comparison contrib/perf.py @ 30143:2d858c771760

perf: introduce safeattrsetter to replace direct attribute assignment

Referring not-existing attribute immediately causes failure, but
assigning a value to such attribute doesn't.

For example, perf.py has code paths below, which assign a value to
not-existing attribute. This causes incorrect performance measurement,
but these code paths are executed successfully.

  - "repo._tags = None" in perftags()
    recent Mercurial has tags cache information in repo._tagscache

  - "branchmap.write = lambda repo: None" in perfbranchmap()
    branchmap cache is written out by branchcache.write() in branchmap.py

"util.safehasattr() before assignment" can avoid this issue, but might
increase mistake at "copy & paste" attribute name or so.

To centralize (1) examining existence of, (2) assigning a value to,
and (3) restoring an old value to the attribute, this patch introduces
safeattrsetter(). This is used to replace direct attribute assignment
in subsequent patches.

Encapsulation of restoring is needed to completely remove direct
attribute assignment from perf.py, even though restoring isn't needed
so often.

30142:3dcaf1c4e90d

    fm.write('user', ' user %f', m[1])
    fm.write('sys',  ' sys %f', m[2])
    fm.write('count',  ' (best of %d)', count)
    fm.plain('\n')

@command('perfwalk', formatteropts)
def perfwalk(ui, repo, *pats, **opts):
    timer, fm = gettimer(ui, opts)
    try:
        m = scmutil.match(repo[None], pats, {})

30143:2d858c771760

    fm.write('user', ' user %f', m[1])
    fm.write('sys',  ' sys %f', m[2])
    fm.write('count',  ' (best of %d)', count)
    fm.plain('\n')

# utilities for historical portability

def safeattrsetter(obj, name, ignoremissing=False):
    """Ensure that 'obj' has 'name' attribute before subsequent setattr

    This function is aborted, if 'obj' doesn't have 'name' attribute
    at runtime. This avoids overlooking removal of an attribute, which
    breaks assumption of performance measurement, in the future.

    This function returns the object to (1) assign a new value, and
    (2) restore an original value to the attribute.

    If 'ignoremissing' is true, missing 'name' attribute doesn't cause
    abortion, and this function returns None. This is useful to
    examine an attribute, which isn't ensured in all Mercurial
    versions.
    """
    if not util.safehasattr(obj, name):
        if ignoremissing:
            return None
        raise error.Abort(("missing attribute %s of %s might break assumption"
                           " of performance measurement") % (name, obj))

    origvalue = getattr(obj, name)
    class attrutil(object):
        def set(self, newvalue):
            setattr(obj, name, newvalue)
        def restore(self):
            setattr(obj, name, origvalue)

    return attrutil()

# perf commands

@command('perfwalk', formatteropts)
def perfwalk(ui, repo, *pats, **opts):
    timer, fm = gettimer(ui, opts)
    try:
        m = scmutil.match(repo[None], pats, {})