[gcc r14-9670] libstdc++: Add dg-require-cpp-feature-test to test feature test macros

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:4a3a1b6b75f921d35bbfef26619e7b5cece3fcf0

commit r14-9670-g4a3a1b6b75f921d35bbfef26619e7b5cece3fcf0
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Mar 22 22:01:50 2024 +0000

    libstdc++: Add dg-require-cpp-feature-test to test feature test macros
    
    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.

Diff:
---
 libstdc++-v3/testsuite/lib/dg-options.exp                |  9 +++++++++
 libstdc++-v3/testsuite/lib/libstdc++.exp                 | 15 +++++++++++++++
 libstdc++-v3/testsuite/std/text_encoding/cons.cc         |  1 +
 libstdc++-v3/testsuite/std/text_encoding/requirements.cc |  1 +
 4 files changed, 26 insertions(+)

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 6cd71b68225..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>