libstdc++: Make VERIFY a variadic macro

This defines the testsuite assertion macro VERIFY so that it allows
un-parenthesized expressions containing commas. This matches how assert
is defined in C++26, following the approval of P2264R7.

The primary motivation is to allow expressions that the preprocessor
splits into multiple arguments, e.g.
VERIFY( vec == std::vector<int>{1,2,3,4} );

To achieve this, VERIFY is redefined as a variadic macro and then the
arguments are grouped together again through the use of __VA_ARGS__.

The implementation is complex due to the following points:

- The arguments __VA_ARGS__ are contextually-converted to bool, so that
  scoped enums and types that are not contextually convertible to bool
  cannot be used with VERIFY.
- bool(__VA_ARGS__) is used so that multiple arguments (i.e. those which
  are separated by top-level commas) are ill-formed. Nested commas are
  allowed, but likely mistakes such as VERIFY( cond, "some string" ) are
  ill-formed.
- The bool(__VA_ARGS__) expression needs to be unevaluated, so that we
  don't evaluate __VA_ARGS__ more than once. The simplest way to do that
  would be just sizeof bool(__VA_ARGS__), without parentheses to avoid a
  vexing parse for VERIFY(bool(i)). However that wouldn't work for e.g.
  VERIFY( []{ return true; }() ), because lambda expressions are not
  allowed in unevaluated contexts until C++20. So we use another
  conditional expression with bool(__VA_ARGS__) as the unevaluated
  operand.

libstdc++-v3/ChangeLog:

	* testsuite/util/testsuite_hooks.h (VERIFY): Define as variadic
	macro.
	* testsuite/ext/verify_neg.cc: New test.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>

0 files changed, 0 insertions, 0 deletions