8 files changed, 355 insertions, 84 deletions

diff --git a/crates/assists/src/handlers/generate_enum_match_method.rs b/crates/assists/src/handlers/generate_enum_match_method.rs
new file mode 100644
index 000000000..ee89d4208
--- /dev/null
+++ b/crates/assists/src/handlers/generate_enum_match_method.rs
@@ -0,0 +1,221 @@
+use stdx::{format_to, to_lower_snake_case};
+use syntax::ast::{self, AstNode, NameOwner};
+use syntax::{ast::VisibilityOwner, T};
+use test_utils::mark;
+
+use crate::{utils::find_struct_impl, AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: generate_enum_match_method
+//
+// Generate an `is_` method for an enum variant.
+//
+// ```
+// enum Version {
+//  Undefined,
+//  Minor$0,
+//  Major,
+// }
+// ```
+// ->
+// ```
+// enum Version {
+//  Undefined,
+//  Minor,
+//  Major,
+// }
+//
+// impl Version {
+//     /// Returns `true` if the version is [`Minor`].
+//     fn is_minor(&self) -> bool {
+//         matches!(self, Self::Minor)
+//     }
+// }
+// ```
+pub(crate) fn generate_enum_match_method(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let variant = ctx.find_node_at_offset::<ast::Variant>()?;
+    let variant_name = variant.name()?;
+    let parent_enum = variant.parent_enum();
+    if !matches!(variant.kind(), ast::StructKind::Unit) {
+        mark::hit!(test_gen_enum_match_on_non_unit_variant_not_implemented);
+        return None;
+    }
+
+    let enum_lowercase_name = to_lower_snake_case(&parent_enum.name()?.to_string());
+    let fn_name = to_lower_snake_case(&variant_name.to_string());
+
+    // Return early if we've found an existing new fn
+    let impl_def = find_struct_impl(
+        &ctx,
+        &ast::AdtDef::Enum(parent_enum.clone()),
+        format!("is_{}", fn_name).as_str(),
+    )?;
+
+    let target = variant.syntax().text_range();
+    acc.add(
+        AssistId("generate_enum_match_method", AssistKind::Generate),
+        "Generate an `is_` method for an enum variant",
+        target,
+        |builder| {
+            let mut buf = String::with_capacity(512);
+
+            if impl_def.is_some() {
+                buf.push('\n');
+            }
+
+            let vis = parent_enum.visibility().map_or(String::new(), |v| format!("{} ", v));
+
+            format_to!(
+                buf,
+                "    /// Returns `true` if the {} is [`{}`].
+    {}fn is_{}(&self) -> bool {{
+        matches!(self, Self::{})
+    }}",
+                enum_lowercase_name,
+                variant_name,
+                vis,
+                fn_name,
+                variant_name
+            );
+
+            let start_offset = impl_def
+                .and_then(|impl_def| {
+                    buf.push('\n');
+                    let start = impl_def
+                        .syntax()
+                        .descendants_with_tokens()
+                        .find(|t| t.kind() == T!['{'])?
+                        .text_range()
+                        .end();
+
+                    Some(start)
+                })
+                .unwrap_or_else(|| {
+                    buf = generate_impl_text(&parent_enum, &buf);
