::new(d.file, d.match_expr.clone().into())).range,
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    fn check_diagnostics_no_bails(ra_fixture: &str) {
+        cov_mark::check_count!(validate_match_bailed_out, 0);
+        crate::tests::check_diagnostics(ra_fixture)
+    }
+
+    #[test]
+    fn empty_tuple() {
+        check_diagnostics_no_bails(
+            r#"
+fn main() {
+    match () { }
+        //^^ error: missing match arm
+    match (()) { }
+        //^^^^ error: missing match arm
+
+    match () { _ => (), }
+    match () { () => (), }
+    match (()) { (()) => (), }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn tuple_of_two_empty_tuple() {
+        check_diagnostics_no_bails(
+            r#"
+fn main() {
+    match ((), ()) { }
+        //^^^^^^^^ error: missing match arm
+
+    match ((), ()) { ((), ()) => (), }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn boolean() {
+        check_diagnostics_no_bails(
+            r#"
+fn test_main() {
+    match false { }
+        //^^^^^ error: missing match arm
+    match false { true => (), }
+        //^^^^^ error: missing match arm
+    match (false, true) {}
+        //^^^^^^^^^^^^^ error: missing match arm
+    match (false, true) { (true, true) => (), }
+        //^^^^^^^^^^^^^ error: missing match arm
+    match (false, true) {
+        //^^^^^^^^^^^^^ error: missing match arm
+        (false, true) => (),
+        (false, false) => (),
+        (true, false) => (),
+    }
+    match (false, true) { (true, _x) => (), }
+        //^^^^^^^^^^^^^ error: missing match arm
+
+    match false { true => (), false => (), }
+    match (false, true) {
+        (false, _) => (),
+        (true, false) => (),
+        (_, true) => (),
+    }
+    match (false, true) {
+        (true, true) => (),
+        (true, false) => (),
+        (false, true) => (),
+        (false, false) => (),
+    }
+    match (false, true) {
+        (true, _x) => (),
+        (false, true) => (),
+        (false, false) => (),
+    }
+    match (false, true, false) {
+        (false, ..) => (),
+        (true, ..) => (),
+    }
+    match (false, true, false) {
+        (.., false) => (),
+        (.., true) => (),
+    }
+    match (false, true, false) { (..) => (), }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn tuple_of_tuple_and_bools() {
+        check_diagnostics_no_bails(
+            r#"
+fn main() {
+    match (false, ((), false)) {}
+        //^^^^^^^^^^^^^^^^^^^^ error: missing match arm
+    match (false, ((), false)) { (true, ((), true)) => (), }
+        //^^^^^^^^^^^^^^^^^^^^ error: missing match arm
+    match (false, ((), false)) { (true, _) => (), }
+        //^^^^^^^^^^^^^^^^^^^^ error: missing match arm
+
+    match (false, ((), false)) {
+        (true, ((), true)) => (),
+        (true, ((), false)) => (),
+        (false, ((), true)) => (),
+        (false, ((), false)) => (),
+    }
+    match (false, ((), false)) {
+        (true, ((), true)) => (),
+        (true, ((), false)) => (),
+        (false, _) => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn enums() {
+        check_diagnostics_no_bails(
+            r#"
+enum Either { A, B, }
+
+fn main() {
+    match Either::A { }
+        //^^^^^^^^^ error: missing match arm
+    match Either::B { Either::A => (), }
+        //^^^^^^^^^ error: missing match arm
+
+    match &Either::B {
+        //^^^^^^^^^^ error: missing match arm
+        Either::A => (),
+    }
+
+    match Either::B {
+        Either::A => (), Either::B => (),
+    }
+    match &Either::B {
+        Either::A => (), Either::B => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn enum_containing_bool() {
+        check_diagnostics_no_bails(
+            r#"
+enum Either { A(bool), B }
+
+fn main() {
+    match Either::B { }
+        //^^^^^^^^^ error: missing match arm
+    match Either::B {
+        //^^^^^^^^^ error: missing match arm
+        Either::A(true) => (), Either::B => ()
+    }
+
+    match Either::B {
+        Either::A(true) => (),
+        Either::A(false) => (),
+        Either::B => (),
+    }
+    match Either::B {
+        Either::B => (),
+        _ => (),
+    }
+    match Either::B {
+        Either::A(_) => (),
+        Either::B => (),
+    }
+
+}
+        "#,
+        );
+    }
+
+    #[test]
+    fn enum_different_sizes() {
+        check_diagnostics_no_bails(
+            r#"
+enum Either { A(bool), B(bool, bool) }
+
+fn main() {
+    match Either::A(false) {
+        //^^^^^^^^^^^^^^^^ error: missing match arm
+        Either::A(_) => (),
+        Either::B(false, _) => (),
+    }
+
+    match Either::A(false) {
+        Either::A(_) => (),
+        Either::B(true, _) => (),
+        Either::B(false, _) => (),
+    }
+    match Either::A(false) {
+        Either::A(true) | Either::A(false) => (),
+        Either::B(true, _) => (),
+        Either::B(false, _) => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn tuple_of_enum_no_diagnostic() {
+        check_diagnostics_no_bails(
+            r#"
+enum Either { A(bool), B(bool, bool) }
+enum Either2 { C, D }
+
+fn main() {
+    match (Either::A(false), Either2::C) {
+        (Either::A(true), _) | (Either::A(false), _) => (),
+        (Either::B(true, _), Either2::C) => (),
+        (Either::B(false, _), Either2::C) => (),
+        (Either::B(_, _), Either2::D) => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn or_pattern_no_diagnostic() {
+        check_diagnostics_no_bails(
+            r#"
+enum Either {A, B}
+
+fn main() {
+    match (Either::A, Either::B) {
+        (Either::A | Either::B, _) => (),
+    }
+}"#,
+        )
+    }
+
+    #[test]
+    fn mismatched_types() {
+        cov_mark::check_count!(validate_match_bailed_out, 4);
+        // Match statements with arms that don't match the
+        // expression pattern do not fire this diagnostic.
+        check_diagnostics(
+            r#"
+enum Either { A, B }
+enum Either2 { C, D }
+
+fn main() {
+    match Either::A {
+        Either2::C => (),
+        Either2::D => (),
+    }
+    match (true, false) {
+        (true, false, true) => (),
+        (true) => (),
+    }
+    match (true, false) { (true,) => {} }
+    match (0) { () => () }
+    match Unresolved::Bar { Unresolved::Baz => () }
+}
+        "#,
+        );
+    }
+
+    #[test]
+    fn mismatched_types_in_or_patterns() {
+        cov_mark::check_count!(validate_match_bailed_out, 2);
+        check_diagnostics(
+            r#"
+fn main() {
+    match false { true | () => {} }
+    match (false,) { (true | (),) => {} }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn malformed_match_arm_tuple_enum_missing_pattern() {
+        // We are testing to be sure we don't panic here when the match
+        // arm `Either::B` is missing its pattern.
+        check_diagnostics_no_bails(
+            r#"
+enum Either { A, B(u32) }
+
+fn main() {
+    match Either::A {
+        Either::A => (),
+        Either::B() => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn malformed_match_arm_extra_fields() {
+        cov_mark::check_count!(validate_match_bailed_out, 2);
+        check_diagnostics(
+            r#"
+enum A { B(isize, isize), C }
+fn main() {
+    match A::B(1, 2) {
+        A::B(_, _, _) => (),
+    }
+    match A::B(1, 2) {
+        A::C(_) => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn expr_diverges() {
+        cov_mark::check_count!(validate_match_bailed_out, 2);
+        check_diagnostics(
+            r#"
+enum Either { A, B }
+
+fn main() {
+    match loop {} {
+        Either::A => (),
+        Either::B => (),
+    }
+    match loop {} {
+        Either::A => (),
+    }
+    match loop { break Foo::A } {
+        //^^^^^^^^^^^^^^^^^^^^^ error: missing match arm
+        Either::A => (),
+    }
+    match loop { break Foo::A } {
+        Either::A => (),
+        Either::B => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn expr_partially_diverges() {
+        check_diagnostics_no_bails(
+            r#"
+enum Either<T> { A(T), B }
+
+fn foo() -> Either<!> { Either::B }
+fn main() -> u32 {
+    match foo() {
+        Either::A(val) => val,
+        Either::B => 0,
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn enum_record() {
+        check_diagnostics_no_bails(
+            r#"
+enum Either { A { foo: bool }, B }
+
+fn main() {
+    let a = Either::A { foo: true };
+    match a { }
+        //^ error: missing match arm
+    match a { Either::A { foo: true } => () }
+        //^ error: missing match arm
+    match a {
+        Either::A { } => (),
+      //^^^^^^^^^ error: missing structure fields:
+      //        | - foo
+        Either::B => (),
+    }
+    match a {
+        //^ error: missing match arm
+        Either::A { } => (),
+    } //^^^^^^^^^ error: missing structure fields:
+      //        | - foo
+
+    match a {
+        Either::A { foo: true } => (),
+        Either::A { foo: false } => (),
+        Either::B => (),
+    }
+    match a {
+        Either::A { foo: _ } => (),
+        Either::B => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn enum_record_fields_out_of_order() {
+        check_diagnostics_no_bails(
+            r#"
+enum Either {
+    A { foo: bool, bar: () },
+    B,
+}
+
+fn main() {
+    let a = Either::A { foo: true, bar: () };
+    match a {
+        //^ error: missing match arm
+        Either::A { bar: (), foo: false } => (),
+        Either::A { foo: true, bar: () } => (),
+    }
+
+    match a {
+        Either::A { bar: (), foo: false } => (),
+        Either::A { foo: true, bar: () } => (),
+        Either::B => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn enum_record_ellipsis() {
+        check_diagnostics_no_bails(
+            r#"
+enum Either {
+    A { foo: bool, bar: bool },
+    B,
+}
+
+fn main() {
+    let a = Either::B;
+    match a {
+        //^ error: missing match arm
+        Either::A { foo: true, .. } => (),
+        Either::B => (),
+    }
+    match a {
+        //^ error: missing match arm
+        Either::A { .. } => (),
+    }
+
+    match a {
+        Either::A { foo: true, .. } => (),
+        Either::A { foo: false, .. } => (),
+        Either::B => (),
+    }
+
+    match a {
+        Either::A { .. } => (),
+        Either::B => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn enum_tuple_partial_ellipsis() {
+        check_diagnostics_no_bails(
+            r#"
+enum Either {
+    A(bool, bool, bool, bool),
+    B,
+}
+
+fn main() {
+    match Either::B {
+        //^^^^^^^^^ error: missing match arm
+        Either::A(true, .., true) => (),
+        Either::A(true, .., false) => (),
+        Either::A(false, .., false) => (),
+        Either::B => (),
+    }
+    match Either::B {
+        //^^^^^^^^^ error: missing match arm
+        Either::A(true, .., true) => (),
+        Either::A(true, .., false) => (),
+        Either::A(.., true) => (),
+        Either::B => (),
+    }
+
+    match Either::B {
+        Either::A(true, .., true) => (),
+        Either::A(true, .., false) => (),
+        Either::A(false, .., true) => (),
+        Either::A(false, .., false) => (),
+        Either::B => (),
+    }
+    match Either::B {
+        Either::A(true, .., true) => (),
+        Either::A(true, .., false) => (),
+        Either::A(.., true) => (),
+        Either::A(.., false) => (),
+        Either::B => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn never() {
+        check_diagnostics_no_bails(
+            r#"
+enum Never {}
+
+fn enum_(never: Never) {
+    match never {}
+}
+fn enum_ref(never: &Never) {
+    match never {}
+        //^^^^^ error: missing match arm
+}
+fn bang(never: !) {
+    match never {}
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn unknown_type() {
+        cov_mark::check_count!(validate_match_bailed_out, 1);
+
+        check_diagnostics(
+            r#"
+enum Option<T> { Some(T), None }
+
+fn main() {
+    // `Never` is deliberately not defined so that it's an uninferred type.
