[include-cleaner] Make handling of enum constants similar to members

We were treating enum constants more like regular decls, which results
in ignoring type aliases/exports.
This patch brings the handling to be closer to member-like decls, with
one caveat. When we encounter reference to an enum constant we still
report an explicit reference to the particular enum constant, as
otherwise we might not see any references to the enum itself.

Also drops implicit references from qualified names to containers, as
we already have explicit references from the qualifier to relevant
container.

Differential Revision: https://reviews.llvm.org/D158515

clang-tools-extra/include-cleaner/lib/WalkAST.cpp

@@ -126,13 +126,22 @@ class ASTWalker : public RecursiveASTVisitor<ASTWalker> {
   }
 
   bool VisitDeclRefExpr(DeclRefExpr *DRE) {
-    // Static class members are handled here, as they don't produce MemberExprs.
-    if (DRE->getFoundDecl()->isCXXClassMember()) {
-      if (auto *Qual = DRE->getQualifier())
-        report(DRE->getLocation(), Qual->getAsRecordDecl(), RefType::Implicit);
-    } else {
-      report(DRE->getLocation(), DRE->getFoundDecl());
+    auto *FD = DRE->getFoundDecl();
+    // For refs to non-meber-like decls, use the found decl.
+    // For member-like decls, we should have a reference from the qualifier to
+    // the container decl instead, which is preferred as it'll handle
+    // aliases/exports properly.
+    if (!FD->isCXXClassMember() && !llvm::isa<EnumConstantDecl>(FD)) {
+      report(DRE->getLocation(), FD);
+      return true;
     }
+    // If the ref is without a qualifier, and is a member, ignore it. As it is
+    // available in current context due to some other construct (e.g. base
+    // specifiers, using decls) that has to spell the name explicitly.
+    // If it's an enum constant, it must be due to prior decl. Report references
+    // to it instead.
+    if (llvm::isa<EnumConstantDecl>(FD) && !DRE->hasQualifier())
+      report(DRE->getLocation(), FD);
     return true;
   }
 

clang-tools-extra/include-cleaner/unittests/WalkASTTest.cpp

@@ -50,7 +50,7 @@ std::vector<Decl::Kind> testWalk(llvm::StringRef TargetCode,
   Inputs.ExtraFiles["target.h"] = Target.code().str();
   Inputs.ExtraArgs.push_back("-include");
   Inputs.ExtraArgs.push_back("target.h");
-  Inputs.ExtraArgs.push_back("-std=c++17");
+  Inputs.ExtraArgs.push_back("-std=c++20");
   TestAST AST(Inputs);
   const auto &SM = AST.sourceManager();
 
@@ -114,7 +114,7 @@ TEST(WalkAST, DeclRef) {
   testWalk("int $explicit^x;", "int y = ^x;");
   testWalk("int $explicit^foo();", "int y = ^foo();");
   testWalk("namespace ns { int $explicit^x; }", "int y = ns::^x;");
-  testWalk("struct $implicit^S { static int x; };", "int y = S::^x;");
+  testWalk("struct S { static int x; };", "int y = S::^x;");
   // Canonical declaration only.
   testWalk("extern int $explicit^x; int x;", "int y = ^x;");
   // Return type of `foo` isn't used.
@@ -309,6 +309,14 @@ TEST(WalkAST, Alias) {
     namespace ns { using ::$explicit^Foo; }
     template<> struct ns::Foo<int> {};)cpp",
            "ns::^Foo<int> x;");
+  testWalk(R"cpp(
+    namespace ns { enum class foo { bar }; }
+    using ns::foo;)cpp",
+           "auto x = foo::^bar;");
+  testWalk(R"cpp(
+    namespace ns { enum foo { bar }; }
+    using ns::foo::$explicit^bar;)cpp",
+           "auto x = ^bar;");
 }
 
 TEST(WalkAST, Using) {
@@ -338,6 +346,8 @@ TEST(WalkAST, Using) {
     }
     using ns::$explicit^Y;)cpp",
            "^Y<int> x;");
+  testWalk("namespace ns { enum E {A}; } using enum ns::$explicit^E;",
+           "auto x = ^A;");
 }
 
 TEST(WalkAST, Namespaces) {
@@ -399,10 +409,10 @@ TEST(WalkAST, NestedTypes) {
 }
 
 TEST(WalkAST, MemberExprs) {
-  testWalk("struct $implicit^S { static int f; };", "void foo() { S::^f; }");
-  testWalk("struct B { static int f; }; struct $implicit^S : B {};",
+  testWalk("struct S { static int f; };", "void foo() { S::^f; }");
+  testWalk("struct B { static int f; }; struct S : B {};",
            "void foo() { S::^f; }");
-  testWalk("struct B { static void f(); }; struct $implicit^S : B {};",
+  testWalk("struct B { static void f(); }; struct S : B {};",
            "void foo() { S::^f; }");
   testWalk("struct B { static void f(); }; ",
            "struct S : B { void foo() { ^f(); } };");