+                    parent_enum.syntax().text_range().end()
+                });
+
+            builder.insert(start_offset, buf);
+        },
+    )
+}
+
+// Generates the surrounding `impl Type { <code> }` including type and lifetime
+// parameters
+fn generate_impl_text(strukt: &ast::Enum, code: &str) -> String {
+    let mut buf = String::with_capacity(code.len());
+    buf.push_str("\n\nimpl ");
+    buf.push_str(strukt.name().unwrap().text());
+    format_to!(buf, " {{\n{}\n}}", code);
+    buf
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::mark;
+
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    fn check_not_applicable(ra_fixture: &str) {
+        check_assist_not_applicable(generate_enum_match_method, ra_fixture)
+    }
+
+    #[test]
+    fn test_generate_enum_match_from_variant() {
+        check_assist(
+            generate_enum_match_method,
+            r#"
+enum Variant {
+    Undefined,
+    Minor$0,
+    Major,
+}"#,
+            r#"enum Variant {
+    Undefined,
+    Minor,
+    Major,
+}
+
+impl Variant {
+    /// Returns `true` if the variant is [`Minor`].
+    fn is_minor(&self) -> bool {
+        matches!(self, Self::Minor)
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_generate_enum_match_already_implemented() {
+        check_not_applicable(
+            r#"
+enum Variant {
+    Undefined,
+    Minor$0,
+    Major,
+}
+
+impl Variant {
+    fn is_minor(&self) -> bool {
+        matches!(self, Self::Minor)
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_add_from_impl_no_element() {
+        mark::check!(test_gen_enum_match_on_non_unit_variant_not_implemented);
+        check_not_applicable(
+            r#"
+enum Variant {
+    Undefined,
+    Minor(u32)$0,
+    Major,
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_generate_enum_match_from_variant_with_one_variant() {
+        check_assist(
+            generate_enum_match_method,
+            r#"enum Variant { Undefi$0ned }"#,
+            r#"
+enum Variant { Undefined }
+
+impl Variant {
+    /// Returns `true` if the variant is [`Undefined`].
+    fn is_undefined(&self) -> bool {
+        matches!(self, Self::Undefined)
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_generate_enum_match_from_variant_with_visibility_marker() {
+        check_assist(
+            generate_enum_match_method,
+            r#"
+pub(crate) enum Variant {
+    Undefined,
+    Minor$0,
+    Major,
+}"#,
+            r#"pub(crate) enum Variant {
+    Undefined,
+    Minor,
+    Major,
+}
+
+impl Variant {
+    /// Returns `true` if the variant is [`Minor`].
+    pub(crate) fn is_minor(&self) -> bool {
+        matches!(self, Self::Minor)
+    }
+}"#,
+        );
+    }
+}
diff --git a/crates/assists/src/handlers/generate_new.rs b/crates/assists/src/handlers/generate_new.rs
index b7390855a..84832273f 100644
--- a/crates/assists/src/handlers/generate_new.rs
+++ b/crates/assists/src/handlers/generate_new.rs
@@ -1,4 +1,3 @@
-use hir::Adt;
 use itertools::Itertools;
 use stdx::format_to;
 use syntax::{
@@ -6,7 +5,7 @@ use syntax::{
     SmolStr, T,
 };
 
