Re: [PATCH 1/2] libstdc++: Add dg-require-cpp-feature-test to test feature test macros

[Jonathan Wakely <jwakely@redhat.com>]

Pushed to trunk.

On Sat, 23 Mar 2024 at 00:22, Jonathan Wakely <jwakely@redhat.com> wrote:
>
> Thoughts? There are only a few uses for this presently, but I can see it
> being useful often in future. The library exposes which features it
> supports in a standardized way, so we can use those in tests to skip
> tests for features that aren't available on all targets.
>
> The obvious downside is that it becomes harder to notice if a particular
> feature is missing on all targets, because we don't get FAILs we just
> skip all tests as UNSUPPORTED. And the checks for whether <version>
> correctly defines the macro become redundant, because the test won't
> even get run if it doesn't. But we won't use this dg-require for many
> tests, only the ones where support is target-dependent because it relies
> on something non-standard or not available on all targets (like
> nl_langinfo_l or libbacktrace).
>
> -- >8 -
>
> This adds a new dejagnu directive which can be used to make a test
> depend on a feature test macro such as __cpp_lib_text_encoding. This is
> mroe flexible than writing a new dg-require-xxx for each feature.
>
> libstdc++-v3/ChangeLog:
>
>         * testsuite/lib/dg-options.exp (dg-require-cpp-feature-test):
>         New proc.
>         * testsuite/lib/libstdc++.exp (check_v3_target_cpp_feature_test):
>         New proc.
>         * testsuite/std/text_encoding/cons.cc: Use new directive to skip
>         the test if the __cpp_lib_text_encoding feature test macro is
>         not defined.
>         * testsuite/std/text_encoding/requirements.cc: Likewise.
> ---
>  libstdc++-v3/testsuite/lib/dg-options.exp         |  9 +++++++++
>  libstdc++-v3/testsuite/lib/libstdc++.exp          | 15 +++++++++++++++
>  libstdc++-v3/testsuite/std/text_encoding/cons.cc  |  1 +
>  .../testsuite/std/text_encoding/requirements.cc   |  3 ++-
>  4 files changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/testsuite/lib/dg-options.exp b/libstdc++-v3/testsuite/lib/dg-options.exp
> index 00ca678a53a..802bfc0b492 100644
> --- a/libstdc++-v3/testsuite/lib/dg-options.exp
> +++ b/libstdc++-v3/testsuite/lib/dg-options.exp
> @@ -277,6 +277,15 @@ proc dg-require-target-fs-lwt { args } {
>      return
>  }
>
> +proc dg-require-cpp-feature-test { n args } {
> +    if { ![ check_v3_target_cpp_feature_test $args ] } {
> +       upvar dg-do-what dg-do-what
> +       set dg-do-what [list [lindex ${dg-do-what} 0] "N" "P"]
> +       return
> +    }
> +    return
> +}
> +
>  proc add_options_for_no_pch { flags } {
>      # Remove any inclusion of bits/stdc++.h from the options.
>      regsub -all -- "-include bits/stdc...h" $flags "" flags
> diff --git a/libstdc++-v3/testsuite/lib/libstdc++.exp b/libstdc++-v3/testsuite/lib/libstdc++.exp
> index 7466fb51c58..2b31c950826 100644
> --- a/libstdc++-v3/testsuite/lib/libstdc++.exp
> +++ b/libstdc++-v3/testsuite/lib/libstdc++.exp
> @@ -1134,6 +1134,21 @@ proc v3_check_preprocessor_condition { name cond { inc "" } } {
>      return [v3_try_preprocess name $code $flags]
>  }
>
> +# Return 1 if libstdc++ defines macro for the current target, 0 otherwise.
> +proc check_v3_target_cpp_feature_test { cond } {
> +    global cxxflags
> +    set cxxflags_saved $cxxflags
> +    # Use the latest standard, so that all feature test macros are defined.
> +    # We need to do it here, because this check happens before v3-dg-runtest
> +    # runs its loop to test multiple times with different -std options.
> +    # This should be updated when a new -std is added.
> +    set cxxflags "$cxxflags -std=gnu++26"
> +    set inc "#include <version>"
> +    set result [v3_check_preprocessor_condition cpp_feature_test "$cond" $inc]
> +    set cxxflags $cxxflags_saved
> +    return $result
> +}
> +
>  # Return 1 if Debug Mode is active, 0 otherwise.
>  proc check_v3_target_debug_mode { } {
>      global cxxflags
> diff --git a/libstdc++-v3/testsuite/std/text_encoding/cons.cc b/libstdc++-v3/testsuite/std/text_encoding/cons.cc
> index 8fcc2ec8c3b..4196e32ea8b 100644
> --- a/libstdc++-v3/testsuite/std/text_encoding/cons.cc
> +++ b/libstdc++-v3/testsuite/std/text_encoding/cons.cc
> @@ -1,4 +1,5 @@
>  // { dg-do run { target c++26 } }
> +// { dg-require-cpp-feature-test "__cpp_lib_text_encoding" }
>
>  #include <text_encoding>
>  #include <string_view>
> diff --git a/libstdc++-v3/testsuite/std/text_encoding/requirements.cc b/libstdc++-v3/testsuite/std/text_encoding/requirements.cc
> index a1d5d6baee1..3889b250688 100644
> --- a/libstdc++-v3/testsuite/std/text_encoding/requirements.cc
> +++ b/libstdc++-v3/testsuite/std/text_encoding/requirements.cc
> @@ -1,4 +1,5 @@
>  // { dg-do compile { target c++26 } }
> +// { dg-require-cpp-feature-test __cpp_lib_text_encoding }
>  // { dg-add-options no_pch }
>
>  #include <text_encoding>
>