+    match Option::<Never>::None {
+        None => (),
+        Some(never) => match never {},
+    }
+    match Option::<Never>::None {
+        //^^^^^^^^^^^^^^^^^^^^^ error: missing match arm
+        Option::Some(_never) => {},
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn tuple_of_bools_with_ellipsis_at_end_missing_arm() {
+        check_diagnostics_no_bails(
+            r#"
+fn main() {
+    match (false, true, false) {
+        //^^^^^^^^^^^^^^^^^^^^ error: missing match arm
+        (false, ..) => (),
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn tuple_of_bools_with_ellipsis_at_beginning_missing_arm() {
+        check_diagnostics_no_bails(
+            r#"
+fn main() {
+    match (false, true, false) {
+        //^^^^^^^^^^^^^^^^^^^^ error: missing match arm
+        (.., false) => (),
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn tuple_of_bools_with_ellipsis_in_middle_missing_arm() {
+        check_diagnostics_no_bails(
+            r#"
+fn main() {
+    match (false, true, false) {
+        //^^^^^^^^^^^^^^^^^^^^ error: missing match arm
+        (true, .., false) => (),
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn record_struct() {
+        check_diagnostics_no_bails(
+            r#"struct Foo { a: bool }
+fn main(f: Foo) {
+    match f {}
+        //^ error: missing match arm
+    match f { Foo { a: true } => () }
+        //^ error: missing match arm
+    match &f { Foo { a: true } => () }
+        //^^ error: missing match arm
+    match f { Foo { a: _ } => () }
+    match f {
+        Foo { a: true } => (),
+        Foo { a: false } => (),
+    }
+    match &f {
+        Foo { a: true } => (),
+        Foo { a: false } => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn tuple_struct() {
+        check_diagnostics_no_bails(
+            r#"struct Foo(bool);
+fn main(f: Foo) {
+    match f {}
+        //^ error: missing match arm
+    match f { Foo(true) => () }
+        //^ error: missing match arm
+    match f {
+        Foo(true) => (),
+        Foo(false) => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn unit_struct() {
+        check_diagnostics_no_bails(
+            r#"struct Foo;
+fn main(f: Foo) {
+    match f {}
+        //^ error: missing match arm
+    match f { Foo => () }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn record_struct_ellipsis() {
+        check_diagnostics_no_bails(
+            r#"struct Foo { foo: bool, bar: bool }
+fn main(f: Foo) {
+    match f { Foo { foo: true, .. } => () }
+        //^ error: missing match arm
+    match f {
+        //^ error: missing match arm
+        Foo { foo: true, .. } => (),
+        Foo { bar: false, .. } => ()
+    }
+    match f { Foo { .. } => () }
+    match f {
+        Foo { foo: true, .. } => (),
+        Foo { foo: false, .. } => ()
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn internal_or() {
+        check_diagnostics_no_bails(
+            r#"
+fn main() {
+    enum Either { A(bool), B }
+    match Either::B {
+        //^^^^^^^^^ error: missing match arm
+        Either::A(true | false) => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn no_panic_at_unimplemented_subpattern_type() {
+        cov_mark::check_count!(validate_match_bailed_out, 1);
+
+        check_diagnostics(
+            r#"
+struct S { a: char}
+fn main(v: S) {
+    match v { S{ a }      => {} }
+    match v { S{ a: _x }  => {} }
+    match v { S{ a: 'a' } => {} }
+    match v { S{..}       => {} }
+    match v { _           => {} }
+    match v { }
+        //^ error: missing match arm
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn binding() {
+        check_diagnostics_no_bails(
+            r#"
+fn main() {
+    match true {
+        _x @ true => {}
+        false     => {}
+    }
+    match true { _x @ true => {} }
+        //^^^^ error: missing match arm
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn binding_ref_has_correct_type() {
+        cov_mark::check_count!(validate_match_bailed_out, 1);
+
+        // Asserts `PatKind::Binding(ref _x): bool`, not &bool.
+        // If that's not true match checking will panic with "incompatible constructors"
+        // FIXME: make facilities to test this directly like `tests::check_infer(..)`
+        check_diagnostics(
+            r#"
+enum Foo { A }
+fn main() {
+    // FIXME: this should not bail out but current behavior is such as the old algorithm.
+    // ExprValidator::validate_match(..) checks types of top level patterns incorrecly.
+    match Foo::A {
+        ref _x => {}
+        Foo::A => {}
+    }
+    match (true,) {
+        (ref _x,) => {}
+        (true,) => {}
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn enum_non_exhaustive() {
+        check_diagnostics_no_bails(
+            r#"
+//- /lib.rs crate:lib
+#[non_exhaustive]
+pub enum E { A, B }
+fn _local() {
+    match E::A { _ => {} }
+    match E::A {
+        E::A => {}
+        E::B => {}
+    }
+    match E::A {
+        E::A | E::B => {}
+    }
+}
+
+//- /main.rs crate:main deps:lib
+use lib::E;
+fn main() {
+    match E::A { _ => {} }
+    match E::A {
+        //^^^^ error: missing match arm
+        E::A => {}
+        E::B => {}
+    }
+    match E::A {
+        //^^^^ error: missing match arm
+        E::A | E::B => {}
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn match_guard() {
+        check_diagnostics_no_bails(
+            r#"
+fn main() {
+    match true {
+        true if false => {}
+        true          => {}
+        false         => {}
+    }
+    match true {
+        //^^^^ error: missing match arm
+        true if false => {}
+        false         => {}
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn pattern_type_is_of_substitution() {
+        cov_mark::check!(match_check_wildcard_expanded_to_substitutions);
+        check_diagnostics_no_bails(
+            r#"
+struct Foo<T>(T);
+struct Bar;
+fn main() {
+    match Foo(Bar) {
+        _ | Foo(Bar) => {}
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn record_struct_no_such_field() {
+        cov_mark::check_count!(validate_match_bailed_out, 1);
+
+        check_diagnostics(
+            r#"
+struct Foo { }
+fn main(f: Foo) {
+    match f { Foo { bar } => () }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn match_ergonomics_issue_9095() {
+        check_diagnostics_no_bails(
+            r#"
+enum Foo<T> { A(T) }
+fn main() {
+    match &Foo::A(true) {
+        _ => {}
+        Foo::A(_) => {}
+    }
+}
+"#,
+        );
+    }
+
+    mod false_negatives {
+        //! The implementation of match checking here is a work in progress. As we roll this out, we
+        //! prefer false negatives to false positives (ideally there would be no false positives). This
+        //! test module should document known false negatives. Eventually we will have a complete
+        //! implementation of match checking and this module will be empty.
+        //!
+        //! The reasons for documenting known false negatives:
+        //!
+        //!   1. It acts as a backlog of work that can be done to improve the behavior of the system.
+        //!   2. It ensures the code doesn't panic when handling these cases.
+        use super::*;
+
+        #[test]
+        fn integers() {
+            cov_mark::check_count!(validate_match_bailed_out, 1);
+
+            // We don't currently check integer exhaustiveness.
+            check_diagnostics(
+                r#"
+fn main() {
+    match 5 {
+        10 => (),
+        11..20 => (),
+    }
+}
+"#,
+            );
+        }
+
+        #[test]
+        fn reference_patterns_at_top_level() {
+            cov_mark::check_count!(validate_match_bailed_out, 1);
+
+            check_diagnostics(
+                r#"
+fn main() {
+    match &false {
+        &true => {}
+    }
+}
+            "#,
+            );
+        }
+
+        #[test]
+        fn reference_patterns_in_fields() {
+            cov_mark::check_count!(validate_match_bailed_out, 2);
+
+            check_diagnostics(
+                r#"
+fn main() {
+    match (&false,) {
+        (true,) => {}
+    }
+    match (&false,) {
+        (&true,) => {}
+    }
+}
+            "#,
+            );
+        }
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/missing_ok_or_some_in_tail_expr.rs b/crates/ide_diagnostics/src/handlers/missing_ok_or_some_in_tail_expr.rs
new file mode 100644
index 000000000..63de54570
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/missing_ok_or_some_in_tail_expr.rs
@@ -0,0 +1,229 @@
+use hir::db::AstDatabase;
+use ide_db::{assists::Assist, source_change::SourceChange};
+use syntax::AstNode;
+use text_edit::TextEdit;
+
+use crate::{fix, Diagnostic, DiagnosticsContext};
+
+// Diagnostic: missing-ok-or-some-in-tail-expr
+//
+// This diagnostic is triggered if a block that should return `Result` returns a value not wrapped in `Ok`,
+// or if a block that should return `Option` returns a value not wrapped in `Some`.