-use crate::{AssistContext, AssistId, AssistKind, Assists};
+use crate::{utils::find_struct_impl, AssistContext, AssistId, AssistKind, Assists};
 
 // Assist: generate_new
 //
@@ -38,7 +37,7 @@ pub(crate) fn generate_new(acc: &mut Assists, ctx: &AssistContext) -> Option<()>
     };
 
     // Return early if we've found an existing new fn
-    let impl_def = find_struct_impl(&ctx, &strukt)?;
+    let impl_def = find_struct_impl(&ctx, &ast::AdtDef::Struct(strukt.clone()), "new")?;
 
     let target = strukt.syntax().text_range();
     acc.add(AssistId("generate_new", AssistKind::Generate), "Generate `new`", target, |builder| {
@@ -111,65 +110,6 @@ fn generate_impl_text(strukt: &ast::Struct, code: &str) -> String {
     buf
 }
 
-// Uses a syntax-driven approach to find any impl blocks for the struct that
-// exist within the module/file
-//
-// Returns `None` if we've found an existing `new` fn
-//
-// FIXME: change the new fn checking to a more semantic approach when that's more
-// viable (e.g. we process proc macros, etc)
-fn find_struct_impl(ctx: &AssistContext, strukt: &ast::Struct) -> Option<Option<ast::Impl>> {
-    let db = ctx.db();
-    let module = strukt.syntax().ancestors().find(|node| {
-        ast::Module::can_cast(node.kind()) || ast::SourceFile::can_cast(node.kind())
-    })?;
-
-    let struct_def = ctx.sema.to_def(strukt)?;
-
-    let block = module.descendants().filter_map(ast::Impl::cast).find_map(|impl_blk| {
-        let blk = ctx.sema.to_def(&impl_blk)?;
-
-        // FIXME: handle e.g. `struct S<T>; impl<U> S<U> {}`
-        // (we currently use the wrong type parameter)
-        // also we wouldn't want to use e.g. `impl S<u32>`
-        let same_ty = match blk.target_ty(db).as_adt() {
-            Some(def) => def == Adt::Struct(struct_def),
-            None => false,
-        };
-        let not_trait_impl = blk.target_trait(db).is_none();
-
-        if !(same_ty && not_trait_impl) {
-            None
-        } else {
-            Some(impl_blk)
-        }
-    });
-
-    if let Some(ref impl_blk) = block {
-        if has_new_fn(impl_blk) {
-            return None;
-        }
-    }
-
-    Some(block)
-}
-
-fn has_new_fn(imp: &ast::Impl) -> bool {
-    if let Some(il) = imp.assoc_item_list() {
-        for item in il.assoc_items() {
-            if let ast::AssocItem::Fn(f) = item {
-                if let Some(name) = f.name() {
-                    if name.text().eq_ignore_ascii_case("new") {
-                        return true;
-                    }
-                }
-            }
-        }
-    }
-
-    false
-}
-
 #[cfg(test)]
 mod tests {
     use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
diff --git a/crates/assists/src/lib.rs b/crates/assists/src/lib.rs
index 062a902ab..83fbf6986 100644
--- a/crates/assists/src/lib.rs
+++ b/crates/assists/src/lib.rs
@@ -127,6 +127,7 @@ mod handlers {
     mod flip_trait_bound;
     mod generate_default_from_enum_variant;
     mod generate_derive;
+    mod generate_enum_match_method;
     mod generate_from_impl_for_enum;
     mod generate_function;
     mod generate_impl;
@@ -185,6 +186,7 @@ mod handlers {
             flip_trait_bound::flip_trait_bound,
             generate_default_from_enum_variant::generate_default_from_enum_variant,
             generate_derive::generate_derive,
+            generate_enum_match_method::generate_enum_match_method,
             generate_from_impl_for_enum::generate_from_impl_for_enum,
             generate_function::generate_function,
             generate_impl::generate_impl,
diff --git a/crates/assists/src/tests/generated.rs b/crates/assists/src/tests/generated.rs
index e84f208a3..0dbb05f2a 100644
--- a/crates/assists/src/tests/generated.rs
+++ b/crates/assists/src/tests/generated.rs
@@ -460,6 +460,34 @@ struct Point {
 }
 
 #[test]
+fn doctest_generate_enum_match_method() {
+    check_doc_test(
+        "generate_enum_match_method",
+        r#####"
+enum Version {
+ Undefined,
+ Minor$0,
+ Major,
+}
+"#####,
+        r#####"
+enum Version {
+ Undefined,
+ Minor,
+ Major,
+}
+
+impl Version {
+    /// Returns `true` if the version is [`Minor`].
+    fn is_minor(&self) -> bool {
+        matches!(self, Self::Minor)
+    }
+}
+"#####,
+    )
+}
+
+#[test]
 fn doctest_generate_from_impl_for_enum() {
     check_doc_test(
         "generate_from_impl_for_enum",
diff --git a/crates/assists/src/utils.rs b/crates/assists/src/utils.rs
index 4e762e18b..3842558d8 100644
--- a/crates/assists/src/utils.rs
+++ b/crates/assists/src/utils.rs
@@ -2,7 +2,7 @@
 
 use std::ops;
 
-use hir::HasSource;
+use hir::{Adt, HasSource};
 use ide_db::{helpers::SnippetCap, RootDatabase};
 use itertools::Itertools;
 use syntax::{
@@ -15,7 +15,10 @@ use syntax::{
     SyntaxNode, TextSize, T,
 };
 
