Allow overriding programs from the command line

People coming from autotools are used to having easy access for
overriding programs. This should ease that transition.

mesonbuild/coredata.py

@@ -572,6 +572,9 @@ def __init__(self, options: argparse.Namespace, scratch_dir: str, meson_command:
         self.options: 'MutableKeyedOptionDictType' = {}
         self.cross_files = self.__load_config_files(options, scratch_dir, 'cross')
         self.compilers: PerMachine[T.Dict[str, Compiler]] = PerMachine(OrderedDict(), OrderedDict())
+        self.program_aliases: PerMachine[T.Dict[str, str]] = PerMachine(
+            self.__parse_program_aliases(options, MachineChoice.BUILD),
+            self.__parse_program_aliases(options, MachineChoice.HOST))
 
         # Set of subprojects that have already been initialized once, this is
         # required to be stored and reloaded with the coredata, as we don't
@@ -595,6 +598,24 @@ def __init__(self, options: argparse.Namespace, scratch_dir: str, meson_command:
         self.builtin_options_libdir_cross_fixup()
         self.init_builtins('')
 
+    @staticmethod
+    def __parse_program_aliases(options: argparse.Namespace, for_machine: MachineChoice) -> OrderedDict[str, str]:
+        alias_map: OrderedDict[str, str] = OrderedDict()
+        aliases: T.List[str]
+        if for_machine == MachineChoice.HOST:
+            aliases = options.native_program
+        elif for_machine == MachineChoice.BUILD:
+            aliases = options.cross_program
+
+        for a in aliases:
+            parts = a.split('=', 1)
+            if len(parts) == 1:
+                pass
+
+            alias_map[parts[0]] = parts[1]
+
+        return alias_map
+
     @staticmethod
     def __load_config_files(options: argparse.Namespace, scratch_dir: str, ftype: str) -> T.List[str]:
         # Need to try and make the passed filenames absolute because when the
@@ -1040,6 +1061,9 @@ def emit_base_options_warnings(self, enabled_opts: T.List[OptionKey]) -> None:
             mlog.warning('Base option \'b_bitcode\' is enabled, which is incompatible with many linker options. Incompatible options such as \'b_asneeded\' have been disabled.', fatal=False)
             mlog.warning('Please see https://mesonbuild.com/Builtin-options.html#Notes_about_Apple_Bitcode_support for more details.', fatal=False)
 
+    def get_program_aliases(self, for_machine: MachineChoice) -> T.Dict[str, str]:
+        return self.program_aliases[for_machine]
+
 class CmdLineFileParser(configparser.ConfigParser):
     def __init__(self) -> None:
         # We don't want ':' as key delimiter, otherwise it would break when

mesonbuild/interpreter/interpreter.py

@@ -1552,6 +1552,28 @@ def add_languages_for(self, args: T.List[str], required: bool, for_machine: Mach
 
         return success
 
+    def program_from_alias(self, for_machine: MachineChoice, prognames: T.List[mesonlib.FileOrString],
+                           extra_info: T.List[mlog.TV_Loggable]) -> T.Optional[ExternalProgram]:
+        program_aliases = self.coredata.get_program_aliases(for_machine)
+        if not program_aliases:
+            return None
+
+        for p in prognames:
+            if isinstance(p, mesonlib.File):
+                continue # Always points to a local (i.e. self generated) file.
+            if not isinstance(p, str):
+                raise InterpreterException('Executable name must be a string')
+
+            alias = program_aliases.get(p, None)
+            if not alias:
+                return None
+
+            prog = ExternalProgram(p, command=alias, silent=True)
+            if not isinstance(prog, NonExistingExternalProgram):
+                extra_info.append(mlog.blue('(alias)'))
+                return prog
+        return None
+
     def program_from_file_for(self, for_machine: MachineChoice, prognames: T.List[mesonlib.FileOrString]
                               ) -> T.Optional[ExternalProgram]:
         for p in prognames:
@@ -1669,6 +1691,10 @@ def program_lookup(self, args: T.List[mesonlib.FileOrString], for_machine: Machi
         if progobj:
             return progobj
 
+        progobj = self.program_from_alias(for_machine, args, extra_info)
+        if progobj:
+            return progobj
+
         if args[0] == 'meson':
             # Override find_program('meson') to return what we were invoked with
             return ExternalProgram('meson', self.environment.get_build_command(), silent=True)

mesonbuild/msetup.py

@@ -18,6 +18,8 @@
 from pathlib import Path
 import typing as T
 
+from mesonbuild.utils.universal import MachineChoice
+
 from . import build, coredata, environment, interpreter, mesonlib, mintro, mlog
 from .mesonlib import MesonException
 
@@ -59,6 +61,14 @@ def add_arguments(parser: argparse.ArgumentParser) -> None:
                              'newer version of meson.')
     parser.add_argument('--clearcache', action='store_true', default=False,
                         help='Clear cached state (e.g. found dependencies). Since 1.3.0.')
+    parser.add_argument('--native-program',
+                        default=[],
+                        action='append',
+                        help='Provide a native program override. Since 1.4.0.')
+    parser.add_argument('--cross-program',
+                        default=[],
+                        action='append',
+                        help='Provide a non-native program override. Since 1.4.0.')
     parser.add_argument('builddir', nargs='?', default=None)
     parser.add_argument('sourcedir', nargs='?', default=None)
 
@@ -256,6 +266,8 @@ def _generate(self, env: environment.Environment, capture: bool, vslite_ctx: T.O
                 # read from a pipe and wrote into a private file.
                 self.options.cross_file = env.coredata.cross_files
                 self.options.native_file = env.coredata.config_files
+                self.options.cross_program = env.coredata.get_program_aliases(MachineChoice.HOST)
+                self.options.native_program = env.coredata.get_program_aliases(MachineChoice.BUILD)
                 coredata.write_cmd_line_file(self.build_dir, self.options)
             else:
                 coredata.update_cmd_line_file(self.build_dir, self.options)

mesonbuild/programs.py

@@ -40,7 +40,7 @@ class ExternalProgram(mesonlib.HoldableObject):
     windows_exts = ('exe', 'msc', 'com', 'bat', 'cmd')
     for_machine = MachineChoice.BUILD
 
-    def __init__(self, name: str, command: T.Optional[T.List[str]] = None,
+    def __init__(self, name: str, command: T.Optional[T.Union[str, T.List[str]]] = None,
                  silent: bool = False, search_dir: T.Optional[str] = None,
                  extra_search_dirs: T.Optional[T.List[str]] = None):
         self.name = name