+//
+// Example:
+//
+// ```rust
+// fn foo() -> Result<u8, ()> {
+//     10
+// }
+// ```
+pub(crate) fn missing_ok_or_some_in_tail_expr(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::MissingOkOrSomeInTailExpr,
+) -> Diagnostic {
+    Diagnostic::new(
+        "missing-ok-or-some-in-tail-expr",
+        format!("wrap return expression in {}", d.required),
+        ctx.sema.diagnostics_display_range(d.expr.clone().map(|it| it.into())).range,
+    )
+    .with_fixes(fixes(ctx, d))
+}
+
+fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::MissingOkOrSomeInTailExpr) -> Option<Vec<Assist>> {
+    let root = ctx.sema.db.parse_or_expand(d.expr.file_id)?;
+    let tail_expr = d.expr.value.to_node(&root);
+    let tail_expr_range = tail_expr.syntax().text_range();
+    let replacement = format!("{}({})", d.required, tail_expr.syntax());
+    let edit = TextEdit::replace(tail_expr_range, replacement);
+    let source_change =
+        SourceChange::from_text_edit(d.expr.file_id.original_file(ctx.sema.db), edit);
+    let name = if d.required == "Ok" { "Wrap with Ok" } else { "Wrap with Some" };
+    Some(vec![fix("wrap_tail_expr", name, source_change, tail_expr_range)])
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_diagnostics, check_fix};
+
+    #[test]
+    fn test_wrap_return_type_option() {
+        check_fix(
+            r#"
+//- /main.rs crate:main deps:core
+use core::option::Option::{self, Some, None};
+
+fn div(x: i32, y: i32) -> Option<i32> {
+    if y == 0 {
+        return None;
+    }
+    x / y$0
+}
+//- /core/lib.rs crate:core
+pub mod result {
+    pub enum Result<T, E> { Ok(T), Err(E) }
+}
+pub mod option {
+    pub enum Option<T> { Some(T), None }
+}
+"#,
+            r#"
+use core::option::Option::{self, Some, None};
+
+fn div(x: i32, y: i32) -> Option<i32> {
+    if y == 0 {
+        return None;
+    }
+    Some(x / y)
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_wrap_return_type() {
+        check_fix(
+            r#"
+//- /main.rs crate:main deps:core
+use core::result::Result::{self, Ok, Err};
+
+fn div(x: i32, y: i32) -> Result<i32, ()> {
+    if y == 0 {
+        return Err(());
+    }
+    x / y$0
+}
+//- /core/lib.rs crate:core
+pub mod result {
+    pub enum Result<T, E> { Ok(T), Err(E) }
+}
+pub mod option {
+    pub enum Option<T> { Some(T), None }
+}
+"#,
+            r#"
+use core::result::Result::{self, Ok, Err};
+
+fn div(x: i32, y: i32) -> Result<i32, ()> {
+    if y == 0 {
+        return Err(());
+    }
+    Ok(x / y)
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_wrap_return_type_handles_generic_functions() {
+        check_fix(
+            r#"
+//- /main.rs crate:main deps:core
+use core::result::Result::{self, Ok, Err};
+
+fn div<T>(x: T) -> Result<T, i32> {
+    if x == 0 {
+        return Err(7);
+    }
+    $0x
+}
+//- /core/lib.rs crate:core
+pub mod result {
+    pub enum Result<T, E> { Ok(T), Err(E) }
+}
+pub mod option {
+    pub enum Option<T> { Some(T), None }
+}
+"#,
+            r#"
+use core::result::Result::{self, Ok, Err};
+
+fn div<T>(x: T) -> Result<T, i32> {
+    if x == 0 {
+        return Err(7);
+    }
+    Ok(x)
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_wrap_return_type_handles_type_aliases() {
+        check_fix(
+            r#"
+//- /main.rs crate:main deps:core
+use core::result::Result::{self, Ok, Err};
+
+type MyResult<T> = Result<T, ()>;
+
+fn div(x: i32, y: i32) -> MyResult<i32> {
+    if y == 0 {
+        return Err(());
+    }
+    x $0/ y
+}
+//- /core/lib.rs crate:core
+pub mod result {
+    pub enum Result<T, E> { Ok(T), Err(E) }
+}
+pub mod option {
+    pub enum Option<T> { Some(T), None }
+}
+"#,
+            r#"
+use core::result::Result::{self, Ok, Err};
+
+type MyResult<T> = Result<T, ()>;
+
+fn div(x: i32, y: i32) -> MyResult<i32> {
+    if y == 0 {
+        return Err(());
+    }
+    Ok(x / y)
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_wrap_return_type_not_applicable_when_expr_type_does_not_match_ok_type() {
+        check_diagnostics(
+            r#"
+//- /main.rs crate:main deps:core
+use core::result::Result::{self, Ok, Err};
+
+fn foo() -> Result<(), i32> { 0 }
+
+//- /core/lib.rs crate:core
+pub mod result {
+    pub enum Result<T, E> { Ok(T), Err(E) }
+}
+pub mod option {
+    pub enum Option<T> { Some(T), None }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_wrap_return_type_not_applicable_when_return_type_is_not_result_or_option() {
+        check_diagnostics(
+            r#"
+//- /main.rs crate:main deps:core
+use core::result::Result::{self, Ok, Err};
+
+enum SomeOtherEnum { Ok(i32), Err(String) }
+
+fn foo() -> SomeOtherEnum { 0 }
+
+//- /core/lib.rs crate:core
+pub mod result {
+    pub enum Result<T, E> { Ok(T), Err(E) }
+}
+pub mod option {
+    pub enum Option<T> { Some(T), None }
+}
+"#,
+        );
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/missing_unsafe.rs b/crates/ide_diagnostics/src/handlers/missing_unsafe.rs
new file mode 100644
index 000000000..7acd9228a
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/missing_unsafe.rs
@@ -0,0 +1,101 @@
+use crate::{Diagnostic, DiagnosticsContext};
+
+// Diagnostic: missing-unsafe
+//
+// This diagnostic is triggered if an operation marked as `unsafe` is used outside of an `unsafe` function or block.
+pub(crate) fn missing_unsafe(ctx: &DiagnosticsContext<'_>, d: &hir::MissingUnsafe) -> Diagnostic {
+    Diagnostic::new(
+        "missing-unsafe",
+        "this operation is unsafe and requires an unsafe function or block",
+        ctx.sema.diagnostics_display_range(d.expr.clone().map(|it| it.into())).range,
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    #[test]
+    fn missing_unsafe_diagnostic_with_raw_ptr() {
+        check_diagnostics(
+            r#"
+fn main() {
+    let x = &5 as *const usize;
+    unsafe { let y = *x; }
+    let z = *x;
+}         //^^ error: this operation is unsafe and requires an unsafe function or block
+"#,
+        )
+    }
+
+    #[test]
+    fn missing_unsafe_diagnostic_with_unsafe_call() {
+        check_diagnostics(
+            r#"
+struct HasUnsafe;
+
+impl HasUnsafe {
+    unsafe fn unsafe_fn(&self) {
+        let x = &5 as *const usize;
+        let y = *x;
+    }
+}
+
+unsafe fn unsafe_fn() {
+    let x = &5 as *const usize;
+    let y = *x;
+}
+
+fn main() {
+    unsafe_fn();
+  //^^^^^^^^^^^ error: this operation is unsafe and requires an unsafe function or block
+    HasUnsafe.unsafe_fn();
+  //^^^^^^^^^^^^^^^^^^^^^ error: this operation is unsafe and requires an unsafe function or block
+    unsafe {
+        unsafe_fn();
+        HasUnsafe.unsafe_fn();
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn missing_unsafe_diagnostic_with_static_mut() {
+        check_diagnostics(
+            r#"
+struct Ty {
+    a: u8,
+}
+
+static mut STATIC_MUT: Ty = Ty { a: 0 };
+
+fn main() {
+    let x = STATIC_MUT.a;
+          //^^^^^^^^^^ error: this operation is unsafe and requires an unsafe function or block
+    unsafe {
+        let x = STATIC_MUT.a;
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn no_missing_unsafe_diagnostic_with_safe_intrinsic() {
+        check_diagnostics(
+            r#"
+extern "rust-intrinsic" {
+    pub fn bitreverse(x: u32) -> u32; // Safe intrinsic
+    pub fn floorf32(x: f32) -> f32; // Unsafe intrinsic
+}
+
+fn main() {
+    let _ = bitreverse(12);
+    let _ = floorf32(12.0);
+          //^^^^^^^^^^^^^^ error: this operation is unsafe and requires an unsafe function or block
+}
+"#,
+        );
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/no_such_field.rs b/crates/ide_diagnostics/src/handlers/no_such_field.rs
new file mode 100644
index 000000000..92e8867f4
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/no_such_field.rs
@@ -0,0 +1,283 @@
+use hir::{db::AstDatabase, HasSource, HirDisplay, Semantics};
+use ide_db::{base_db::FileId, source_change::SourceChange, RootDatabase};
+use syntax::{
+    ast::{self, edit::IndentLevel, make},
+    AstNode,
+};
+use text_edit::TextEdit;
+
+use crate::{fix, Assist, Diagnostic, DiagnosticsContext};
+
+// Diagnostic: no-such-field
+//
+// This diagnostic is triggered if created structure does not have field provided in record.
+pub(crate) fn no_such_field(ctx: &DiagnosticsContext<'_>, d: &hir::NoSuchField) -> Diagnostic {
+    Diagnostic::new(
+        "no-such-field",
+        "no such field",
+        ctx.sema.diagnostics_display_range(d.field.clone().map(|it| it.into())).range,
+    )
+    .with_fixes(fixes(ctx, d))
+}
+
+fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::NoSuchField) -> Option<Vec<Assist>> {
+    let root = ctx.sema.db.parse_or_expand(d.field.file_id)?;
+    missing_record_expr_field_fixes(
+        &ctx.sema,
+        d.field.file_id.original_file(ctx.sema.db),
+        &d.field.value.to_node(&root),
+    )
+}
+
+fn missing_record_expr_field_fixes(
+    sema: &Semantics<RootDatabase>,
+    usage_file_id: FileId,
+    record_expr_field: &ast::RecordExprField,
+) -> Option<Vec<Assist>> {
+    let record_lit = ast::RecordExpr::cast(record_expr_field.syntax().parent()?.parent()?)?;
+    let def_id = sema.resolve_variant(record_lit)?;
+    let module;
+    let def_file_id;
+    let record_fields = match def_id {
+        hir::VariantDef::Struct(s) => {
+            module = s.module(sema.db);
+            let source = s.source(sema.db)?;
+            def_file_id = source.file_id;
+            let fields = source.value.field_list()?;
+            record_field_list(fields)?
+        }
+        hir::VariantDef::Union(u) => {
+            module = u.module(sema.db);
+            let source = u.source(sema.db)?;
+            def_file_id = source.file_id;
+            source.value.record_field_list()?
+        }
+        hir::VariantDef::Variant(e) => {
+            module = e.module(sema.db);
+            let source = e.source(sema.db)?;
+            def_file_id = source.file_id;
+            let fields = source.value.field_list()?;
+            record_field_list(fields)?