-use crate::ast_transform::{self, AstTransform, QualifyPaths, SubstituteTypeParams};
+use crate::{
+    assist_context::AssistContext,
+    ast_transform::{self, AstTransform, QualifyPaths, SubstituteTypeParams},
+};
 
 pub(crate) fn unwrap_trivial_block(block: ast::BlockExpr) -> ast::Expr {
     extract_trivial_expression(&block)
@@ -267,3 +270,71 @@ pub(crate) fn does_pat_match_variant(pat: &ast::Pat, var: &ast::Pat) -> bool {
 
     pat_head == var_head
 }
+
+// Uses a syntax-driven approach to find any impl blocks for the struct that
+// exist within the module/file
+//
+// Returns `None` if we've found an existing `new` fn
+//
+// FIXME: change the new fn checking to a more semantic approach when that's more
+// viable (e.g. we process proc macros, etc)
+pub(crate) fn find_struct_impl(
+    ctx: &AssistContext,
+    strukt: &ast::AdtDef,
+    name: &str,
+) -> Option<Option<ast::Impl>> {
+    let db = ctx.db();
+    let module = strukt.syntax().ancestors().find(|node| {
+        ast::Module::can_cast(node.kind()) || ast::SourceFile::can_cast(node.kind())
+    })?;
+
+    let struct_def = match strukt {
+        ast::AdtDef::Enum(e) => Adt::Enum(ctx.sema.to_def(e)?),
+        ast::AdtDef::Struct(s) => Adt::Struct(ctx.sema.to_def(s)?),
+        ast::AdtDef::Union(u) => Adt::Union(ctx.sema.to_def(u)?),
+    };
+
+    let block = module.descendants().filter_map(ast::Impl::cast).find_map(|impl_blk| {
+        let blk = ctx.sema.to_def(&impl_blk)?;
+
+        // FIXME: handle e.g. `struct S<T>; impl<U> S<U> {}`
+        // (we currently use the wrong type parameter)
+        // also we wouldn't want to use e.g. `impl S<u32>`
+
+        let same_ty = match blk.target_ty(db).as_adt() {
+            Some(def) => def == struct_def,
+            None => false,
+        };
+        let not_trait_impl = blk.target_trait(db).is_none();
+
+        if !(same_ty && not_trait_impl) {
+            None
+        } else {
+            Some(impl_blk)
+        }
+    });
+
+    if let Some(ref impl_blk) = block {
+        if has_fn(impl_blk, name) {
+            return None;
+        }
+    }
+
+    Some(block)
+}
+
+fn has_fn(imp: &ast::Impl, rhs_name: &str) -> bool {
+    if let Some(il) = imp.assoc_item_list() {
+        for item in il.assoc_items() {
+            if let ast::AssocItem::Fn(f) = item {
+                if let Some(name) = f.name() {
+                    if name.text().eq_ignore_ascii_case(rhs_name) {
+                        return true;
+                    }
+                }
+            }
+        }
+    }
+
+    false
+}
diff --git a/crates/hir_def/src/nameres/path_resolution.rs b/crates/hir_def/src/nameres/path_resolution.rs
index f2b59172d..036e389b0 100644
--- a/crates/hir_def/src/nameres/path_resolution.rs
+++ b/crates/hir_def/src/nameres/path_resolution.rs
@@ -108,7 +108,6 @@ impl DefMap {
         shadow: BuiltinShadowMode,
     ) -> ResolvePathResult {
         let mut result = ResolvePathResult::empty(ReachedFixedPoint::No);
-        result.segment_index = Some(usize::max_value());
 
         let mut arc;
         let mut current_map = self;
@@ -128,7 +127,11 @@ impl DefMap {
             }
             // FIXME: this doesn't seem right; what if the different namespace resolutions come from different crates?
             result.krate = result.krate.or(new.krate);
-            result.segment_index = result.segment_index.min(new.segment_index);
+            result.segment_index = match (result.segment_index, new.segment_index) {
+                (Some(idx), None) => Some(idx),
+                (Some(old), Some(new)) => Some(old.max(new)),
+                (None, new) => new,
+            };
 
             match &current_map.block {
                 Some(block) => {
diff --git a/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs b/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs
index 14e4d92f0..3ab36caf2 100644
--- a/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs
+++ b/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs
@@ -5,7 +5,7 @@
 // from file /compiler/rustc_lint/src/nonstandard_style.rs
 
