[clang] print correct context for diagnostics suppressed by deduction

This patch makes it so the correct instantiation context is printed
for diagnostics suppessed by template argument deduction.

The context is saved along with the suppressed diagnostic, and
when the declaration they were attached to becomes used, we print
the correct context, instead of whatever context was at this point.

Author: mizvekov

clang/docs/ReleaseNotes.rst

@@ -146,6 +146,8 @@ Bug Fixes to C++ Support
 ^^^^^^^^^^^^^^^^^^^^^^^^
 
 - Clang is now better at keeping track of friend function template instance contexts. (#GH55509)
+- Clang now prints the correct instantiation context for diagnostics suppressed
+  by template argument deduction.
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/include/clang/Sema/Sema.h

@@ -1909,7 +1909,22 @@ class Sema final : public SemaBase {
   /// '\#pragma clang attribute push' directives to the given declaration.
   void AddPragmaAttributes(Scope *S, Decl *D);
 
-  void PrintPragmaAttributeInstantiationPoint();
+  using DiagFuncRef =
+      llvm::function_ref<void(SourceLocation, PartialDiagnostic)>;
+  auto getDefaultDiagFunc() {
+    return [this](SourceLocation Loc, PartialDiagnostic PD) {
+      // This bypasses a lof of the filters in the diag engine, as it's
+      // to be used to attach notes to diagnostics which have already
+      // been filtered through.
+      DiagnosticBuilder Builder(Diags.Report(Loc, PD.getDiagID()));
+      PD.Emit(Builder);
+    };
+  }
+
+  void PrintPragmaAttributeInstantiationPoint(DiagFuncRef DiagFunc);
+  void PrintPragmaAttributeInstantiationPoint() {
+    PrintPragmaAttributeInstantiationPoint(getDefaultDiagFunc());
+  }
 
   void DiagnoseUnterminatedPragmaAttribute();
 
@@ -13263,18 +13278,22 @@ class Sema final : public SemaBase {
   void pushCodeSynthesisContext(CodeSynthesisContext Ctx);
   void popCodeSynthesisContext();
 
-  void PrintContextStack() {
+  void PrintContextStack(DiagFuncRef DiagFunc) {
     if (!CodeSynthesisContexts.empty() &&
         CodeSynthesisContexts.size() != LastEmittedCodeSynthesisContextDepth) {
-      PrintInstantiationStack();
+      PrintInstantiationStack(DiagFunc);
       LastEmittedCodeSynthesisContextDepth = CodeSynthesisContexts.size();
     }
     if (PragmaAttributeCurrentTargetDecl)
-      PrintPragmaAttributeInstantiationPoint();
+      PrintPragmaAttributeInstantiationPoint(DiagFunc);
   }
+  void PrintContextStack() { PrintContextStack(getDefaultDiagFunc()); }
   /// Prints the current instantiation stack through a series of
   /// notes.
-  void PrintInstantiationStack();
+  void PrintInstantiationStack(DiagFuncRef DiagFunc);
+  void PrintInstantiationStack() {
+    PrintInstantiationStack(getDefaultDiagFunc());
+  }
 
   /// Determines whether we are currently in a context where
   /// template argument substitution failures are not considered

clang/lib/Sema/Sema.cpp

@@ -1654,11 +1654,20 @@ void Sema::EmitDiagnostic(unsigned DiagID, const DiagnosticBuilder &DB) {
     }
 
     case DiagnosticIDs::SFINAE_Suppress:
+      if (DiagnosticsEngine::Level Level = getDiagnostics().getDiagnosticLevel(
+              DiagInfo.getID(), DiagInfo.getLocation());
+          Level == DiagnosticsEngine::Ignored)
+        return;
       // Make a copy of this suppressed diagnostic and store it with the
       // template-deduction information;
       if (*Info) {
-        (*Info)->addSuppressedDiagnostic(DiagInfo.getLocation(),
-                       PartialDiagnostic(DiagInfo, Context.getDiagAllocator()));
+        (*Info)->addSuppressedDiagnostic(
+            DiagInfo.getLocation(),
+            PartialDiagnostic(DiagInfo, Context.getDiagAllocator()));
+        if (!Diags.getDiagnosticIDs()->isNote(DiagID))
+          PrintContextStack([Info](SourceLocation Loc, PartialDiagnostic PD) {
+            (*Info)->addSuppressedDiagnostic(Loc, std::move(PD));
+          });
       }
 
       // Suppress this diagnostic.

clang/lib/Sema/SemaAttr.cpp

@@ -1216,10 +1216,10 @@ void Sema::AddPragmaAttributes(Scope *S, Decl *D) {
   }
 }
 
-void Sema::PrintPragmaAttributeInstantiationPoint() {
+void Sema::PrintPragmaAttributeInstantiationPoint(DiagFuncRef DiagFunc) {
   assert(PragmaAttributeCurrentTargetDecl && "Expected an active declaration");
-  Diags.Report(PragmaAttributeCurrentTargetDecl->getBeginLoc(),
-               diag::note_pragma_attribute_applied_decl_here);
+  DiagFunc(PragmaAttributeCurrentTargetDecl->getBeginLoc(),
+           PDiag(diag::note_pragma_attribute_applied_decl_here));
 }
 
 void Sema::DiagnosePrecisionLossInComplexDivision() {

clang/lib/Sema/SemaExpr.cpp

@@ -225,9 +225,10 @@ bool Sema::DiagnoseUseOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
     // emit them now.
     auto Pos = SuppressedDiagnostics.find(D->getCanonicalDecl());
     if (Pos != SuppressedDiagnostics.end()) {
-      for (const PartialDiagnosticAt &Suppressed : Pos->second)
-        Diag(Suppressed.first, Suppressed.second);
-
+      for (const auto &[DiagLoc, PD] : Pos->second) {
+        DiagnosticBuilder Builder(Diags.Report(DiagLoc, PD.getDiagID()));
+        PD.Emit(Builder);
+      }
       // Clear out the list of suppressed diagnostics, so that we don't emit
       // them again for this specialization. However, we don't obsolete this
       // entry from the table, because we want to avoid ever emitting these