Fix PR#62594 : static lambda call operator is not convertible to function pointer on win32

[faisalv]

Summary

See issue https://github.com/llvm/llvm-project/issues/62594

This code does not work on win32:

cpp
  auto lstatic = []()  static  { return 0;  };
  int (*f2)(void) = lstatic;

Since a calling convention such as CC_X86ThisCall can rightly interfere with the implicit pointer to function conversion if erroneously marked on a static function, the fix entails checking the 'static' specifier on the lambda declarator prior to assigning it a calling convention of an non-static member (which pre-c++23 made sense).

[aaron.ballman]

Can you also add a release note for the fix? The changes generally LGTM

clang/test/SemaCXX/cxx23-static-callop-lambda-expression.cpp

12

33

Please add the newline to the file.

[shafik]

LGTM

[royjacobson]

@shafik @aaron.ballman does any of you want to commandeer this diff? seems simple enough of a change

[shafik]

In D150075#4646487, @royjacobson wrote:

@shafik @aaron.ballman does any of you want to commandeer this diff? seems simple enough of a change

I think Aaron might be better since he is more familiar with Windows.

[faisalv]

Sorry about the delay - this patch has landed - https://github.com/llvm/llvm-project/commit/5bdd5d064d5171b2d5ff6268528cfffd2f86b8ea
Thanks!

clang/lib/Sema/SemaType.cpp

           D.getTypeObject(I).Kind == DeclaratorChunk::MemberPointer;
     } else if (D.getContext() == DeclaratorContext::LambdaExpr) {
       // This can only be a call operator for a lambda, which is an instance
-      // method.
-      IsCXXInstanceMethod = true;
+      // method, unless explicitly specified as 'static'.
+      IsCXXInstanceMethod =
+          D.getDeclSpec().getStorageClassSpec() != DeclSpec::SCS_static;
     } else {
       // We're the innermost decl chunk, so must be a function declarator.
       assert(D.isFunctionDeclarator());

clang/test/SemaCXX/cxx23-static-callop-lambda-expression.cpp

+// RUN: %clang_cc1 -std=c++23 -fsyntax-only -verify %s
+
+
+namespace ns1 {
+  auto lstatic = []() static { return 3; }; 
+  int (*f2)(void) = lstatic;   
+    
+}
+
+namespace ns1_1 {
+  
+  auto lstatic = []() static consteval  //expected-note {{declared here}} expected-error{{cannot take address of consteval call}}
+  { return 3; };   
+  
+  // FIXME: the above error should indicate that it was triggered below.
+  int (*f2)(void) = lstatic;   
+    
+}
+
+
+namespace ns2 {
+  auto lstatic = []() static { return 3; }; 
+  constexpr int (*f2)(void) = lstatic;                              
+  static_assert(lstatic() == f2());
+}
+
+namespace ns3 {
+  void main() {
+    static int x = 10;
+    auto L = []() static { return x; };
+  }
+}
 No newline at end of file