 /// Converts an identifier to an UpperCamelCase form.
-/// Returns `None` if the string is already is UpperCamelCase.
+/// Returns `None` if the string is already in UpperCamelCase.
 pub(crate) fn to_camel_case(ident: &str) -> Option<String> {
     if is_camel_case(ident) {
         return None;
@@ -17,7 +17,7 @@ pub(crate) fn to_camel_case(ident: &str) -> Option<String> {
         .split('_')
         .filter(|component| !component.is_empty())
         .map(|component| {
-            let mut camel_cased_component = String::new();
+            let mut camel_cased_component = String::with_capacity(component.len());
 
             let mut new_word = true;
             let mut prev_is_lower_case = true;
@@ -30,9 +30,9 @@ pub(crate) fn to_camel_case(ident: &str) -> Option<String> {
                 }
 
                 if new_word {
-                    camel_cased_component.push_str(&c.to_uppercase().to_string());
+                    camel_cased_component.extend(c.to_uppercase());
                 } else {
-                    camel_cased_component.push_str(&c.to_lowercase().to_string());
+                    camel_cased_component.extend(c.to_lowercase());
                 }
 
                 prev_is_lower_case = c.is_lowercase();
@@ -41,16 +41,16 @@ pub(crate) fn to_camel_case(ident: &str) -> Option<String> {
 
             camel_cased_component
         })
-        .fold((String::new(), None), |(acc, prev): (String, Option<String>), next| {
+        .fold((String::new(), None), |(acc, prev): (_, Option<String>), next| {
             // separate two components with an underscore if their boundary cannot
             // be distinguished using a uppercase/lowercase case distinction
-            let join = if let Some(prev) = prev {
-                let l = prev.chars().last().unwrap();
-                let f = next.chars().next().unwrap();
-                !char_has_case(l) && !char_has_case(f)
-            } else {
-                false
-            };
+            let join = prev
+                .and_then(|prev| {
+                    let f = next.chars().next()?;
+                    let l = prev.chars().last()?;
+                    Some(!char_has_case(l) && !char_has_case(f))
+                })
+                .unwrap_or(false);
             (acc + if join { "_" } else { "" } + &next, Some(next))
         })
         .0;
@@ -92,14 +92,12 @@ fn is_camel_case(name: &str) -> bool {
     let mut fst = None;
     // start with a non-lowercase letter rather than non-uppercase
     // ones (some scripts don't have a concept of upper/lowercase)
-    !name.chars().next().unwrap().is_lowercase()
+    name.chars().next().map_or(true, |c| !c.is_lowercase())
         && !name.contains("__")
         && !name.chars().any(|snd| {
-            let ret = match (fst, snd) {
-                (None, _) => false,
-                (Some(fst), snd) => {
-                    char_has_case(fst) && snd == '_' || char_has_case(snd) && fst == '_'
-                }
+            let ret = match fst {
+                None => false,
+                Some(fst) => char_has_case(fst) && snd == '_' || char_has_case(snd) && fst == '_',
             };
             fst = Some(snd);
 
diff --git a/docs/dev/README.md b/docs/dev/README.md
index 9c0af68e3..9b9b18102 100644
--- a/docs/dev/README.md
+++ b/docs/dev/README.md
@@ -114,6 +114,14 @@ npm run lint
 
 Do see [./style.md](./style.md).
 
+# How to ...
+
+* ... add an assist? [#7535](https://github.com/rust-analyzer/rust-analyzer/pull/7535)
+* ... add a new protocol extension? [#4569](https://github.com/rust-analyzer/rust-analyzer/pull/4569)
+* ... add a new configuration option? [#7451](https://github.com/rust-analyzer/rust-analyzer/pull/7451)
+* ... add a new completion? [#6964](https://github.com/rust-analyzer/rust-analyzer/pull/6964)
+* ... allow new syntax in the parser? [#7338](https://github.com/rust-analyzer/rust-analyzer/pull/7338)
+
 # Logging
 
 Logging is done by both rust-analyzer and VS Code, so it might be tricky to