r372178 - Ignore exception specifier mismatch when merging redeclarations

[Reid Kleckner via cfe-commits]

Author: rnk
Date: Tue Sep 17 13:29:10 2019
New Revision: 372178

URL: http://llvm.org/viewvc/llvm-project?rev=372178&view=rev
Log:
Ignore exception specifier mismatch when merging redeclarations

Exception specifiers are now part of the function type in C++17.
Normally, it is illegal to redeclare the same function or specialize a
template with a different exception specifier, but under
-fms-compatibility, we accept it with a warning. Without this change,
the function types would not match due to the exception specifier, and
clang would claim that the types were "incompatible". Now we emit the
warning and merge the redeclaration as we would in C++14 and earlier.

Fixes PR42842, which is about compiling _com_ptr_t in C++17.

Based on a patch by Alex Fusco <alexfusco at google.com>!

Differential Revision: https://reviews.llvm.org/D67590

Modified:
    cfe/trunk/lib/Sema/SemaDecl.cpp
    cfe/trunk/test/SemaCXX/ms-exception-spec.cpp

Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDecl.cpp?rev=372178&r1=372177&r2=372178&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDecl.cpp Tue Sep 17 13:29:10 2019
@@ -3562,7 +3562,12 @@ bool Sema::MergeFunctionDecl(FunctionDec
       }
     }
 
-    if (OldQTypeForComparison == NewQType)
+    // If the function types are compatible, merge the declarations. Ignore the
+    // exception specifier because it was already checked above in
+    // CheckEquivalentExceptionSpec, and we don't want follow-on diagnostics
+    // about incompatible types under -fms-compatibility.
+    if (Context.hasSameFunctionTypeIgnoringExceptionSpec(OldQTypeForComparison,
+                                                         NewQType))
       return MergeCompatibleFunctionDecls(New, Old, S, MergeTypeWithOld);
 
     // If the types are imprecise (due to dependent constructs in friends or

Modified: cfe/trunk/test/SemaCXX/ms-exception-spec.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/ms-exception-spec.cpp?rev=372178&r1=372177&r2=372178&view=diff
==============================================================================
--- cfe/trunk/test/SemaCXX/ms-exception-spec.cpp (original)
+++ cfe/trunk/test/SemaCXX/ms-exception-spec.cpp Tue Sep 17 13:29:10 2019
@@ -1,9 +1,36 @@
-// RUN: %clang_cc1 %s -fsyntax-only -verify -fms-compatibility -fexceptions -fcxx-exceptions
+// RUN: %clang_cc1 -std=c++11 %s -fsyntax-only -verify -fms-compatibility -fexceptions -fcxx-exceptions
+// RUN: %clang_cc1 -std=c++17 %s -fsyntax-only -verify -fms-compatibility -fexceptions -fcxx-exceptions
 
+// FIXME: Should -fms-compatibility soften these errors into warnings to match
+// MSVC? In practice, MSVC never implemented dynamic exception specifiers, so
+// there isn't much Windows code in the wild that uses them.
+#if __cplusplus >= 201703L
+// expected-error at +3 {{ISO C++17 does not allow dynamic exception specifications}}
+// expected-note at +2 {{use 'noexcept(false)' instead}}
+#endif
 void f() throw(...) { }
 
 namespace PR28080 {
 struct S;           // expected-note {{forward declaration}}
+#if __cplusplus >= 201703L
+// expected-error at +3 {{ISO C++17 does not allow dynamic exception specifications}}
+// expected-note at +2 {{use 'noexcept(false)' instead}}
+#endif
 void fn() throw(S); // expected-warning {{incomplete type}} expected-note{{previous declaration}}
 void fn() throw();  // expected-warning {{does not match previous declaration}}
 }
+
+template <typename T> struct FooPtr {
+  template <typename U> FooPtr(U *p) : m_pT(nullptr) {}
+
+  template <>
+      // FIXME: It would be better if this note pointed at the primary template
+      // above.
+      // expected-note at +1 {{previous declaration is here}}
+  FooPtr(T *pInterface) throw() // expected-warning {{exception specification in declaration does not match previous declaration}}
+      : m_pT(pInterface) {}
+
+  T *m_pT;
+};
+struct Bar {};
+template struct FooPtr<Bar>; // expected-note {{requested here}}