Add add_languages(native:)

v2:
Retain not using logical-and, to avoid short-circuiting side-effects
of add_languages()

docs/markdown/Reference-manual.md

@@ -54,9 +54,9 @@ Like `add_global_arguments` but the arguments are passed to the linker.
   bool add_languages(*langs*)
 ```
 
-Add support for new programming languages. Equivalent to having them
-in the `project` declaration. This function is usually used to add
-languages that are only used on some platforms like this:
+Add programming languages used by the project. Equivalent to having them in the
+`project` declaration. This function is usually used to add languages that are
+only used under some conditions, like this:
 
 ```meson
 project('foobar', 'c')
@@ -68,12 +68,18 @@ if add_languages('cpp', required : false)
 endif
 ```
 
-Takes one keyword argument, `required`. It defaults to `true`, which
-means that if any of the languages specified is not found, Meson will
-halt. Returns true if all languages specified were found and false
-otherwise. Since *0.47.0* the value of a
-[`feature`](Build-options.md#features) option can also be passed to
-the `required` keyword argument.
+Takes the following keyword arguments:
+
+- `required` defaults to `true`, which means that if any of the languages
+specified is not found, Meson will halt. Since *0.47.0* the value of a
+[`feature`](Build-options.md#features) option can also be passed.
+
+- `native` if set to `true`, the language will be used to compile for the build
+  machine, if `false`, for the host machine. If omitted, the language may be
+  used for either. Since *0.54.0*. The default may change to `false` in a future
+  meson version.
+
+Returns `true` if all languages specified were found and `false` otherwise.
 
 ### add_project_arguments()
 

docs/markdown/snippets/native_compiler_not_required.md

@@ -0,0 +1,5 @@
+## Native (build machine) compilers not always required
+
+`add_languages()` gained a `native:` keyword, indicating if a native or cross
+compiler is to be used. Currently, for backwards compatibility, if the keyword
+is absent, that means both are used.

mesonbuild/interpreter.py

@@ -2080,7 +2080,7 @@ _base_test_args = {'args', 'depends', 'env', 'should_fail', 'timeout', 'workdir'
 
 permitted_kwargs = {'add_global_arguments': {'language', 'native'},
                     'add_global_link_arguments': {'language', 'native'},
-                    'add_languages': {'required'},
+                    'add_languages': {'required', 'native'},
                     'add_project_link_arguments': {'language', 'native'},
                     'add_project_arguments': {'language', 'native'},
                     'add_test_setup': {'exe_wrapper', 'gdb', 'timeout_multiplier', 'env', 'is_default'},
@@ -2908,11 +2908,13 @@ external dependencies (including libraries) must go to "dependencies".''')
         self.build.projects[self.subproject] = proj_name
         mlog.log('Project name:', mlog.bold(proj_name))
         mlog.log('Project version:', mlog.bold(self.project_version))
-        self.add_languages(proj_langs, True)
+        self.add_languages(proj_langs, True, MachineChoice.BUILD)
+        self.add_languages(proj_langs, True, MachineChoice.HOST)
         self.set_backend()
         if not self.is_subproject():
             self.check_stdlibs()
 
+    @FeatureNewKwargs('add_languages', '0.54.0', ['native'])
     @permittedKwargs(permitted_kwargs['add_languages'])
     @stringArgs
     def func_add_languages(self, node, args, kwargs):
@@ -2921,7 +2923,15 @@ external dependencies (including libraries) must go to "dependencies".''')
             for lang in sorted(args, key=compilers.sort_clink):
                 mlog.log('Compiler for language', mlog.bold(lang), 'skipped: feature', mlog.bold(feature), 'disabled')
             return False
-        return self.add_languages(args, required)
+        if 'native' in kwargs:
+            return self.add_languages(args, required, self.machine_from_native_kwarg(kwargs))
+        else:
+            # absent 'native' means 'both' for backwards compatibility
+            mlog.warning('add_languages is missing native:, assuming languages are required for both host and build.',
+                         location=self.current_node)
+            success = self.add_languages(args, required, MachineChoice.BUILD)
+            success &= self.add_languages(args, required, MachineChoice.HOST)
+            return success
 
     def get_message_string_arg(self, arg):
         if isinstance(arg, list):
@@ -3009,9 +3019,8 @@ external dependencies (including libraries) must go to "dependencies".''')
         self.validate_arguments(args, 0, [])
         raise Exception()
 
-    def add_languages(self, args: T.Sequence[str], required: bool) -> bool:
-        success = self.add_languages_for(args, required, MachineChoice.BUILD)
-        success &= self.add_languages_for(args, required, MachineChoice.HOST)
+    def add_languages(self, args: T.Sequence[str], required: bool, for_machine: MachineChoice) -> bool:
+        success = self.add_languages_for(args, required, for_machine)
         if not self.coredata.is_cross_build():
             self.coredata.copy_build_options_from_regular_ones()
         return success

test cases/common/85 add language/meson.build

@@ -6,3 +6,6 @@ assert(add_languages('cpp'), 'Add_languages returned false on success')
 assert(not add_languages('klingon', required : false), 'Add_languages returned true on failure.')
 
 test('C++', executable('cppprog', 'prog.cc'))
+
+add_languages('c', native: true)
+add_languages('c', native: false)