c_std, cpp_std: Change to a list of desired versions in preference order

Projects that prefer GNU C but can fallback to ISO C can now set for
example `default_options: 'c_std=gnu11,c11'` and it will use gnu11 when
available, fallback to c11 otherwise. It is an error only if none of the
values are supported by the current compiler.

This allows to deprecate gnuXX values from MSVC compiler, that means
that `default_options: 'c_std=gnu11'` will now print warning with MSVC
but still fallback to 'c11' value. No warning is printed if at least one
of the values is valid, i.e. `default_options: 'c_std=gnu11,c11'`.

In the future that deprecation warning will become an hard error because
`c_std=gnu11` should mean GNU is required, for projects that cannot be
built with MSVC for example.

1 files changed, 40 insertions, 36 deletions

diff --git a/mesonbuild/compilers/cpp.py b/mesonbuild/compilers/cpp.py
index 8c8043763..3e9668262 100644
--- a/mesonbuild/compilers/cpp.py
+++ b/mesonbuild/compilers/cpp.py
@@ -55,6 +55,10 @@ if T.TYPE_CHECKING:
 else:
     CompilerMixinBase = object
 
+_ALL_STDS = ['c++98', 'c++0x', 'c++03', 'c++1y', 'c++1z', 'c++11', 'c++14', 'c++17', 'c++2a', 'c++20', 'c++23']
+_ALL_STDS += [f'gnu{std[1:]}' for std in _ALL_STDS]
+_ALL_STDS += ['vc++11', 'vc++14', 'vc++17', 'vc++20', 'vc++latest', 'c++latest']
+
 
 def non_msvc_eh_options(eh: str, args: T.List[str]) -> None:
     if eh == 'none':
@@ -178,11 +182,7 @@ class CPPCompiler(CLikeCompiler, Compiler):
         opts = super().get_options()
         key = OptionKey('std', machine=self.for_machine, lang=self.language)
         opts.update({
-            key: coredata.UserComboOption(
-                'C++ language standard to use',
-                ['none'],
-                'none',
-            ),
+            key: coredata.UserStdOption('C++', _ALL_STDS),
         })
         return opts
 
@@ -257,17 +257,15 @@ class ClangCPPCompiler(_StdCPPLibMixin, ClangCompiler, CPPCompiler):
             key.evolve('rtti'): coredata.UserBooleanOption('Enable RTTI', True),
         })
         cppstd_choices = [
-            'none', 'c++98', 'c++03', 'c++11', 'c++14', 'c++17', 'c++1z',
-            'c++2a', 'c++20', 'gnu++11', 'gnu++14', 'gnu++17', 'gnu++1z',
-            'gnu++2a', 'gnu++20',
+            'c++98', 'c++03', 'c++11', 'c++14', 'c++17', 'c++1z', 'c++2a', 'c++20',
         ]
         if version_compare(self.version, self._CPP23_VERSION):
             cppstd_choices.append('c++23')
-            cppstd_choices.append('gnu++23')
         if version_compare(self.version, self._CPP26_VERSION):
             cppstd_choices.append('c++26')
-            cppstd_choices.append('gnu++26')
-        opts[key.evolve('std')].choices = cppstd_choices
+        std_opt = opts[key.evolve('std')]
+        assert isinstance(std_opt, coredata.UserStdOption), 'for mypy'
+        std_opt.set_versions(cppstd_choices, gnu=True)
         if self.info.is_windows() or self.info.is_cygwin():
             opts.update({
                 key.evolve('winlibs'): coredata.UserArrayOption(
@@ -371,10 +369,9 @@ class ArmclangCPPCompiler(ArmclangCompiler, CPPCompiler):
                 'default',
             ),
         })
-        opts[key].choices = [
-            'none', 'c++98', 'c++03', 'c++11', 'c++14', 'c++17', 'gnu++98',
-            'gnu++03', 'gnu++11', 'gnu++14', 'gnu++17',
-        ]
+        std_opt = opts[key]
+        assert isinstance(std_opt, coredata.UserStdOption), 'for mypy'
+        std_opt.set_versions(['c++98', 'c++03', 'c++11', 'c++14', 'c++17'], gnu=True)
         return opts
 
     def get_option_compile_args(self, options: 'KeyedOptionDictType') -> T.List[str]:
@@ -426,17 +423,16 @@ class GnuCPPCompiler(_StdCPPLibMixin, GnuCompiler, CPPCompiler):
             )
         })
         cppstd_choices = [
-            'none', 'c++98', 'c++03', 'c++11', 'c++14', 'c++17', 'c++1z',
-            'c++2a', 'c++20', 'gnu++03', 'gnu++11', 'gnu++14', 'gnu++17',
-            'gnu++1z', 'gnu++2a', 'gnu++20',
+            'c++98', 'c++03', 'c++11', 'c++14', 'c++17', 'c++1z',
+            'c++2a', 'c++20',
         ]
         if version_compare(self.version, '>=12.2.0'):
             cppstd_choices.append('c++23')
-            cppstd_choices.append('gnu++23')
         if version_compare(self.version, '>=14.0.0'):
             cppstd_choices.append('c++26')
-            cppstd_choices.append('gnu++26')
-        opts[key].choices = cppstd_choices
+        std_opt = opts[key]
+        assert isinstance(std_opt, coredata.UserStdOption), 'for mypy'
+        std_opt.set_versions(cppstd_choices, gnu=True)
         if self.info.is_windows() or self.info.is_cygwin():
             opts.update({
                 key.evolve('winlibs'): coredata.UserArrayOption(
@@ -513,21 +509,21 @@ class ElbrusCPPCompiler(ElbrusCompiler, CPPCompiler):
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = CPPCompiler.get_options(self)
 
