[include-cleaner] Report refs for enum constants used through namespace aliases (#106706)

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

@@ -15,6 +15,7 @@
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprCXX.h"
+#include "clang/AST/NestedNameSpecifier.h"
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/AST/TemplateBase.h"
 #include "clang/AST/TemplateName.h"
@@ -23,9 +24,11 @@
 #include "clang/Basic/IdentifierTable.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/Specifiers.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/STLFunctionalExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/Casting.h"
+#include "llvm/Support/ErrorHandling.h"
 
 namespace clang::include_cleaner {
 namespace {
@@ -125,6 +128,24 @@ public:
     return true;
   }
 
+  bool qualifierIsNamespaceOrNone(DeclRefExpr *DRE) {
+    const auto *Qual = DRE->getQualifier();
+    if (!Qual)
+      return true;
+    switch (Qual->getKind()) {
+    case NestedNameSpecifier::Namespace:
+    case NestedNameSpecifier::NamespaceAlias:
+    case NestedNameSpecifier::Global:
+      return true;
+    case NestedNameSpecifier::TypeSpec:
+    case NestedNameSpecifier::TypeSpecWithTemplate:
+    case NestedNameSpecifier::Super:
+    case NestedNameSpecifier::Identifier:
+      return false;
+    }
+    llvm_unreachable("Unknown value for NestedNameSpecifierKind");
+  }
+
   bool VisitDeclRefExpr(DeclRefExpr *DRE) {
     auto *FD = DRE->getFoundDecl();
     // Prefer the underlying decl if FoundDecl isn't a shadow decl, e.g:
@@ -146,10 +167,8 @@ public:
     //
     // If it's an enum constant, it must be due to prior decl. Report references
     // to it when qualifier isn't a type.
-    if (llvm::isa<EnumConstantDecl>(FD)) {
-      if (!DRE->getQualifier() || DRE->getQualifier()->getAsNamespace())
-        report(DRE->getLocation(), FD);
-    }
+    if (llvm::isa<EnumConstantDecl>(FD) && qualifierIsNamespaceOrNone(DRE))
+      report(DRE->getLocation(), FD);
     return true;
   }
 

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

@@ -534,6 +534,9 @@ TEST(WalkAST, Enums) {
   testWalk(R"(namespace ns { enum E { A = 42 }; }
               struct S { using ns::E::A; };)",
            "int e = S::^A;");
+  testWalk(R"(namespace ns { enum E { $explicit^A = 42 }; })",
+           "namespace z = ns; int e = z::^A;");
+  testWalk(R"(enum E { $explicit^A = 42 };)", "int e = ::^A;");
 }
 
 TEST(WalkAST, InitializerList) {