tests/test-diff-reverse.t

repoview: discard filtered changelog if index isn't shared with unfiltered

Before this patch, revisions rollbacked at failure of previous
transaction might be visible at subsequent operations unintentionally,
if repoview object is reused even after failure of transaction:
e.g. command server and HTTP server are typical cases.

'repoview' uses the tuple of values below of unfiltered changelog as
"the key" to examine validity of filtered changelog cache.

     - length
     - tip node
     - filtered revisions (as hashed value)
     - '_delayed' field

'repoview' compares between "the key" of unfiltered changelog at
previous caching and now, and reuses filtered changelog cache if no
change is detected.

But this comparison indicates only that there is no change between
unfiltered 'repo.changelog' at last caching and now, but not that
filtered changelog cache is valid for current unfiltered one.

'repoview' uses "shallow copy" of unfiltered changelog to create
filtered changelog cache. In this case, 'index' buffer of unfiltered
changelog is also referred by filtered changelog.

At failure of transaction, unfiltered changelog itself is invalidated
(= un-referred) on the 'repo' side (see 0a7610758c42 also). But
'index' of it still contains revisions to be rollbacked at this
failure, and is referred by filtered changelog.

Therefore, even if there is no change between unfiltered
'repo.changelog' at last caching and now, steps below makes rollbacked
revisions visible via filtered changelog unintentionally.

  1. instantiate unfiltered changelog as 'repo.changelog'
     (call it CL1)

  2. make filtered (= shallow copy of) CL1
     (call it FCL1)

  3. cache FCL1 with "the key" of CL1

  4. revisions are appended to 'index', which is shared by CL1 and FCL1

  5. invalidate 'repo.changelog' (= CL1) at failure of transaction

  6. instantiate 'repo.changelog' again at next operation
     (call it CL2)

     CL2 doesn't have revisions added at (4), because it is
     instantiated from '00changelog.i', which isn't changed while
     failed transaction.

  7. compare between "the key" of CL1 and CL2

  8. FCL1 cached at (3) is reused, because comparison at (7) doesn't
     detect change between CL1 at (1) and CL2

  9. revisions rollbacked at (5) are visible via FCL1 unintentionally,
     because FCL1 still refers 'index' changed at (4)

The root cause of this issue is that there is no examination about
validity of filtered changelog cache against current unfiltered one.

This patch discards filtered changelog cache, if its 'index' object
isn't shared with unfiltered one.

BTW, at the time of this patch, redundant truncation of
'00changelog.i' at failure of transaction (see 0a7610758c42 for
detail) often prevents "hg serve" from making already rollbacked
revisions visible, because updating timestamps of '00changelog.i' by
truncation makes "hg serve" discard old repoview object with invalid
filtered changelog cache.

This is reason why this issue is overlooked before this patch, even
though test-bundle2-exchange.t has tests in similar situation: failure
of "hg push" via HTTP by pretxnclose hook on server side doesn't
prevent subsequent commands from looking up outgoing revisions
correctly.

But timestamp on the filesystem doesn't have enough resolution for
recent computation power, and it can't be assumed that this avoidance
always works as expected.

Therefore, without this patch, this issue might appear occasionally.

  $ hg init

  $ cat > a <<EOF
  > a
  > b
  > c
  > EOF
  $ hg ci -Am adda
  adding a

  $ cat > a <<EOF
  > d
  > e
  > f
  > EOF
  $ hg ci -m moda

  $ hg diff --reverse -r0 -r1
  diff -r 2855cdcfcbb7 -r 8e1805a3cf6e a
  --- a/a	Thu Jan 01 00:00:00 1970 +0000
  +++ b/a	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,3 +1,3 @@
  -d
  -e
  -f
  +a
  +b
  +c

  $ cat >> a <<EOF
  > g
  > h
  > EOF
  $ hg diff --reverse --nodates
  diff -r 2855cdcfcbb7 a
  --- a/a
  +++ b/a
  @@ -1,5 +1,3 @@
   d
   e
   f
  -g
  -h

should show removed file 'a' as being added
  $ hg revert a
  $ hg rm a
  $ hg diff --reverse --nodates a
  diff -r 2855cdcfcbb7 a
  --- /dev/null
  +++ b/a
  @@ -0,0 +1,3 @@
  +d
  +e
  +f

should show added file 'b' as being removed
  $ echo b >> b
  $ hg add b
  $ hg diff --reverse --nodates b
  diff -r 2855cdcfcbb7 b
  --- a/b
  +++ /dev/null
  @@ -1,1 +0,0 @@
  -b