Improve tracebacks for ImportErrors in conftest

changelog/3332.feature.rst

@@ -0,0 +1,4 @@
+Improve the error displayed when a ``conftest.py`` file could not be imported.
+
+In order to implement this, a new ``chain`` parameter was added to ``ExceptionInfo.getrepr``
+to show or hide chained tracebacks in Python 3 (defaults to ``True``).

src/_pytest/_code/__init__.py

@@ -4,6 +4,7 @@
 from .code import ExceptionInfo  # noqa
 from .code import Frame  # noqa
 from .code import Traceback  # noqa
+from .code import filter_traceback  # noqa
 from .code import getrawcode  # noqa
 from .source import Source  # noqa
 from .source import compile_ as compile  # noqa

src/_pytest/_code/code.py

@@ -6,8 +6,10 @@
 from inspect import CO_VARARGS, CO_VARKEYWORDS
 
 import attr
+import pluggy
 import re
 from weakref import ref
+import _pytest
 from _pytest.compat import _PY2, _PY3, PY35, safe_str
 from six import text_type
 import py
@@ -451,13 +453,35 @@ def getrepr(
         tbfilter=True,
         funcargs=False,
         truncate_locals=True,
+        chain=True,
     ):
-        """ return str()able representation of this exception info.
-            showlocals: show locals per traceback entry
-            style: long|short|no|native traceback style
-            tbfilter: hide entries (where __tracebackhide__ is true)
+        """
+        Return str()able representation of this exception info.
+
+        :param bool showlocals:
+            Show locals per traceback entry.
+            Ignored if ``style=="native"``.
+
+        :param str style: long|short|no|native traceback style
+
+        :param bool abspath:
+            If paths should be changed to absolute or left unchanged.
+
+        :param bool tbfilter:
+            Hide entries that contain a local variable ``__tracebackhide__==True``.
+            Ignored if ``style=="native"``.
+
+        :param bool funcargs:
+            Show fixtures ("funcargs" for legacy purposes) per traceback entry.
+
+        :param bool truncate_locals:
+            With ``showlocals==True``, make sure locals can be safely represented as strings.
+
+        :param bool chain: if chained exceptions in Python 3 should be shown.
+
+        .. versionchanged:: 3.9
 
-            in case of style==native, tbfilter and showlocals is ignored.
+            Added the ``chain`` parameter.
         """
         if style == "native":
             return ReprExceptionInfo(
@@ -476,6 +500,7 @@ def getrepr(
             tbfilter=tbfilter,
             funcargs=funcargs,
             truncate_locals=truncate_locals,
+            chain=chain,
         )
         return fmt.repr_excinfo(self)
 
@@ -516,6 +541,7 @@ class FormattedExcinfo(object):
     tbfilter = attr.ib(default=True)
     funcargs = attr.ib(default=False)
     truncate_locals = attr.ib(default=True)
+    chain = attr.ib(default=True)
     astcache = attr.ib(default=attr.Factory(dict), init=False, repr=False)
 
     def _getindent(self, source):
@@ -735,15 +761,19 @@ def repr_excinfo(self, excinfo):
                     reprcrash = None
 
                 repr_chain += [(reprtraceback, reprcrash, descr)]
-                if e.__cause__ is not None:
+                if e.__cause__ is not None and self.chain:
                     e = e.__cause__
                     excinfo = (
                         ExceptionInfo((type(e), e, e.__traceback__))
                         if e.__traceback__
                         else None
                     )
                     descr = "The above exception was the direct cause of the following exception:"
-                elif e.__context__ is not None and not e.__suppress_context__:
+                elif (
+                    e.__context__ is not None
+                    and not e.__suppress_context__
+                    and self.chain
+                ):
                     e = e.__context__
                     excinfo = (
                         ExceptionInfo((type(e), e, e.__traceback__))
@@ -979,3 +1009,36 @@ def is_recursion_error(excinfo):
             return "maximum recursion depth exceeded" in str(excinfo.value)
         except UnicodeError:
             return False
+
+
+# relative paths that we use to filter traceback entries from appearing to the user;
+# see filter_traceback
+# note: if we need to add more paths than what we have now we should probably use a list
+# for better maintenance
+
+_PLUGGY_DIR = py.path.local(pluggy.__file__.rstrip("oc"))
+# pluggy is either a package or a single module depending on the version
+if _PLUGGY_DIR.basename == "__init__.py":
+    _PLUGGY_DIR = _PLUGGY_DIR.dirpath()
+_PYTEST_DIR = py.path.local(_pytest.__file__).dirpath()
+_PY_DIR = py.path.local(py.__file__).dirpath()
+
+
+def filter_traceback(entry):
+    """Return True if a TracebackEntry instance should be removed from tracebacks:
+    * dynamically generated code (no code to show up for it);
+    * internal traceback from pytest or its internal libraries, py and pluggy.
+    """
+    # entry.path might sometimes return a str object when the entry
+    # points to dynamically generated code
+    # see https://bitbucket.org/pytest-dev/py/issues/71
+    raw_filename = entry.frame.code.raw.co_filename
+    is_generated = "<" in raw_filename and ">" in raw_filename
+    if is_generated:
+        return False
+    # entry.path might point to a non-existing file, in which case it will
+    # also return a str object. see #1133
+    p = py.path.local(entry.path)
+    return (
+        not p.relto(_PLUGGY_DIR) and not p.relto(_PYTEST_DIR) and not p.relto(_PY_DIR)
+    )

