ENH: capture and report build errors when rebuilding editable wheels

When editable-verbose is not enabled, redirect the build output to a
file. When the build fails, parse this file to look for the build
error and append it to the ImportError exception message.

Fixes #820.

Author: dnicolodi

mesonpy/_editable.py

@@ -319,7 +319,7 @@ def _work_to_do(self, env: dict[str, str]) -> bool:
             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)
+        p = subprocess.run(dry_run_build_cmd, cwd=self._build_path, env=env, check=False, 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)
@@ -332,15 +332,39 @@ def _rebuild(self) -> Node:
             env[MARKER] = os.pathsep.join((env.get(MARKER, ''), self._build_path))
 
             if self._verbose or bool(env.get(VERBOSE, '')):
+                log_path = None
                 # We want to show some output only if there is some work to do.
                 if self._work_to_do(env):
                     build_command = ' '.join(self._build_cmd)
                     print(f'meson-python: building {self._name}: {build_command}', flush=True)
                     subprocess.run(self._build_cmd, cwd=self._build_path, env=env, check=True)
             else:
-                subprocess.run(self._build_cmd, cwd=self._build_path, env=env, stdout=subprocess.DEVNULL, check=True)
+                # Redirect build log to file.
+                log_path = os.path.join(self._build_path, 'meson-python-build-log.txt')
+                with open(log_path, 'w') as log:
+                    subprocess.run(self._build_cmd, cwd=self._build_path, env=env, check=True,
+                                   stderr=subprocess.STDOUT, stdout=log)
         except subprocess.CalledProcessError as exc:
-            raise ImportError(f're-building the {self._name} meson-python editable wheel package failed') from exc
+            msg = f're-building the {self._name} meson-python editable wheel package failed'
+            if log_path:
+                with open(log_path, 'r') as log:
+                    # Skip to the error.
+                    for line in log:
+                        if line.startswith('FAILED: '):
+                            break
+                    else:
+                        # When no `FAILED: ` line is found, rewind to the
+                        # beginning of the log.
+                        log.seek(0)
+                    if line.strip().endswith(' build.ninja'):
+                        # When the error occureed when rebuilding `ninja.build`,
+                        # the meson output appears before the `FAILED: ` line.
+                        # Rewind the build log to the beginning to report the
+                        # error.
+                        log.seek(0)
+                    error = log.read()
+                msg = f'{msg}:\n{error}'
+            raise ImportError(msg) from exc
 
         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

@@ -335,9 +335,43 @@ def test_editable_rebuild_error(package_purelib_and_platlib, tmp_path, verbose):
             # Import module and trigger rebuild: the build fails and ImportErrror is raised
             stdout = io.StringIO()
             with redirect_stdout(stdout):
-                with pytest.raises(ImportError, match='re-building the purelib-and-platlib '):
+                with pytest.raises(ImportError, match='re-building the purelib-and-platlib ') as exc:
                     import plat  # noqa: F401
             assert not verbose or stdout.getvalue().startswith('meson-python: building ')
+            assert verbose or 'ninja: build stopped: subcommand failed.' in exc.value.msg
+
+        finally:
+            del sys.meta_path[0]
+            sys.modules.pop('pure', None)
+            path.write_text(code)
+
+
+def test_editable_reconfigure_error(package_purelib_and_platlib, tmp_path):
+    with mesonpy._project({'builddir': os.fspath(tmp_path)}) as project:
+
+        finder = _editable.MesonpyMetaFinder(
+            project._metadata.name, {'plat', 'pure'},
+            os.fspath(tmp_path), project._build_command,
+            verbose=False,
+        )
+        path = package_purelib_and_platlib / 'meson.build'
+        code = path.read_text()
+
+        try:
+            # Install editable hooks
+            sys.meta_path.insert(0, finder)
+
+            # Emit an error during reconfigure
+            with open(path, 'a') as f:
+                f.write('\n\nerror(\'injected error\')\n')
+
+            # Import module and trigger rebuild: the build fails and ImportErrror is raised
+            stdout = io.StringIO()
+            with redirect_stdout(stdout):
+                with pytest.raises(ImportError, match='re-building the purelib-and-platlib ') as exc:
+                    import plat  # noqa: F401
+            assert 'ERROR: Problem encountered: injected error' in exc.value.msg
+            assert 'ninja: error: rebuilding \'build.ninja\': subcommand failed' in exc.value.msg
 
         finally:
             del sys.meta_path[0]