[clang]Transform uninstantiated ExceptionSpec in TemplateInstantiator (llvm#68878)

Fixes llvm#68543, llvm#42496

Author: HerrCai0907

clang/docs/ReleaseNotes.rst

@@ -474,6 +474,10 @@ Bug Fixes in This Version
   cannot be used with ``Release`` mode builds. (`#68237 <https://github.com/llvm/llvm-project/issues/68237>`_).
 - Fix crash in evaluating ``constexpr`` value for invalid template function.
   Fixes (`#68542 <https://github.com/llvm/llvm-project/issues/68542>`_)
+- Clang will correctly evaluate ``noexcept`` expression for template functions
+  of template classes. Fixes
+  (`#68543 <https://github.com/llvm/llvm-project/issues/68543>`_,
+  `#42496 <https://github.com/llvm/llvm-project/issues/42496>`_)
 - Fixed an issue when a shift count larger than ``__INT64_MAX__``, in a right
   shift operation, could result in missing warnings about
   ``shift count >= width of type`` or internal compiler error.

clang/lib/Sema/SemaTemplateDeduction.cpp

@@ -3367,7 +3367,14 @@ Sema::TemplateDeductionResult Sema::SubstituteExplicitTemplateArguments(
     SmallVector<QualType, 4> ExceptionStorage;
     if (getLangOpts().CPlusPlus17 &&
         SubstExceptionSpec(Function->getLocation(), EPI.ExceptionSpec,
-                           ExceptionStorage, MLTAL))
+                           ExceptionStorage,
+                           getTemplateInstantiationArgs(
+                               FunctionTemplate, nullptr, /*Final=*/true,
+                               /*Innermost=*/SugaredExplicitArgumentList,
+                               /*RelativeToPrimary=*/false,
+                               /*Pattern=*/nullptr,
+                               /*ForConstraintInstantiation=*/false,
+                               /*SkipForSpecialization=*/true)))
       return TDK_SubstitutionFailure;
 
     *FunctionType = BuildFunctionType(ResultType, ParamTypes,

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -1335,6 +1335,11 @@ namespace {
     /// declaration.
     NamedDecl *TransformFirstQualifierInScope(NamedDecl *D, SourceLocation Loc);
 
+    bool TransformExceptionSpec(SourceLocation Loc,
+                                FunctionProtoType::ExceptionSpecInfo &ESI,
+                                SmallVectorImpl<QualType> &Exceptions,
+                                bool &Changed);
+
     /// Rebuild the exception declaration and register the declaration
     /// as an instantiated local.
     VarDecl *RebuildExceptionDecl(VarDecl *ExceptionDecl,
@@ -1617,6 +1622,18 @@ Decl *TemplateInstantiator::TransformDefinition(SourceLocation Loc, Decl *D) {
   return Inst;
 }
 
+bool TemplateInstantiator::TransformExceptionSpec(
+    SourceLocation Loc, FunctionProtoType::ExceptionSpecInfo &ESI,
+    SmallVectorImpl<QualType> &Exceptions, bool &Changed) {
+  if (ESI.Type == EST_Uninstantiated) {
+    ESI.NoexceptExpr = cast<FunctionProtoType>(ESI.SourceTemplate->getType())
+                           ->getNoexceptExpr();
+    ESI.Type = EST_DependentNoexcept;
+    Changed = true;
+  }
+  return inherited::TransformExceptionSpec(Loc, ESI, Exceptions, Changed);
+}
+
 NamedDecl *
 TemplateInstantiator::TransformFirstQualifierInScope(NamedDecl *D,
                                                      SourceLocation Loc) {
@@ -2684,8 +2701,6 @@ bool Sema::SubstExceptionSpec(SourceLocation Loc,
                               FunctionProtoType::ExceptionSpecInfo &ESI,
                               SmallVectorImpl<QualType> &ExceptionStorage,
                               const MultiLevelTemplateArgumentList &Args) {
-  assert(ESI.Type != EST_Uninstantiated);
-
   bool Changed = false;
   TemplateInstantiator Instantiator(*this, Args, Loc, DeclarationName());
   return Instantiator.TransformExceptionSpec(Loc, ESI, ExceptionStorage,

clang/test/SemaCXX/dependent-noexcept-uninstantiated.cpp

@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c++17 %s
+// expected-no-diagnostics
+
+using A = int;
+using B = char;
+
+template <class T> struct C {
+  template <class V> void f0() noexcept(sizeof(T) == sizeof(A) && sizeof(V) == sizeof(B)) {}
+};
+
+void (C<int>::*tmp1)() noexcept = &C<A>::f0<B>;