Macro expansion error in C/C++ for _Pragma

[mcserep]

PPMacroCallback::MacroExpands deliberately omits expanding #pragma statements and other preprocessor directives:

CodeCompass/plugins/cpp/parser/src/ppmacrocallback.cpp

Lines 73 to 77 in d2b0ee6

	// If this is a # at the start of a line, discard it from the token stream.
	// We don't want the re-preprocess step to see #defines, #includes or other
	// preprocessor directives.
	if (tok.is(clang::tok::hash) && tok.isAtStartOfLine())
	continue;

However, pragmas can also be defined with the _Pragma operator, see reference:
https://gcc.gnu.org/onlinedocs/cpp/Pragmas.html

C99 introduced the _Pragma operator. This feature addresses a major problem with ‘#pragma’: being a directive, it cannot be produced as the result of macro expansion. _Pragma is an operator, much like sizeof or defined, and can be embedded in a macro.

Consider the following MWE, which will produce multiple errors, as the pragmas will be seemingly re-preprocessed.

#define CF_ASSUME_NONNULL_BEGIN _Pragma("clang assume_nonnull begin")
#define CF_ASSUME_NONNULL_END   _Pragma("clang assume_nonnull end")

CF_ASSUME_NONNULL_BEGIN  // error: already inside '#pragma clang assume_nonnull'
int bar = 42;
CF_ASSUME_NONNULL_END    // error: not currently inside '#pragma clang assume_nonnull'