[clang] [Clang][Sema] Defer instantiation of exception specification until after partial ordering when determining primary template (PR #82417)

[Krystian Stasiowski via cfe-commits]

https://github.com/sdkrystian updated https://github.com/llvm/llvm-project/pull/82417

>From 16b6ce3b1895c15ce896c5e8dcbe29ee1274d38b Mon Sep 17 00:00:00 2001
From: Krystian Stasiowski <sdkrystian at gmail.com>
Date: Tue, 20 Feb 2024 14:03:50 -0500
Subject: [PATCH] [Clang][Sema] Defer instantiation of exception specification
 until after partial ordering when determining primary template

---
 clang/lib/Sema/SemaTemplate.cpp               | 10 ++++-
 clang/lib/Sema/SemaTemplateDeduction.cpp      | 14 +++----
 clang/test/CXX/except/except.spec/p13.cpp     | 38 +++++++++++++++++++
 .../SemaTemplate/class-template-noexcept.cpp  | 14 +------
 4 files changed, 54 insertions(+), 22 deletions(-)
 create mode 100644 clang/test/CXX/except/except.spec/p13.cpp

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 1a975a8d0a0df5..9c75438011010a 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -9706,9 +9706,17 @@ bool Sema::CheckFunctionTemplateSpecialization(
   if (Result == Candidates.end())
     return true;
 
-  // Ignore access information;  it doesn't figure into redeclaration checking.
   FunctionDecl *Specialization = cast<FunctionDecl>(*Result);
+  auto *SpecializationFPT =
+      Specialization->getType()->castAs<FunctionProtoType>();
+  // If the function has a dependent exception specification, resolve it after
+  // we have selected the primary template so we can check whether it matches.
+  if (getLangOpts().CPlusPlus17 &&
+      isUnresolvedExceptionSpec(SpecializationFPT->getExceptionSpecType()) &&
+      !ResolveExceptionSpec(FD->getLocation(), SpecializationFPT))
+    return true;
 
+  // Ignore access information;  it doesn't figure into redeclaration checking.
   FunctionTemplateSpecializationInfo *SpecInfo
     = Specialization->getTemplateSpecializationInfo();
   assert(SpecInfo && "Function template specialization info missing?");
diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 47cc22310c4eec..563491f76f5478 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -4632,11 +4632,9 @@ TemplateDeductionResult Sema::DeduceTemplateArguments(
                                                Info.getLocation()))
     return TemplateDeductionResult::MiscellaneousDeductionFailure;
 
-  // If the function has a dependent exception specification, resolve it now,
-  // so we can check that the exception specification matches.
   auto *SpecializationFPT =
       Specialization->getType()->castAs<FunctionProtoType>();
-  if (getLangOpts().CPlusPlus17 &&
+  if (IsAddressOfFunction && getLangOpts().CPlusPlus17 &&
       isUnresolvedExceptionSpec(SpecializationFPT->getExceptionSpecType()) &&
       !ResolveExceptionSpec(Info.getLocation(), SpecializationFPT))
     return TemplateDeductionResult::MiscellaneousDeductionFailure;
@@ -4662,11 +4660,11 @@ TemplateDeductionResult Sema::DeduceTemplateArguments(
   // specialization with respect to arguments of compatible pointer to function
   // types, template argument deduction fails.
   if (!ArgFunctionType.isNull()) {
-    if (IsAddressOfFunction
-            ? !isSameOrCompatibleFunctionType(
-                  Context.getCanonicalType(SpecializationType),
-                  Context.getCanonicalType(ArgFunctionType))
-            : !Context.hasSameType(SpecializationType, ArgFunctionType)) {
+    if (IsAddressOfFunction ? !isSameOrCompatibleFunctionType(
+                                  Context.getCanonicalType(SpecializationType),
+                                  Context.getCanonicalType(ArgFunctionType))
+                            : !Context.hasSameFunctionTypeIgnoringExceptionSpec(
+                                  SpecializationType, ArgFunctionType)) {
       Info.FirstArg = TemplateArgument(SpecializationType);
       Info.SecondArg = TemplateArgument(ArgFunctionType);
       return TemplateDeductionResult::NonDeducedMismatch;
diff --git a/clang/test/CXX/except/except.spec/p13.cpp b/clang/test/CXX/except/except.spec/p13.cpp
new file mode 100644
index 00000000000000..6a4f699ed340d2
--- /dev/null
+++ b/clang/test/CXX/except/except.spec/p13.cpp
@@ -0,0 +1,38 @@
+// RUN: %clang_cc1 -fexceptions -fcxx-exceptions -fsyntax-only -verify %s
+
+struct A {
+  static constexpr bool x = true;
+};
+
+template<typename T, typename U>
+void f(T, U) noexcept(T::x);
+
+template<typename T, typename U>
+void f(T, U*) noexcept(T::x);
+
+template<typename T, typename U>
+void f(T, U**) noexcept(T::y); // expected-error {{no member named 'y' in 'A'}}
+
+template<typename T, typename U>
+void f(T, U***) noexcept(T::x);
+
+template<>
+void f(A, int*) noexcept; // expected-note {{previous declaration is here}}
+
+template<>
+void f(A, int*); // expected-error {{'f<A, int>' is missing exception specification 'noexcept'}}
+
+template<>
+void f(A, int**) noexcept; // expected-error {{exception specification in declaration does not match previous declaration}}
+                           // expected-note at -1 {{in instantiation of exception specification for 'f<A, int>' requested here}}
+                           // expected-note at -2 {{previous declaration is here}}
+
+// FIXME: Exception specification is currently set to EST_None if instantiation fails.
+template<>
+void f(A, int**);
+
+template<>
+void f(A, int***) noexcept; // expected-note {{previous declaration is here}}
+
+template<>
+void f(A, int***); // expected-error {{'f<A, int>' is missing exception specification 'noexcept'}}
diff --git a/clang/test/SemaTemplate/class-template-noexcept.cpp b/clang/test/SemaTemplate/class-template-noexcept.cpp
index 5c4ac090f3166d..14d2e36bc0bfae 100644
--- a/clang/test/SemaTemplate/class-template-noexcept.cpp
+++ b/clang/test/SemaTemplate/class-template-noexcept.cpp
@@ -2,9 +2,7 @@
 // RUN: %clang_cc1 -std=c++11 -verify %s
 // RUN: %clang_cc1 -std=c++17 -verify %s
 // RUN: %clang_cc1 -std=c++1z -verify %s
-#if __cplusplus >= 201703
-// expected-no-diagnostics
-#endif
+
 class A {
 public:
   static const char X;
@@ -14,19 +12,9 @@ const char A::X = 0;
 template<typename U> void func() noexcept(U::X);
 
 template<class... B, char x>
-#if __cplusplus >= 201703
-void foo(void(B...) noexcept(x)) {} 
-#else
 void foo(void(B...) noexcept(x)) {} // expected-note{{candidate template ignored}}
-#endif
 
 void bar()
 {
-#if __cplusplus >= 201703
-  foo(func<A>);
-#else
   foo(func<A>);	// expected-error{{no matching function for call}}
-#endif	
 }
-
-