src/_pytest/config/__init__.py

@@ -3,7 +3,6 @@
 import argparse
 import inspect
 import shlex
-import traceback
 import types
 import warnings
 import copy
@@ -19,29 +18,21 @@
 import _pytest.hookspec  # the extension point definitions
 import _pytest.assertion
 from pluggy import PluginManager, HookimplMarker, HookspecMarker
+from _pytest._code import ExceptionInfo, filter_traceback
 from _pytest.compat import safe_str
 from .exceptions import UsageError, PrintHelp
 from .findpaths import determine_setup, exists
 
 hookimpl = HookimplMarker("pytest")
 hookspec = HookspecMarker("pytest")
 
-# pytest startup
-#
-
 
 class ConftestImportFailure(Exception):
     def __init__(self, path, excinfo):
         Exception.__init__(self, path, excinfo)
         self.path = path
         self.excinfo = excinfo
 
-    def __str__(self):
-        etype, evalue, etb = self.excinfo
-        formatted = traceback.format_tb(etb)
-        # The level of the tracebacks we want to print is hand crafted :(
-        return repr(evalue) + "\n" + "".join(formatted[2:])
-
 
 def main(args=None, plugins=None):
     """ return exit code, after performing an in-process test run.
@@ -57,10 +48,20 @@ def main(args=None, plugins=None):
         try:
             config = _prepareconfig(args, plugins)
         except ConftestImportFailure as e:
+            exc_info = ExceptionInfo(e.excinfo)
             tw = py.io.TerminalWriter(sys.stderr)
-            for line in traceback.format_exception(*e.excinfo):
+            tw.line(
+                "ImportError while loading conftest '{e.path}'.".format(e=e), red=True
+            )
+            exc_info.traceback = exc_info.traceback.filter(filter_traceback)
+            exc_repr = (
+                exc_info.getrepr(style="short", chain=False)
+                if exc_info.traceback
+                else exc_info.exconly()
+            )
+            formatted_tb = safe_str(exc_repr)
+            for line in formatted_tb.splitlines():
                 tw.line(line.rstrip(), red=True)
-            tw.line("ERROR: could not load %s\n" % (e.path,), red=True)
             return 4
         else:
             try:

src/_pytest/python.py

@@ -16,7 +16,7 @@
 from _pytest.config import hookimpl
 
 import _pytest
-import pluggy
+from _pytest._code import filter_traceback
 from _pytest import fixtures
 from _pytest import nodes
 from _pytest import deprecated
@@ -46,37 +46,6 @@
 )
 from _pytest.warning_types import RemovedInPytest4Warning, PytestWarning
 
