clang-cl: Allow clang-cl (when compiling C) to pass std to underlying clang)

This allows a wider array of standard support than would be available
directly from clang-cl, emulating MSVC stds.

mesonbuild/compilers/c.py

@@ -1,4 +1,4 @@
-# Copyright 2012-2017 The Meson development team
+# Copyright 2012-2020 The Meson development team
 
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -107,27 +107,20 @@ class CCompiler(CLikeCompiler, Compiler):
         return opts
 
 
-class ClangCCompiler(ClangCompiler, CCompiler):
+class _ClangCStds(CompilerMixinBase):
+
+    """Mixin class for clang based compilers for setting C standards.
+
+    This is used by both ClangCCompiler and ClangClCompiler, as they share
+    the same versions
+    """
 
     _C17_VERSION = '>=6.0.0'
     _C18_VERSION = '>=8.0.0'
     _C2X_VERSION = '>=9.0.0'
 
-    def __init__(self, exelist: T.List[str], version: str, for_machine: MachineChoice, is_cross: bool,
-                 info: 'MachineInfo', exe_wrapper: T.Optional['ExternalProgram'] = None,
-                 linker: T.Optional['DynamicLinker'] = None,
-                 defines: T.Optional[T.Dict[str, str]] = None,
-                 full_version: T.Optional[str] = None):
-        CCompiler.__init__(self, exelist, version, for_machine, is_cross, info, exe_wrapper, linker=linker, full_version=full_version)
-        ClangCompiler.__init__(self, defines)
-        default_warn_args = ['-Wall', '-Winvalid-pch']
-        self.warn_args = {'0': [],
-                          '1': default_warn_args,
-                          '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
-
     def get_options(self) -> 'OptionDictType':
-        opts = CCompiler.get_options(self)
+        opts = super().get_options()
         c_stds = ['c89', 'c99', 'c11']
         g_stds = ['gnu89', 'gnu99', 'gnu11']
         # https://releases.llvm.org/6.0.0/tools/clang/docs/ReleaseNotes.html
@@ -142,6 +135,26 @@ class ClangCCompiler(ClangCompiler, CCompiler):
             c_stds += ['c2x']
             g_stds += ['gnu2x']
         opts['std'].choices = ['none'] + c_stds + g_stds  # type: ignore
+        return opts
+
+
+class ClangCCompiler(_ClangCStds, ClangCompiler, CCompiler):
+
+    def __init__(self, exelist: T.List[str], version: str, for_machine: MachineChoice, is_cross: bool,
+                 info: 'MachineInfo', exe_wrapper: T.Optional['ExternalProgram'] = None,
+                 linker: T.Optional['DynamicLinker'] = None,
+                 defines: T.Optional[T.Dict[str, str]] = None,
+                 full_version: T.Optional[str] = None):
+        CCompiler.__init__(self, exelist, version, for_machine, is_cross, info, exe_wrapper, linker=linker, full_version=full_version)
+        ClangCompiler.__init__(self, defines)
+        default_warn_args = ['-Wall', '-Winvalid-pch']
+        self.warn_args = {'0': [],
+                          '1': default_warn_args,
+                          '2': default_warn_args + ['-Wextra'],
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
+
+    def get_options(self) -> 'OptionDictType':
+        opts = super().get_options()
         if self.info.is_windows() or self.info.is_cygwin():
             opts.update({
                 'winlibs': coredata.UserArrayOption(
@@ -431,7 +444,7 @@ class VisualStudioCCompiler(MSVCCompiler, VisualStudioLikeCCompilerMixin, CCompi
         return args
 
 
-class ClangClCCompiler(ClangClCompiler, VisualStudioLikeCCompilerMixin, CCompiler):
+class ClangClCCompiler(_ClangCStds, ClangClCompiler, VisualStudioLikeCCompilerMixin, CCompiler):
     def __init__(self, exelist: T.List[str], version: str, for_machine: MachineChoice,
                  is_cross: bool, info: 'MachineInfo', target: str,
                  exe_wrapper: T.Optional['ExternalProgram'] = None,
@@ -442,24 +455,10 @@ class ClangClCCompiler(ClangClCompiler, VisualStudioLikeCCompilerMixin, CCompile
                            full_version=full_version)
         ClangClCompiler.__init__(self, target)
 
-    def get_options(self) -> 'OptionDictType':
-        # Clang-cl can compile up to c99, but doesn't have a std-swtich for
-        # them. Unlike recent versions of MSVC it doesn't (as of 10.0.1)
-        # support c11
-        opts = super().get_options()
-        c_stds = ['none', 'c89', 'c99',
-                  # Need to have these to be compatible with projects
-                  # that set c_std to e.g. gnu99.
-                  # https://github.com/mesonbuild/meson/issues/7611
-                  'gnu89', 'gnu90', 'gnu9x', 'gnu99']
-        opts['std'].choices = c_stds  # type: ignore
-        return opts
     def get_option_compile_args(self, options: 'OptionDictType') -> T.List[str]:
-        if options['std'].value.startswith('gnu'):
-            mlog.warning(
-                'Clang-cl does not actually support gnu standards, and '
-                'meson will instead demote to the nearest ISO C standard. This '
-                'may cause compilation to fail.', once=True)
+        std = options['std'].value
+        if std != "none":
+            return ['/clang:-std={}'.format(std)]
         return []