Use a callable __tracebackhide__ for filtering

While this leads to slightly more complicated user code for the common
case (checking if the exception is of a given type) it's easier to
implement and more flexible.

CHANGELOG.rst

@@ -23,8 +23,9 @@
   Thanks `@omarkohl`_ for the complete PR (`#1502`_) and `@nicoddemus`_ for the
   implementation tips.
 
-* ``__tracebackhide__`` can now also be set to an exception type (or a list of
+* ``__tracebackhide__`` can now also be set to a callable which then can decide
-  exception types) to only filter exceptions of that type.
+  whether to filter the traceback based on the ``ExceptionInfo`` object passed
+  to it.
 
 *
 

_pytest/_code/code.py

@@ -140,8 +140,8 @@ class TracebackEntry(object):
     _repr_style = None
     exprinfo = None
 
-    def __init__(self, rawentry, exctype=None):
+    def __init__(self, rawentry, excinfo=None):
-        self._exctype = exctype
+        self._excinfo = excinfo
         self._rawentry = rawentry
         self.lineno = rawentry.tb_lineno - 1
 
@@ -218,16 +218,12 @@ class TracebackEntry(object):
 
     source = property(getsource)
 
-    def _is_exception_type(self, obj):
-        return isinstance(obj, type) and issubclass(obj, Exception)
-
     def ishidden(self):
         """ return True if the current frame has a var __tracebackhide__
             resolving to True
 
-            If __tracebackhide__ is set to an exception type, or a list/tuple,
+            If __tracebackhide__ is a callable, it gets called with the
-            the traceback is only hidden if the exception which happened is of
+            ExceptionInfo instance and can decide whether to hide the traceback.
-            the given type(s).
 
             mostly for internal use
         """
@@ -239,13 +235,8 @@ class TracebackEntry(object):
             except KeyError:
                 return False
 
-        if self._is_exception_type(tbh):
+        if callable(tbh):
-            assert self._exctype is not None
+            return tbh(self._excinfo)
-            return issubclass(self._exctype, tbh)
-        elif (isinstance(tbh, (list, tuple)) and
-              all(self._is_exception_type(e) for e in tbh)):
-            assert self._exctype is not None
-            return issubclass(self._exctype, tuple(tbh))
         else:
             return tbh
 
@@ -272,13 +263,13 @@ class Traceback(list):
         access to Traceback entries.
     """
     Entry = TracebackEntry
-    def __init__(self, tb, exctype=None):
+    def __init__(self, tb, excinfo=None):
-        """ initialize from given python traceback object and exc type. """
+        """ initialize from given python traceback object and ExceptionInfo """
-        self._exctype = exctype
+        self._excinfo = excinfo
         if hasattr(tb, 'tb_next'):
             def f(cur):
                 while cur is not None:
-                    yield self.Entry(cur, exctype=exctype)
+                    yield self.Entry(cur, excinfo=excinfo)
                     cur = cur.tb_next
             list.__init__(self, f(tb))
         else:
@@ -302,7 +293,7 @@ class Traceback(list):
                  not codepath.relto(excludepath)) and
                 (lineno is None or x.lineno == lineno) and
                 (firstlineno is None or x.frame.code.firstlineno == firstlineno)):
-                return Traceback(x._rawentry, self._exctype)
+                return Traceback(x._rawentry, self._excinfo)
         return self
 
     def __getitem__(self, key):
@@ -321,7 +312,7 @@ class Traceback(list):
             by default this removes all the TracebackItems which are hidden
             (see ishidden() above)
         """
-        return Traceback(filter(fn, self), self._exctype)
+        return Traceback(filter(fn, self), self._excinfo)
 
     def getcrashentry(self):
         """ return last non-hidden traceback entry that lead
@@ -385,7 +376,7 @@ class ExceptionInfo(object):
         #: the exception type name
         self.typename = self.type.__name__
         #: the exception traceback (_pytest._code.Traceback instance)
-        self.traceback = _pytest._code.Traceback(self.tb, exctype=self.type)
+        self.traceback = _pytest._code.Traceback(self.tb, excinfo=self)
 
     def __repr__(self):
         return "<ExceptionInfo %s tblen=%d>" % (self.typename, len(self.traceback))

doc/en/example/simple.rst

@@ -216,16 +216,18 @@ Let's run our little function::
     test_checkconfig.py:8: Failed
     1 failed in 0.12 seconds
 
-If you only want to hide certain exception classes, you can also set
+If you only want to hide certain exceptions, you can set ``__tracebackhide__``
-``__tracebackhide__`` to an exception type or a list of exception types::
+to a callable which gets the ``ExceptionInfo`` object. You can for example use
+this to make sure unexpected exception types aren't hidden::
 
+    import operator
     import pytest
 
     class ConfigException(Exception):
         pass
 
     def checkconfig(x):
-        __tracebackhide__ = ConfigException
+        __tracebackhide__ = operator.methodcaller('errisinstance', ConfigException)
         if not hasattr(x, "config"):
             raise ConfigException("not configured: %s" %(x,))
 

testing/code/test_excinfo.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 
+import operator
 import _pytest
 import py
 import pytest
@@ -145,10 +146,10 @@ class TestTraceback_f_g_h:
         assert len(ntraceback) == len(traceback) - 1
 
     @pytest.mark.parametrize('tracebackhide, matching', [
-        (ValueError, True),
+        (lambda info: True, True),
-        (IndexError, False),
+        (lambda info: False, False),
-        ([ValueError, IndexError], True),
+        (operator.methodcaller('errisinstance', ValueError), True),
-        ((ValueError, IndexError), True),
+        (operator.methodcaller('errisinstance', IndexError), False),
     ])
     def test_traceback_filter_selective(self, tracebackhide, matching):
         def f():
@@ -475,7 +476,7 @@ raise ValueError()
             f_globals = {}
 
         class FakeTracebackEntry(_pytest._code.Traceback.Entry):
-            def __init__(self, tb, exctype=None):
+            def __init__(self, tb, excinfo=None):
                 self.lineno = 5+3
 
             @property