-# relative paths that we use to filter traceback entries from appearing to the user;
-# see filter_traceback
-# note: if we need to add more paths than what we have now we should probably use a list
-# for better maintenance
-_pluggy_dir = py.path.local(pluggy.__file__.rstrip("oc"))
-# pluggy is either a package or a single module depending on the version
-if _pluggy_dir.basename == "__init__.py":
-    _pluggy_dir = _pluggy_dir.dirpath()
-_pytest_dir = py.path.local(_pytest.__file__).dirpath()
-_py_dir = py.path.local(py.__file__).dirpath()
-
-
-def filter_traceback(entry):
-    """Return True if a TracebackEntry instance should be removed from tracebacks:
-    * dynamically generated code (no code to show up for it);
-    * internal traceback from pytest or its internal libraries, py and pluggy.
-    """
-    # entry.path might sometimes return a str object when the entry
-    # points to dynamically generated code
-    # see https://bitbucket.org/pytest-dev/py/issues/71
-    raw_filename = entry.frame.code.raw.co_filename
-    is_generated = "<" in raw_filename and ">" in raw_filename
-    if is_generated:
-        return False
-    # entry.path might point to a non-existing file, in which case it will
-    # also return a str object. see #1133
-    p = py.path.local(entry.path)
-    return (
-        not p.relto(_pluggy_dir) and not p.relto(_pytest_dir) and not p.relto(_py_dir)
-    )
-
 
 def pyobj_property(name):
     def get(self):

testing/acceptance_test.py

@@ -133,9 +133,16 @@ def test_not_collectable_arguments(self, testdir):
         assert result.ret
         result.stderr.fnmatch_lines(["*ERROR: not found:*{}".format(p2.basename)])
 
-    def test_issue486_better_reporting_on_conftest_load_failure(self, testdir):
+    def test_better_reporting_on_conftest_load_failure(self, testdir, request):
+        """Show a user-friendly traceback on conftest import failures (#486, #3332)"""
         testdir.makepyfile("")
-        testdir.makeconftest("import qwerty")
+        testdir.makeconftest(
+            """
+            def foo():
+                import qwerty
+            foo()
+        """
+        )
         result = testdir.runpytest("--help")
         result.stdout.fnmatch_lines(
             """
@@ -144,10 +151,23 @@ def test_issue486_better_reporting_on_conftest_load_failure(self, testdir):
         """
         )
         result = testdir.runpytest()
+        dirname = request.node.name + "0"
+        exc_name = (
+            "ModuleNotFoundError" if sys.version_info >= (3, 6) else "ImportError"
+        )
         result.stderr.fnmatch_lines(
-            """
-            *ERROR*could not load*conftest.py*
-        """
+            [
+                "ImportError while loading conftest '*{sep}{dirname}{sep}conftest.py'.".format(
+                    dirname=dirname, sep=os.sep
+                ),
+                "conftest.py:3: in <module>",
+                "    foo()",
+                "conftest.py:2: in foo",
+                "    import qwerty",
+                "E   {}: No module named {q}qwerty{q}".format(
+                    exc_name, q="'" if six.PY3 else ""
+                ),
+            ]
         )
 
     def test_early_skip(self, testdir):

testing/code/test_excinfo.py

@@ -1184,20 +1184,28 @@ def h():
         assert tw.lines[47] == ":15: AttributeError"
 
     @pytest.mark.skipif("sys.version_info[0] < 3")
-    def test_exc_repr_with_raise_from_none_chain_suppression(self, importasmod):
+    @pytest.mark.parametrize("mode", ["from_none", "explicit_suppress"])
+    def test_exc_repr_chain_suppression(self, importasmod, mode):
+        """Check that exc repr does not show chained exceptions in Python 3.
+        - When the exception is raised with "from None"
+        - Explicitly suppressed with "chain=False" to ExceptionInfo.getrepr().
+        """
+        raise_suffix = " from None" if mode == "from_none" else ""
         mod = importasmod(
             """
             def f():
                 try:
                     g()
                 except Exception:
-                    raise AttributeError() from None
+                    raise AttributeError(){raise_suffix}
             def g():
                 raise ValueError()
-        """
+        """.format(
+                raise_suffix=raise_suffix
+            )
         )
         excinfo = pytest.raises(AttributeError, mod.f)
-        r = excinfo.getrepr(style="long")
+        r = excinfo.getrepr(style="long", chain=mode != "explicit_suppress")
         tw = TWMock()
         r.toterminal(tw)
         for line in tw.lines:
@@ -1207,7 +1215,9 @@ def g():
         assert tw.lines[2] == "        try:"
         assert tw.lines[3] == "            g()"
         assert tw.lines[4] == "        except Exception:"
-        assert tw.lines[5] == ">           raise AttributeError() from None"
+        assert tw.lines[5] == ">           raise AttributeError(){}".format(
+            raise_suffix
+        )
         assert tw.lines[6] == "E           AttributeError"
         assert tw.lines[7] == ""
         line = tw.get_write_msg(8)