[clang] 2edb89c - Lex arguments for __has_cpp_attribute and friends as expanded tokens

[Richard Smith via cfe-commits]

 On Mon, 18 Oct 2021 at 12:48, Aaron Ballman <aaron at aaronballman.com> wrote:

> On Mon, Oct 18, 2021 at 3:33 PM Richard Smith <richard at metafoo.co.uk>
> wrote:
> >
> > On Sun, 17 Oct 2021 at 04:58, Aaron Ballman via cfe-commits <
> cfe-commits at lists.llvm.org> wrote:
> >>
> >>
> >> Author: Aaron Ballman
> >> Date: 2021-10-17T07:54:48-04:00
> >> New Revision: 2edb89c746848c52964537268bf03e7906bf2542
> >>
> >> URL:
> https://github.com/llvm/llvm-project/commit/2edb89c746848c52964537268bf03e7906bf2542
> >> DIFF:
> https://github.com/llvm/llvm-project/commit/2edb89c746848c52964537268bf03e7906bf2542.diff
> >>
> >> LOG: Lex arguments for __has_cpp_attribute and friends as expanded
> tokens
> >>
> >> The C and C++ standards require the argument to __has_cpp_attribute and
> >> __has_c_attribute to be expanded ([cpp.cond]p5). It would make little
> sense
> >> to expand the argument to those operators but not expand the argument to
> >> __has_attribute and __has_declspec, so those were both also changed in
> this
> >> patch.
> >>
> >> Note that it might make sense for the other builtins to also expand
> their
> >> argument, but it wasn't as clear to me whether the behavior would be
> correct
> >> there, and so they were left for a future revision.
> >>
> >> Added:
> >>     clang/test/Preprocessor/has_attribute_errors.cpp
> >>
> >> Modified:
> >>     clang/docs/ReleaseNotes.rst
> >>     clang/lib/Lex/PPMacroExpansion.cpp
> >>     clang/test/Preprocessor/has_attribute.c
> >>     clang/test/Preprocessor/has_attribute.cpp
> >>     clang/test/Preprocessor/has_c_attribute.c
> >>
> >> Removed:
> >>
> >>
> >>
> >>
> ################################################################################
> >> diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
> >> index 6501a4870e2a6..263eae83036df 100644
> >> --- a/clang/docs/ReleaseNotes.rst
> >> +++ b/clang/docs/ReleaseNotes.rst
> >> @@ -110,6 +110,13 @@ Attribute Changes in Clang
> >>    attribute is handled instead, e.g. in ``handleDeclAttribute``.
> >>    (This was changed in order to better support attributes in code
> completion).
> >>
> >> +- __has_cpp_attribute, __has_c_attribute, __has_attribute, and
> __has_declspec
> >> +  will now macro expand their argument. This causes a change in
> behavior for
> >> +  code using ``__has_cpp_attribute(__clang__::attr)`` (and same for
> >> +  ``__has_c_attribute``) where it would previously expand to ``0`` for
> all
> >> +  attributes, but will now issue an error due to the expansion of the
> >> +  predefined ``__clang__`` macro.
> >> +
> >>  Windows Support
> >>  ---------------
> >>
> >>
> >> diff  --git a/clang/lib/Lex/PPMacroExpansion.cpp
> b/clang/lib/Lex/PPMacroExpansion.cpp
> >> index bf19f538647e6..5a0fa5184e38b 100644
> >> --- a/clang/lib/Lex/PPMacroExpansion.cpp
> >> +++ b/clang/lib/Lex/PPMacroExpansion.cpp
> >> @@ -1293,7 +1293,7 @@ static bool EvaluateHasIncludeNext(Token &Tok,
> >>  /// integer values.
> >>  static void EvaluateFeatureLikeBuiltinMacro(llvm::raw_svector_ostream&
> OS,
> >>                                              Token &Tok, IdentifierInfo
> *II,
> >> -                                            Preprocessor &PP,
> >> +                                            Preprocessor &PP, bool
> ExpandArgs,
> >>                                              llvm::function_ref<
> >>                                                int(Token &Tok,
> >>                                                    bool
> &HasLexedNextTok)> Op) {
> >> @@ -1319,7 +1319,10 @@ static void
> EvaluateFeatureLikeBuiltinMacro(llvm::raw_svector_ostream& OS,
> >>    bool SuppressDiagnostic = false;
> >>    while (true) {
> >>      // Parse next token.
> >> -    PP.LexUnexpandedToken(Tok);
> >> +    if (ExpandArgs)
> >> +      PP.Lex(Tok);
> >> +    else
> >> +      PP.LexUnexpandedToken(Tok);
> >
> >
> > How does this handle things like:
> >
> > #define RPAREN )
> > #if __has_attribute(clang::fallthrough RPAREN
> >
> > ? I think that should be an error: the ) token should not be produced by
> macro expansion, analogous to the behavior of function-like macros. But I
> imagine unless we're careful here, we'll allow that macro expansion to
> terminate the "macro".
>
> I agree, I think that should be an error. We handle it reasonably too; I
> get:
>
> error: missing ')' after 'clang'
>
> though it appears there is some compiler divergence here:
> https://godbolt.org/z/c84cb3PW7


Oops, I meant __has_cpp_attribute, not __has_attribute. We mishandle that
one just like GCC: https://godbolt.org/z/Ej84Kca16
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