Cache exception raised in fixtures according to their scope

Without this if a session scoped fixture fails it's setup it will
be re-tried each time it is requested.  Especially in case of
skip or failure exceptions this can be undesirable, but caching
makes sense for all exceptions.

CHANGELOG

@@ -1,6 +1,8 @@
 NEXT (2.6)
 -----------------------------------
 
+- Cache exceptions from fixtures according to their scope (issue 467).
+
 - fix issue514: teach assertion reinterpretation about private class attributes
 
 - change -v output to include full node IDs of tests.  Users can copy
@@ -59,10 +61,6 @@ NEXT (2.6)
 
 - fix issue483: trial/py33 works now properly.  Thanks Daniel Grana for PR.
 
-- improve example for pytest integration with "python setup.py test"
-  which now has a generic "-a" or "--pytest-args" option where you
-  can pass additional options as a quoted string.  Thanks Trevor Bekolay.
-
 - simplified internal capturing mechanism and made it more robust
   against tests or setups changing FD1/FD2, also better integrated
   now with pytest.pdb() in single tests.
@@ -89,9 +87,6 @@ NEXT (2.6)
   functions, including unittest-style Classes.  If set to False, the 
   test will not be collected.  
 
-- fix issue512: show "<notset>" for arguments which might not be set
-  in monkeypatch plugin.  Improves output in documentation.
-
 
 2.5.2
 -----------------------------------

_pytest/python.py

@@ -1337,7 +1337,7 @@ class FixtureRequest(FuncargnamesCompatAttr):
             except FixtureLookupError:
                 if argname == "request":
                     class PseudoFixtureDef:
-                        cached_result = (self, [0])
+                        cached_result = (self, [0], None)
                     return PseudoFixtureDef
                 raise
             result = self._getfuncargvalue(fixturedef)
@@ -1810,7 +1810,7 @@ class FixtureDef:
         kwargs = {}
         for argname in self.argnames:
             fixturedef = request._get_active_fixturedef(argname)
-            result, arg_cache_key = fixturedef.cached_result
+            result, arg_cache_key, exc = fixturedef.cached_result
             kwargs[argname] = result
             if argname != "request":
                 fixturedef.addfinalizer(self.finish)
@@ -1818,13 +1818,12 @@ class FixtureDef:
         my_cache_key = request.param_index
         cached_result = getattr(self, "cached_result", None)
         if cached_result is not None:
-            #print argname, "Found cached_result", cached_result
-            #print argname, "param_index", param_index
-            result, cache_key = cached_result
+            result, cache_key, err = cached_result
             if my_cache_key == cache_key:
-                #print request.fixturename, "CACHE HIT", repr(my_cache_key)
-                return result
-            #print request.fixturename, "CACHE MISS"
+                if err is not None:
+                    py.builtin._reraise(*err)
+                else:
+                    return result
             # we have a previous but differently parametrized fixture instance
             # so we need to tear it down before creating a new one
             self.finish()
@@ -1841,9 +1840,13 @@ class FixtureDef:
                 fixturefunc = getimfunc(self.func)
                 if fixturefunc != self.func:
                     fixturefunc = fixturefunc.__get__(request.instance)
-            result = call_fixture_func(fixturefunc, request, kwargs,
-                                       self.yieldctx)
-        self.cached_result = (result, my_cache_key)
+            try:
+                result = call_fixture_func(fixturefunc, request, kwargs,
+                                           self.yieldctx)
+            except Exception:
+                self.cached_result = (None, my_cache_key, sys.exc_info())
+                raise
+        self.cached_result = (result, my_cache_key, None)
         return result
 
     def __repr__(self):

testing/python/fixture.py

@@ -1430,6 +1430,25 @@ class TestFixtureMarker:
         reprec = testdir.inline_run()
         reprec.assertoutcome(passed=3)
 
+    def test_scope_session_exc(self, testdir):
+        testdir.makepyfile("""
+            import pytest
+            l = []
+            @pytest.fixture(scope="session")
+            def fix():
+                l.append(1)
+                pytest.skip('skipping')
+
+            def test_1(fix):
+                pass
+            def test_2(fix):
+                pass
+            def test_last():
+                assert l == [1]
+        """)
+        reprec = testdir.inline_run()
+        reprec.assertoutcome(skipped=2, passed=1)
+
     def test_scope_module_uses_session(self, testdir):
         testdir.makepyfile("""
             import pytest