+        }
+    };
+    let def_file_id = def_file_id.original_file(sema.db);
+
+    let new_field_type = sema.type_of_expr(&record_expr_field.expr()?)?;
+    if new_field_type.is_unknown() {
+        return None;
+    }
+    let new_field = make::record_field(
+        None,
+        make::name(&record_expr_field.field_name()?.text()),
+        make::ty(&new_field_type.display_source_code(sema.db, module.into()).ok()?),
+    );
+
+    let last_field = record_fields.fields().last()?;
+    let last_field_syntax = last_field.syntax();
+    let indent = IndentLevel::from_node(last_field_syntax);
+
+    let mut new_field = new_field.to_string();
+    if usage_file_id != def_file_id {
+        new_field = format!("pub(crate) {}", new_field);
+    }
+    new_field = format!("\n{}{}", indent, new_field);
+
+    let needs_comma = !last_field_syntax.to_string().ends_with(',');
+    if needs_comma {
+        new_field = format!(",{}", new_field);
+    }
+
+    let source_change = SourceChange::from_text_edit(
+        def_file_id,
+        TextEdit::insert(last_field_syntax.text_range().end(), new_field),
+    );
+
+    return Some(vec![fix(
+        "create_field",
+        "Create field",
+        source_change,
+        record_expr_field.syntax().text_range(),
+    )]);
+
+    fn record_field_list(field_def_list: ast::FieldList) -> Option<ast::RecordFieldList> {
+        match field_def_list {
+            ast::FieldList::RecordFieldList(it) => Some(it),
+            ast::FieldList::TupleFieldList(_) => None,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_diagnostics, check_fix};
+
+    #[test]
+    fn no_such_field_diagnostics() {
+        check_diagnostics(
+            r#"
+struct S { foo: i32, bar: () }
+impl S {
+    fn new() -> S {
+        S {
+      //^ 💡 error: missing structure fields:
+      //|    - bar
+            foo: 92,
+            baz: 62,
+          //^^^^^^^ 💡 error: no such field
+        }
+    }
+}
+"#,
+        );
+    }
+    #[test]
+    fn no_such_field_with_feature_flag_diagnostics() {
+        check_diagnostics(
+            r#"
+//- /lib.rs crate:foo cfg:feature=foo
+struct MyStruct {
+    my_val: usize,
+    #[cfg(feature = "foo")]
+    bar: bool,
+}
+
+impl MyStruct {
+    #[cfg(feature = "foo")]
+    pub(crate) fn new(my_val: usize, bar: bool) -> Self {
+        Self { my_val, bar }
+    }
+    #[cfg(not(feature = "foo"))]
+    pub(crate) fn new(my_val: usize, _bar: bool) -> Self {
+        Self { my_val }
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn no_such_field_enum_with_feature_flag_diagnostics() {
+        check_diagnostics(
+            r#"
+//- /lib.rs crate:foo cfg:feature=foo
+enum Foo {
+    #[cfg(not(feature = "foo"))]
+    Buz,
+    #[cfg(feature = "foo")]
+    Bar,
+    Baz
+}
+
+fn test_fn(f: Foo) {
+    match f {
+        Foo::Bar => {},
+        Foo::Baz => {},
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn no_such_field_with_feature_flag_diagnostics_on_struct_lit() {
+        check_diagnostics(
+            r#"
+//- /lib.rs crate:foo cfg:feature=foo
+struct S {
+    #[cfg(feature = "foo")]
+    foo: u32,
+    #[cfg(not(feature = "foo"))]
+    bar: u32,
+}
+
+impl S {
+    #[cfg(feature = "foo")]
+    fn new(foo: u32) -> Self {
+        Self { foo }
+    }
+    #[cfg(not(feature = "foo"))]
+    fn new(bar: u32) -> Self {
+        Self { bar }
+    }
+    fn new2(bar: u32) -> Self {
+        #[cfg(feature = "foo")]
+        { Self { foo: bar } }
+        #[cfg(not(feature = "foo"))]
+        { Self { bar } }
+    }
+    fn new2(val: u32) -> Self {
+        Self {
+            #[cfg(feature = "foo")]
+            foo: val,
+            #[cfg(not(feature = "foo"))]
+            bar: val,
+        }
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn no_such_field_with_type_macro() {
+        check_diagnostics(
+            r#"
+macro_rules! Type { () => { u32 }; }
+struct Foo { bar: Type![] }
+
+impl Foo {
+    fn new() -> Self {
+        Foo { bar: 0 }
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_add_field_from_usage() {
+        check_fix(
+            r"
+fn main() {
+    Foo { bar: 3, baz$0: false};
+}
+struct Foo {
+    bar: i32
+}
+",
+            r"
+fn main() {
+    Foo { bar: 3, baz: false};
+}
+struct Foo {
+    bar: i32,
+    baz: bool
+}
+",
+        )
+    }
+
+    #[test]
+    fn test_add_field_in_other_file_from_usage() {
+        check_fix(
+            r#"
+//- /main.rs
+mod foo;
+
+fn main() {
+    foo::Foo { bar: 3, $0baz: false};
+}
+//- /foo.rs
+struct Foo {
+    bar: i32
+}
+"#,
+            r#"
+struct Foo {
+    bar: i32,
+    pub(crate) baz: bool
+}
+"#,
+        )
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/remove_this_semicolon.rs b/crates/ide_diagnostics/src/handlers/remove_this_semicolon.rs
new file mode 100644
index 000000000..4e639f214
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/remove_this_semicolon.rs
@@ -0,0 +1,61 @@
+use hir::db::AstDatabase;
+use ide_db::source_change::SourceChange;
+use syntax::{ast, AstNode};
+use text_edit::TextEdit;
+
+use crate::{fix, Assist, Diagnostic, DiagnosticsContext};
+
+// Diagnostic: remove-this-semicolon
+//
+// This diagnostic is triggered when there's an erroneous `;` at the end of the block.
+pub(crate) fn remove_this_semicolon(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::RemoveThisSemicolon,
+) -> Diagnostic {
+    Diagnostic::new(
+        "remove-this-semicolon",
+        "remove this semicolon",
+        ctx.sema.diagnostics_display_range(d.expr.clone().map(|it| it.into())).range,
+    )
+    .with_fixes(fixes(ctx, d))
+}
+
+fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::RemoveThisSemicolon) -> Option<Vec<Assist>> {
+    let root = ctx.sema.db.parse_or_expand(d.expr.file_id)?;
+
+    let semicolon = d
+        .expr
+        .value
+        .to_node(&root)
+        .syntax()
+        .parent()
+        .and_then(ast::ExprStmt::cast)
+        .and_then(|expr| expr.semicolon_token())?
+        .text_range();
+
+    let edit = TextEdit::delete(semicolon);
+    let source_change =
+        SourceChange::from_text_edit(d.expr.file_id.original_file(ctx.sema.db), edit);
+
+    Some(vec![fix("remove_semicolon", "Remove this semicolon", source_change, semicolon)])
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_diagnostics, check_fix};
+
+    #[test]
+    fn missing_semicolon() {
+        check_diagnostics(
+            r#"
+fn test() -> i32 { 123; }
+                 //^^^ 💡 error: remove this semicolon
+"#,
+        );
+    }
+
+    #[test]
+    fn remove_semicolon() {
+        check_fix(r#"fn f() -> i32 { 92$0; }"#, r#"fn f() -> i32 { 92 }"#);
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/replace_filter_map_next_with_find_map.rs b/crates/ide_diagnostics/src/handlers/replace_filter_map_next_with_find_map.rs
new file mode 100644
index 000000000..cd87a10bb
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/replace_filter_map_next_with_find_map.rs
@@ -0,0 +1,179 @@
+use hir::{db::AstDatabase, InFile};
+use ide_db::source_change::SourceChange;
+use syntax::{
+    ast::{self, ArgListOwner},
+    AstNode, TextRange,
+};
+use text_edit::TextEdit;
+
+use crate::{fix, Assist, Diagnostic, DiagnosticsContext, Severity};
+
+// Diagnostic: replace-filter-map-next-with-find-map
+//
+// This diagnostic is triggered when `.filter_map(..).next()` is used, rather than the more concise `.find_map(..)`.
+pub(crate) fn replace_filter_map_next_with_find_map(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::ReplaceFilterMapNextWithFindMap,
+) -> Diagnostic {
+    Diagnostic::new(
+        "replace-filter-map-next-with-find-map",
+        "replace filter_map(..).next() with find_map(..)",
+        ctx.sema.diagnostics_display_range(InFile::new(d.file, d.next_expr.clone().into())).range,
+    )
+    .severity(Severity::WeakWarning)
+    .with_fixes(fixes(ctx, d))
+}
+
+fn fixes(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::ReplaceFilterMapNextWithFindMap,
+) -> Option<Vec<Assist>> {
+    let root = ctx.sema.db.parse_or_expand(d.file)?;
+    let next_expr = d.next_expr.to_node(&root);
+    let next_call = ast::MethodCallExpr::cast(next_expr.syntax().clone())?;
+
+    let filter_map_call = ast::MethodCallExpr::cast(next_call.receiver()?.syntax().clone())?;
+    let filter_map_name_range = filter_map_call.name_ref()?.ident_token()?.text_range();
+    let filter_map_args = filter_map_call.arg_list()?;
+
+    let range_to_replace =
+        TextRange::new(filter_map_name_range.start(), next_expr.syntax().text_range().end());
+    let replacement = format!("find_map{}", filter_map_args.syntax().text());
+    let trigger_range = next_expr.syntax().text_range();
+
+    let edit = TextEdit::replace(range_to_replace, replacement);
+
+    let source_change = SourceChange::from_text_edit(d.file.original_file(ctx.sema.db), edit);
+
+    Some(vec![fix(
+        "replace_with_find_map",
+        "Replace filter_map(..).next() with find_map()",
+        source_change,
+        trigger_range,
+    )])
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_fix;
+
+    // Register the required standard library types to make the tests work
+    #[track_caller]
+    fn check_diagnostics(ra_fixture: &str) {
+        let prefix = r#"
+//- /main.rs crate:main deps:core
+use core::iter::Iterator;
+use core::option::Option::{self, Some, None};
+"#;
+        let suffix = r#"
+//- /core/lib.rs crate:core
+pub mod option {
+    pub enum Option<T> { Some(T), None }
+}
+pub mod iter {
+    pub trait Iterator {
+        type Item;
+        fn filter_map<B, F>(self, f: F) -> FilterMap where F: FnMut(Self::Item) -> Option<B> { FilterMap }
+        fn next(&mut self) -> Option<Self::Item>;
+    }
+    pub struct FilterMap {}
+    impl Iterator for FilterMap {
+        type Item = i32;
+        fn next(&mut self) -> i32 { 7 }
+    }
+}
+"#;
+        crate::tests::check_diagnostics(&format!("{}{}{}", prefix, ra_fixture, suffix))
+    }
+
+    #[test]
+    fn replace_filter_map_next_with_find_map2() {
+        check_diagnostics(
+            r#"
+    fn foo() {
+        let m = [1, 2, 3].iter().filter_map(|x| Some(92)).next();
+    }         //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 💡 weak: replace filter_map(..).next() with find_map(..)
