Re: [PATCH 1/1 v2] c++/106423: Fix pragma suppression of -Wc++20-compat diagnostics.

[Jason Merrill <jason@redhat.com>]

Sorry for the delay, I'm travelling with limited internet. I will commit it
early next week if no one beats me to it.

On Thu, Aug 11, 2022, 2:45 PM Tom Honermann via Gcc-patches <
gcc-patches@gcc.gnu.org> wrote:

> If there are no further concerns, could a C++ or libcpp maintainer
> please commit this for me?
>
> Thank you!
>
> Tom.
>
> On 8/4/22 12:42 PM, Tom Honermann via Gcc-patches wrote:
> > Are there any further concerns with this patch? If not, I extend my
> > gratitude to anyone so kind as to commit this for me as I don't have
> > commit access.
> >
> > I just noticed that I neglected to add a ChangeLog entry for the
> > comment addition to gcc/cp/parser.cc. Noted inline below. I can
> > re-send the patch with that update if desired.
> >
> > Tom.
> >
> > On 8/1/22 2:49 PM, Tom Honermann wrote:
> >> Gcc's '#pragma GCC diagnostic' directives are processed in "early mode"
> >> (see handle_pragma_diagnostic_early) for the C++ frontend and, as such,
> >> require that the target diagnostic option be enabled for the
> >> preprocessor
> >> (see c_option_is_from_cpp_diagnostics).  This change modifies the
> >> -Wc++20-compat option definition to register it as a preprocessor option
> >> so that its associated diagnostics can be suppressed.  The changes also
> >> implicitly disable the option in C++20 and later modes.  These changes
> >> are consistent with the definition of the -Wc++11-compat option.
> >>
> >> This support is motivated by the need to suppress the following
> >> diagnostic
> >> otherwise issued in C++17 and earlier modes due to the char8_t typedef
> >> present in the uchar.h header file in glibc 2.36.
> >>    warning: identifier ‘char8_t’ is a keyword in C++20 [-Wc++20-compat]
> >>
> >> Tests are added to validate suppression of both -Wc++11-compat and
> >> -Wc++20-compat related diagnostics (fixes were only needed for the C++20
> >> case).
> >>
> >> Fixeshttps://gcc.gnu.org/PR106423.
> >>
> >> gcc/c-family/ChangeLog:
> >>     * c-opts.cc (c_common_post_options): Disable -Wc++20-compat
> >> diagnostics
> >>     in C++20 and later.
> >>     * c.opt (Wc++20-compat): Enable hooks for the preprocessor.
> >
> > gcc/cp/ChangeLog:
> >     * parser.cc (cp_lexer_saving_tokens): Add comment regarding
> > diagnostic requirements.
> >
> >>
> >> gcc/testsuite/ChangeLog:
> >>     * g++.dg/cpp0x/keywords2.C: New test.
> >>     * g++.dg/cpp2a/keywords2.C: New test.
> >>
> >> libcpp/ChangeLog:
> >>     * include/cpplib.h (cpp_warning_reason): Add CPP_W_CXX20_COMPAT.
> >>     * init.cc (cpp_create_reader): Add cpp_warn_cxx20_compat.
> >> ---
> >>   gcc/c-family/c-opts.cc                 |  7 +++++++
> >>   gcc/c-family/c.opt                     |  2 +-
> >>   gcc/cp/parser.cc                       |  5 ++++-
> >>   gcc/testsuite/g++.dg/cpp0x/keywords2.C | 16 ++++++++++++++++
> >>   gcc/testsuite/g++.dg/cpp2a/keywords2.C | 13 +++++++++++++
> >>   libcpp/include/cpplib.h                |  4 ++++
> >>   libcpp/init.cc                         |  1 +
> >>   7 files changed, 46 insertions(+), 2 deletions(-)
> >>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/keywords2.C
> >>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/keywords2.C
> >>
> >> diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc
> >> index b9f01a65ed7..1ea37ba9742 100644
> >> --- a/gcc/c-family/c-opts.cc
> >> +++ b/gcc/c-family/c-opts.cc
> >> @@ -1046,6 +1046,13 @@ c_common_post_options (const char **pfilename)
> >>     else if (warn_narrowing == -1)
> >>       warn_narrowing = 0;
> >>   +  if (cxx_dialect >= cxx20)
> >> +    {
> >> +      /* Don't warn about C++20 compatibility changes in C++20 or
> >> later.  */
> >> +      warn_cxx20_compat = 0;
> >> +      cpp_opts->cpp_warn_cxx20_compat = 0;
> >> +    }
> >> +
> >>     /* C++17 has stricter evaluation order requirements; let's use
> >> some of them
> >>        for earlier C++ as well, so chaining works as expected. */
> >>     if (c_dialect_cxx ()
> >> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
> >> index 44e1a60ce24..dfdebd596ef 100644
