view tests/test-import-unknown.t @ 18040:fe8caf28d580

strip: make query to get new bookmark target cheaper

The current query to get the new bookmark target for stripped revisions
involves multiple walks up the DAG, and is really expensive, taking over 2.5
seconds on a repository with over 400,000 changesets even if just one
changeset is being stripped.

A slightly simplified version of the current query is

max(heads(::<tostrip> - <tostrip>))

We make two observations here.

1. For any set s, max(heads(s)) == max(s). That is because revision numbers
   define a topological order, so that the element with the highest revision
   number in s will not have any children in s.

2. For any set s, max(::s - s) == max(parents(s) - s). In other words, the
   ancestor of s with the highest revision number not in s is a parent of one
   of the revs in s. Why? Because if it were an ancestor but not a parent of s,
   it would have a descendant that would be a parent of s. This descendant
   would have a higher revision number, leading to a contradiction.

Combining these two observations, we rewrite the revset query as

max(parents(<tostrip>) - <tostrip>)

The time complexity is now linear in the number of changesets being stripped.
For the above repository, the query now takes 0.1 seconds when one changeset
is stripped. This speeds up operations that use repair.strip, like the rebase
and strip commands.

  $ cat <<EOF >> $HGRCPATH
  > [extensions]
  > purge =
  > EOF

  $ hg init test
  $ cd test
  $ echo a > changed
  $ echo a > removed
  $ echo a > source
  $ hg ci -Am addfiles
  adding changed
  adding removed
  adding source
  $ echo a >> changed
  $ echo a > added
  $ hg add added
  $ hg rm removed
  $ hg cp source copied
  $ hg diff --git > ../unknown.diff

Test adding on top of an unknown file

  $ hg up -qC 0
  $ hg purge
  $ echo a > added
  $ hg import --no-commit ../unknown.diff
  applying ../unknown.diff
  file added already exists
  1 out of 1 hunks FAILED -- saving rejects to file added.rej
  abort: patch failed to apply
  [255]

Test modifying an unknown file

  $ hg revert -aq
  $ hg purge
  $ hg rm changed
  $ hg ci -m removechanged
  $ echo a > changed
  $ hg import --no-commit ../unknown.diff
  applying ../unknown.diff
  abort: cannot patch changed: file is not tracked
  [255]

Test removing an unknown file

  $ hg up -qC 0
  $ hg purge
  $ hg rm removed
  $ hg ci -m removeremoved
  created new head
  $ echo a > removed
  $ hg import --no-commit ../unknown.diff
  applying ../unknown.diff
  abort: cannot patch removed: file is not tracked
  [255]

Test copying onto an unknown file

  $ hg up -qC 0
  $ hg purge
  $ echo a > copied
  $ hg import --no-commit ../unknown.diff
  applying ../unknown.diff
  abort: cannot create copied: destination already exists
  [255]

  $ cd ..