+"#,
+        );
+    }
+
+    #[test]
+    fn replace_filter_map_next_with_find_map_no_diagnostic_without_next() {
+        check_diagnostics(
+            r#"
+fn foo() {
+    let m = [1, 2, 3]
+        .iter()
+        .filter_map(|x| Some(92))
+        .len();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn replace_filter_map_next_with_find_map_no_diagnostic_with_intervening_methods() {
+        check_diagnostics(
+            r#"
+fn foo() {
+    let m = [1, 2, 3]
+        .iter()
+        .filter_map(|x| Some(92))
+        .map(|x| x + 2)
+        .len();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn replace_filter_map_next_with_find_map_no_diagnostic_if_not_in_chain() {
+        check_diagnostics(
+            r#"
+fn foo() {
+    let m = [1, 2, 3]
+        .iter()
+        .filter_map(|x| Some(92));
+    let n = m.next();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn replace_with_wind_map() {
+        check_fix(
+            r#"
+//- /main.rs crate:main deps:core
+use core::iter::Iterator;
+use core::option::Option::{self, Some, None};
+fn foo() {
+    let m = [1, 2, 3].iter().$0filter_map(|x| Some(92)).next();
+}
+//- /core/lib.rs crate:core
+pub mod option {
+    pub enum Option<T> { Some(T), None }
+}
+pub mod iter {
+    pub trait Iterator {
+        type Item;
+        fn filter_map<B, F>(self, f: F) -> FilterMap where F: FnMut(Self::Item) -> Option<B> { FilterMap }
+        fn next(&mut self) -> Option<Self::Item>;
+    }
+    pub struct FilterMap {}
+    impl Iterator for FilterMap {
+        type Item = i32;
+        fn next(&mut self) -> i32 { 7 }
+    }
+}
+"#,
+            r#"
+use core::iter::Iterator;
+use core::option::Option::{self, Some, None};
+fn foo() {
+    let m = [1, 2, 3].iter().find_map(|x| Some(92));
+}
+"#,
+        )
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/unimplemented_builtin_macro.rs b/crates/ide_diagnostics/src/handlers/unimplemented_builtin_macro.rs
new file mode 100644
index 000000000..e879de75c
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/unimplemented_builtin_macro.rs
@@ -0,0 +1,16 @@
+use crate::{Diagnostic, DiagnosticsContext, Severity};
+
+// Diagnostic: unimplemented-builtin-macro
+//
+// This diagnostic is shown for builtin macros which are not yet implemented by rust-analyzer
+pub(crate) fn unimplemented_builtin_macro(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::UnimplementedBuiltinMacro,
+) -> Diagnostic {
+    Diagnostic::new(
+        "unimplemented-builtin-macro",
+        "unimplemented built-in macro".to_string(),
+        ctx.sema.diagnostics_display_range(d.node.clone()).range,
+    )
+    .severity(Severity::WeakWarning)
+}
diff --git a/crates/ide_diagnostics/src/handlers/unlinked_file.rs b/crates/ide_diagnostics/src/handlers/unlinked_file.rs
new file mode 100644
index 000000000..8e601fa48
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/unlinked_file.rs
@@ -0,0 +1,298 @@
+//! Diagnostic emitted for files that aren't part of any crate.
+
+use hir::db::DefDatabase;
+use ide_db::{
+    base_db::{FileId, FileLoader, SourceDatabase, SourceDatabaseExt},
+    source_change::SourceChange,
+    RootDatabase,
+};
+use syntax::{
+    ast::{self, ModuleItemOwner, NameOwner},
+    AstNode, TextRange, TextSize,
+};
+use text_edit::TextEdit;
+
+use crate::{fix, Assist, Diagnostic, DiagnosticsContext};
+
+// Diagnostic: unlinked-file
+//
+// This diagnostic is shown for files that are not included in any crate, or files that are part of
+// crates rust-analyzer failed to discover. The file will not have IDE features available.
+pub(crate) fn unlinked_file(ctx: &DiagnosticsContext, acc: &mut Vec<Diagnostic>, file_id: FileId) {
+    // Limit diagnostic to the first few characters in the file. This matches how VS Code
+    // renders it with the full span, but on other editors, and is less invasive.
+    let range = ctx.sema.db.parse(file_id).syntax_node().text_range();
+    // FIXME: This is wrong if one of the first three characters is not ascii: `//Ы`.
+    let range = range.intersect(TextRange::up_to(TextSize::of("..."))).unwrap_or(range);
+
+    acc.push(
+        Diagnostic::new("unlinked-file", "file not included in module tree", range)
+            .with_fixes(fixes(ctx, file_id)),
+    );
+}
+
+fn fixes(ctx: &DiagnosticsContext, file_id: FileId) -> Option<Vec<Assist>> {
+    // If there's an existing module that could add `mod` or `pub mod` items to include the unlinked file,
+    // suggest that as a fix.
+
+    let source_root = ctx.sema.db.source_root(ctx.sema.db.file_source_root(file_id));
+    let our_path = source_root.path_for_file(&file_id)?;
+    let module_name = our_path.name_and_extension()?.0;
+
+    // Candidates to look for:
+    // - `mod.rs` in the same folder
+    //   - we also check `main.rs` and `lib.rs`
+    // - `$dir.rs` in the parent folder, where `$dir` is the directory containing `self.file_id`
+    let parent = our_path.parent()?;
+    let mut paths = vec![parent.join("mod.rs")?, parent.join("lib.rs")?, parent.join("main.rs")?];
+
+    // `submod/bla.rs` -> `submod.rs`
+    if let Some(newmod) = (|| {
+        let name = parent.name_and_extension()?.0;
+        parent.parent()?.join(&format!("{}.rs", name))
+    })() {
+        paths.push(newmod);
+    }
+
+    for path in &paths {
+        if let Some(parent_id) = source_root.file_for_path(path) {
+            for krate in ctx.sema.db.relevant_crates(*parent_id).iter() {
+                let crate_def_map = ctx.sema.db.crate_def_map(*krate);
+                for (_, module) in crate_def_map.modules() {
+                    if module.origin.is_inline() {
+                        // We don't handle inline `mod parent {}`s, they use different paths.
+                        continue;
+                    }
+
+                    if module.origin.file_id() == Some(*parent_id) {
+                        return make_fixes(ctx.sema.db, *parent_id, module_name, file_id);
+                    }
+                }
+            }
+        }
+    }
+
+    None
+}
+
+fn make_fixes(
+    db: &RootDatabase,
+    parent_file_id: FileId,
+    new_mod_name: &str,
+    added_file_id: FileId,
+) -> Option<Vec<Assist>> {
+    fn is_outline_mod(item: &ast::Item) -> bool {
+        matches!(item, ast::Item::Module(m) if m.item_list().is_none())
+    }
+
+    let mod_decl = format!("mod {};", new_mod_name);
+    let pub_mod_decl = format!("pub mod {};", new_mod_name);
+
+    let ast: ast::SourceFile = db.parse(parent_file_id).tree();
+
+    let mut mod_decl_builder = TextEdit::builder();
+    let mut pub_mod_decl_builder = TextEdit::builder();
+
+    // If there's an existing `mod m;` statement matching the new one, don't emit a fix (it's
+    // probably `#[cfg]`d out).
+    for item in ast.items() {
+        if let ast::Item::Module(m) = item {
+            if let Some(name) = m.name() {
+                if m.item_list().is_none() && name.to_string() == new_mod_name {
+                    cov_mark::hit!(unlinked_file_skip_fix_when_mod_already_exists);
+                    return None;
+                }
+            }
+        }
+    }
+
+    // If there are existing `mod m;` items, append after them (after the first group of them, rather).
+    match ast
+        .items()
+        .skip_while(|item| !is_outline_mod(item))
+        .take_while(|item| is_outline_mod(item))
+        .last()
+    {
+        Some(last) => {
+            cov_mark::hit!(unlinked_file_append_to_existing_mods);
+            let offset = last.syntax().text_range().end();
+            mod_decl_builder.insert(offset, format!("\n{}", mod_decl));
+            pub_mod_decl_builder.insert(offset, format!("\n{}", pub_mod_decl));
+        }
+        None => {
+            // Prepend before the first item in the file.
+            match ast.items().next() {
+                Some(item) => {
+                    cov_mark::hit!(unlinked_file_prepend_before_first_item);
+                    let offset = item.syntax().text_range().start();
+                    mod_decl_builder.insert(offset, format!("{}\n\n", mod_decl));
+                    pub_mod_decl_builder.insert(offset, format!("{}\n\n", pub_mod_decl));
+                }
+                None => {
+                    // No items in the file, so just append at the end.
+                    cov_mark::hit!(unlinked_file_empty_file);
+                    let offset = ast.syntax().text_range().end();
+                    mod_decl_builder.insert(offset, format!("{}\n", mod_decl));
+                    pub_mod_decl_builder.insert(offset, format!("{}\n", pub_mod_decl));
+                }
+            }
+        }
+    }
+
+    let trigger_range = db.parse(added_file_id).tree().syntax().text_range();
+    Some(vec![
+        fix(
+            "add_mod_declaration",
+            &format!("Insert `{}`", mod_decl),
+            SourceChange::from_text_edit(parent_file_id, mod_decl_builder.finish()),
+            trigger_range,
+        ),
+        fix(
+            "add_pub_mod_declaration",
+            &format!("Insert `{}`", pub_mod_decl),
+            SourceChange::from_text_edit(parent_file_id, pub_mod_decl_builder.finish()),
+            trigger_range,
+        ),
+    ])
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_diagnostics, check_fix, check_fixes, check_no_fix};
+
+    #[test]
+    fn unlinked_file_prepend_first_item() {
+        cov_mark::check!(unlinked_file_prepend_before_first_item);
+        // Only tests the first one for `pub mod` since the rest are the same
+        check_fixes(
+            r#"
+//- /main.rs
+fn f() {}
+//- /foo.rs
+$0
+"#,
+            vec![
+                r#"
+mod foo;
+
+fn f() {}
+"#,
+                r#"
+pub mod foo;
+
+fn f() {}
+"#,
+            ],
+        );
+    }
+
+    #[test]
+    fn unlinked_file_append_mod() {
+        cov_mark::check!(unlinked_file_append_to_existing_mods);
+        check_fix(
+            r#"
+//- /main.rs
+//! Comment on top
+
+mod preexisting;
+
+mod preexisting2;
+
+struct S;
+
+mod preexisting_bottom;)
+//- /foo.rs
+$0
+"#,
+            r#"
+//! Comment on top
+
+mod preexisting;
+
+mod preexisting2;
+mod foo;
+
+struct S;
+
+mod preexisting_bottom;)
+"#,
+        );
+    }
+
+    #[test]
+    fn unlinked_file_insert_in_empty_file() {
+        cov_mark::check!(unlinked_file_empty_file);
+        check_fix(
+            r#"
+//- /main.rs
+//- /foo.rs
+$0
+"#,
+            r#"
+mod foo;
+"#,
+        );
+    }
+
+    #[test]
+    fn unlinked_file_old_style_modrs() {
+        check_fix(
+            r#"
+//- /main.rs
+mod submod;
+//- /submod/mod.rs
+// in mod.rs
+//- /submod/foo.rs
+$0
+"#,
+            r#"
+// in mod.rs
+mod foo;
+"#,
+        );
+    }
+
+    #[test]
+    fn unlinked_file_new_style_mod() {
+        check_fix(
+            r#"
+//- /main.rs
+mod submod;
+//- /submod.rs
+//- /submod/foo.rs
+$0
+"#,
+            r#"
+mod foo;
+"#,
+        );
+    }
+
+    #[test]
+    fn unlinked_file_with_cfg_off() {
+        cov_mark::check!(unlinked_file_skip_fix_when_mod_already_exists);
+        check_no_fix(
+            r#"
+//- /main.rs
+#[cfg(never)]
+mod foo;
+
+//- /foo.rs
+$0
+"#,
+        );
+    }
+
+    #[test]
+    fn unlinked_file_with_cfg_on() {
+        check_diagnostics(
+            r#"
+//- /main.rs
+#[cfg(not(never))]
+mod foo;
+
+//- /foo.rs
+"#,
+        );
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/unresolved_extern_crate.rs b/crates/ide_diagnostics/src/handlers/unresolved_extern_crate.rs
new file mode 100644
index 000000000..74e4a69c6
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/unresolved_extern_crate.rs
@@ -0,0 +1,49 @@
+use crate::{Diagnostic, DiagnosticsContext};
+
+// Diagnostic: unresolved-extern-crate
+//
+// This diagnostic is triggered if rust-analyzer is unable to discover referred extern crate.
