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

@@ -332,15 +332,28 @@ 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, stdout=log, check=True)
         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
+                    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 +335,10 @@ 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]