run-tests: mechanism to report exceptions during test execution

Sometimes when running tests you introduce a ton of exceptions.
The most extreme example of this is running Mercurial with Python 3,
which currently spews thousands of exceptions when running the test
harness.

This commit adds an opt-in feature to run-tests.py to aggregate
exceptions encountered by `hg` when running tests.

When --exceptions is used, the test harness enables the
"logexceptions" extension in the test environment. This extension
wraps the Mercurial function to handle exceptions and writes
information about the exception to a random filename in a directory
defined by the test harness via an environment variable. At the
end of the test harness, these files are parsed, aggregated, and
a list of all unique Mercurial frames triggering exceptions is
printed in order of frequency.

This feature is intended to aid Python 3 development. I've only
really tested it on Python 3. There is no shortage of improvements
that could be made. e.g. we could write a separate file containing
the exception report - maybe even an HTML report. We also don't
capture which tests demonstrate the exceptions, so there's no turnkey
way to test whether a code change made an exception disappear.
Perfect is the enemy of good. I think the current patch is useful
enough to land. Whoever uses it can send patches to imprve its
usefulness.

Differential Revision: https://phab.mercurial-scm.org/D1477

.hgignore

@@ -24,6 +24,7 @@ tests/.testtimes*
 tests/.hypothesis
 tests/hypothesis-generated
 tests/annotated
+tests/exceptions
 tests/*.err
 tests/htmlcov
 build

tests/logexceptions.py

@@ -0,0 +1,73 @@
+# logexceptions.py - Write files containing info about Mercurial exceptions
+#
+# Copyright 2017 Matt Mackall <mpm@selenic.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+import inspect
+import os
+import sys
+import traceback
+import uuid
+
+from mercurial import (
+    dispatch,
+    extensions,
+)
+
+def handleexception(orig, ui):
+    res = orig(ui)
+
+    if not ui.environ.get(b'HGEXCEPTIONSDIR'):
+        return res
+
+    dest = os.path.join(ui.environ[b'HGEXCEPTIONSDIR'],
+                        str(uuid.uuid4()).encode('ascii'))
+
+    exc_type, exc_value, exc_tb = sys.exc_info()
+
+    stack = []
+    tb = exc_tb
+    while tb:
+        stack.append(tb)
+        tb = tb.tb_next
+    stack.reverse()
+
+    hgframe = 'unknown'
+    hgline = 'unknown'
+
+    # Find the first Mercurial frame in the stack.
+    for tb in stack:
+        mod = inspect.getmodule(tb)
+        if not mod.__name__.startswith(('hg', 'mercurial')):
+            continue
+
+        frame = tb.tb_frame
+
+        try:
+            with open(inspect.getsourcefile(tb), 'r') as fh:
+                hgline = fh.readlines()[frame.f_lineno - 1].strip()
+        except (IndexError, OSError):
+            pass
+
+        hgframe = '%s:%d' % (frame.f_code.co_filename, frame.f_lineno)
+        break
+
+    primary = traceback.extract_tb(exc_tb)[-1]
+    primaryframe = '%s:%d' % (primary.filename, primary.lineno)
+
+    with open(dest, 'wb') as fh:
+        parts = [
+            str(exc_value),
+            primaryframe,
+            hgframe,
+            hgline,
+        ]
+        fh.write(b'\0'.join(p.encode('utf-8', 'replace') for p in parts))
+
+def extsetup(ui):
+    extensions.wrapfunction(dispatch, 'handlecommandexception',
+                            handleexception)

tests/run-tests.py

@@ -46,6 +46,7 @@
 from __future__ import absolute_import, print_function
 
 import argparse
+import collections
 import difflib
 import distutils.version as version
 import errno
@@ -373,7 +374,7 @@ def getparser():
         help="install and use chg wrapper in place of hg")
     hgconf.add_argument("--compiler",
         help="compiler to build with")
-    hgconf.add_argument('--extra-config-opt', action="append",
+    hgconf.add_argument('--extra-config-opt', action="append", default=[],
         help='set the given config opt in the test hgrc')
     hgconf.add_argument("-l", "--local", action="store_true",
         help="shortcut for --with-hg=<testdir>/../hg, "
@@ -404,6 +405,8 @@ def getparser():
         help="colorisation: always|auto|never (default: auto)")
     reporting.add_argument("-c", "--cover", action="store_true",
         help="print a test coverage report")
+    reporting.add_argument('--exceptions', action='store_true',
+        help='log all exceptions and generate an exception report')
     reporting.add_argument("-H", "--htmlcov", action="store_true",
         help="create an HTML report of the coverage of the files")
     reporting.add_argument("--json", action="store_true",
@@ -2115,6 +2118,18 @@ class TextTestRunner(unittest.TextTestRunner):
                     os.environ['PYTHONHASHSEED'])
             if self._runner.options.time:
                 self.printtimes(result.times)
+
+            if self._runner.options.exceptions:
+                exceptions = aggregateexceptions(
+                    os.path.join(self._runner._outputdir, b'exceptions'))
+                total = sum(exceptions.values())
+
+                self.stream.writeln('Exceptions Report:')
+                self.stream.writeln('%d total from %d frames' %
+                                    (total, len(exceptions)))
+                for (frame, line, exc), count in exceptions.most_common():
+                    self.stream.writeln('%d\t%s: %s' % (count, frame, exc))
+
             self.stream.flush()
 
         return result
@@ -2501,6 +2516,23 @@ class TestRunner(object):
 
         self._coveragefile = os.path.join(self._testdir, b'.coverage')
 
+        if self.options.exceptions:
+            exceptionsdir = os.path.join(self._outputdir, b'exceptions')
+            try:
+                os.makedirs(exceptionsdir)
+            except OSError as e:
+                if e.errno != errno.EEXIST:
+                    raise
+
+            # Remove all existing exception reports.
+            for f in os.listdir(exceptionsdir):
+                os.unlink(os.path.join(exceptionsdir, f))
+
+            osenvironb[b'HGEXCEPTIONSDIR'] = exceptionsdir
+            logexceptions = os.path.join(self._testdir, b'logexceptions.py')
+            self.options.extra_config_opt.append(
+                'extensions.logexceptions=%s' % logexceptions.decode('utf-8'))
+
         vlog("# Using TESTDIR", self._testdir)
         vlog("# Using RUNTESTDIR", osenvironb[b'RUNTESTDIR'])
         vlog("# Using HGTMP", self._hgtmp)
@@ -2953,6 +2985,24 @@ class TestRunner(object):
                 print("WARNING: Did not find prerequisite tool: %s " %
                       p.decode("utf-8"))
 
+def aggregateexceptions(path):
+    exceptions = collections.Counter()
+
+    for f in os.listdir(path):
+        with open(os.path.join(path, f), 'rb') as fh:
+            data = fh.read().split(b'\0')
+            if len(data) != 4:
+                continue
+
+            exc, mainframe, hgframe, hgline = data
+            exc = exc.decode('utf-8')
+            mainframe = mainframe.decode('utf-8')
+            hgframe = hgframe.decode('utf-8')
+            hgline = hgline.decode('utf-8')
+            exceptions[(hgframe, hgline, exc)] += 1
+
+    return exceptions
+
 if __name__ == '__main__':
     runner = TestRunner()