[PATCH V2] error: make HintException a mix-in class not derived from BaseException (API)

Yuya Nishihara yuya at tcha.org
Sat Jul 9 02:20:36 EDT 2016

# HG changeset patch
# User Yuya Nishihara <yuya at tcha.org>
# Date 1468042110 -32400
#      Sat Jul 09 14:28:30 2016 +0900
# Node ID bf279db10eb66c70322b062ef1818ddfb06e6daa
# Parent  b4d117cee636be8a566f56e84d4b351a736a1299
error: make HintException a mix-in class not derived from BaseException (API)

HintException is unrelated to the hierarchy of errors. It is an implementation
detail whether a class inherits from HintException or not, a sort of "private
inheritance" in C++.

New Hint isn't an exception class, which prevents catching error by its type:

    except error.Hint:

Unfortunately, this passes on PyPy 5.3.1, but not on Python 2, and raises more
detailed TypeError on Python 3.

diff --git a/mercurial/error.py b/mercurial/error.py
--- a/mercurial/error.py
+++ b/mercurial/error.py
@@ -15,12 +15,17 @@ from __future__ import absolute_import
 # Do not import anything here, please
-class HintException(Exception):
+class Hint(object):
+    """Mix-in to provide a hint of an error
+    This should come first in the inheritance list to consume **kw and pass
+    only *args to the exception class.
+    """
     def __init__(self, *args, **kw):
-        Exception.__init__(self, *args)
+        super(Hint, self).__init__(*args)
         self.hint = kw.get('hint')
-class RevlogError(HintException):
+class RevlogError(Hint, Exception):
 class FilteredIndexError(IndexError):
@@ -50,10 +55,10 @@ class ManifestLookupError(LookupError):
 class CommandError(Exception):
     """Exception raised on errors in parsing the command line."""
-class InterventionRequired(HintException):
+class InterventionRequired(Hint, Exception):
     """Exception raised when a command requires human intervention."""
-class Abort(HintException):
+class Abort(Hint, Exception):
     """Raised if a command needs to print an error and exit."""
 class HookLoadError(Abort):
@@ -87,10 +92,10 @@ class ResponseExpected(Abort):
         from .i18n import _
         Abort.__init__(self, _('response expected'))
-class OutOfBandError(HintException):
+class OutOfBandError(Hint, Exception):
     """Exception raised when a remote repo reports failure"""
-class ParseError(HintException):
+class ParseError(Hint, Exception):
     """Raised when parsing config files and {rev,file}sets (msg[, pos])"""
 class UnknownIdentifier(ParseError):
@@ -102,7 +107,7 @@ class UnknownIdentifier(ParseError):
         self.function = function
         self.symbols = symbols
-class RepoError(HintException):
+class RepoError(Hint, Exception):
 class RepoLookupError(RepoError):

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