Merge #9255

9255: internal: remove DiagnosticWithFix infra r=matklad a=matklad

bors r+
🤖

Co-authored-by: Aleksey Kladov <[email protected]>

4 files changed, 678 insertions, 249 deletions

diff --git a/crates/ide/src/diagnostics/fixes.rs b/crates/ide/src/diagnostics/fixes.rs
deleted file mode 100644
index e4bd90c3f..000000000
--- a/crates/ide/src/diagnostics/fixes.rs
+++ /dev/null
@@ -1,25 +0,0 @@
-//! Provides a way to attach fixes to the diagnostics.
-//! The same module also has all curret custom fixes for the diagnostics implemented.
-mod change_case;
-
-use hir::{diagnostics::Diagnostic, Semantics};
-use ide_assists::AssistResolveStrategy;
-use ide_db::RootDatabase;
-
-use crate::Assist;
-
-/// A [Diagnostic] that potentially has some fixes available.
-///
-/// [Diagnostic]: hir::diagnostics::Diagnostic
-pub(crate) trait DiagnosticWithFixes: Diagnostic {
-    /// `resolve` determines if the diagnostic should fill in the `edit` field
-    /// of the assist.
-    ///
-    /// If `resolve` is false, the edit will be computed later, on demand, and
-    /// can be omitted.
-    fn fixes(
-        &self,
-        sema: &Semantics<RootDatabase>,
-        _resolve: &AssistResolveStrategy,
-    ) -> Option<Vec<Assist>>;
-}
diff --git a/crates/ide/src/diagnostics/fixes/change_case.rs b/crates/ide/src/diagnostics/fixes/change_case.rs
deleted file mode 100644
index db1a37cd6..000000000
--- a/crates/ide/src/diagnostics/fixes/change_case.rs
+++ /dev/null
@@ -1,155 +0,0 @@
-use hir::{db::AstDatabase, diagnostics::IncorrectCase, InFile, Semantics};
-use ide_assists::{Assist, AssistResolveStrategy};
-use ide_db::{base_db::FilePosition, RootDatabase};
-use syntax::AstNode;
-
-use crate::{
-    diagnostics::{unresolved_fix, DiagnosticWithFixes},
-    references::rename::rename_with_semantics,
-};
-
-impl DiagnosticWithFixes for IncorrectCase {
-    fn fixes(
-        &self,
-        sema: &Semantics<RootDatabase>,
-        resolve: &AssistResolveStrategy,
-    ) -> Option<Vec<Assist>> {
-        let root = sema.db.parse_or_expand(self.file)?;
-        let name_node = self.ident.to_node(&root);
-
-        let name_node = InFile::new(self.file, name_node.syntax());
-        let frange = name_node.original_file_range(sema.db);
-        let file_position = FilePosition { file_id: frange.file_id, offset: frange.range.start() };
-
-        let label = format!("Rename to {}", self.suggested_text);
-        let mut res = unresolved_fix("change_case", &label, frange.range);
-        if resolve.should_resolve(&res.id) {
-            let source_change = rename_with_semantics(sema, file_position, &self.suggested_text);
-            res.source_change = Some(source_change.ok().unwrap_or_default());
-        }
-
-        Some(vec![res])
-    }
-}
-
-#[cfg(test)]
-mod change_case {
-    use crate::{
-        diagnostics::tests::{check_diagnostics, check_fix},
-        fixture, AssistResolveStrategy, DiagnosticsConfig,
-    };
-
-    #[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$0: &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() {
-        let input = r#"fn FOO$0() {}"#;
-        let expected = r#"fn foo() {}"#;
-
-        let (analysis, file_position) = fixture::position(input);
-        let diagnostics = analysis
-            .diagnostics(
-                &DiagnosticsConfig::default(),
-                AssistResolveStrategy::All,
-                file_position.file_id,
-            )
-            .unwrap();
-        assert_eq!(diagnostics.len(), 1);
-
-        check_fix(input, expected);
-    }
-}
diff --git a/crates/ide/src/diagnostics/incorrect_case.rs b/crates/ide/src/diagnostics/incorrect_case.rs
new file mode 100644
index 000000000..832394400
--- /dev/null
+++ b/crates/ide/src/diagnostics/incorrect_case.rs
@@ -0,0 +1,488 @@
+use hir::{db::AstDatabase, InFile};
+use ide_assists::Assist;
+use ide_db::base_db::FilePosition;
+use syntax::AstNode;
+
+use crate::{
+    diagnostics::{unresolved_fix, Diagnostic, DiagnosticsContext},
+    references::rename::rename_with_semantics,
+    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(super) 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 name_node = InFile::new(d.file, name_node.syntax());
+    let frange = name_node.original_file_range(ctx.sema.db);
+    let file_position = FilePosition { file_id: frange.file_id, offset: frange.range.start() };
+
+    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 = rename_with_semantics(&ctx.sema, file_position, &d.suggested_text);
+        res.source_change = Some(source_change.ok().unwrap_or_default());
+    }
+
+    Some(vec![res])
+}
+
+#[cfg(test)]
+mod change_case {
+    use crate::{
+        diagnostics::tests::{check_diagnostics, check_fix},
+        fixture, AssistResolveStrategy, DiagnosticsConfig,
+    };
