Interpreter: Fix c_stdlib usage

- Exceptions raised during subproject setup were ignored.
- Allow c_stdlib in native file, was already half supported.
- Eliminate usage of subproject variable name by overriding
  '<lang>_stdlib' dependency name.

cross/ownstdlib.txt

@@ -10,4 +10,4 @@ endian = 'little'
 
 [properties]
 
-c_stdlib = ['mylibc', 'mylibc_dep'] # Subproject name, dependency name
+c_stdlib = 'mylibc' # Subproject name

docs/markdown/Cross-compilation.md

@@ -268,7 +268,7 @@ invocation to use in your cross file is the following:
 
 ```ini
 [properties]
-c_stdlib = ['mylibc', 'mylibc_dep'] # Subproject name, dependency name
+c_stdlib = ['mylibc', 'mylibc_dep'] # Subproject name, variable name
 ```
 
 This specifies that C standard library is provided in the Meson
@@ -277,6 +277,18 @@ is used on every cross built C target in the entire source tree
 (including subprojects) and the standard library is disabled. The
 build definitions of these targets do not need any modification.
 
+Note that it is supported for any language, not only `c`, using `<lang>_stdlib`
+property.
+
+Since *0.56.0* the variable name parameter is no longer required as long as the
+subproject calls `meson.override_dependency('c_stdlib', mylibc_dep)`.
+The above example becomes:
+
+```ini
+[properties]
+c_stdlib = 'mylibc'
+```
+
 ## Changing cross file settings
 
 Cross file settings are only read when the build directory is set up

docs/markdown/snippets/stdlib.md

@@ -0,0 +1,6 @@
+## Custom standard library
+
+- It is not limited to cross builds any more, `<lang>_stdlib` property can be
+  set in native files.
+- The variable name parameter is no longer required as long as the subproject
+  calls `meson.override_dependency('c_stdlib', mylibc_dep)`.

mesonbuild/backend/backends.py

@@ -657,7 +657,7 @@ class Backend:
         # First, the trivial ones that are impossible to override.
         #
         # Add -nostdinc/-nostdinc++ if needed; can't be overridden
-        commands += self.get_cross_stdlib_args(target, compiler)
+        commands += self.get_no_stdlib_args(target, compiler)
         # Add things like /NOLOGO or -pipe; usually can't be overridden
         commands += compiler.get_always_args()
         # Only add warning-flags by default if the buildtype enables it, and if

mesonbuild/backend/ninjabackend.py

@@ -2088,12 +2088,15 @@ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47485'''))
         mod_files = _scan_fortran_file_deps(src, srcdir, dirname, tdeps, compiler)
         return mod_files
 
-    def get_cross_stdlib_args(self, target, compiler):
-        if self.environment.machines.matches_build_machine(target.for_machine):
+    def get_no_stdlib_args(self, target, compiler):
+        if compiler.language in self.build.stdlibs[target.for_machine]:
+            return compiler.get_no_stdinc_args()
         return []
-        if not self.environment.properties.host.has_stdlib(compiler.language):
+
+    def get_no_stdlib_link_args(self, target, linker):
+        if hasattr(linker, 'language') and linker.language in self.build.stdlibs[target.for_machine]:
+            return linker.get_no_stdlib_link_args()
         return []
-        return compiler.get_no_stdinc_args()
 
     def get_compile_debugfile_args(self, compiler, target, objfile):
         # The way MSVC uses PDB files is documented exactly nowhere so
@@ -2520,14 +2523,6 @@ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47485'''))
             elem.add_item('CROSS', '--cross-host=' + self.environment.machines[target.for_machine].system)
         self.add_build(elem)
 
-    def get_cross_stdlib_link_args(self, target, linker):
-        if isinstance(target, build.StaticLibrary) or \
-           self.environment.machines.matches_build_machine(target.for_machine):
-            return []
-        if not self.environment.properties.host.has_stdlib(linker.language):
-            return []
-        return linker.get_no_stdlib_link_args()
-
     def get_import_filename(self, target):
         return os.path.join(self.get_target_dir(target), target.import_filename)
 
@@ -2689,7 +2684,7 @@ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47485'''))
                                                      linker,
                                                      isinstance(target, build.SharedModule))
         # Add -nostdlib if needed; can't be overridden
-        commands += self.get_cross_stdlib_link_args(target, linker)
+        commands += self.get_no_stdlib_link_args(target, linker)
         # Add things like /NOLOGO; usually can't be overridden
         commands += linker.get_linker_always_args()
         # Add buildtype linker args: optimization level, etc.

