1305246 - hg log for dom/media/ipc/VideoDecoderManagerParent.cpp doesn't contain all revisions

Status: RESOLVED INVALID

(Developer Services :: Mercurial: hg.mozilla.org, defect)

Description

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/filelog/tip/dom/media/ipc/VideoDecoderManagerParent.cpp
has pushes for bug 1288618 only from 2016-09-15, but e.g. https://hg.mozilla.org/mozilla-central/rev/70e4b38cd629 and https://hg.mozilla.org/mozilla-central/rev/70e4b38cd629 from 2016-09-22 are missing.

These patches landed on 2016-09-21 and got backed out, is there already a backout cleanup script active which could have caused this?

Comment 1

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

Same output if I run |hg log dom/media/ipc/VideoDecoderManagerParent.cpp| locally.

Comment 2

[Gregory Szorc [:gps]]

Can confirm the behavior.

Mercurial stores history of each path checked into version control separately. And, when you do `hg log <path>` it looks at this per-path history to show entries. (This is why `hg log <file>` is fast.)

We can see the actual history for that path by using `hg debugindex`:

$ hg debugindex dom/media/ipc/VideoDecoderManagerParent.cpp
   rev    offset  length   base linkrev nodeid       p1           p2
     0         0    1778      0  314066 1d7e56bcf729 000000000000 000000000000
     1      1778     278      0  314067 25dab5cdbf92 1d7e56bcf729 000000000000
     2      2056      36      0  314085 6bb39a23ebec 25dab5cdbf92 000000000000
     3      2092     554      0  315017 8b5665d02fc4 25dab5cdbf92 000000000000

4 entries. The "linkrev" column corresponds to the revision in the changelog this entry is for. We can look up those changesets:

  $ hg log -r '314066 or 314067 or 314085 or 315017' -T '{node} {desc|firstline}\n'
  f981edef8f81d2f897adc6e6170a9da9c64f9d18 Bug 1288618 - Part 13: Add VideoDecoderManager protocol. r=dvander
  f2da4a56dc4f1ab1a00a6fdef687cb97d6222609 Bug 1288618 - Part 14: Add PVideoDecoder protocol for individual decoders. r=cpearce,dvander
  dce59210b50d6e36a13270c475029d8d8332ee89 Backed out changeset f2da4a56dc4f (bug 1288618)
  2b4457a0428bfa161ac6a65d7453d0eb17a66dcb Bug 1302918 - Add PVideoBridge to share textures with the compositor. r=dvander,nical

This matches what hgweb and `hg log` say.

The reason there are only 4 entries in the file is because the backout and relanding resulted in the file same content. So a new storage entry wasn't needed. And, since `hg log` only traverses the file history, it is skipping changesets that effectively resulted in no new content.

I /thought/ `hg log -f` was supposed to traverse the changelog and look for extra changesets essentially doing "no new storage" changes. But I guess it doesn't. Let me ask some other Mercurial developers about this...

Comment 3

[Gregory Szorc [:gps]]

`hg log --removed <file>` will show the missing entries. I forgot about that flag.

--removed does make `hg log` much slower, which is why it isn't enabled by default.