+pub(crate) fn unresolved_extern_crate(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::UnresolvedExternCrate,
+) -> Diagnostic {
+    Diagnostic::new(
+        "unresolved-extern-crate",
+        "unresolved extern crate",
+        ctx.sema.diagnostics_display_range(d.decl.clone().map(|it| it.into())).range,
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    #[test]
+    fn unresolved_extern_crate() {
+        check_diagnostics(
+            r#"
+//- /main.rs crate:main deps:core
+extern crate core;
+  extern crate doesnotexist;
+//^^^^^^^^^^^^^^^^^^^^^^^^^^ error: unresolved extern crate
+//- /lib.rs crate:core
+"#,
+        );
+    }
+
+    #[test]
+    fn extern_crate_self_as() {
+        cov_mark::check!(extern_crate_self_as);
+        check_diagnostics(
+            r#"
+//- /lib.rs
+  extern crate doesnotexist;
+//^^^^^^^^^^^^^^^^^^^^^^^^^^ error: unresolved extern crate
+// Should not error.
+extern crate self as foo;
+struct Foo;
+use foo::Foo as Bar;
+"#,
+        );
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/unresolved_import.rs b/crates/ide_diagnostics/src/handlers/unresolved_import.rs
new file mode 100644
index 000000000..e52a88459
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/unresolved_import.rs
@@ -0,0 +1,90 @@
+use crate::{Diagnostic, DiagnosticsContext};
+
+// Diagnostic: unresolved-import
+//
+// This diagnostic is triggered if rust-analyzer is unable to resolve a path in
+// a `use` declaration.
+pub(crate) fn unresolved_import(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::UnresolvedImport,
+) -> Diagnostic {
+    Diagnostic::new(
+        "unresolved-import",
+        "unresolved import",
+        ctx.sema.diagnostics_display_range(d.decl.clone().map(|it| it.into())).range,
+    )
+    // This currently results in false positives in the following cases:
+    // - `cfg_if!`-generated code in libstd (we don't load the sysroot correctly)
+    // - `core::arch` (we don't handle `#[path = "../<path>"]` correctly)
+    // - proc macros and/or proc macro generated code
+    .experimental()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    #[test]
+    fn unresolved_import() {
+        check_diagnostics(
+            r#"
+use does_exist;
+use does_not_exist;
+  //^^^^^^^^^^^^^^ error: unresolved import
+
+mod does_exist {}
+"#,
+        );
+    }
+
+    #[test]
+    fn unresolved_import_in_use_tree() {
+        // Only the relevant part of a nested `use` item should be highlighted.
+        check_diagnostics(
+            r#"
+use does_exist::{Exists, DoesntExist};
+                       //^^^^^^^^^^^ error: unresolved import
+
+use {does_not_exist::*, does_exist};
+   //^^^^^^^^^^^^^^^^^ error: unresolved import
+
+use does_not_exist::{
+    a,
+  //^ error: unresolved import
+    b,
+  //^ error: unresolved import
+    c,
+  //^ error: unresolved import
+};
+
+mod does_exist {
+    pub struct Exists;
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn dedup_unresolved_import_from_unresolved_crate() {
+        check_diagnostics(
+            r#"
+//- /main.rs crate:main
+mod a {
+    extern crate doesnotexist;
+  //^^^^^^^^^^^^^^^^^^^^^^^^^^ error: unresolved extern crate
+
+    // Should not error, since we already errored for the missing crate.
+    use doesnotexist::{self, bla, *};
+
+    use crate::doesnotexist;
+      //^^^^^^^^^^^^^^^^^^^ error: unresolved import
+}
+
+mod m {
+    use super::doesnotexist;
+      //^^^^^^^^^^^^^^^^^^^ error: unresolved import
+}
+"#,
+        );
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/unresolved_macro_call.rs b/crates/ide_diagnostics/src/handlers/unresolved_macro_call.rs
new file mode 100644
index 000000000..f0f7725db
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/unresolved_macro_call.rs
@@ -0,0 +1,84 @@
+use hir::{db::AstDatabase, InFile};
+use syntax::{AstNode, SyntaxNodePtr};
+
+use crate::{Diagnostic, DiagnosticsContext};
+
+// Diagnostic: unresolved-macro-call
+//
+// This diagnostic is triggered if rust-analyzer is unable to resolve the path
+// to a macro in a macro invocation.
+pub(crate) fn unresolved_macro_call(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::UnresolvedMacroCall,
+) -> Diagnostic {
+    let last_path_segment = ctx.sema.db.parse_or_expand(d.macro_call.file_id).and_then(|root| {
+        d.macro_call
+            .value
+            .to_node(&root)
+            .path()
+            .and_then(|it| it.segment())
+            .and_then(|it| it.name_ref())
+            .map(|it| InFile::new(d.macro_call.file_id, SyntaxNodePtr::new(it.syntax())))
+    });
+    let diagnostics = last_path_segment.unwrap_or_else(|| d.macro_call.clone().map(|it| it.into()));
+
+    Diagnostic::new(
+        "unresolved-macro-call",
+        format!("unresolved macro `{}!`", d.path),
+        ctx.sema.diagnostics_display_range(diagnostics).range,
+    )
+    .experimental()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    #[test]
+    fn unresolved_macro_diag() {
+        check_diagnostics(
+            r#"
+fn f() {
+    m!();
+} //^ error: unresolved macro `m!`
+
+"#,
+        );
+    }
+
+    #[test]
+    fn test_unresolved_macro_range() {
+        check_diagnostics(
+            r#"
+foo::bar!(92);
+   //^^^ error: unresolved macro `foo::bar!`
+"#,
+        );
+    }
+
+    #[test]
+    fn unresolved_legacy_scope_macro() {
+        check_diagnostics(
+            r#"
+macro_rules! m { () => {} }
+
+m!(); m2!();
+    //^^ error: unresolved macro `self::m2!`
+"#,
+        );
+    }
+
+    #[test]
+    fn unresolved_module_scope_macro() {
+        check_diagnostics(
+            r#"
+mod mac {
+#[macro_export]
+macro_rules! m { () => {} } }
+
+self::m!(); self::m2!();
+                //^^ error: unresolved macro `self::m2!`
+"#,
+        );
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/unresolved_module.rs b/crates/ide_diagnostics/src/handlers/unresolved_module.rs
new file mode 100644
index 000000000..61fc43604
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/unresolved_module.rs
@@ -0,0 +1,110 @@
+use hir::db::AstDatabase;
+use ide_db::{assists::Assist, base_db::AnchoredPathBuf, source_change::FileSystemEdit};
+use syntax::AstNode;
+
+use crate::{fix, Diagnostic, DiagnosticsContext};
+
+// Diagnostic: unresolved-module
+//
+// This diagnostic is triggered if rust-analyzer is unable to discover referred module.
+pub(crate) fn unresolved_module(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::UnresolvedModule,
+) -> Diagnostic {
+    Diagnostic::new(
+        "unresolved-module",
+        "unresolved module",
+        ctx.sema.diagnostics_display_range(d.decl.clone().map(|it| it.into())).range,
+    )
+    .with_fixes(fixes(ctx, d))
+}
+
+fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::UnresolvedModule) -> Option<Vec<Assist>> {
+    let root = ctx.sema.db.parse_or_expand(d.decl.file_id)?;
+    let unresolved_module = d.decl.value.to_node(&root);
+    Some(vec![fix(
+        "create_module",
+        "Create module",
+        FileSystemEdit::CreateFile {
+            dst: AnchoredPathBuf {
+                anchor: d.decl.file_id.original_file(ctx.sema.db),
+                path: d.candidate.clone(),
+            },
+            initial_contents: "".to_string(),
+        }
+        .into(),
+        unresolved_module.syntax().text_range(),
+    )])
+}
+
+#[cfg(test)]
+mod tests {
+    use expect_test::expect;
+
+    use crate::tests::{check_diagnostics, check_expect};
+
+    #[test]
+    fn unresolved_module() {
+        check_diagnostics(
+            r#"
+//- /lib.rs
+mod foo;
+  mod bar;
+//^^^^^^^^ 💡 error: unresolved module
+mod baz {}
+//- /foo.rs
+"#,
+        );
+    }
+
+    #[test]
+    fn test_unresolved_module_diagnostic() {
+        check_expect(
+            r#"mod foo;"#,
+            expect![[r#"
+                [
+                    Diagnostic {
+                        code: DiagnosticCode(
+                            "unresolved-module",
+                        ),
+                        message: "unresolved module",
+                        range: 0..8,
+                        severity: Error,
+                        unused: false,
+                        experimental: false,
+                        fixes: Some(
+                            [
+                                Assist {
+                                    id: AssistId(
+                                        "create_module",
+                                        QuickFix,
+                                    ),
+                                    label: "Create module",
+                                    group: None,
+                                    target: 0..8,
+                                    source_change: Some(
+                                        SourceChange {
+                                            source_file_edits: {},
+                                            file_system_edits: [
+                                                CreateFile {
+                                                    dst: AnchoredPathBuf {
+                                                        anchor: FileId(
+                                                            0,
+                                                        ),
+                                                        path: "foo.rs",
+                                                    },
+                                                    initial_contents: "",
+                                                },
+                                            ],
+                                            is_snippet: false,
+                                        },
+                                    ),
+                                },
+                            ],
+                        ),
+                    },
+                ]
+            "#]],
+        );
+    }
+}
diff --git a/crates/ide_diagnostics/src/handlers/unresolved_proc_macro.rs b/crates/ide_diagnostics/src/handlers/unresolved_proc_macro.rs
new file mode 100644
index 000000000..fde1d1323
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/unresolved_proc_macro.rs
@@ -0,0 +1,27 @@
+use crate::{Diagnostic, DiagnosticsContext, Severity};
+
+// Diagnostic: unresolved-proc-macro
+//
+// This diagnostic is shown when a procedural macro can not be found. This usually means that
+// procedural macro support is simply disabled (and hence is only a weak hint instead of an error),
+// but can also indicate project setup problems.
