Default arguments followed by ellipsis not allowed in in-class function declarations

[ckwastra]

Test code (CE):

void f(int = {}...); // OK

struct S {
  void f(int = {}...); // Clang: error: unexpected end of default
                       // argument expression
  void g(int...);      // OK
};

void S::g(int = {}...) {} // OK

As shown above, this syntax compiles fine for function declarations outside the class, but not for in-class ones. This is inconsistent behavior.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Vincent X (ckwastra)

Test code ([CE](https://godbolt.org/z/sonKejdv1)):

void f(int = {}...); // OK

struct S {
  void f(int = {}...); // Clang: error: unexpected end of default
                       // argument expression
  void g(int...);      // OK
};

void S::g(int = {}...) {} // OK

As shown above, this syntax compiles fine for function declarations outside the class, but not for in-class ones. This is inconsistent behavior.

[shafik]

For clarity this is fine: https://godbolt.org/z/Wh4Gbv9o1

void f(int = {},...); 

struct S {
  void f(int = {},...); 
                       
  void g(int,...);      
};

void S::g(int = {},...) {} 

Note gcc also rejects the original example but edg do not: https://godbolt.org/z/j9Pxj1oqo

[Halalaluyafail3]

Note gcc also rejects the original example but edg/MSVC do not: https://godbolt.org/z/j9Pxj1oqo

The link you sent shows MSVC erroring on the original example:

<source>(4): error C2143: syntax error: missing ';' before '...'
<source>(4): error C2059: syntax error: '...'
<source>(7): error C2059: syntax error: '<L_GRAMMAR_end_class>'