c++: warn about using keywords as identifiers [PR106111]

  In C++03, -Wc++11-compat should warn about

  int constexpr;

since 'constexpr' is a keyword in C++11.  Jonathan reports that
we don't emit a similar warning for 'alignas' or 'alignof', and,
as I found out, 'thread_local'.

Similarly, we don't warn for most C++20 keywords.  That happens
because RID_LAST_CXX20 hasn't been updated in a while.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

	PR c++/106111

gcc/c-family/ChangeLog:

	* c-common.h (enum rid): Update RID_LAST_CXX20.

gcc/cp/ChangeLog:

	* parser.cc (cp_lexer_get_preprocessor_token): Also warn about
	RID_ALIGNOF, RID_ALIGNAS, RID_THREAD.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/keywords1.C: New test.
	* g++.dg/cpp2a/keywords1.C: New test.
---
 gcc/c-family/c-common.h                |  2 +-
 gcc/cp/parser.cc                       | 10 +++++++---
 gcc/testsuite/g++.dg/cpp0x/keywords1.C | 15 +++++++++++++++
 gcc/testsuite/g++.dg/cpp2a/keywords1.C | 12 ++++++++++++
 4 files changed, 35 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/keywords1.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/keywords1.C


base-commit: b01c075e7e6d84da846c2ff9087433a30ebeb0d2
  

On 6/29/22 12:11, Marek Polacek wrote:
> In C++03, -Wc++11-compat should warn about
> 
>    int constexpr;
> 
> since 'constexpr' is a keyword in C++11.  Jonathan reports that
> we don't emit a similar warning for 'alignas' or 'alignof', and,
> as I found out, 'thread_local'.
> 
> Similarly, we don't warn for most C++20 keywords.  That happens
> because RID_LAST_CXX20 hasn't been updated in a while.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK.

> 	PR c++/106111
> 
> gcc/c-family/ChangeLog:
> 
> 	* c-common.h (enum rid): Update RID_LAST_CXX20.
> 
> gcc/cp/ChangeLog:
> 
> 	* parser.cc (cp_lexer_get_preprocessor_token): Also warn about
> 	RID_ALIGNOF, RID_ALIGNAS, RID_THREAD.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/keywords1.C: New test.
> 	* g++.dg/cpp2a/keywords1.C: New test.
> ---
>   gcc/c-family/c-common.h                |  2 +-
>   gcc/cp/parser.cc                       | 10 +++++++---
>   gcc/testsuite/g++.dg/cpp0x/keywords1.C | 15 +++++++++++++++
>   gcc/testsuite/g++.dg/cpp2a/keywords1.C | 12 ++++++++++++
>   4 files changed, 35 insertions(+), 4 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/keywords1.C
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/keywords1.C
> 
> diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
> index 47442c95a53..a1e6a55158d 100644
> --- a/gcc/c-family/c-common.h
> +++ b/gcc/c-family/c-common.h
> @@ -271,7 +271,7 @@ enum rid
>     RID_FIRST_CXX11 = RID_CONSTEXPR,
>     RID_LAST_CXX11 = RID_STATIC_ASSERT,
>     RID_FIRST_CXX20 = RID_CONSTINIT,
> -  RID_LAST_CXX20 = RID_CONSTINIT,
> +  RID_LAST_CXX20 = RID_CO_RETURN,
>     RID_FIRST_AT = RID_AT_ENCODE,
>     RID_LAST_AT = RID_AT_IMPLEMENTATION,
>     RID_FIRST_PQ = RID_IN,
> diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
> index da2f370cdca..cc6525e0509 100644
> --- a/gcc/cp/parser.cc
> +++ b/gcc/cp/parser.cc
> @@ -890,10 +890,14 @@ cp_lexer_get_preprocessor_token (unsigned flags, cp_token *token)
>         else
>   	{
>             if (warn_cxx11_compat
> -              && C_RID_CODE (token->u.value) >= RID_FIRST_CXX11
> -              && C_RID_CODE (token->u.value) <= RID_LAST_CXX11)
> +	      && ((C_RID_CODE (token->u.value) >= RID_FIRST_CXX11
> +		   && C_RID_CODE (token->u.value) <= RID_LAST_CXX11)
> +		  /* These are outside the CXX11 range.  */
> +		  || C_RID_CODE (token->u.value) == RID_ALIGNOF
> +		  || C_RID_CODE (token->u.value) == RID_ALIGNAS
> +		  || C_RID_CODE (token->u.value)== RID_THREAD))
>               {
> -              /* Warn about the C++0x keyword (but still treat it as
> +	      /* Warn about the C++11 keyword (but still treat it as
>                    an identifier).  */
>   	      warning_at (token->location, OPT_Wc__11_compat,
>   			  "identifier %qE is a keyword in C++11",
> diff --git a/gcc/testsuite/g++.dg/cpp0x/keywords1.C b/gcc/testsuite/g++.dg/cpp0x/keywords1.C
> new file mode 100644
> index 00000000000..2b2ab6404ea
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/keywords1.C
> @@ -0,0 +1,15 @@
> +// PR c++/106111
> +// { dg-do compile { target c++98_only } }
> +// { dg-options "-Wc++11-compat" }
> +
> +int alignof; // { dg-warning "is a keyword in C\\\+\\\+11" }
> +int alignas; // { dg-warning "is a keyword in C\\\+\\\+11" }
> +int constexpr; // { dg-warning "is a keyword in C\\\+\\\+11" }
> +int decltype; // { dg-warning "is a keyword in C\\\+\\\+11" }
> +int noexcept; // { dg-warning "is a keyword in C\\\+\\\+11" }
> +int nullptr; // { dg-warning "is a keyword in C\\\+\\\+11" }
> +int static_assert; // { dg-warning "is a keyword in C\\\+\\\+11" }
> +int thread_local; // { dg-warning "is a keyword in C\\\+\\\+11" }
> +int _Alignas;
> +int _Alignof;
> +int _Thread_local;
> diff --git a/gcc/testsuite/g++.dg/cpp2a/keywords1.C b/gcc/testsuite/g++.dg/cpp2a/keywords1.C
> new file mode 100644
> index 00000000000..7f4dba2d3b7
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/keywords1.C
> @@ -0,0 +1,12 @@
> +// PR c++/106111
> +// { dg-do compile { target c++17_down } }
> +// { dg-options "-Wc++20-compat -Wc++11-compat -Wc++14-compat -Wc++17-compat" }
> +
> +int constinit; // { dg-warning "is a keyword in C\\\+\\\+20" }
> +int consteval; // { dg-warning "is a keyword in C\\\+\\\+20" }
> +int requires; // { dg-warning "is a keyword in C\\\+\\\+20" }
> +int concept; // { dg-warning "is a keyword in C\\\+\\\+20" }
> +int co_await; // { dg-warning "is a keyword in C\\\+\\\+20" }
> +int co_yield; // { dg-warning "is a keyword in C\\\+\\\+20" }
> +int co_return; // { dg-warning "is a keyword in C\\\+\\\+20" }
> +int char8_t; // { dg-warning "is a keyword in C\\\+\\\+20" }
> 
> base-commit: b01c075e7e6d84da846c2ff9087433a30ebeb0d2