filemerge: add support for partial conflict resolution by external tool
A common class of merge conflicts is in imports/#includes/etc. It's
relatively easy to write a tool that can resolve these conflicts,
perhaps by naively just unioning the statements and leaving any
cleanup to other tools to do later [1]. Such specialized tools cannot
generally resolve all conflicts in a file, of course. Let's therefore
call them "partial merge tools". Note that the internal simplemerge
algorithm is such a partial merge tool - one that only resolves
trivial "conflicts" where one side is unchanged or both sides change
in the same way.
One can also imagine having smarter language-aware partial tools that
merge the AST. It may be useful for such tools to interactively let
the user resolve any conflicts it can't resolve itself. However,
having the option of implementing it as a partial merge tool means
that the developer doesn't *need* to create a UI for it. Instead, the
user can resolve any remaining conflicts with their regular merge tool
(e.g. `:merge3` or `meld).
We don't currently have a way to let the user define such partial
merge tools. That's what this patch addresses. It lets the user
configure partial merge tools to run. Each tool can be configured to
run only on files matching certain patterns (e.g. "*.py"). The tool
takes three inputs (local, base, other) and resolves conflicts by
updating these in place. For example, let's say the inputs are these:
base:
```
import sys
def main():
print('Hello')
```
local:
```
import os
import sys
def main():
print('Hi')
```
other:
```
import re
import sys
def main():
print('Howdy')
```
A partial merge tool could now resolve the conflicting imports by
replacing the import statements in *all* files by the following
snippet, while leaving the remainder of the files unchanged.
```
import os
import re
import sys
```
As a result, simplemerge and any regular merge tool that runs after
the partial merge tool(s) will consider the imports to be
non-conflicting and will only present the conflict in `main()` to the
user.
Differential Revision: https://phab.mercurial-scm.org/D12356
$ hg init
$ echo a > a
$ hg commit -A -ma
adding a
$ echo b >> a
$ hg commit -mb
$ echo c >> a
$ hg commit -mc
$ hg up 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo d >> a
$ hg commit -md
created new head
$ hg up 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo e >> a
$ hg commit -me
created new head
$ hg up 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
Should fail because not at a head:
$ hg merge
abort: working directory not at a head revision
(use 'hg update' or merge with an explicit revision)
[255]
$ hg up
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
updated to "f25cbe84d8b3: e"
2 other heads for branch "default"
Should fail because > 2 heads:
$ HGMERGE=internal:other; export HGMERGE
$ hg merge
abort: branch 'default' has 3 heads - please merge with an explicit rev
(run 'hg heads .' to see heads, specify rev with -r)
[255]
Should succeed (we're specifying commands.merge.require-rev=True just to test
that it allows merge to succeed if we specify a revision):
$ hg merge 2 --config commands.merge.require-rev=True
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg id -Tjson
[
{
"bookmarks": [],
"branch": "default",
"dirty": "+",
"id": "f25cbe84d8b320e298e7703f18a25a3959518c23+2d95304fed5d89bc9d70b2a0d02f0d567469c3ab+",
"node": "ffffffffffffffffffffffffffffffffffffffff",
"parents": ["f25cbe84d8b320e298e7703f18a25a3959518c23", "2d95304fed5d89bc9d70b2a0d02f0d567469c3ab"],
"tags": ["tip"]
}
]
$ hg commit -mm1
Should fail because we didn't specify a revision (even though it would have
succeeded without this):
$ hg merge --config commands.merge.require-rev=True
abort: configuration requires specifying revision to merge with
[10]
Should succeed - 2 heads:
$ hg merge -P
changeset: 3:ea9ff125ff88
parent: 1:1846eede8b68
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: d
$ hg merge
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg commit -mm2
$ hg id -r 1 -Tjson
[
{
"bookmarks": [],
"branch": "default",
"id": "1846eede8b6886d8cc8a88c96a687b7fe8f3b9d1",
"node": "1846eede8b6886d8cc8a88c96a687b7fe8f3b9d1",
"tags": []
}
]
Should fail because we didn't specify a revision (even though it would have
failed without this due to being on tip, but this check comes first):
$ hg merge --config commands.merge.require-rev=True
abort: configuration requires specifying revision to merge with
[10]
Should fail because at tip:
$ hg merge
abort: nothing to merge
[255]
$ hg up 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
Should fail because there is only one head:
$ hg merge
abort: nothing to merge
(use 'hg update' instead)
[255]
$ hg up 3
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo f >> a
$ hg branch foobranch
marked working directory as branch foobranch
(branches are permanent and global, did you want a bookmark?)
$ hg commit -mf
Should fail because merge with other branch:
$ hg merge
abort: branch 'foobranch' has one head - please merge with an explicit rev
(run 'hg heads' to see all heads, specify rev with -r)
[255]
Test for issue2043: ensure that 'merge -P' shows ancestors of 6 that
are not ancestors of 7, regardless of where their common ancestors are.
Merge preview not affected by common ancestor:
$ hg up -q 7
$ hg merge -q -P 6
2:2d95304fed5d
4:f25cbe84d8b3
5:a431fabd6039
6:e88e33f3bf62
Test experimental destination revset
$ hg log -r '_destmerge()'
abort: branch 'foobranch' has one head - please merge with an explicit rev
(run 'hg heads' to see all heads, specify rev with -r)
[255]
(on a branch with a two heads)
$ hg up 5
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo f >> a
$ hg commit -mf
created new head
$ hg log -r '_destmerge()'
changeset: 6:e88e33f3bf62
parent: 5:a431fabd6039
parent: 3:ea9ff125ff88
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: m2
(from the other head)
$ hg log -r '_destmerge(e88e33f3bf62)'
changeset: 8:b613918999e2
tag: tip
parent: 5:a431fabd6039
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: f
(from unrelated branch)
$ hg log -r '_destmerge(foobranch)'
abort: branch 'foobranch' has one head - please merge with an explicit rev
(run 'hg heads' to see all heads, specify rev with -r)
[255]