+
+    #[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$0: &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() {
+        let input = r#"fn FOO$0() {}"#;
+        let expected = r#"fn foo() {}"#;
+
+        let (analysis, file_position) = fixture::position(input);
+        let diagnostics = analysis
+            .diagnostics(
+                &DiagnosticsConfig::default(),
+                AssistResolveStrategy::All,
+                file_position.file_id,
+            )
+            .unwrap();
+        assert_eq!(diagnostics.len(), 1);
+
+        check_fix(input, expected);
+    }
+
+    #[test]
+    fn incorrect_function_name() {
+        check_diagnostics(
+            r#"
+fn NonSnakeCaseName() {}
+// ^^^^^^^^^^^^^^^^ 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) {}
+    // ^^^^^^^^^ Parameter `SomeParam` should have snake_case name, e.g. `some_param`
+
+fn foo2(ok_param: &str, CAPS_PARAM: u8) {}
+                     // ^^^^^^^^^^ 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;
+     // ^^^^^^^^^^ Variable `SOME_VALUE` should have snake_case name, e.g. `some_value`
+    let AnotherValue = 20;
+     // ^^^^^^^^^^^^ Variable `AnotherValue` should have snake_case name, e.g. `another_value`
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_struct_names() {
+        check_diagnostics(
+            r#"
+struct non_camel_case_name {}
+    // ^^^^^^^^^^^^^^^^^^^ Structure `non_camel_case_name` should have CamelCase name, e.g. `NonCamelCaseName`
+
+struct SCREAMING_CASE {}
+    // ^^^^^^^^^^^^^^ 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 }
+                 // ^^^^^^^^^ Field `SomeField` should have snake_case name, e.g. `some_field`
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_enum_names() {
+        check_diagnostics(
+            r#"
+enum some_enum { Val(u8) }
+  // ^^^^^^^^^ Enum `some_enum` should have CamelCase name, e.g. `SomeEnum`
+
+enum SOME_ENUM {}
+  // ^^^^^^^^^ 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) }
+             // ^^^^^^^^^^^^ Variant `SOME_VARIANT` should have CamelCase name, e.g. `SomeVariant`
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_const_name() {
+        check_diagnostics(
+            r#"
+const some_weird_const: u8 = 10;
+   // ^^^^^^^^^^^^^^^^ 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;
+    // ^^^^^^^^^^^^^^^^ 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;
+    // ^^^^^^^^^^ Structure `someStruct` should have CamelCase name, e.g. `SomeStruct`
+
+impl someStruct {
+    fn SomeFunc(&self) {
+    // ^^^^^^^^ Function `SomeFunc` should have snake_case name, e.g. `some_func`
+        let WHY_VAR_IS_CAPS = 10;
+         // ^^^^^^^^^^^^^^^ 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 => (),
+     // ^^^^^^^^ 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]
+    #[ignore]
+    fn bug_trait_inside_fn() {
+        // FIXME:
+        // This is broken, and in fact, should not even be looked at by this
+        // lint in the first place. There's weird stuff going on in the
+        // collection phase.
+        // It's currently being brought in by:
+        // * validate_func on `a` recursing into modules
+        // * then it finds the trait and then the function while iterating
+        //   through modules
+        // * then validate_func is called on Dirty
+        // * ... which then proceeds to look at some unknown module taking no
+        //   attrs from either the impl or the fn a, and then finally to the root
+        //   module
+        //
+        // It should find the attribute on the trait, but it *doesn't even see
+        // the trait* as far as I can tell.
+
+        check_diagnostics(
+            r#"
+trait T { fn a(); }
+struct U {}
+impl T for U {
+    fn a() {
+        // this comes out of bitflags, mostly
+        #[allow(non_snake_case)]
+        trait __BitFlags {
+            const HiImAlsoBad: u8 = 2;
+            #[inline]
+            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]
+    #[ignore]
+    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 {
+    // ^^^^^^^^^ Trait `BAD_TRAIT` should have CamelCase name, e.g. `BadTrait`
+    fn BAD_FUNCTION();
+    // ^^^^^^^^^^^^ Function `BAD_FUNCTION` should have snake_case name, e.g. `bad_function`
+    fn BadFunction();
+    // ^^^^^^^^^^^^ Function `BadFunction` should have snake_case name, e.g. `bad_function`
+}
+    "#,
+        );
+    }
+
+    #[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/src/diagnostics/unlinked_file.rs b/crates/ide/src/diagnostics/unlinked_file.rs
index 51fe0f360..a5b2e3399 100644
--- a/crates/ide/src/diagnostics/unlinked_file.rs
+++ b/crates/ide/src/diagnostics/unlinked_file.rs
@@ -1,11 +1,6 @@
 //! Diagnostic emitted for files that aren't part of any crate.
 
