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annotate: increase refcount of each revisions correctly (issue3841)

Before this patch, refcount (managed in "needed") of parents of each
revisions in "visit" is increased, only when parent is not annotated
yet (examined by "p not in hist").

But this causes less refcount of the revision like "A" in the tree
below ("A" is assumed as the second parent of "C"):

    A --- B --- C
      \       /
       \-----/

Steps of annotation for "C" in this case are shown below:

  1. for "C"
    1.1 increase refcount of "B"
    1.2 increase refcount of "A" (=> 1)
    1.3 defer annotation for "C"

  2. for "A"
    2.1 annotate for "A" (=> put result into "hist[A]")
    2.2 clear "pcache[A]" ("pcache[A] = []")

  3. for "B"
    3.1 not increase refcount of "A", because "A not in hist" is False
    3.2 annotate for "B"
    3.3 decrease refcount of "A" (=> 0)
    3.4 delete "hist[A]", even though "A" is still needed by "C"
    3.5 clear "pcache[B]"

  4. for "C", again
    4.1 not increase refcount of "B", because "B not in hist" is False
    4.2 increase refcount of "A" (=> 1)
    4.3 defer annotation for "C"

  5. for "A", again
    5.1 annotate for "A" (=> put result into "hist[A]", again)
    5.2 clear "pcache[A]"

  6. for "C", once again
    6.1 not increase refcount of "B", because "B not in hist" is False
    6.2 not increase refcount of "A", because "A not in hist" is False
    6.3 annotate for "C"
    6.4 decrease refcount of "A", and delete "hist[A]"
    6.5 decrease refcount of "B", and delete "hist[B]"
    6.6 clear "pcache[C]"

At step (5.1), annotation for "A" mis-recognizes that all lines are
created at "A", because "pcache[A]" already cleared at step (2.2)
prevents from scanning ancestors of "A".

So, annotation for "C" or its descendants loses information about "A"
or its ancestors.

The root cause of this problem is that refcount of "A" is decreased at
step (3.3), even though it isn't increased at step (3.1).

To increase refcount correctly, this patch increases refcount of each
parents of each revisions:

  - regardless of "p not in hist" or not, and
  - only once for each revisions in "visit" (by "not pcached")

In fact, this problem should occur only on legacy repositories in
which a filelog includes the merging between the revision and its
ancestor (as the second parent), because:

  - tree is scanned in depth-first

    without such merging, revisions in "visit" refer different
    revisions as parent each other

  - recent Mercurial doesn't allow such merging

    changelog and manifest can include such merging someway, but
    filelogs can't, because "localrepository._filecommit()" converts
    such merging request to linear history.

This patch tests merging cases below: these cases are from filelog of
"mercurial/commands.py" in the repository of Mercurial itself.

  - both parents are same

        10 --- 11 --- 12
                  \_/

        filelogrev: changesetid:
          10          00ea3613f82c
          11          fc4a6e5b5812
          12          4f802588cdfb

  - the second parent is also ancestor of the first one

        37 --- 38 --- 39 --- 40
                  \________/

        filelogrev: changesetid:
          37          f8d56da6ac8f
          38          38919e1c254d
          39          d3400605d246
          40          f06a4a3b86a7

Mercurial
=========

Mercurial is a fast, easy to use, distributed revision control tool
for software developers.

Basic install:

 $ make            # see install targets
 $ make install    # do a system-wide install
 $ hg debuginstall # sanity-check setup
 $ hg              # see help

Running without installing:

 $ make local      # build for inplace usage
 $ ./hg --version  # should show the latest version

See http://mercurial.selenic.com/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.