+//
+// If you are seeing a lot of "proc macro not expanded" warnings, you can add this option to the
+// `rust-analyzer.diagnostics.disabled` list to prevent them from showing. Alternatively you can
+// enable support for procedural macros (see `rust-analyzer.procMacro.enable`).
+pub(crate) fn unresolved_proc_macro(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::UnresolvedProcMacro,
+) -> Diagnostic {
+    // Use more accurate position if available.
+    let display_range = d
+        .precise_location
+        .unwrap_or_else(|| ctx.sema.diagnostics_display_range(d.node.clone()).range);
+    // FIXME: it would be nice to tell the user whether proc macros are currently disabled
+    let message = match &d.macro_name {
+        Some(name) => format!("proc macro `{}` not expanded", name),
+        None => "proc macro not expanded".to_string(),
+    };
+
+    Diagnostic::new("unresolved-proc-macro", message, display_range).severity(Severity::WeakWarning)
+}
diff --git a/crates/ide_diagnostics/src/handlers/useless_braces.rs b/crates/ide_diagnostics/src/handlers/useless_braces.rs
new file mode 100644
index 000000000..8b9330e04
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/useless_braces.rs
@@ -0,0 +1,148 @@
+use ide_db::{base_db::FileId, source_change::SourceChange};
+use itertools::Itertools;
+use syntax::{ast, AstNode, SyntaxNode, TextRange};
+use text_edit::TextEdit;
+
+use crate::{fix, Diagnostic, Severity};
+
+// Diagnostic: unnecessary-braces
+//
+// Diagnostic for unnecessary braces in `use` items.
+pub(crate) fn useless_braces(
+    acc: &mut Vec<Diagnostic>,
+    file_id: FileId,
+    node: &SyntaxNode,
+) -> Option<()> {
+    let use_tree_list = ast::UseTreeList::cast(node.clone())?;
+    if let Some((single_use_tree,)) = use_tree_list.use_trees().collect_tuple() {
+        // If there is a comment inside the bracketed `use`,
+        // assume it is a commented out module path and don't show diagnostic.
+        if use_tree_list.has_inner_comment() {
+            return Some(());
+        }
+
+        let use_range = use_tree_list.syntax().text_range();
+        let edit = remove_braces(&single_use_tree).unwrap_or_else(|| {
+            let to_replace = single_use_tree.syntax().text().to_string();
+            let mut edit_builder = TextEdit::builder();
+            edit_builder.delete(use_range);
+            edit_builder.insert(use_range.start(), to_replace);
+            edit_builder.finish()
+        });
+
+        acc.push(
+            Diagnostic::new(
+                "unnecessary-braces",
+                "Unnecessary braces in use statement".to_string(),
+                use_range,
+            )
+            .severity(Severity::WeakWarning)
+            .with_fixes(Some(vec![fix(
+                "remove_braces",
+                "Remove unnecessary braces",
+                SourceChange::from_text_edit(file_id, edit),
+                use_range,
+            )])),
+        );
+    }
+
+    Some(())
+}
+
+fn remove_braces(single_use_tree: &ast::UseTree) -> Option<TextEdit> {
+    let use_tree_list_node = single_use_tree.syntax().parent()?;
+    if single_use_tree.path()?.segment()?.self_token().is_some() {
+        let start = use_tree_list_node.prev_sibling_or_token()?.text_range().start();
+        let end = use_tree_list_node.text_range().end();
+        return Some(TextEdit::delete(TextRange::new(start, end)));
+    }
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_diagnostics, check_fix};
+
+    #[test]
+    fn test_check_unnecessary_braces_in_use_statement() {
+        check_diagnostics(
+            r#"
+use a;
+use a::{c, d::e};
+
+mod a {
+    mod c {}
+    mod d {
+        mod e {}
+    }
+}
+"#,
+        );
+        check_diagnostics(
+            r#"
+use a;
+use a::{
+    c,
+    // d::e
+};
+
+mod a {
+    mod c {}
+    mod d {
+        mod e {}
+    }
+}
+"#,
+        );
+        check_fix(
+            r#"
+mod b {}
+use {$0b};
+"#,
+            r#"
+mod b {}
+use b;
+"#,
+        );
+        check_fix(
+            r#"
+mod b {}
+use {b$0};
+"#,
+            r#"
+mod b {}
+use b;
+"#,
+        );
+        check_fix(
+            r#"
+mod a { mod c {} }
+use a::{c$0};
+"#,
+            r#"
+mod a { mod c {} }
+use a::c;
+"#,
+        );
+        check_fix(
+            r#"
+mod a {}
+use a::{self$0};
+"#,
+            r#"
+mod a {}
+use a;
+"#,
+        );
+        check_fix(
+            r#"
+mod a { mod c {} mod d { mod e {} } }
+use a::{c, d::{e$0}};
+"#,
+            r#"
+mod a { mod c {} mod d { mod e {} } }
+use a::{c, d::e};
+"#,
+        );
+    }
+}
diff --git a/crates/ide_diagnostics/src/lib.rs b/crates/ide_diagnostics/src/lib.rs
new file mode 100644
index 000000000..6ad1b4373
--- /dev/null
+++ b/crates/ide_diagnostics/src/lib.rs
@@ -0,0 +1,374 @@
+//! Diagnostics rendering and fixits.
+//!
+//! Most of the diagnostics originate from the dark depth of the compiler, and
+//! are originally expressed in term of IR. When we emit the diagnostic, we are
+//! usually not in the position to decide how to best "render" it in terms of
+//! user-authored source code. We are especially not in the position to offer
+//! fixits, as the compiler completely lacks the infrastructure to edit the
+//! source code.
+//!
+//! Instead, we "bubble up" raw, structured diagnostics until the `hir` crate,
+//! where we "cook" them so that each diagnostic is formulated in terms of `hir`
+//! types. Well, at least that's the aspiration, the "cooking" is somewhat
+//! ad-hoc at the moment. Anyways, we get a bunch of ide-friendly diagnostic
+//! structs from hir, and we want to render them to unified serializable
+//! representation (span, level, message) here. If we can, we also provide
+//! fixits. By the way, that's why we want to keep diagnostics structured
+//! internally -- so that we have all the info to make fixes.
+//!
+//! We have one "handler" module per diagnostic code. Such a module contains
+//! rendering, optional fixes and tests. It's OK if some low-level compiler
+//! functionality ends up being tested via a diagnostic.
+//!
+//! There are also a couple of ad-hoc diagnostics implemented directly here, we
+//! don't yet have a great pattern for how to do them properly.
+
+mod handlers {
+    pub(crate) mod break_outside_of_loop;
+    pub(crate) mod inactive_code;
+    pub(crate) mod incorrect_case;
+    pub(crate) mod macro_error;
+    pub(crate) mod mismatched_arg_count;
+    pub(crate) mod missing_fields;
+    pub(crate) mod missing_match_arms;
+    pub(crate) mod missing_ok_or_some_in_tail_expr;
+    pub(crate) mod missing_unsafe;
+    pub(crate) mod no_such_field;
+    pub(crate) mod remove_this_semicolon;
+    pub(crate) mod replace_filter_map_next_with_find_map;
+    pub(crate) mod unimplemented_builtin_macro;
+    pub(crate) mod unresolved_extern_crate;
+    pub(crate) mod unresolved_import;
+    pub(crate) mod unresolved_macro_call;
+    pub(crate) mod unresolved_module;
+    pub(crate) mod unresolved_proc_macro;
+
+    // The handlers bellow are unusual, the implement the diagnostics as well.
+    pub(crate) mod field_shorthand;
+    pub(crate) mod useless_braces;
+    pub(crate) mod unlinked_file;
+}
+
+use hir::{diagnostics::AnyDiagnostic, Semantics};
+use ide_db::{
+    assists::{Assist, AssistId, AssistKind, AssistResolveStrategy},
+    base_db::{FileId, SourceDatabase},
+    label::Label,
+    source_change::SourceChange,
+    RootDatabase,
+};
+use rustc_hash::FxHashSet;
+use syntax::{ast::AstNode, TextRange};
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub struct DiagnosticCode(pub &'static str);
+
+impl DiagnosticCode {
+    pub fn as_str(&self) -> &str {
+        self.0
+    }
+}
+
+#[derive(Debug)]
+pub struct Diagnostic {
+    pub code: DiagnosticCode,
+    pub message: String,
+    pub range: TextRange,
+    pub severity: Severity,
+    pub unused: bool,
+    pub experimental: bool,
+    pub fixes: Option<Vec<Assist>>,
+}
+
+impl Diagnostic {
+    fn new(code: &'static str, message: impl Into<String>, range: TextRange) -> Diagnostic {
+        let message = message.into();
+        Diagnostic {
+            code: DiagnosticCode(code),
+            message,
+            range,
+            severity: Severity::Error,
+            unused: false,
+            experimental: false,
+            fixes: None,
+        }
+    }
+
+    fn experimental(mut self) -> Diagnostic {
+        self.experimental = true;
+        self
+    }
+
+    fn severity(mut self, severity: Severity) -> Diagnostic {
+        self.severity = severity;
+        self
+    }
+
+    fn with_fixes(mut self, fixes: Option<Vec<Assist>>) -> Diagnostic {
+        self.fixes = fixes;
+        self
+    }
+
+    fn with_unused(mut self, unused: bool) -> Diagnostic {
+        self.unused = unused;
+        self
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+pub enum Severity {
+    Error,
+    // We don't actually emit this one yet, but we should at some point.
