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Fix a diagnoses-valid in C++20 with variadic macros

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C++20 and later allow you to pass no argument for the ... parameter in
a variadic macro, whereas earlier language modes and C disallow it.

We no longer diagnose in C++20 and later modes. This fixes PR51609.
This commit is contained in:
Aaron Ballman 2021-10-09 08:20:20 -04:00
parent a1f0f847ff
commit af971365a2
3 changed files with 21 additions and 1 deletions
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4
clang/include/clang/Basic/DiagnosticLexKinds.td
View File

@ -412,6 +412,10 @@ def ext_embedded_directive : Extension<
def ext_missing_varargs_arg : Extension<
"must specify at least one argument for '...' parameter of variadic macro">,
InGroup<GNUZeroVariadicMacroArguments>;
def warn_cxx17_compat_missing_varargs_arg : Warning<
"passing no argument for the '...' parameter of a variadic macro is "
"incompatible with C++ standards before C++20">,
InGroup<CXXPre20Compat>, DefaultIgnore;
def ext_empty_fnmacro_arg : Extension<
"empty macro arguments are a C99 feature">, InGroup<C99>;
def warn_cxx98_compat_empty_fnmacro_arg : Warning<

6
clang/lib/Lex/PPMacroExpansion.cpp
View File

@ -988,7 +988,11 @@ MacroArgs *Preprocessor::ReadMacroCallArgumentList(Token &MacroName,
// If the macro contains the comma pasting extension, the diagnostic
// is suppressed; we know we'll get another diagnostic later.
if (!MI->hasCommaPasting()) {
Diag(Tok, diag::ext_missing_varargs_arg);
// C++20 allows this construct, but standards before C++20 and all C
// standards do not allow the construct (we allow it as an extension).
Diag(Tok, getLangOpts().CPlusPlus20
? diag::warn_cxx17_compat_missing_varargs_arg
: diag::ext_missing_varargs_arg);
Diag(MI->getDefinitionLoc(), diag::note_macro_here)
<< MacroName.getIdentifierInfo();
}

12
clang/test/Preprocessor/empty_va_arg.cpp Normal file
View File

@ -0,0 +1,12 @@
// RUN: %clang_cc1 -Eonly -std=c++17 -pedantic -verify %s
// RUN: %clang_cc1 -Eonly -std=c17 -pedantic -verify -x c %s
// RUN: %clang_cc1 -Eonly -std=c++20 -pedantic -Wpre-c++20-compat -verify=compat %s
#define FOO(x, ...) // expected-note {{macro 'FOO' defined here}} \
// compat-note {{macro 'FOO' defined here}}
int main() {
FOO(42) // expected-warning {{must specify at least one argument for '...' parameter of variadic macro}} \
// compat-warning {{passing no argument for the '...' parameter of a variadic macro is incompatible with C++ standards before C++20}}
}