mesonbuild/dependencies/base.py

@@ -2301,7 +2301,7 @@ def get_dep_identifier(name, kwargs) -> T.Tuple:
         # 'required' is irrelevant for caching; the caller handles it separately
         # 'fallback' subprojects cannot be cached -- they must be initialized
         # 'default_options' is only used in fallback case
-        if key in ('version', 'native', 'required', 'fallback', 'default_options'):
+        if key in ('version', 'native', 'required', 'fallback', 'default_options', 'force_fallback'):
             continue
         # All keyword arguments are strings, ints, or lists (or lists of lists)
         if isinstance(value, list):

mesonbuild/interpreter.py

@@ -2572,21 +2572,25 @@ class Interpreter(InterpreterBase):
         return self.variables
 
     def check_stdlibs(self):
-        for for_machine in MachineChoice:
+        machine_choices = [MachineChoice.HOST]
+        if self.coredata.is_cross_build():
+            machine_choices.append(MachineChoice.BUILD)
+        for for_machine in machine_choices:
             props = self.build.environment.properties[for_machine]
             for l in self.coredata.compilers[for_machine].keys():
                 try:
                     di = mesonlib.stringlistify(props.get_stdlib(l))
-                    if len(di) != 2:
-                        raise InterpreterException('Stdlib definition for %s should have exactly two elements.'
-                                                   % l)
-                    projname, depname = di
-                    subproj = self.do_subproject(projname, 'meson', {})
-                    self.build.stdlibs.host[l] = subproj.get_variable_method([depname], {})
                 except KeyError:
-                    pass
-                except InvalidArguments:
-                    pass
+                    continue
+                if len(di) == 1:
+                    FeatureNew.single_use('stdlib without variable name', '0.56.0', self.subproject)
+                kwargs = {'fallback': di,
+                          'native': for_machine is MachineChoice.BUILD,
+                          'force_fallback': True,
+                          }
+                name = display_name = l + '_stdlib'
+                dep = self.dependency_impl(name, display_name, kwargs)
+                self.build.stdlibs[for_machine][l] = dep
 
     def import_module(self, modname):
         if modname in self.modules:
@@ -3682,9 +3686,11 @@ external dependencies (including libraries) must go to "dependencies".''')
 
         wrap_mode = self.coredata.get_builtin_option('wrap_mode')
         force_fallback_for = self.coredata.get_builtin_option('force_fallback_for')
+        force_fallback = kwargs.get('force_fallback', False)
         forcefallback = has_fallback and (wrap_mode == WrapMode.forcefallback or \
                                           name in force_fallback_for or \
-                                          dirname in force_fallback_for)
+                                          dirname in force_fallback_for or \
+                                          force_fallback)
         if name != '' and not forcefallback:
             self._handle_featurenew_dependencies(name)
             kwargs['required'] = required and not has_fallback
@@ -4786,8 +4792,7 @@ Try setting b_lundef to false instead.'''.format(self.coredata.base_options['b_s
         target = targetclass(name, self.subdir, self.subproject, for_machine, sources, objs, self.environment, kwargs)
         target.project_version = self.project_version
 
-        if not self.environment.machines.matches_build_machine(for_machine):
-            self.add_cross_stdlib_info(target)
+        self.add_stdlib_info(target)
         l = targetholder(target, self)
         self.add_target(name, l.held_object)
         self.project_args_frozen = True
@@ -4811,23 +4816,19 @@ This will become a hard error in the future.''', location=self.current_node)
             kwargs['d_import_dirs'] = cleaned_items
 
     def get_used_languages(self, target):
-        result = {}
+        result = set()
         for i in target.sources:
-            # TODO other platforms
-            for lang, c in self.coredata.compilers.host.items():
+            for lang, c in self.coredata.compilers[target.for_machine].items():
                 if c.can_compile(i):
-                    result[lang] = True
+                    result.add(lang)
                     break
         return result
 
-    def add_cross_stdlib_info(self, target):
-        if target.for_machine != MachineChoice.HOST:
-            return
+    def add_stdlib_info(self, target):
         for l in self.get_used_languages(target):
-            props = self.environment.properties.host
-            if props.has_stdlib(l) \
-                    and self.subproject != props.get_stdlib(l)[0]:
-                target.add_deps(self.build.stdlibs.host[l])
+            dep = self.build.stdlibs[target.for_machine].get(l, None)
+            if dep:
+                target.add_deps(dep)
 
     def check_sources_exist(self, subdir, sources):
         for s in sources:

run_unittests.py

@@ -5054,6 +5054,28 @@ recommended as it is not supported on some platforms''')
         self.build()
         self.run_tests()
 
+    @unittest.skipUnless(is_linux(), 'Requires ASM compiler currently only available on Linux CI runners')
+    def test_nostdlib(self):
+        testdir = os.path.join(self.unit_test_dir, '79 nostdlib')
+        machinefile = os.path.join(self.builddir, 'machine.txt')
+        with open(machinefile, 'w') as f:
+            f.write(textwrap.dedent('''
+                [properties]
+                c_stdlib = 'mylibc'
+                '''))
+
+        # Test native C stdlib
+        self.meson_native_file = machinefile
+        self.init(testdir)
+        self.build()
+
+        # Test cross C stdlib
+        self.new_builddir()
+        self.meson_native_file = None
+        self.meson_cross_file = machinefile
+        self.init(testdir)
+        self.build()
+
 class FailureTests(BasePlatformTests):
     '''
     Tests that test failure conditions. Build files here should be dynamically

test cases/unit/79 nostdlib/subprojects/mylibc/meson.build

@@ -9,3 +9,5 @@ libc = static_library('c', 'libc.c', 'stubstart.s')
 mylibc_dep = declare_dependency(link_with : libc,
   include_directories : include_directories('.')
 )
+
+meson.override_dependency('c_stdlib', mylibc_dep)