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On Tue, Aug 30, 2022 at 09:10:37PM +0000, Joseph Myers wrote:
> I'm seeing build failures of glibc for powerpc64, as illustrated by the
> following C code:
>
> #if 0
> \NARG
> #endif
>
> (the actual sysdeps/powerpc/powerpc64/sysdep.h code is inside #ifdef
> __ASSEMBLER__).
>
> This shows some problems with this feature - and with delimited escape
> sequences - as it affects C. It's fine to accept it as an extension
> inside string and character literals, because \N or \u{...} would be
> invalid in the absence of the feature (i.e. the syntax for such literals
> fails to match, meaning that the rule about undefined behavior for a
> single ' or " as a pp-token applies). But outside string and character
> literals, the usual lexing rules apply, the \ is a pp-token on its own and
> the code is valid at the preprocessing level, and with expansion of macros
> appearing before or after the \ (e.g. u defined as a macro in the \u{...}
> case) it may be valid code at the language level as well. I don't know
> what older C++ versions say about this, but for C this means e.g.
>
> #define z(x) 0
> #define a z(
> int x = a\NARG);
>
> needs to be accepted as expanding to "int x = 0;", not interpreted as
> using the \N feature in an identifier and produce an error.
The following patch changes this, so that:
1) outside of string/character literals, \N without following { is never
treated as an error nor warning, it is silently treated as \ separate
token followed by whatever is after it
2) \u{123} and \N{LATIN SMALL LETTER A WITH ACUTE} are not handled as
extension at all outside of string/character literals in the strict
standard modes (-std=c*) except for -std=c++{23,2b}, only in the
-std=gnu* modes, because it changes behavior on valid sources, e.g.
#define z(x) 0
#define a z(
int x = a\u{123});
int y = a\N{LATIN SMALL LETTER A WITH ACUTE});
3) introduces -Wunicode warning (on by default) and warns for cases
of what looks like invalid delimited escape sequence or named
universal character escape outside of string/character literals
and is treated as separate tokens
2022-09-07 Jakub Jelinek <jakub@redhat.com>
libcpp/
* include/cpplib.h (struct cpp_options): Add cpp_warn_unicode member.
(enum cpp_warning_reason): Add CPP_W_UNICODE.
* init.cc (cpp_create_reader): Initialize cpp_warn_unicode.
* charset.cc (_cpp_valid_ucn): In possible identifier contexts, don't
handle \u{ or \N{ specially in -std=c* modes except -std=c++2{3,b}.
In possible identifier contexts, don't emit an error and punt
if \N isn't followed by {, or if \N{} surrounds some lower case
letters or _. In possible identifier contexts when not C++23, don't
emit an error but warning about unknown character names and treat as
separate tokens. When treating as separate tokens \u{ or \N{, emit
warnings.
gcc/
* doc/invoke.texi (-Wno-unicode): Document.
gcc/c-family/
* c.opt (Winvalid-utf8): Use ObjC instead of objC. Remove
" in comments" from description.
(Wunicode): New option.
gcc/testsuite/
* c-c++-common/cpp/delimited-escape-seq-4.c: New test.
* c-c++-common/cpp/delimited-escape-seq-5.c: New test.
* c-c++-common/cpp/delimited-escape-seq-6.c: New test.
* c-c++-common/cpp/delimited-escape-seq-7.c: New test.
* c-c++-common/cpp/named-universal-char-escape-5.c: New test.
* c-c++-common/cpp/named-universal-char-escape-6.c: New test.
* c-c++-common/cpp/named-universal-char-escape-7.c: New test.
* g++.dg/cpp23/named-universal-char-escape1.C: New test.
* g++.dg/cpp23/named-universal-char-escape2.C: New test.