Make -P (pdb) work better with exceptions triggered from events

Previously, if an exception was raised from an event listener, and the
`-P` option was specified, the debugger would be started not for the
original error but for the `ExtensionError` wrapping it that was
raised by `EventManager.emit`.  That made it difficult to debug the
error.

With this change, when `-P` is specified, wrapping of errors in
`ExtensionError` is disabled, which allows pdb to debug the original
error.

sphinx/application.py

@@ -131,7 +131,8 @@ def __init__(self, srcdir: str, confdir: Optional[str], outdir: str, doctreedir:
                  buildername: str, confoverrides: Dict = None,
                  status: Optional[IO] = sys.stdout, warning: Optional[IO] = sys.stderr,
                  freshenv: bool = False, warningiserror: bool = False, tags: List[str] = None,
-                 verbosity: int = 0, parallel: int = 0, keep_going: bool = False) -> None:
+                 verbosity: int = 0, parallel: int = 0, keep_going: bool = False,
+                 pdb: bool = False) -> None:
         self.phase = BuildPhase.INITIALIZATION
         self.verbosity = verbosity
         self.extensions: Dict[str, Extension] = {}
@@ -173,6 +174,7 @@ def __init__(self, srcdir: str, confdir: Optional[str], outdir: str, doctreedir:
             self.warningiserror = False
         else:
             self.warningiserror = warningiserror
+        self.pdb = pdb
         logging.setup(self, self._status, self._warning)
 
         self.events = EventManager(self)

sphinx/cmd/build.py

@@ -272,7 +272,8 @@ def build_main(argv: List[str] = sys.argv[1:]) -> int:
             app = Sphinx(args.sourcedir, args.confdir, args.outputdir,
                          args.doctreedir, args.builder, confoverrides, status,
                          warning, args.freshenv, args.warningiserror,
-                         args.tags, args.verbosity, args.jobs, args.keep_going)
+                         args.tags, args.verbosity, args.jobs, args.keep_going,
+                         args.pdb)
             app.build(args.force_all, filenames)
             return app.statuscode
     except (Exception, KeyboardInterrupt) as exc:

sphinx/events.py

@@ -98,6 +98,9 @@ def emit(self, name: str, *args: Any,
             except SphinxError:
                 raise
             except Exception as exc:
+                if self.app.pdb:
+                    # Just pass through the error, so that it can be debugged.
+                    raise
                 modname = safe_getattr(listener.handler, '__module__', None)
                 raise ExtensionError(__("Handler %r for event %r threw an exception") %
                                      (listener.handler, name), exc, modname=modname) from exc

tests/test_events.py

@@ -19,11 +19,16 @@ def test_event_priority():
     assert result == [3, 1, 2, 5, 4]
 
 
+class FakeApp:
+    def __init__(self, pdb: bool=False):
+        self.pdb = pdb
+
+
 def test_event_allowed_exceptions():
     def raise_error(app):
         raise RuntimeError
 
-    events = EventManager(object())  # pass an dummy object as an app
+    events = EventManager(FakeApp())  # pass an dummy object as an app
     events.connect('builder-inited', raise_error, priority=500)
 
     # all errors are converted to ExtensionError
@@ -33,3 +38,19 @@ def raise_error(app):
     # Allow RuntimeError (pass-through)
     with pytest.raises(RuntimeError):
         events.emit('builder-inited', allowed_exceptions=(RuntimeError,))
+
+
+def test_event_pdb():
+    def raise_error(app):
+        raise RuntimeError
+
+    events = EventManager(FakeApp(pdb=True))  # pass an dummy object as an app
+    events.connect('builder-inited', raise_error, priority=500)
+
+    # errors aren't converted
+    with pytest.raises(RuntimeError):
+        events.emit('builder-inited')
+
+    # Allow RuntimeError (pass-through)
+    with pytest.raises(RuntimeError):
+        events.emit('builder-inited', allowed_exceptions=(RuntimeError,))