[AST] Preserve more structure in UsingEnumDecl node.

- store NestedNameSpecifier & Loc for the qualifiers
  This information was entirely missing from the AST.
- expose the location information for qualifier/identifier/typedefs as typeloc
  This allows many traversals/astmatchers etc to handle these generically along
  with other references. The decl vs type split can help preserve typedef
  sugar when https://github.com/llvm/llvm-project/issues/57659 is resolved.
- fix the SourceRange of UsingEnumDecl to include 'using'.

Fixes https://github.com/clangd/clangd/issues/1283

Differential Revision: https://reviews.llvm.org/D134303

4 files changed, 51 insertions, 0 deletions

diff --git a/clang-tools-extra/clangd/FindTarget.cpp b/clang-tools-extra/clangd/FindTarget.cpp
index dea5cb7f5028..f76bedee0351 100644
--- a/clang-tools-extra/clangd/FindTarget.cpp
+++ b/clang-tools-extra/clangd/FindTarget.cpp
@@ -629,6 +629,12 @@ llvm::SmallVector<ReferenceLoc> refInDecl(const Decl *D,
                                    DeclRelation::Underlying, Resolver)});
     }
 
+    void VisitUsingEnumDecl(const UsingEnumDecl *D) {
+      // "using enum ns::E" is a non-declaration reference.
+      // The reference is covered by the embedded typeloc.
+      // Don't use the default VisitNamedDecl, which would report a declaration.
+    }
+
     void VisitNamespaceAliasDecl(const NamespaceAliasDecl *D) {
       // For namespace alias, "namespace Foo = Target;", we add two references.
       // Add a declaration reference for Foo.
diff --git a/clang-tools-extra/clangd/unittests/FindTargetTests.cpp b/clang-tools-extra/clangd/unittests/FindTargetTests.cpp
index fd25e8059e81..57838eafd651 100644
--- a/clang-tools-extra/clangd/unittests/FindTargetTests.cpp
+++ b/clang-tools-extra/clangd/unittests/FindTargetTests.cpp
@@ -1267,6 +1267,15 @@ TEST_F(FindExplicitReferencesTest, All) {
         )cpp",
         "0: targets = {ns}\n"
         "1: targets = {ns::global}, qualifier = 'ns::'\n"},
+       // Using enum declarations.
+       {R"cpp(
+          namespace ns { enum class A {}; }
+          void foo() {
+            using enum $0^ns::$1^A;
+          }
+        )cpp",
+        "0: targets = {ns}\n"
+        "1: targets = {ns::A}, qualifier = 'ns::'\n"},
        // Simple types.
        {R"cpp(
          struct Struct { int a; };
diff --git a/clang-tools-extra/clangd/unittests/SelectionTests.cpp b/clang-tools-extra/clangd/unittests/SelectionTests.cpp
index 239566a35861..bd3df2404fcf 100644
--- a/clang-tools-extra/clangd/unittests/SelectionTests.cpp
+++ b/clang-tools-extra/clangd/unittests/SelectionTests.cpp
@@ -531,6 +531,33 @@ TEST(SelectionTest, CommonAncestor) {
         void func() { [[__^func__]]; }
         )cpp",
        "PredefinedExpr"},
+
+      // using enum
+      {R"cpp(
+        namespace ns { enum class A {}; };
+        using enum ns::[[^A]];
+        )cpp",
+       "EnumTypeLoc"},
+      {R"cpp(
+        namespace ns { enum class A {}; using B = A; };
+        using enum ns::[[^B]];
+        )cpp",
+       "TypedefTypeLoc"},
+      {R"cpp(
+        namespace ns { enum class A {}; };
+        using enum [[^ns::]]A;
+        )cpp",
+       "NestedNameSpecifierLoc"},
+      {R"cpp(
+        namespace ns { enum class A {}; };
+        [[using ^enum ns::A]];
+        )cpp",
+       "UsingEnumDecl"},
+      {R"cpp(
+        namespace ns { enum class A {}; };
+        [[^using enum ns::A]];
+        )cpp",
+       "UsingEnumDecl"},
   };
 
   for (const Case &C : Cases) {
@@ -541,6 +568,7 @@ TEST(SelectionTest, CommonAncestor) {
     TU.Code = std::string(Test.code());
 
     TU.ExtraArgs.push_back("-xobjective-c++");
+    TU.ExtraArgs.push_back("-std=c++20");
 
     auto AST = TU.build();
     auto T = makeSelectionTree(C.Code, AST);
diff --git a/clang-tools-extra/clangd/unittests/SemanticHighlightingTests.cpp b/clang-tools-extra/clangd/unittests/SemanticHighlightingTests.cpp
index 32f0f58ade2c..e851bea5e632 100644
--- a/clang-tools-extra/clangd/unittests/SemanticHighlightingTests.cpp
+++ b/clang-tools-extra/clangd/unittests/SemanticHighlightingTests.cpp
@@ -828,6 +828,14 @@ sizeof...($TemplateParameter[[Elements]]);
         typedef int $Primitive_decl[[MyTypedef]];
         enum $Enum_decl[[MyEnum]] : $Primitive[[MyTypedef]] {};
       )cpp",
+      // Using enum
+      R"cpp(
+      enum class $Enum_decl[[Color]] { $EnumConstant_decl_readonly[[Black]] };
+      namespace $Namespace_decl[[ns]] {
+        using enum $Enum[[Color]];
+        $Enum[[Color]] $Variable_decl[[ModelT]] = $EnumConstant[[Black]];
+      }
+      )cpp",
       // Issue 1096
       R"cpp(
         void $Function_decl[[Foo]]();