[clang] [Clang][Sema] fix noexecpt mismatch of friend declaration (PR #102267)

[Younan Zhang via cfe-commits]

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@@ -4698,7 +4698,22 @@ void Sema::InstantiateExceptionSpec(SourceLocation PointOfInstantiation,
   // Enter the scope of this instantiation. We don't use
   // PushDeclContext because we don't have a scope.
   Sema::ContextRAII savedContext(*this, Decl);
+
+  FunctionDecl *Source = Proto->getExtProtoInfo().ExceptionSpec.SourceTemplate;
+  FunctionTemplateDecl *SourceTemplate = Source->getDescribedFunctionTemplate();
+  llvm::SmallDenseMap<clang::Decl *, clang::Decl *> InstTemplateParams;
+  if (CurrentInstantiationScope && SourceTemplate)
+    if (TemplateParameterList *TPL = SourceTemplate->getTemplateParameters())
+      for (NamedDecl *TemplateParam : *TPL)
+        if (auto *Found =
+                CurrentInstantiationScope->findInstantiationOf(TemplateParam))
+          if (auto *InstTemplateParam = Found->dyn_cast<clang::Decl *>())
+            InstTemplateParams[TemplateParam] = InstTemplateParam;
+
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zyn0217 wrote:

> ... the same way we normalize constraints prior to comparing them.

Which means we don't need an individual instantiation scope for the noexcept specification thereafter, so the question here could be resolved naturally I presume?

https://github.com/llvm/llvm-project/pull/102267