-use hir::{
-    db::DefDatabase,
-    diagnostics::{Diagnostic, DiagnosticCode},
-    InFile,
-};
-use ide_assists::AssistResolveStrategy;
+use hir::db::DefDatabase;
 use ide_db::{
     base_db::{FileId, FileLoader, SourceDatabase, SourceDatabaseExt},
     source_change::SourceChange,
@@ -13,92 +8,77 @@ use ide_db::{
 };
 use syntax::{
     ast::{self, ModuleItemOwner, NameOwner},
-    AstNode, SyntaxNodePtr,
+    AstNode, TextRange, TextSize,
 };
 use text_edit::TextEdit;
 
 use crate::{
-    diagnostics::{fix, fixes::DiagnosticWithFixes},
-    Assist,
+    diagnostics::{fix, DiagnosticsContext},
+    Assist, Diagnostic,
 };
 
+#[derive(Debug)]
+pub(crate) struct UnlinkedFile {
+    pub(crate) file: FileId,
+}
+
 // 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.
-#[derive(Debug)]
-pub(crate) struct UnlinkedFile {
-    pub(crate) file_id: FileId,
-    pub(crate) node: SyntaxNodePtr,
+pub(super) fn unlinked_file(ctx: &DiagnosticsContext, d: &UnlinkedFile) -> Diagnostic {
+    // 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(d.file).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);
+
+    Diagnostic::new("unlinked-file", "file not included in module tree", range)
+        .with_fixes(fixes(ctx, d))
 }
 
-impl Diagnostic for UnlinkedFile {
-    fn code(&self) -> DiagnosticCode {
-        DiagnosticCode("unlinked-file")
-    }
+fn fixes(ctx: &DiagnosticsContext, d: &UnlinkedFile) -> 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.
 
-    fn message(&self) -> String {
-        "file not included in module tree".to_string()
-    }
+    let source_root = ctx.sema.db.source_root(ctx.sema.db.file_source_root(d.file));
+    let our_path = source_root.path_for_file(&d.file)?;
+    let module_name = our_path.name_and_extension()?.0;
 
-    fn display_source(&self) -> InFile<SyntaxNodePtr> {
-        InFile::new(self.file_id.into(), self.node.clone())
-    }
+    // 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")?];
 
-    fn as_any(&self) -> &(dyn std::any::Any + Send + 'static) {
-        self
+    // `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);
     }
-}
 
-impl DiagnosticWithFixes for UnlinkedFile {
-    fn fixes(
-        &self,
-        sema: &hir::Semantics<RootDatabase>,
-        _resolve: &AssistResolveStrategy,
-    ) -> 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 = sema.db.source_root(sema.db.file_source_root(self.file_id));
-        let our_path = source_root.path_for_file(&self.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;
+                    }
 
-        for path in &paths {
-            if let Some(parent_id) = source_root.file_for_path(path) {
-                for krate in sema.db.relevant_crates(*parent_id).iter() {
-                    let crate_def_map = 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(sema.db, *parent_id, module_name, self.file_id);
-                        }
+                    if module.origin.file_id() == Some(*parent_id) {
+                        return make_fixes(ctx.sema.db, *parent_id, module_name, d.file);
                     }
                 }
             }
         }
-
-        None
     }
+
+    None
 }
 
 fn make_fixes(
@@ -181,3 +161,144 @@ fn make_fixes(
         ),
     ])
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::diagnostics::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
+"#,
+        );
+    }
+}