[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:

> ... including when checking constraints ...

This might not be the case for template parameters, as we (almost always, in my recollection) would have transformed the associated template parameters before calling the constraint matching function, so...

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