[Clang] Duplicate diagnostics

Author: zhy-tju

clang/include/clang/Sema/DeclSpec.h

@@ -76,23 +76,13 @@ class CXXScopeSpec {
   NestedNameSpecifierLocBuilder Builder;
   ArrayRef<TemplateParameterList *> TemplateParamLists;
 
-  /// Flag indicating whether an incomplete-type diagnostic
-  /// has already been emitted for this scope specifier.
-  bool HadIncompleteTypeError = false;
-
 public:
   SourceRange getRange() const { return Range; }
   void setRange(SourceRange R) { Range = R; }
   void setBeginLoc(SourceLocation Loc) { Range.setBegin(Loc); }
   void setEndLoc(SourceLocation Loc) { Range.setEnd(Loc); }
   SourceLocation getBeginLoc() const { return Range.getBegin(); }
   SourceLocation getEndLoc() const { return Range.getEnd(); }
-  
-  /// Return true if an incomplete-type diagnostic has already been emitted.
-  bool hasIncompleteTypeError() const { return HadIncompleteTypeError; }
-
-  /// Mark that an incomplete-type error was emitted for this scope.
-  void setIncompleteTypeError(bool v = true) { HadIncompleteTypeError = v; }
 
   void setTemplateParamLists(ArrayRef<TemplateParameterList *> L) {
     TemplateParamLists = L;

clang/include/clang/Sema/Sema.h

@@ -1555,6 +1555,12 @@ class Sema final : public SemaBase {
   Sema(const Sema &) = delete;
   void operator=(const Sema &) = delete;
 
+  /// Used to suppress duplicate diagnostics for incomplete types
+  /// in nested name specifiers (e.g. `incomplete::type`).
+  /// Without this, Clang may emit the same error multiple times
+  /// in C++20 or later, due to multiple semantic passes over the scope.
+  llvm::DenseSet<const TagDecl *> IncompleteDiagSet;
+
   /// The handler for the FileChanged preprocessor events.
   ///
   /// Used for diagnostics that implement custom semantic analysis for #include

clang/lib/Sema/SemaCXXScopeSpec.cpp

@@ -206,22 +206,21 @@ bool Sema::RequireCompleteDeclContext(CXXScopeSpec &SS,
   if (tag->isBeingDefined())
     return false;
 
+  // Avoid emitting duplicate diagnostics for the same tag.
+  // This happens in C++20+ due to more aggressive semantic analysis.
+  if (IncompleteDiagSet.contains(tag))
+    return true;
+
   SourceLocation loc = SS.getLastQualifierNameLoc();
   if (loc.isInvalid()) loc = SS.getRange().getBegin();
 
-  // If an incomplete-type error has already been emitted for this scope,
-  // suppress duplicate diagnostics to avoid noisy repeated messages.
-  if (SS.hasIncompleteTypeError())
-    return true;
-
   // The type must be complete.
   if (RequireCompleteType(loc, type, diag::err_incomplete_nested_name_spec,
                           SS.getRange())) {
-    SS.SetInvalid(SS.getRange());
+    // mark as diagnosed
+    IncompleteDiagSet.insert(tag); 
 
-    // Remember that we've already diagnosed this incomplete type,
-    // so later checks won't emit redundant diagnostics.
-    SS.setIncompleteTypeError();
+    SS.SetInvalid(SS.getRange());
 
     return true;
   }