[Clang] Remove the wrong assumption when rebuilding SizeOfPackExprs for constraint normalization

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -1736,23 +1736,13 @@ namespace {
                                      SourceLocation RParenLoc,
                                      std::optional<unsigned> Length,
                                      ArrayRef<TemplateArgument> PartialArgs) {
-      if (SemaRef.CodeSynthesisContexts.back().Kind !=
-          Sema::CodeSynthesisContext::ConstraintNormalization)
-        return inherited::RebuildSizeOfPackExpr(OperatorLoc, Pack, PackLoc,
-                                                RParenLoc, Length, PartialArgs);
-
-#ifndef NDEBUG
-      for (auto *Iter = TemplateArgs.begin(); Iter != TemplateArgs.end();
-           ++Iter)
-        for (const TemplateArgument &TA : Iter->Args)
-          assert(TA.getKind() != TemplateArgument::Pack || TA.pack_size() == 1);
-#endif
-      Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(
-          SemaRef, /*NewSubstitutionIndex=*/0);
-      Decl *NewPack = TransformDecl(PackLoc, Pack);
-      if (!NewPack)
-        return ExprError();
-
+      Decl *NewPack = Pack;
+      if (SemaRef.CodeSynthesisContexts.back().Kind ==
+          Sema::CodeSynthesisContext::ConstraintNormalization) {
+        NewPack = TransformDecl(PackLoc, Pack);
+        if (!NewPack)
+          return ExprError();
+      }
       return inherited::RebuildSizeOfPackExpr(OperatorLoc,
                                               cast<NamedDecl>(NewPack), PackLoc,
                                               RParenLoc, Length, PartialArgs);
@@ -1881,6 +1871,15 @@ Decl *TemplateInstantiator::TransformDecl(SourceLocation Loc, Decl *D) {
       TemplateArgument Arg = TemplateArgs(TTP->getDepth(), TTP->getPosition());
 
       if (TTP->isParameterPack()) {
+        // We might not have an index for pack expansion when normalizing
+        // constraint expressions. In that case, resort to instantiation scopes
+        // for the transformed declarations.
+        if (SemaRef.ArgumentPackSubstitutionIndex == -1 &&
+            SemaRef.CodeSynthesisContexts.back().Kind ==
+                Sema::CodeSynthesisContext::ConstraintNormalization) {
+          return SemaRef.FindInstantiatedDecl(Loc, cast<NamedDecl>(D),
+                                              TemplateArgs);
+        }
         assert(Arg.getKind() == TemplateArgument::Pack &&
                "Missing argument pack");
         Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);

clang/test/SemaTemplate/concepts-out-of-line-def.cpp

@@ -703,6 +703,25 @@ C v;
 
 } // namespace GH93099
 
+namespace GH115098 {
+
+template <typename... Ts> struct c {
+  template <typename T>
+    requires(sizeof...(Ts) > 0)
+  friend bool operator==(c, c);
+};
+
+template <typename... Ts> struct d {
+  template <typename T>
+    requires(sizeof...(Ts) > 0)
+  friend bool operator==(d, d);
+};
+
+template struct c<int>;
+template struct d<int, int>;
+
+} // namespace GH115098
+
 namespace GH114685 {
 
 template <typename T> struct ptr {