comparison tests/test-fix.t @ 40570:ad71c792a8d8

fix: add extra field to fixed revisions to avoid creating obsolescence cycles

The extra field prevents sequential invocations of fix from producing the same
hash twice. Previously, this could cause problems because it would create an
obsolescence cycle instead of the expected new successor.

This change also adds an explicit check for whether a new revision should be
committed. Until now, the code relied on memctx.commit() to quietly do nothing
if the node already exists. Because of the new extra field, this no longer
covers the case where we don't want to replace an unchanged node.

Differential Revision: https://phab.mercurial-scm.org/D5245

40569:19e1c26213f1

  6
  7
  8

  $ cd ..

40570:ad71c792a8d8

  6
  7
  8

  $ cd ..

It's possible for repeated applications of a fixer tool to create cycles in the
generated content of a file. For example, two users with different versions of
a code formatter might fight over the formatting when they run hg fix. In the
absence of other changes, this means we could produce commits with the same
hash in subsequent runs of hg fix. This is a problem unless we support
obsolescence cycles well. We avoid this by adding an extra field to the
successor which forces it to have a new hash. That's why this test creates
three revisions instead of two.

  $ hg init cyclictool
  $ cd cyclictool

  $ cat >> .hg/hgrc <<EOF
  > [fix]
  > swapletters:command = tr ab ba
  > swapletters:pattern = foo
  > EOF

  $ echo ab > foo
  $ hg commit -Aqm foo

  $ hg fix -r 0
  $ hg fix -r 1

  $ hg cat -r 0 foo --hidden
  ab
  $ hg cat -r 1 foo --hidden
  ba
  $ hg cat -r 2 foo
  ab

  $ cd ..