Merge #11713

11713: Complete associated consts in patterns  r=jonas-schievink a=hi-rustin

Try close https://github.com/rust-analyzer/rust-analyzer/issues/11555

Co-authored-by: hi-rustin <rustin.liu@gmail.com>
Co-authored-by: Jonas Schievink <jonasschievink@gmail.com>

crates/ide_completion/src/completions/pattern.rs

@@ -137,25 +137,30 @@ fn pattern_path_completion(
                         }
                     }
                 }
+                res @ (hir::PathResolution::TypeParam(_)
+                | hir::PathResolution::SelfType(_)
+                | hir::PathResolution::Def(hir::ModuleDef::Adt(hir::Adt::Struct(_)))
+                | hir::PathResolution::Def(hir::ModuleDef::Adt(hir::Adt::Enum(_)))
+                | hir::PathResolution::Def(hir::ModuleDef::Adt(hir::Adt::Union(_)))) => {
+                    let ty = match res {
+                        hir::PathResolution::TypeParam(param) => param.ty(ctx.db),
+                        hir::PathResolution::SelfType(impl_def) => impl_def.self_ty(ctx.db),
+                        hir::PathResolution::Def(hir::ModuleDef::Adt(hir::Adt::Struct(s))) => {
+                            s.ty(ctx.db)
+                        }
                         hir::PathResolution::Def(hir::ModuleDef::Adt(hir::Adt::Enum(e))) => {
                             cov_mark::hit!(enum_plain_qualified_use_tree);
                             e.variants(ctx.db)
                                 .into_iter()
                                 .for_each(|variant| acc.add_enum_variant(ctx, variant, None));
+                            e.ty(ctx.db)
+                        }
+                        hir::PathResolution::Def(hir::ModuleDef::Adt(hir::Adt::Union(u))) => {
+                            u.ty(ctx.db)
                         }
-                res @ (hir::PathResolution::TypeParam(_) | hir::PathResolution::SelfType(_)) => {
-                    let ty = match res {
-                        hir::PathResolution::TypeParam(param) => param.ty(ctx.db),
-                        hir::PathResolution::SelfType(impl_def) => impl_def.self_ty(ctx.db),
                         _ => return,
                     };
 
-                    if let Some(hir::Adt::Enum(e)) = ty.as_adt() {
-                        e.variants(ctx.db)
-                            .into_iter()
-                            .for_each(|variant| acc.add_enum_variant(ctx, variant, None));
-                    }
-
                     let traits_in_scope = ctx.scope.visible_traits();
                     let mut seen = FxHashSet::default();
                     ty.iterate_path_candidates(
@@ -165,13 +170,20 @@ fn pattern_path_completion(
                         ctx.module,
                         None,
                         |item| {
-                            // Note associated consts cannot be referenced in patterns
+                            match item {
-                            if let AssocItem::TypeAlias(ta) = item {
+                                AssocItem::TypeAlias(ta) => {
                                     // We might iterate candidates of a trait multiple times here, so deduplicate them.
                                     if seen.insert(item) {
                                         acc.add_type_alias(ctx, ta);
                                     }
                                 }
+                                AssocItem::Const(c) => {
+                                    if seen.insert(item) {
+                                        acc.add_const(ctx, c);
+                                    }
+                                }
+                                _ => {}
+                            }
                             None::<()>
                         },
                     );

crates/ide_completion/src/tests/pattern.rs

@@ -306,6 +306,7 @@ fn func() {
             ev TupleV(…)   TupleV(u32)
             ev RecordV {…} RecordV { field: u32 }
             ev UnitV       UnitV
+            ct ASSOC_CONST const ASSOC_CONST: ()
         "#]],
     );
 }
@@ -444,3 +445,75 @@ fn foo() {
         expect![[r#""#]],
     );
 }
+
+#[test]
+fn completes_associated_const() {
+    check_empty(
+        r#"
+#[derive(PartialEq, Eq)]
+struct Ty(u8);
+
+impl Ty {
+    const ABC: Self = Self(0);
+}
+
+fn f(t: Ty) {
+    match t {
+        Ty::$0 => {}
+        _ => {}
+    }
+}
+"#,
+        expect![[r#"
+            ct ABC const ABC: Self
+        "#]],
+    );
+
+    check_empty(
+        r#"
+enum MyEnum {}
+
+impl MyEnum {
+    pub const A: i32 = 123;
+    pub const B: i32 = 456;
+}
+
+fn f(e: MyEnum) {
+    match e {
+        MyEnum::$0 => {}
+        _ => {}
+    }
+}
+"#,
+        expect![[r#"
+            ct A pub const A: i32
+            ct B pub const B: i32
+        "#]],
+    );
+
+    check_empty(
+        r#"
+#[repr(C)]
+union U {
+    i: i32,
+    f: f32,
+}
+
+impl U {
+    pub const C: i32 = 123;
+    pub const D: i32 = 456;
+}
+
+fn f(u: U) {
+    match u {
+        U::$0 => {}
+        _ => {}
+    }
+}
+"#,
+        expect![[r#"
+            ct C pub const C: i32
+            ct D pub const D: i32
+        "#]],
+    )
+}