On 26/02/2018 08:11, Yuya Nishihara wrote:
On Mon, 26 Feb 2018 11:45:03 +0100, Feld Boris wrote:
On 13/02/2018 12:47, Yuya Nishihara wrote:
On Mon, 12 Feb 2018 18:00:52 +0100, Boris Feld wrote:
# HG changeset patch
# User Boris Feld <boris.f...@octobus.net>
# Date 1518448909 -3600
# Mon Feb 12 16:21:49 2018 +0100
# Node ID b0f45e1376e2d0f32023e197c51802bc21c60490
# Parent f02fd7ca256d044c4a51c3f3fc0ecaf95d23e03d
# EXP-Topic noname
# Available At https://bitbucket.org/octobus/mercurial-devel/
# hg pull https://bitbucket.org/octobus/mercurial-devel/ -r
b0f45e1376e2
revset: skip old style lookup if external whitespace are detected
Since label cannot contains leading or trailing whitespace we can skip looking
for them. This is useful in repository with slow labels (eg: special type of
tags). Short command running on a specific revision can benefit from such
shortcut.
eg on a repository where loading tags take 0.4s:
1: hg log --template '{node}\n' --rev 'rev(0)'
0.560 seconds
2: hg log --template '{node}\n' --rev ' rev(0)'
0.109 seconds
Seems okay, but isn't it too obscure that prefixing with ' ' is the fast
way of querying?
Yes, it is a bit obscure but it's the best solution we came up with
existing code. I sent a new patch that implements the fast path at the
individual name-space level in a way that seems cleaner and more useful.
Another solution is we could force revset evaluation using a `set:` (or
`revset:`) prefix. This way we could have both a clean and explicit way
of implementing the fast path.
That isn't possible because "set:whatever" can be a range between "set"
and whatever. ;)
The proposal here is to define a prefix for which we break backward
compatibility. If we do so, people with a "<set>" label will have to use:
"<set>":whatever
to get a similar effect.
Instead, maybe we can make lookup() to not search slow labels assuming these
labeling schemes didn't exist in pre-revset era.
We are afraid it is a bit more complex than that. Because `rev(0)` is a
valid tag and a valid bookmark, we don't think we can ever skip this
lookup call (yes, in our case, both tags and bookmarks are expensive to
load).
If loading plain tags and bookmarks is expensive, yeah, there would be no
fast path of lookup().
Alternatively, we could add
a config knob to switch off the old-style range support.
Having a config knob for this seems weird. We don't expect users to find
it and really understand what the config is about. It would be useful
for large corporate users with centralized config, but they would need
to set the flag on every one of their scripts/servers involving Mercurial.
IMHO, config knob is easier to learn than using the ' ' prefix. I would say
WTF if I taught to use the ' ' to make hg fast. And I think this config can
be switched on by tweakdefaults because lookup() exists only for backward
compatibility. (We might still want to allow dashes in symbols, though.)
Dropping the older lookup methods seems impractical. Right now, `rev(0)`
is a valid tag. So dropping legacy lookup means all these things will
have to be heavily quoted: (eg: hg log -r '"version-4(candidate2)"').
(In practice, even `"rev(0)"` is also a valid tag, starting and escaping
fest).
A longer terms solution would be to support configuring constraints on
labels. If tags can be configured to only match a specific pattern we
could skip lookup for data that does not match it very quickly. To be
fully enforced it probably need to a part of the .hg/requires so it is a
heavier change. It also needs to be more than just a hook so that the
lookup logic is aware of it and can fast path it. Such approach work in
our use-case but is also more specific and requires more
configuration(work?).
We could use the same approach as the V2 series proposed here:
https://www.mercurial-scm.org/pipermail/mercurial-devel/2018-February/112087.html
However, we think it still makes sense to have an easy and standard way
to force something to be evaluated as a revset as it's not possible as
of today.
Here is a summary of the idea we've discussed so far:
1) Using some kind of prefix, breaking BC for people using the prefix as
a label:
`revs:rev(42)` → directly evaluated as `rev(42)`
`"revs":rev(42)` → force "revs" as a label
2) Adding a special revset for revset evaluation.
`revset("rev(42)")` → directly evaluated `rev(42)`
3) adding strange special case: (leading space, parents).
` rev(42)` → directly evaluated as `rev(42)`
`(rev(42))` → directly evaluated as `rev(42)`
4) Config flag to disable legacy parsing (force quote for strange labels).
5) Full-featured label patterns enforcement as described earlier in this
email.
We agree fast-pathing on (3) is a bit too obscure.
We find (4) to be impractical (and likely to break unexpected stuff).
(5) is a good solution but significantly heavier to write and much more
specific.
So we would be happy if we could agree on a way to go for (1) or maybe
(2). We prefer (1) because it is closer than what we do for fileset. The
one time BC should be specific enough to not be a real issue. (`revs` is
the best prefix we can think of).
Cheers,
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