tests/test-narrow-trackedcmd.t

revlog: automatically read from opened file handles

The revlog reading code commonly opens a new file handle for
reading on demand. There is support for passing a file handle
to revlog.revision(). But it is marked as an internal argument.

When revlogs are written, we write() data as it is available. But
we don't flush() data until all revisions are written.

Putting these two traits together, it is possible for an in-process
revlog reader during active writes to trigger the opening of a new
file handle on a file with unflushed writes. The reader won't have
access to all "available" revlog data (as it hasn't been flushed).
And with the introduction of the previous patch, this can lead to
the revlog raising an error due to a partial read.

I witnessed this behavior when applying changegroup data (via
`hg pull`) before issue6006 was fixed via different means. Having
this and the previous patch in play would have helped cause errors
earlier rather than manifesting as hash verification failures.

While this has been a long-standing issue, I believe the relatively
new delta computation code has tickled it into being more common.
This is because the new delta computation code will compute deltas
in more scenarios. This can lead to revlog reading. While the delta
computation code is probably supposed to reuse file handles, it
appears it isn't doing so in all circumstances.

But the issue runs deeper than that. Theoretically, any code can
access revision data during revlog writes. It appears we were just
getting lucky that it wasn't. (The "add revision callback" passed to
addgroup() provides an avenue to do this.)

If I changed the revlog's behavior to not cache the full revision
text or to clear caches after revision insertion during addgroup(),
I was able to produce crashes 100% of the time when writing changelog
revisions. This is because changelog's add revision callback attempts
to resolve the revision data to access the changed files list. And
without the revision's fulltext being cached, we performed a revlog
read, which required opening a new file handle. This attempted to read
unflushed data, leading to a partial read and a crash.

This commit teaches the revlog to store the file handles used for
writing multiple revisions during addgroup(). It also teaches the
code for resolving a file handle when reading to use these handles,
if available. This ensures that *any* reads (regardless of their
source) use the active writing file handles, if available. These
file handles have access to the unflushed data because they wrote it.
This allows reads to complete without issue.

Differential Revision: https://phab.mercurial-scm.org/D5267

#testcases flat tree
  $ . "$TESTDIR/narrow-library.sh"

#if tree
  $ cat << EOF >> $HGRCPATH
  > [experimental]
  > treemanifest = 1
  > EOF
#endif

  $ hg init master
  $ cd master
  $ cat >> .hg/hgrc <<EOF
  > [narrow]
  > serveellipses=True
  > EOF

  $ mkdir inside
  $ echo 'inside' > inside/f
  $ hg add inside/f
  $ hg commit -m 'add inside'

  $ mkdir widest
  $ echo 'widest' > widest/f
  $ hg add widest/f
  $ hg commit -m 'add widest'

  $ mkdir outside
  $ echo 'outside' > outside/f
  $ hg add outside/f
  $ hg commit -m 'add outside'

  $ cd ..

narrow clone the inside file

  $ hg clone --narrow ssh://user@dummy/master narrow --include inside
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 1 changes to 1 files
  new changesets *:* (glob)
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd narrow
  $ hg tracked
  I path:inside
  $ ls
  inside
  $ cat inside/f
  inside
  $ cd ..

add more upstream files which we will include in a wider narrow spec

  $ cd master

  $ mkdir wider
  $ echo 'wider' > wider/f
  $ hg add wider/f
  $ echo 'widest v2' > widest/f
  $ hg commit -m 'add wider, update widest'

  $ echo 'widest v3' > widest/f
  $ hg commit -m 'update widest v3'

  $ echo 'inside v2' > inside/f
  $ hg commit -m 'update inside'

  $ mkdir outside2
  $ echo 'outside2' > outside2/f
  $ hg add outside2/f
  $ hg commit -m 'add outside2'

  $ echo 'widest v4' > widest/f
  $ hg commit -m 'update widest v4'

  $ hg log -T "{if(ellipsis, '...')}{rev}: {desc}\n"
  7: update widest v4
  6: add outside2
  5: update inside
  4: update widest v3
  3: add wider, update widest
  2: add outside
  1: add widest
  0: add inside

  $ cd ..

Testing the --import-rules flag of `hg tracked` command

  $ cd narrow
  $ hg tracked --import-rules
  hg tracked: option --import-rules requires argument
  hg tracked [OPTIONS]... [REMOTE]
  
  show or change the current narrowspec
  
  options ([+] can be repeated):
  
      --addinclude VALUE [+]       new paths to include
      --removeinclude VALUE [+]    old paths to no longer include
      --addexclude VALUE [+]       new paths to exclude
      --import-rules VALUE         import narrowspecs from a file
      --removeexclude VALUE [+]    old paths to no longer exclude
      --clear                      whether to replace the existing narrowspec
      --force-delete-local-changes forces deletion of local changes when
                                   narrowing
   -e --ssh CMD                    specify ssh command to use
      --remotecmd CMD              specify hg command to run on the remote side
      --insecure                   do not verify server certificate (ignoring
                                   web.cacerts config)
  
  (use 'hg tracked -h' to show more help)
  [255]
  $ hg tracked --import-rules doesnotexist
  abort: cannot read narrowspecs from '$TESTTMP/narrow/doesnotexist': $ENOENT$
  [255]

  $ cat > specs <<EOF
  > %include foo
  > [include]
  > path:widest/
  > [exclude]
  > path:inside/
  > EOF

  $ hg tracked --import-rules specs
  abort: including other spec files using '%include' is not supported in narrowspec
  [255]

  $ cat > specs <<EOF
  > [include]
  > outisde
  > [exclude]
  > inside
  > EOF

  $ hg tracked --import-rules specs
  comparing with ssh://user@dummy/master
  searching for changes
  looking for local changes to affected paths
  deleting data/inside/f.i
  deleting meta/inside/00manifest.i (tree !)
  no changes found
  saved backup bundle to $TESTTMP/narrow/.hg/strip-backup/*-widen.hg (glob)
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 0 changes to 0 files
  new changesets *:* (glob)
  $ hg tracked
  I path:outisde
  X path:inside

Testing the --import-rules flag with --addinclude and --addexclude

  $ cat > specs <<EOF
  > [include]
  > widest
  > EOF

  $ hg tracked --import-rules specs --addinclude 'wider/'
  comparing with ssh://user@dummy/master
  searching for changes
  no changes found
  saved backup bundle to $TESTTMP/narrow/.hg/strip-backup/*-widen.hg (glob)
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 1 changes to 1 files
  new changesets *:* (glob)
  $ hg tracked
  I path:outisde
  I path:wider
  I path:widest
  X path:inside

  $ cat > specs <<EOF
  > [exclude]
  > outside2
  > EOF

  $ hg tracked --import-rules specs --addexclude 'widest'
  comparing with ssh://user@dummy/master
  searching for changes
  looking for local changes to affected paths
  deleting data/widest/f.i
  deleting meta/widest/00manifest.i (tree !)
  $ hg tracked
  I path:outisde
  I path:wider
  X path:inside
  X path:outside2
  X path:widest

  $ hg tracked --import-rules specs --clear
  The --clear option is not yet supported.
  [1]

Testing with passing a out of wdir file

  $ cat > ../nspecs <<EOF
  > [include]
  > widest
  > EOF

  $ hg tracked --import-rules ../nspecs
  comparing with ssh://user@dummy/master
  searching for changes
  no changes found
  saved backup bundle to $TESTTMP/narrow/.hg/strip-backup/*-widen.hg (glob)
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 0 changes to 0 files
  new changesets *:* (glob)