Improved support for removing the comma preceding __VA_ARGS__ where __VA_ARGS__
is empty in a variadic macro expansion. This fixes a divergence in support for
the ", ## __VA_ARGS__" GCC extension which differed in behaviour when in strict
C99 mode (note: there is no change in behaviour has been made in the gnu99 mode
that clang uses by default). In addition, there is improved support for the
Microsoft alternative extension ", __VA_ARGS__".
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@167613 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Lex/TokenLexer.cpp b/lib/Lex/TokenLexer.cpp
index 2e3e7c3..59b7478 100644
--- a/lib/Lex/TokenLexer.cpp
+++ b/lib/Lex/TokenLexer.cpp
@@ -119,6 +119,55 @@
if (ActualArgs) ActualArgs->destroy(PP);
}
+/// Remove comma ahead of __VA_ARGS__, if present, according to compiler dialect
+/// settings. Returns true if the comma is removed.
+static bool MaybeRemoveCommaBeforeVaArgs(SmallVector<Token, 128> &ResultToks,
+ bool &NextTokGetsSpace,
+ bool HasPasteOperator,
+ MacroInfo *Macro, unsigned MacroArgNo,
+ Preprocessor &PP) {
+ // Is the macro argument __VA_ARGS__?
+ if (!Macro->isVariadic() || MacroArgNo != Macro->getNumArgs()-1)
+ return false;
+
+ // In Microsoft-compatibility mode, a comma is removed in the expansion
+ // of " ... , __VA_ARGS__ " if __VA_ARGS__ is empty. This extension is
+ // not supported by gcc.
+ if (!HasPasteOperator && !PP.getLangOpts().MicrosoftMode)
+ 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.
+ // Microsoft also appears to support this extension, unofficially.
+ if (PP.getLangOpts().C99 && !PP.getLangOpts().GNUMode
+ && Macro->getNumArgs() < 2)
+ return false;
+
+ // Is a comma available to be removed?
+ if (ResultToks.empty() || !ResultToks.back().is(tok::comma))
+ return false;
+
+ // Issue an extension diagnostic for the paste operator.
+ if (HasPasteOperator)
+ PP.Diag(ResultToks.back().getLocation(), diag::ext_paste_comma);
+
+ // Remove the comma.
+ ResultToks.pop_back();
+
+ // If the comma was right after another paste (e.g. "X##,##__VA_ARGS__"),
+ // then removal of the comma should produce a placemarker token (in C99
+ // terms) which we model by popping off the previous ##, giving us a plain
+ // "X" when __VA_ARGS__ is empty.
+ if (!ResultToks.empty() && ResultToks.back().is(tok::hashhash))
+ ResultToks.pop_back();
+
+ // Never add a space, even if the comma, ##, or arg had a space.
+ NextTokGetsSpace = false;
+ return true;
+}
+
/// Expand the arguments of a function-like macro so that we can quickly
/// return preexpanded tokens from Tokens.
void TokenLexer::ExpandFunctionArguments() {
@@ -199,6 +248,14 @@
!ResultToks.empty() && ResultToks.back().is(tok::hashhash);
bool PasteAfter = i+1 != e && Tokens[i+1].is(tok::hashhash);
+ // In Microsoft mode, remove the comma before __VA_ARGS__ to ensure there
+ // are no trailing commas if __VA_ARGS__ is empty.
+ if (!PasteBefore && ActualArgs->isVarargsElidedUse() &&
+ MaybeRemoveCommaBeforeVaArgs(ResultToks, NextTokGetsSpace,
+ /*HasPasteOperator=*/false,
+ Macro, ArgNo, PP))
+ continue;
+
// If it is not the LHS/RHS of a ## operator, we must pre-expand the
// argument and substitute the expanded tokens into the result. This is
// C99 6.10.3.1p1.
@@ -321,23 +378,13 @@
// If this is the __VA_ARGS__ token, and if the argument wasn't provided,
// and if the macro had at least one real argument, and if the token before
- // the ## was a comma, remove the comma.
- if ((unsigned)ArgNo == Macro->getNumArgs()-1 && // is __VA_ARGS__
- ActualArgs->isVarargsElidedUse() && // Argument elided.
- !ResultToks.empty() && ResultToks.back().is(tok::comma)) {
- // Never add a space, even if the comma, ##, or arg had a space.
- NextTokGetsSpace = false;
- // Remove the paste operator, report use of the extension.
- PP.Diag(ResultToks.back().getLocation(), diag::ext_paste_comma);
- ResultToks.pop_back();
-
- // If the comma was right after another paste (e.g. "X##,##__VA_ARGS__"),
- // then removal of the comma should produce a placemarker token (in C99
- // terms) which we model by popping off the previous ##, giving us a plain
- // "X" when __VA_ARGS__ is empty.
- if (!ResultToks.empty() && ResultToks.back().is(tok::hashhash))
- ResultToks.pop_back();
- }
+ // the ## was a comma, remove the comma. This is a GCC extension which is
+ // disabled when using -std=c99.
+ if (ActualArgs->isVarargsElidedUse())
+ MaybeRemoveCommaBeforeVaArgs(ResultToks, NextTokGetsSpace,
+ /*HasPasteOperator=*/true,
+ Macro, ArgNo, PP);
+
continue;
}