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The GNU token paste extension that removes the comma in , ## __VA_ARGS__
conflicts with C99/C++11's requirements when a variadic macro has no named
parameters: according to the standard, an invocation as FOO() gives it a single
empty argument, and concatenation of anything with an empty argument is
well-defined. For this reason, the GNU extension was already disabled in C99
standard-conforming mode. It was not yet disabled in C++11 standard-conforming
mode.
The associated comment suggested that GCC keeps this extension enabled in
C90/C++03 standard-conforming mode, but it actually does not, so rather than
adding a check for C++ language version, this change simply removes the check
for C language version.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D91913
Files:
clang/lib/Lex/TokenLexer.cpp
clang/test/Preprocessor/macro_fn_comma_swallow2.c
Index: clang/test/Preprocessor/macro_fn_comma_swallow2.c
===================================================================
--- clang/test/Preprocessor/macro_fn_comma_swallow2.c
+++ clang/test/Preprocessor/macro_fn_comma_swallow2.c
@@ -1,9 +1,12 @@
// Test the __VA_ARGS__ comma swallowing extensions of various compiler
dialects.
// RUN: %clang_cc1 -E %s | FileCheck -check-prefix=GCC -strict-whitespace %s
+// RUN: %clang_cc1 -E -std=c90 %s | FileCheck -check-prefix=C99
-strict-whitespace %s
// RUN: %clang_cc1 -E -std=c99 %s | FileCheck -check-prefix=C99
-strict-whitespace %s
// RUN: %clang_cc1 -E -std=c11 %s | FileCheck -check-prefix=C99
-strict-whitespace %s
// RUN: %clang_cc1 -E -x c++ %s | FileCheck -check-prefix=GCC
-strict-whitespace %s
+// RUN: %clang_cc1 -E -x c++ -std=c++03 %s | FileCheck -check-prefix=C99
-strict-whitespace %s
+// RUN: %clang_cc1 -E -x c++ -std=c++11 %s | FileCheck -check-prefix=C99
-strict-whitespace %s
// RUN: %clang_cc1 -E -std=gnu99 %s | FileCheck -check-prefix=GCC
-strict-whitespace %s
// RUN: %clang_cc1 -E -fms-compatibility %s | FileCheck -check-prefix=MS
-strict-whitespace %s
// RUN: %clang_cc1 -E -DNAMED %s | FileCheck -check-prefix=GCC
-strict-whitespace %s
Index: clang/lib/Lex/TokenLexer.cpp
===================================================================
--- clang/lib/Lex/TokenLexer.cpp
+++ clang/lib/Lex/TokenLexer.cpp
@@ -148,12 +148,11 @@
return false;
// GCC removes the comma in the expansion of " ... , ## __VA_ARGS__ " if
- // __VA_ARGS__ is empty, but not in strict C99 mode where there are no
- // named arguments, where it remains. In all other modes, including C99
- // with GNU extensions, it is removed regardless of named arguments.
+ // __VA_ARGS__ is empty, but not in strict mode where there are no
+ // named arguments, where it remains. With GNU extensions, it is removed
+ // regardless of named arguments.
// Microsoft also appears to support this extension, unofficially.
- if (PP.getLangOpts().C99 && !PP.getLangOpts().GNUMode
- && Macro->getNumParams() < 2)
+ if (!PP.getLangOpts().GNUMode && Macro->getNumParams() < 2)
return false;
// Is a comma available to be removed?
Index: clang/test/Preprocessor/macro_fn_comma_swallow2.c
===================================================================
--- clang/test/Preprocessor/macro_fn_comma_swallow2.c
+++ clang/test/Preprocessor/macro_fn_comma_swallow2.c
@@ -1,9 +1,12 @@
// Test the __VA_ARGS__ comma swallowing extensions of various compiler dialects.
// RUN: %clang_cc1 -E %s | FileCheck -check-prefix=GCC -strict-whitespace %s
+// RUN: %clang_cc1 -E -std=c90 %s | FileCheck -check-prefix=C99 -strict-whitespace %s
// RUN: %clang_cc1 -E -std=c99 %s | FileCheck -check-prefix=C99 -strict-whitespace %s
// RUN: %clang_cc1 -E -std=c11 %s | FileCheck -check-prefix=C99 -strict-whitespace %s
// RUN: %clang_cc1 -E -x c++ %s | FileCheck -check-prefix=GCC -strict-whitespace %s
+// RUN: %clang_cc1 -E -x c++ -std=c++03 %s | FileCheck -check-prefix=C99 -strict-whitespace %s
+// RUN: %clang_cc1 -E -x c++ -std=c++11 %s | FileCheck -check-prefix=C99 -strict-whitespace %s
// RUN: %clang_cc1 -E -std=gnu99 %s | FileCheck -check-prefix=GCC -strict-whitespace %s
// RUN: %clang_cc1 -E -fms-compatibility %s | FileCheck -check-prefix=MS -strict-whitespace %s
// RUN: %clang_cc1 -E -DNAMED %s | FileCheck -check-prefix=GCC -strict-whitespace %s
Index: clang/lib/Lex/TokenLexer.cpp
===================================================================
--- clang/lib/Lex/TokenLexer.cpp
+++ clang/lib/Lex/TokenLexer.cpp
@@ -148,12 +148,11 @@
return false;
// GCC removes the comma in the expansion of " ... , ## __VA_ARGS__ " if
- // __VA_ARGS__ is empty, but not in strict C99 mode where there are no
- // named arguments, where it remains. In all other modes, including C99
- // with GNU extensions, it is removed regardless of named arguments.
+ // __VA_ARGS__ is empty, but not in strict mode where there are no
+ // named arguments, where it remains. With GNU extensions, it is removed
+ // regardless of named arguments.
// Microsoft also appears to support this extension, unofficially.
- if (PP.getLangOpts().C99 && !PP.getLangOpts().GNUMode
- && Macro->getNumParams() < 2)
+ if (!PP.getLangOpts().GNUMode && Macro->getNumParams() < 2)
return false;
// Is a comma available to be removed?
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