[clang] `_Pragma("clang diagnostic ignored \"-Wconstant-evaluated\"")` with push+pop sometimes doesn't work when there are macros involved

[MitalAshok]

Minimised to https://godbolt.org/z/96d8bnsKa:

#define _LIBCPP_DIAGNOSTIC_POP _Pragma("clang diagnostic pop")

#define A                                                        \
  (_Pragma("clang diagnostic push")                              \
   _Pragma("clang diagnostic ignored \"-Wconstant-evaluated\"")  \
   __builtin_is_constant_evaluated()                             \
   _LIBCPP_DIAGNOSTIC_POP)

#define echo(...) __VA_ARGS__

static_assert(echo(A), "");

<source>:11:20: warning: '__builtin_is_constant_evaluated' will always evaluate to 'true' in a manifestly constant-evaluated expression [-Wconstant-evaluated]
   11 | static_assert(echo(A), "");
      |                    ^
<source>:6:4: note: expanded from macro 'A'
    6 |    __builtin_is_constant_evaluated()                             \
      |    ^

[shafik]

CC @cor3ntin @AaronBallman

[AaronBallman]

Wow, that's interesting behavior -- if you put the _Pragma directly into the macro rather than use expansion, then the diagnostic behavior is as you'd expect: https://godbolt.org/z/Pa5jnc6bK

[AaronBallman]

The preprocessed output is as I'd expect:

# 1 "/app/example.cpp"
# 1 "<built-in>" 1
# 1 "<built-in>" 3
# 469 "<built-in>" 3
# 1 "<command line>" 1
# 1 "<built-in>" 2
# 1 "/app/example.cpp" 2
# 11 "/app/example.cpp"
static_assert((
# 11 "/app/example.cpp"
#pragma clang diagnostic push
# 11 "/app/example.cpp"
#pragma clang diagnostic ignored "-Wconstant-evaluated"
# 11 "/app/example.cpp"
              __builtin_is_constant_evaluated()
# 11 "/app/example.cpp"
#pragma clang diagnostic pop
# 11 "/app/example.cpp"
              ), "");

[nitnelave]

I ran into this by adding/removing a wrapper macro: https://godbolt.org/z/rheK4xnE6