mcompile: replaced backend divination code + cleanup

mesonbuild/mcompile.py

@@ -14,11 +14,12 @@
 
 """Entrypoint script for backend agnostic compile."""
 
+import json
 import os
-import pathlib
 import shutil
 import sys
 import typing as T
+from pathlib import Path
 
 from . import mlog
 from . import mesonlib
@@ -27,6 +28,20 @@ from .mesonlib import MesonException
 if T.TYPE_CHECKING:
     import argparse
 
+def get_backend_from_introspect(builddir: Path) -> str:
+    """
+    Gets `backend` option value from introspection data
+    """
+    path_to_intro = builddir / 'meson-info' / 'intro-buildoptions.json'
+    if not path_to_intro.exists():
+        raise MesonException('`{}` is missing! Directory is not configured yet?'.format(path_to_intro.name))
+    with (path_to_intro).open() as f:
+        schema = json.load(f)
+
+    for option in schema:
+        if option['name'] == 'backend':
+            return option['value']
+    raise MesonException('`{}` is missing `backend` option!'.format(path_to_intro.name))
 
 def add_arguments(parser: 'argparse.ArgumentParser') -> None:
     """Add compile specific arguments."""
@@ -53,24 +68,23 @@ def add_arguments(parser: 'argparse.ArgumentParser') -> None:
         '-C',
         action='store',
         dest='builddir',
-        type=pathlib.Path,
+        type=Path,
         default='.',
         help='The directory containing build files to be built.'
     )
 
 
 def run(options: 'argparse.Namespace') -> int:
-    bdir = options.builddir  # type: pathlib.Path
+    bdir = options.builddir  # type: Path
     if not bdir.exists():
         raise MesonException('Path to builddir {} does not exist!'.format(str(bdir.resolve())))
     if not bdir.is_dir():
         raise MesonException('builddir path should be a directory.')
 
     cmd = []  # type: T.List[str]
-    runner = None  # type T.Optional[str]
-    slns = list(bdir.glob('*.sln'))
 
-    if (bdir / 'build.ninja').exists():
+    backend = get_backend_from_introspect(bdir)
+    if backend == 'ninja':
         runner = os.environ.get('NINJA')
         if not runner:
             if shutil.which('ninja'):
@@ -80,6 +94,7 @@ def run(options: 'argparse.Namespace') -> int:
 
         if runner is None:
             raise MesonException('Cannot find either ninja or samu.')
+        mlog.log('Found runner:', runner)
 
         cmd = [runner, '-C', bdir.as_posix()]
 
@@ -92,8 +107,8 @@ def run(options: 'argparse.Namespace') -> int:
         if options.clean:
             cmd.append('clean')
 
-    # TODO: with python 3.8 this could be `elif slns := bdir.glob('*.sln'):`
+    elif backend.startswith('vs'):
-    elif slns:
+        slns = list(bdir.glob('*.sln'))
         assert len(slns) == 1, 'More than one solution in a project?'
 
         sln = slns[0]
@@ -113,9 +128,7 @@ def run(options: 'argparse.Namespace') -> int:
     # TODO: xcode?
     else:
         raise MesonException(
-            'Could not find any runner or backend for directory {}'.format(bdir.resolve().as_posix()))
+            'Backend `{}` is not yet supported by `compile`. Use generated project files directly instead.'.format(backend))
-
-    mlog.log('Found runner:', runner)
 
     p, *_ = mesonlib.Popen_safe(cmd, stdout=sys.stdout.buffer, stderr=sys.stderr.buffer)