+    // Warning,
+    WeakWarning,
+}
+
+#[derive(Default, Debug, Clone)]
+pub struct DiagnosticsConfig {
+    pub disable_experimental: bool,
+    pub disabled: FxHashSet<String>,
+}
+
+struct DiagnosticsContext<'a> {
+    config: &'a DiagnosticsConfig,
+    sema: Semantics<'a, RootDatabase>,
+    resolve: &'a AssistResolveStrategy,
+}
+
+pub fn diagnostics(
+    db: &RootDatabase,
+    config: &DiagnosticsConfig,
+    resolve: &AssistResolveStrategy,
+    file_id: FileId,
+) -> Vec<Diagnostic> {
+    let _p = profile::span("diagnostics");
+    let sema = Semantics::new(db);
+    let parse = db.parse(file_id);
+    let mut res = Vec::new();
+
+    // [#34344] Only take first 128 errors to prevent slowing down editor/ide, the number 128 is chosen arbitrarily.
+    res.extend(
+        parse.errors().iter().take(128).map(|err| {
+            Diagnostic::new("syntax-error", format!("Syntax Error: {}", err), err.range())
+        }),
+    );
+
+    for node in parse.tree().syntax().descendants() {
+        handlers::useless_braces::useless_braces(&mut res, file_id, &node);
+        handlers::field_shorthand::field_shorthand(&mut res, file_id, &node);
+    }
+
+    let module = sema.to_module_def(file_id);
+
+    let ctx = DiagnosticsContext { config, sema, resolve };
+    if module.is_none() {
+        handlers::unlinked_file::unlinked_file(&ctx, &mut res, file_id);
+    }
+
+    let mut diags = Vec::new();
+    if let Some(m) = module {
+        m.diagnostics(db, &mut diags)
+    }
+
+    for diag in diags {
+        #[rustfmt::skip]
+        let d = match diag {
+            AnyDiagnostic::BreakOutsideOfLoop(d) => handlers::break_outside_of_loop::break_outside_of_loop(&ctx, &d),
+            AnyDiagnostic::IncorrectCase(d) => handlers::incorrect_case::incorrect_case(&ctx, &d),
+            AnyDiagnostic::MacroError(d) => handlers::macro_error::macro_error(&ctx, &d),
+            AnyDiagnostic::MismatchedArgCount(d) => handlers::mismatched_arg_count::mismatched_arg_count(&ctx, &d),
+            AnyDiagnostic::MissingFields(d) => handlers::missing_fields::missing_fields(&ctx, &d),
+            AnyDiagnostic::MissingMatchArms(d) => handlers::missing_match_arms::missing_match_arms(&ctx, &d),
+            AnyDiagnostic::MissingOkOrSomeInTailExpr(d) => handlers::missing_ok_or_some_in_tail_expr::missing_ok_or_some_in_tail_expr(&ctx, &d),
+            AnyDiagnostic::MissingUnsafe(d) => handlers::missing_unsafe::missing_unsafe(&ctx, &d),
+            AnyDiagnostic::NoSuchField(d) => handlers::no_such_field::no_such_field(&ctx, &d),
+            AnyDiagnostic::RemoveThisSemicolon(d) => handlers::remove_this_semicolon::remove_this_semicolon(&ctx, &d),
+            AnyDiagnostic::ReplaceFilterMapNextWithFindMap(d) => handlers::replace_filter_map_next_with_find_map::replace_filter_map_next_with_find_map(&ctx, &d),
+            AnyDiagnostic::UnimplementedBuiltinMacro(d) => handlers::unimplemented_builtin_macro::unimplemented_builtin_macro(&ctx, &d),
+            AnyDiagnostic::UnresolvedExternCrate(d) => handlers::unresolved_extern_crate::unresolved_extern_crate(&ctx, &d),
+            AnyDiagnostic::UnresolvedImport(d) => handlers::unresolved_import::unresolved_import(&ctx, &d),
+            AnyDiagnostic::UnresolvedMacroCall(d) => handlers::unresolved_macro_call::unresolved_macro_call(&ctx, &d),
+            AnyDiagnostic::UnresolvedModule(d) => handlers::unresolved_module::unresolved_module(&ctx, &d),
+            AnyDiagnostic::UnresolvedProcMacro(d) => handlers::unresolved_proc_macro::unresolved_proc_macro(&ctx, &d),
+
+            AnyDiagnostic::InactiveCode(d) => match handlers::inactive_code::inactive_code(&ctx, &d) {
+                Some(it) => it,
+                None => continue,
+            }
+        };
+        res.push(d)
+    }
+
+    res.retain(|d| {
+        !ctx.config.disabled.contains(d.code.as_str())
+            && !(ctx.config.disable_experimental && d.experimental)
+    });
+
+    res
+}
+
+fn fix(id: &'static str, label: &str, source_change: SourceChange, target: TextRange) -> Assist {
+    let mut res = unresolved_fix(id, label, target);
+    res.source_change = Some(source_change);
+    res
+}
+
+fn unresolved_fix(id: &'static str, label: &str, target: TextRange) -> Assist {
+    assert!(!id.contains(' '));
+    Assist {
+        id: AssistId(id, AssistKind::QuickFix),
+        label: Label::new(label),
+        group: None,
+        target,
+        source_change: None,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use expect_test::Expect;
+    use ide_db::{
+        assists::AssistResolveStrategy,
+        base_db::{fixture::WithFixture, SourceDatabaseExt},
+        RootDatabase,
+    };
+    use stdx::trim_indent;
+    use test_utils::{assert_eq_text, extract_annotations};
+
+    use crate::{DiagnosticsConfig, Severity};
+
+    /// Takes a multi-file input fixture with annotated cursor positions,
+    /// and checks that:
+    ///  * a diagnostic is produced
+    ///  * the first diagnostic fix trigger range touches the input cursor position
+    ///  * that the contents of the file containing the cursor match `after` after the diagnostic fix is applied
+    #[track_caller]
+    pub(crate) fn check_fix(ra_fixture_before: &str, ra_fixture_after: &str) {
+        check_nth_fix(0, ra_fixture_before, ra_fixture_after);
+    }
+    /// Takes a multi-file input fixture with annotated cursor positions,
+    /// and checks that:
+    ///  * a diagnostic is produced
+    ///  * every diagnostic fixes trigger range touches the input cursor position
+    ///  * that the contents of the file containing the cursor match `after` after each diagnostic fix is applied
+    pub(crate) fn check_fixes(ra_fixture_before: &str, ra_fixtures_after: Vec<&str>) {
+        for (i, ra_fixture_after) in ra_fixtures_after.iter().enumerate() {
+            check_nth_fix(i, ra_fixture_before, ra_fixture_after)
+        }
+    }
+
+    #[track_caller]
+    fn check_nth_fix(nth: usize, ra_fixture_before: &str, ra_fixture_after: &str) {
+        let after = trim_indent(ra_fixture_after);
+
+        let (db, file_position) = RootDatabase::with_position(ra_fixture_before);
+        let diagnostic = super::diagnostics(
+            &db,
+            &DiagnosticsConfig::default(),
+            &AssistResolveStrategy::All,
+            file_position.file_id,
+        )
+        .pop()
+        .expect("no diagnostics");
+        let fix = &diagnostic.fixes.expect("diagnostic misses fixes")[nth];
+        let actual = {
+            let source_change = fix.source_change.as_ref().unwrap();
+            let file_id = *source_change.source_file_edits.keys().next().unwrap();
+            let mut actual = db.file_text(file_id).to_string();
+
+            for edit in source_change.source_file_edits.values() {
+                edit.apply(&mut actual);
+            }
+            actual
+        };
+
+        assert_eq_text!(&after, &actual);
+        assert!(
+            fix.target.contains_inclusive(file_position.offset),
+            "diagnostic fix range {:?} does not touch cursor position {:?}",
+            fix.target,
+            file_position.offset
+        );
+    }
+
+    /// Checks that there's a diagnostic *without* fix at `$0`.
+    pub(crate) fn check_no_fix(ra_fixture: &str) {
+        let (db, file_position) = RootDatabase::with_position(ra_fixture);
+        let diagnostic = super::diagnostics(
+            &db,
+            &DiagnosticsConfig::default(),
+            &AssistResolveStrategy::All,
+            file_position.file_id,
+        )
+        .pop()
+        .unwrap();
+        assert!(diagnostic.fixes.is_none(), "got a fix when none was expected: {:?}", diagnostic);
+    }
+
+    pub(crate) fn check_expect(ra_fixture: &str, expect: Expect) {
+        let (db, file_id) = RootDatabase::with_single_file(ra_fixture);
+        let diagnostics = super::diagnostics(
+            &db,
+            &DiagnosticsConfig::default(),
+            &AssistResolveStrategy::All,
+            file_id,
+        );
+        expect.assert_debug_eq(&diagnostics)
+    }
+
+    #[track_caller]
+    pub(crate) fn check_diagnostics(ra_fixture: &str) {
+        let mut config = DiagnosticsConfig::default();
+        config.disabled.insert("inactive-code".to_string());
+        check_diagnostics_with_config(config, ra_fixture)
+    }
+
+    #[track_caller]
+    pub(crate) fn check_diagnostics_with_config(config: DiagnosticsConfig, ra_fixture: &str) {
+        let (db, files) = RootDatabase::with_many_files(ra_fixture);
+        for file_id in files {
+            let diagnostics =
+                super::diagnostics(&db, &config, &AssistResolveStrategy::All, file_id);
+
+            let expected = extract_annotations(&*db.file_text(file_id));
+            let mut actual = diagnostics
+                .into_iter()
+                .map(|d| {
+                    let mut annotation = String::new();
+                    if let Some(fixes) = &d.fixes {
+                        assert!(!fixes.is_empty());
+                        annotation.push_str("💡 ")
+                    }
+                    annotation.push_str(match d.severity {
+                        Severity::Error => "error",
+                        Severity::WeakWarning => "weak",
+                    });
+                    annotation.push_str(": ");
+                    annotation.push_str(&d.message);
+                    (d.range, annotation)
+                })
+                .collect::<Vec<_>>();
+            actual.sort_by_key(|(range, _)| range.start());
+            assert_eq!(expected, actual);
+        }
+    }
+
+    #[test]
+    fn test_disabled_diagnostics() {
+        let mut config = DiagnosticsConfig::default();
+        config.disabled.insert("unresolved-module".into());
+
+        let (db, file_id) = RootDatabase::with_single_file(r#"mod foo;"#);
+
+        let diagnostics = super::diagnostics(&db, &config, &AssistResolveStrategy::All, file_id);
+        assert!(diagnostics.is_empty());
+
+        let diagnostics = super::diagnostics(
+            &db,
+            &DiagnosticsConfig::default(),
+            &AssistResolveStrategy::All,
+            file_id,
+        );
+        assert!(!diagnostics.is_empty());
+    }
+}