Re: [PATCH] W/ Clang, compile C/C++ testcases with -Wno-unknown-warning-option

[Gary Benson <gbenson@redhat.com>]

Pedro Alves wrote:
> From 79f1cfddeea957a778c856c879a386901a96609b Mon Sep 17 00:00:00 2001
> From: Pedro Alves <palves@redhat.com>
> Date: Wed, 17 Jun 2020 19:29:37 +0100
> Subject: [PATCH] W/ Clang, compile C/C++ testcases with
>  -Wno-unknown-warning-option
> 
> Some C/C++ testcases unconditionally pass -Wno-foo as additional
> options to disable some warning.  That is OK with GCC, because GCC
> accepts -Wno-foo silently even if it doesn't support -Wfoo.  This is a
> feature which allows disabling warnings with newer compilers without
> breaking builds with older compilers.  Clang however warns about
> unknown -Wno-foo by default, unless you pass
> -Wno-unknown-warning-option as well:
> 
>  $ gcc -Wno-foo test.c
>  * nothing, compiles successfuly *
> 
>  $ clang -Wno-foo test.c
>  warning: unknown warning option '-Wno-foo [-Wunknown-warning-option]
> 
> This commit adds -Wunknown-warning-option centrally in gdb_compile, so
> that individual testcases don't have to worry about breaking older
> Clangs.
> 
> IOW, this avoids this problematic scenario:
> 
> #1 - A testcase compiles successfully with Clang version X.
> #2 - Clang version "X + 1" adds a new warning, enabled by default,
>      which breaks the test.
> #3 - We add -Wno-newwarning to the testcase, fixing the testcase with
>      clang "X + 1".
> #4 - Now building the test with Clang version X no longer works, due
>      to "unknown warning option".
> 
> gdb/testsuite/ChangeLog:
> yyyy-mm-dd  Pedro Alves  <palves@redhat.com>
> 
> 	* lib/gdb.exp (gdb_compile): Update intro comment.  If C/C++ with
> 	Clang, add "-Wno-unknown-warning-option" to the options.
> ---
>  gdb/testsuite/lib/gdb.exp | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
> index f502eb157d8..bbc940a4512 100644
> --- a/gdb/testsuite/lib/gdb.exp
> +++ b/gdb/testsuite/lib/gdb.exp
> @@ -3826,7 +3826,8 @@ set gdb_saved_set_unbuffered_mode_obj ""
>  #   - ldflags=flag: Add FLAG to the linker flags.
>  #   - incdir=path: Add PATH to the searched include directories.
>  #   - libdir=path: Add PATH to the linker searched directories.
> -#   - ada, c++, f77: Compile the file as Ada, C++ or Fortran.
> +#   - ada, c++, f77, f90, rust: Compile the file as Ada, C++,
> +#     Fortran 77, Fortran 90 or Rust.
>  #   - debug: Build with debug information.
>  #   - optimize: Build with optimization.
>  
> @@ -3850,6 +3851,22 @@ proc gdb_compile {source dest type options} {
>  	set new_options [universal_compile_options]
>      }
>  
> +    # Some C/C++ testcases unconditionally pass -Wno-foo as additional
> +    # options to disable some warning.  That is OK with GCC, because
> +    # by design, GCC accepts any -Wno-foo option, even if it doesn't
> +    # support -Wfoo.  Clang however warns about unknown -Wno-foo by
> +    # default, unless you pass -Wno-unknown-warning-option as well.
> +    # We do that here, so that individual testcases don't have to
> +    # worry about it.
> +    if {[lsearch -exact $options getting_compiler_info] == -1
> +	&& [lsearch -exact $options rust] == -1
> +	&& [lsearch -exact $options ada] == -1
> +	&& [lsearch -exact $options f77] == -1
> +	&& [lsearch -exact $options f90] == -1
> +	&& [test_compiler_info "clang-*"]} {
> +	lappend new_options "additional_flags=-Wno-unknown-warning-option"
> +    }
> +
>      # Place (and look for) Fortran `.mod` files in the output
>      # directory for this specific test.
>      if {[lsearch -exact $options f77] != -1 \
> 
> base-commit: 669203174311c5be76744a879563c697cd479853
> -- 
> 2.14.5

Oh, thanks, that looks great.  Could you commit it please?

Cheers,
Gary

-- 
Gary Benson - he / him / his
Principal Software Engineer, Red Hat