ENH: no output in editable verbose mode when there is no work to do

mesonpy/_editable.py

@@ -6,6 +6,7 @@
 
 from __future__ import annotations
 
+import ast
 import functools
 import importlib.abc
 import importlib.machinery
@@ -308,6 +309,21 @@ def find_spec(
         tree = self._rebuild()
         return find_spec(fullname, tree)
 
+    def _work_to_do(self, env: dict[str, str]) -> bool:
+        if sys.platform == 'win32':
+            # On Windows the build command is 'meson compile' eventually with a --ninja-args= option.
+            if self._build_cmd[-1].startswith('--ninja-args='):
+                ninja_args = ast.literal_eval(self._build_cmd[-1].split('=', 1)[1]) + ['-n']
+                dry_run_build_cmd = self._build_cmd[:-1] + [f'--ninja-args={ninja_args!r}']
+            else:
+                dry_run_build_cmd = self._build_cmd + ['--ninja-args=-n']
+        else:
+            dry_run_build_cmd = self._build_cmd + ['-n']
+        # Check adapted from
+        # https://github.com/mesonbuild/meson/blob/a35d4d368a21f4b70afa3195da4d6292a649cb4c/mesonbuild/mtest.py#L1635-L1636
+        p = subprocess.run(dry_run_build_cmd, cwd=self._build_path, env=env, capture_output=True)
+        return b'ninja: no work to do.' not in p.stdout and b'samu: nothing to do' not in p.stdout
+
     @functools.lru_cache(maxsize=1)
     def _rebuild(self) -> Node:
         # skip editable wheel lookup during rebuild: during the build
@@ -317,12 +333,14 @@ def _rebuild(self) -> Node:
         env[MARKER] = os.pathsep.join((env.get(MARKER, ''), self._build_path))
 
         if self._verbose or bool(env.get(VERBOSE, '')):
-            print('+ ' + ' '.join(self._build_cmd))
-            stdout = None
+            # We want to show some output only if there is some work to do
+            if self._work_to_do(env):
+                module_names = ' '.join(sorted(self._top_level_modules))
+                build_command = ' '.join(self._build_cmd)
+                print(f'meson-python: building {module_names} with {build_command!r}', flush=True)
+                subprocess.run(self._build_cmd, cwd=self._build_path, env=env)
         else:
-            stdout = subprocess.DEVNULL
-
-        subprocess.run(self._build_cmd, cwd=self._build_path, env=env, stdout=stdout, check=True)
+            subprocess.run(self._build_cmd, cwd=self._build_path, env=env, stdout=subprocess.DEVNULL)
 
         install_plan_path = os.path.join(self._build_path, 'meson-info', 'intro-install_plan.json')
         with open(install_plan_path, 'r', encoding='utf8') as f:

tests/test_editable.py

@@ -237,3 +237,34 @@ def test_custom_target_install_dir(package_custom_target_dir, tmp_path):
         import package.generated.two  # noqa: F401
     finally:
         del sys.meta_path[0]
+
+
+@pytest.mark.parametrize('verbose', [False, True], ids=('', 'verbose'))
+@pytest.mark.parametrize('args', [[], ['-j1']], ids=('', '-Ccompile-args=-j1'))
+def test_editable_rebuild(package_purelib_and_platlib, tmp_path, verbose, args):
+    with mesonpy._project({'builddir': os.fspath(tmp_path), 'compile-args': args}) as project:
+        finder = _editable.MesonpyMetaFinder({'plat', 'pure'}, os.fspath(tmp_path), project._build_command, verbose=verbose)
+        try:
+            # Install editable hooks
+            sys.meta_path.insert(0, finder)
+            # Import module and trigger rebuild
+            import plat  # noqa: F401
+        finally:
+            del sys.meta_path[0]
+            sys.modules.pop('plat', None)
+
+
+def test_editable_verbose(venv, package_complex, editable_complex, monkeypatch):
+    monkeypatch.setenv('MESONPY_EDITABLE_VERBOSE', '1')
+    venv.pip('install', os.fspath(editable_complex))
+
+    # Importint the module should not result in any output since the project has already been built
+    assert venv.python('-c', 'import complex').strip() == ''
+
+    # Touch a compiled source file and make sure that the build info is output on import
+    package_complex.joinpath('test.pyx').touch()
+    output = venv.python('-c', 'import complex').strip()
+    assert output.startswith('meson-python: building complex with')
+
+    # Another import without file changes should not show any output
+    assert venv.python('-c', 'import complex') == ''