rebase: rewrite core algorithm (issue5578) (issue5630)...
rebase: rewrite core algorithm (issue5578) (issue5630)
"defineparents" is the core algorithm of rebase. The old code has too many
tech debts (like outdated comments, confusing assertions, etc) and is very
error-prone to be improved. This patch rewrites "defineparents" to make the
code easier to reason about, and solve a bunch of issues, including:
- Assertion error: no base found (demonstrated by D212, issue5578)
- Asymmetric result (demonstrated by D211, "F with one parent")
- Wrong new parent (demonstrated by D262, "C':A'A'")
- "revlog index out of range" (demonstrated by D262, issue5630)
- "nothing to merge" (demonstrated by D262)
As a side effect, merge base decision has been made more solid - rebase now
prints out explicitly what could go wrong when it cannot find a unique
suitable merge base.
.. fix:: Issue 5578, Issue 5630
Core rebase algorithm has been rewritten to be more robust.
Differential Revision:
https://phab.mercurial-scm.org/D21