-        cpp_stds = ['none', 'c++98', 'gnu++98']
+        cpp_stds = ['c++98']
         if version_compare(self.version, '>=1.20.00'):
-            cpp_stds += ['c++03', 'c++0x', 'c++11', 'gnu++03', 'gnu++0x', 'gnu++11']
+            cpp_stds += ['c++03', 'c++0x', 'c++11']
         if version_compare(self.version, '>=1.21.00') and version_compare(self.version, '<1.22.00'):
-            cpp_stds += ['c++14', 'gnu++14', 'c++1y', 'gnu++1y']
+            cpp_stds += ['c++14', 'c++1y']
         if version_compare(self.version, '>=1.22.00'):
-            cpp_stds += ['c++14', 'gnu++14']
+            cpp_stds += ['c++14']
         if version_compare(self.version, '>=1.23.00'):
-            cpp_stds += ['c++1y', 'gnu++1y']
+            cpp_stds += ['c++1y']
         if version_compare(self.version, '>=1.24.00'):
-            cpp_stds += ['c++1z', 'c++17', 'gnu++1z', 'gnu++17']
+            cpp_stds += ['c++1z', 'c++17']
         if version_compare(self.version, '>=1.25.00'):
-            cpp_stds += ['c++2a', 'gnu++2a']
+            cpp_stds += ['c++2a']
         if version_compare(self.version, '>=1.26.00'):
-            cpp_stds += ['c++20', 'gnu++20']
+            cpp_stds += ['c++20']
 
         key = OptionKey('std', machine=self.for_machine, lang=self.language)
         opts.update({
@@ -541,7 +537,9 @@ class ElbrusCPPCompiler(ElbrusCompiler, CPPCompiler):
                 False,
             ),
         })
-        opts[key].choices = cpp_stds
+        std_opt = opts[key]
+        assert isinstance(std_opt, coredata.UserStdOption), 'for mypy'
+        std_opt.set_versions(cpp_stds, gnu=True)
         return opts
 
     # Elbrus C++ compiler does not have lchmod, but there is only linker warning, not compiler error.
@@ -615,7 +613,9 @@ class IntelCPPCompiler(IntelGnuLikeCompiler, CPPCompiler):
             key.evolve('rtti'): coredata.UserBooleanOption('Enable RTTI', True),
             key.evolve('debugstl'): coredata.UserBooleanOption('STL debug mode', False),
         })
-        opts[key].choices = ['none'] + c_stds + g_stds
+        std_opt = opts[key]
+        assert isinstance(std_opt, coredata.UserStdOption), 'for mypy'
+        std_opt.set_versions(c_stds + g_stds)
         return opts
 
     def get_option_compile_args(self, options: 'KeyedOptionDictType') -> T.List[str]:
@@ -682,7 +682,9 @@ class VisualStudioLikeCPPCompilerMixin(CompilerMixinBase):
                 msvc_winlibs,
             ),
         })
-        opts[key.evolve('std')].choices = cpp_stds
+        std_opt = opts[key]
+        assert isinstance(std_opt, coredata.UserStdOption), 'for mypy'
+        std_opt.set_versions(cpp_stds)
         return opts
 
     def get_option_compile_args(self, options: 'KeyedOptionDictType') -> T.List[str]:
@@ -846,8 +848,9 @@ class ArmCPPCompiler(ArmCompiler, CPPCompiler):
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = CPPCompiler.get_options(self)
-        key = OptionKey('std', machine=self.for_machine, lang=self.language)
-        opts[key].choices = ['none', 'c++03', 'c++11']
+        std_opt = opts[OptionKey('std', machine=self.for_machine, lang=self.language)]
+        assert isinstance(std_opt, coredata.UserStdOption), 'for mypy'
+        std_opt.set_versions(['c++03', 'c++11'])
         return opts
 
     def get_option_compile_args(self, options: 'KeyedOptionDictType') -> T.List[str]:
@@ -906,8 +909,9 @@ class TICPPCompiler(TICompiler, CPPCompiler):
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = CPPCompiler.get_options(self)
-        key = OptionKey('std', machine=self.for_machine, lang=self.language)
-        opts[key].choices = ['none', 'c++03']
+        std_opt = opts[OptionKey('std', machine=self.for_machine, lang=self.language)]
+        assert isinstance(std_opt, coredata.UserStdOption), 'for mypy'
+        std_opt.set_versions(['c++03'])
         return opts
 
     def get_option_compile_args(self, options: 'KeyedOptionDictType') -> T.List[str]: