compilers/gnu: Split Gnu C++ standard handling into a mixin class

So we can re-use it in the ObjC++ standards

mesonbuild/compilers/cpp.py

@@ -25,7 +25,7 @@ from .mixins.ccrx import CcrxCompiler
 from .mixins.ti import TICompiler
 from .mixins.arm import ArmCompiler, ArmclangCompiler
 from .mixins.visualstudio import MSVCCompiler, ClangClCompiler
-from .mixins.gnu import GnuCompiler, gnu_common_warning_args, gnu_cpp_warning_args
+from .mixins.gnu import GnuCompiler, GnuCPPStds, gnu_common_warning_args, gnu_cpp_warning_args
 from .mixins.intel import IntelGnuLikeCompiler, IntelVisualStudioLikeCompiler
 from .mixins.clang import ClangCompiler, ClangCPPStds
 from .mixins.elbrus import ElbrusCompiler
@@ -417,7 +417,7 @@ class ArmclangCPPCompiler(ArmclangCompiler, CPPCompiler):
         return []
 
 
-class GnuCPPCompiler(_StdCPPLibMixin, GnuCompiler, CPPCompiler):
+class GnuCPPCompiler(_StdCPPLibMixin, GnuCPPStds, GnuCompiler, CPPCompiler):
     def __init__(self, ccache: T.List[str], exelist: T.List[str], version: str, for_machine: MachineChoice, is_cross: bool,
                  info: 'MachineInfo',
                  linker: T.Optional['DynamicLinker'] = None,
@@ -437,7 +437,7 @@ class GnuCPPCompiler(_StdCPPLibMixin, GnuCompiler, CPPCompiler):
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         key = self.form_compileropt_key('std')
-        opts = CPPCompiler.get_options(self)
+        opts = super().get_options()
         self.update_options(
             opts,
             self.create_option(options.UserComboOption,
@@ -454,17 +454,6 @@ class GnuCPPCompiler(_StdCPPLibMixin, GnuCompiler, CPPCompiler):
                                'STL debug mode',
                                False),
         )
-        cppstd_choices = [
-            'c++98', 'c++03', 'c++11', 'c++14', 'c++17', 'c++1z',
-            'c++2a', 'c++20',
-        ]
-        if version_compare(self.version, '>=11.0.0'):
-            cppstd_choices.append('c++23')
-        if version_compare(self.version, '>=14.0.0'):
-            cppstd_choices.append('c++26')
-        std_opt = opts[key]
-        assert isinstance(std_opt, options.UserStdOption), 'for mypy'
-        std_opt.set_versions(cppstd_choices, gnu=True)
         if self.info.is_windows() or self.info.is_cygwin():
             self.update_options(
                 opts,

mesonbuild/compilers/mixins/gnu.py

@@ -657,3 +657,28 @@ class GnuCStds(Compiler):
         assert isinstance(std_opt, UserStdOption), 'for mypy'
         std_opt.set_versions(stds, gnu=True)
         return opts
+
+
+class GnuCPPStds(Compiler):
+
+    """Mixin class for GNU based compilers for setting CPP standards."""
+
+    _CPP23_VERSION = '>=11.0.0'
+    _CPP26_VERSION = '>=14.0.0'
+
+    def get_options(self) -> MutableKeyedOptionDictType:
+        opts = super().get_options()
+
+        stds = [
+            'c++98', 'c++03', 'c++11', 'c++14', 'c++17', 'c++1z',
+            'c++2a', 'c++20',
+        ]
+        if mesonlib.version_compare(self.version, self._CPP23_VERSION):
+            stds.append('c++23')
+        if mesonlib.version_compare(self.version, self._CPP26_VERSION):
+            stds.append('c++26')
+        key = self.form_compileropt_key('std')
+        std_opt = opts[key]
+        assert isinstance(std_opt, UserStdOption), 'for mypy'
+        std_opt.set_versions(stds, gnu=True)
+        return opts