> >> --- a/gcc/c-family/c.opt
> >> +++ b/gcc/c-family/c.opt
> >> @@ -455,7 +455,7 @@ Wc++2a-compat
> >>   C++ ObjC++ Warning Alias(Wc++20-compat) Undocumented
> >>     Wc++20-compat
> >> -C++ ObjC++ Var(warn_cxx20_compat) Warning LangEnabledBy(C++
> >> ObjC++,Wall)
> >> +C++ ObjC++ Var(warn_cxx20_compat) Warning LangEnabledBy(C++
> >> ObjC++,Wall) Init(0) CPP(cpp_warn_cxx20_compat)
> >> CppReason(CPP_W_CXX20_COMPAT)
> >>   Warn about C++ constructs whose meaning differs between ISO C++
> >> 2017 and ISO C++ 2020.
> >>     Wc++11-extensions
> >> diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
> >> index 4f67441eeb1..c3584446827 100644
> >> --- a/gcc/cp/parser.cc
> >> +++ b/gcc/cp/parser.cc
> >> @@ -924,7 +924,10 @@ cp_lexer_saving_tokens (const cp_lexer* lexer)
> >>   /* Store the next token from the preprocessor in *TOKEN. Return true
> >>      if we reach EOF.  If LEXER is NULL, assume we are handling an
> >>      initial #pragma pch_preprocess, and thus want the lexer to return
> >> -   processed strings.  */
> >> +   processed strings.
> >> +
> >> +   Diagnostics issued from this function must have their controlling
> >> option (if
> >> +   any) in c.opt annotated as a libcpp option via the CppReason
> >> property.  */
> >>     static void
> >>   cp_lexer_get_preprocessor_token (unsigned flags, cp_token *token)
> >> diff --git a/gcc/testsuite/g++.dg/cpp0x/keywords2.C
> >> b/gcc/testsuite/g++.dg/cpp0x/keywords2.C
> >> new file mode 100644
> >> index 00000000000..d67d01e31ed
> >> --- /dev/null
> >> +++ b/gcc/testsuite/g++.dg/cpp0x/keywords2.C
> >> @@ -0,0 +1,16 @@
> >> +// { dg-do compile { target c++98_only } }
> >> +// { dg-options "-Wc++11-compat" }
> >> +
> >> +// Validate suppression of -Wc++11-compat diagnostics.
> >> +#pragma GCC diagnostic ignored "-Wc++11-compat"
> >> +int alignof;
> >> +int alignas;
> >> +int constexpr;
> >> +int decltype;
> >> +int noexcept;
> >> +int nullptr;
> >> +int static_assert;
> >> +int thread_local;
> >> +int _Alignas;
> >> +int _Alignof;
> >> +int _Thread_local;
> >> diff --git a/gcc/testsuite/g++.dg/cpp2a/keywords2.C
> >> b/gcc/testsuite/g++.dg/cpp2a/keywords2.C
> >> new file mode 100644
> >> index 00000000000..8714a7b26b7
> >> --- /dev/null
> >> +++ b/gcc/testsuite/g++.dg/cpp2a/keywords2.C
> >> @@ -0,0 +1,13 @@
> >> +// { dg-do compile { target c++17_down } }
> >> +// { dg-options "-Wc++20-compat" }
> >> +
> >> +// Validate suppression of -Wc++20-compat diagnostics.
> >> +#pragma GCC diagnostic ignored "-Wc++20-compat"
> >> +int constinit;
> >> +int consteval;
> >> +int requires;
> >> +int concept;
> >> +int co_await;
> >> +int co_yield;
> >> +int co_return;
> >> +int char8_t;
> >> diff --git a/libcpp/include/cpplib.h b/libcpp/include/cpplib.h
> >> index 3eba6f74b57..9d90c18e4f2 100644
> >> --- a/libcpp/include/cpplib.h
> >> +++ b/libcpp/include/cpplib.h
> >> @@ -547,6 +547,9 @@ struct cpp_options
> >>     /* True if warn about differences between C++98 and C++11. */
> >>     bool cpp_warn_cxx11_compat;
> >>   +  /* True if warn about differences between C++17 and C++20. */
> >> +  bool cpp_warn_cxx20_compat;
> >> +
> >>     /* Nonzero if bidirectional control characters checking is on.
> >> See enum
> >>        cpp_bidirectional_level.  */
> >>     unsigned char cpp_warn_bidirectional;
> >> @@ -655,6 +658,7 @@ enum cpp_warning_reason {
> >>     CPP_W_C90_C99_COMPAT,
> >>     CPP_W_C11_C2X_COMPAT,
> >>     CPP_W_CXX11_COMPAT,
> >> +  CPP_W_CXX20_COMPAT,
> >>     CPP_W_EXPANSION_TO_DEFINED,
> >>     CPP_W_BIDIRECTIONAL
> >>   };
> >> diff --git a/libcpp/init.cc b/libcpp/init.cc
> >> index f4ab83d2145..cca3c1dc1e7 100644
> >> --- a/libcpp/init.cc
> >> +++ b/libcpp/init.cc
> >> @@ -202,6 +202,7 @@ cpp_create_reader (enum c_lang lang,
> >> cpp_hash_table *table,
> >>     CPP_OPTION (pfile, cpp_warn_c90_c99_compat) = -1;
> >>     CPP_OPTION (pfile, cpp_warn_c11_c2x_compat) = -1;
> >>     CPP_OPTION (pfile, cpp_warn_cxx11_compat) = 0;
> >> +  CPP_OPTION (pfile, cpp_warn_cxx20_compat) = 0;
> >>     CPP_OPTION (pfile, cpp_warn_deprecated) = 1;
> >>     CPP_OPTION (pfile, cpp_warn_long_long) = 0;
> >>     CPP_OPTION (pfile, dollars_in_ident) = 1;
>
>