util: create a context manager to handle timing

The context manager is pulled out of the timed decorator function, and
refactored to provide a stats instance, with added tests.

tests/test-util.py

@@ -0,0 +1,135 b''
+# unit tests for mercuril.util utilities
+from __future__ import absolute_import
+
+import contextlib
+import itertools
+import unittest
+
+from mercurial import pycompat, util, utils
+
[e-mail]
+def mocktimer(incr=0.1, *additional_targets):
+    """Replaces util.timer and additional_targets with a mock
+
+    The timer starts at 0. On each call the time incremented by the value
+    of incr. If incr is an iterable, then the time is incremented by the
+    next value from that iterable, looping in a cycle when reaching the end.
+
+    additional_targets must be a sequence of (object, attribute_name) tuples;
+    the mock is set with setattr(object, attribute_name, mock).
+
+    """
+    time = [0]
+    try:
+        incr = itertools.cycle(incr)
+    except TypeError:
+        incr = itertools.repeat(incr)
+
+    def timer():
+        time[0] += next(incr)
+        return time[0]
+
+    # record original values
+    orig = util.timer
+    additional_origs = [(o, a, getattr(o, a)) for o, a in additional_targets]
+
+    # mock out targets
+    util.timer = timer
+    for obj, attr in additional_targets:
+        setattr(obj, attr, timer)
+
+    try:
+        yield
+    finally:
+        # restore originals
+        util.timer = orig
+        for args in additional_origs:
+            setattr(*args)
+
+# attr.s default factory for util.timedstats.start binds the timer we
+# need to mock out.
+_start_default = (util.timedcmstats.start.default, 'factory')
+
[e-mail]
+def capturestderr():
+    """Replace utils.procutil.stderr with a pycompat.bytesio instance
+
+    The instance is made available as the return value of __enter__.
+
+    This contextmanager is reentrant.
+
+    """
+    orig = utils.procutil.stderr
+    utils.procutil.stderr = pycompat.bytesio()
+    try:
+        yield utils.procutil.stderr
+    finally:
+        utils.procutil.stderr = orig
+
+class timedtests(unittest.TestCase):
+    def testtimedcmstatsstr(self):
+        stats = util.timedcmstats()
+        self.assertEqual(str(stats), '<unknown>')
+        stats.elapsed = 12.34
+        self.assertEqual(str(stats), util.timecount(12.34))
+
+    def testtimedcmcleanexit(self):
+        # timestamps 1, 4, elapsed time of 4 - 1 = 3
+        with mocktimer([1, 3], _start_default):
+            with util.timedcm() as stats:
+                # actual context doesn't matter
+                pass
+
+        self.assertEqual(stats.start, 1)
+        self.assertEqual(stats.elapsed, 3)
+        self.assertEqual(stats.level, 1)
+
+    def testtimedcmnested(self):
+        # timestamps 1, 3, 6, 10, elapsed times of 6 - 3 = 3 and 10 - 1 = 9
+        with mocktimer([1, 2, 3, 4], _start_default):
+            with util.timedcm() as outer_stats:
+                with util.timedcm() as inner_stats:
+                    # actual context doesn't matter
+                    pass
+
+        self.assertEqual(outer_stats.start, 1)
+        self.assertEqual(outer_stats.elapsed, 9)
+        self.assertEqual(outer_stats.level, 1)
+
+        self.assertEqual(inner_stats.start, 3)
+        self.assertEqual(inner_stats.elapsed, 3)
+        self.assertEqual(inner_stats.level, 2)
+
+    def testtimedcmexception(self):
+        # timestamps 1, 4, elapsed time of 4 - 1 = 3
+        with mocktimer([1, 3], _start_default):
+            try:
+                with util.timedcm() as stats:
+                    raise ValueError()
+            except ValueError:
+                pass
+
+        self.assertEqual(stats.start, 1)
+        self.assertEqual(stats.elapsed, 3)
+        self.assertEqual(stats.level, 1)
+
+    def testtimeddecorator(self):
+        @util.timed
+        def testfunc(callcount=1):
+            callcount -= 1
+            if callcount:
+                testfunc(callcount)
+
+        # timestamps 1, 2, 3, 4, elapsed time of 3 - 2 = 1 and 4 - 1 = 3
+        with mocktimer(1, _start_default):
+            with capturestderr() as out:
+                testfunc(2)
+
+        self.assertEqual(out.getvalue(), (
+            b'    testfunc: 1.000 s\n'
+            b'  testfunc: 3.000 s\n'
+        ))
+
+if __name__ == '__main__':
+    import silenttestrunner
+    silenttestrunner.main(__name__)

contrib/import-checker.py

@@ -36,6 +36,7 b' allowsymbolimports = ('
     'mercurial.pure.parsers',
     # third-party imports should be directly imported
     'mercurial.thirdparty',
+    'mercurial.thirdparty.attr',
     'mercurial.thirdparty.cbor',
     'mercurial.thirdparty.cbor.cbor2',
     'mercurial.thirdparty.zope',

mercurial/util.py

@@ -36,6 +36,9 b' import traceback'
 import warnings
 import zlib
 
+from .thirdparty import (
+    attr,
+)
 from . import (
     encoding,
     error,
@@ -2874,7 +2877,41 b' timecount = unitcountfn('
     (1, 0.000000001, _('%.3f ns')),
     )
 
-_timenesting = [0]
+@attr.s
+class timedcmstats(object):
+    """Stats information produced by the timedcm context manager on entering."""
+
+    # the starting value of the timer as a float (meaning and resulution is
+    # platform dependent, see util.timer)
+    start = attr.ib(default=attr.Factory(lambda: timer()))
+    # the number of seconds as a floating point value; starts at 0, updated when
+    # the context is exited.
+    elapsed = attr.ib(default=0)
+    # the number of nested timedcm context managers.
+    level = attr.ib(default=1)
+
+    def __str__(self):
+        return timecount(self.elapsed) if self.elapsed else '<unknown>'
+
[e-mail]
+def timedcm():
+    """A context manager that produces timing information for a given context.
+
+    On entering a timedcmstats instance is produced.
+
+    This context manager is reentrant.
+
+    """
+    # track nested context managers
+    timedcm._nested += 1
+    timing_stats = timedcmstats(level=timedcm._nested)
+    try:
+        yield timing_stats
+    finally:
+        timing_stats.elapsed = timer() - timing_stats.start
+        timedcm._nested -= 1
+
+timedcm._nested = 0
 
 def timed(func):
     '''Report the execution time of a function call to stderr.
@@ -2888,18 +2925,12 b' def timed(func):'
     '''
 
     def wrapper(*args, **kwargs):
-        start = timer()
-        indent = 2
-        _timenesting[0] += indent
-        try:
-            return func(*args, **kwargs)
-        finally:
-            elapsed = timer() - start
-            _timenesting[0] -= indent
+        with timedcm() as time_stats:
+            result = func(*args, **kwargs)
             stderr = procutil.stderr
-            stderr.write('%s%s: %s\n' %
-                         (' ' * _timenesting[0], func.__name__,
-                          timecount(elapsed)))
+        stderr.write('%s%s: %s\n' % (
+            ' ' * time_stats.level * 2, func.__name__, time_stats))
+        return result
     return wrapper
 
 _sizeunits = (('m', 2**20), ('k', 2**10), ('g', 2**30),