revset: add a revset for parents in merge state

revset: add a revset for parents in merge state

This may be particularly useful soon, when I'm going to change how `hg
rebase` sets its parents during conflict resolution.

Differential Revision: https://phab.mercurial-scm.org/D8041

--- a/mercurial/revset.py	Fri Jan 10 17:46:10 2020 -0800
+++ b/mercurial/revset.py	Wed Jan 29 11:30:35 2020 -0800
@@ -769,6 +769,38 @@
     return subset
 
 
+@predicate(b'conflictlocal()', safe=True)
+def conflictlocal(repo, subset, x):
+    """The local side of the merge, if currently in an unresolved merge.
+
+    "merge" here includes merge conflicts from e.g. 'hg rebase' or 'hg graft'.
+    """
+    getargs(x, 0, 0, _(b"conflictlocal takes no arguments"))
+    from . import merge
+
+    mergestate = merge.mergestate.read(repo)
+    if mergestate.active() and repo.changelog.hasnode(mergestate.local):
+        return subset & {repo.changelog.rev(mergestate.local)}
+
+    return baseset()
+
+
+@predicate(b'conflictother()', safe=True)
+def conflictother(repo, subset, x):
+    """The other side of the merge, if currently in an unresolved merge.
+
+    "merge" here includes merge conflicts from e.g. 'hg rebase' or 'hg graft'.
+    """
+    getargs(x, 0, 0, _(b"conflictother takes no arguments"))
+    from . import merge
+
+    mergestate = merge.mergestate.read(repo)
+    if mergestate.active() and repo.changelog.hasnode(mergestate.other):
+        return subset & {repo.changelog.rev(mergestate.other)}
+
+    return baseset()
+
+
 @predicate(b'contains(pattern)', weight=100)
 def contains(repo, subset, x):
     """The revision's manifest contains a file matching pattern (but might not

--- a/relnotes/next	Fri Jan 10 17:46:10 2020 -0800
+++ b/relnotes/next	Wed Jan 29 11:30:35 2020 -0800
@@ -3,6 +3,11 @@
  * `hg purge`/`hg clean` can now delete ignored files instead of
    untracked files, with the new -i flag.
 
+ * New `conflictlocal()` and `conflictother()` revsets returns the
+   commits that are being merged, when there are conflicts. Also works
+   for conflicts caused by e.g. `hg graft`.
+
+
 == New Experimental Features ==
 
 

--- a/tests/test-merge4.t	Fri Jan 10 17:46:10 2020 -0800
+++ b/tests/test-merge4.t	Wed Jan 29 11:30:35 2020 -0800
@@ -23,3 +23,37 @@
   abort: cannot commit merge with missing files
   [255]
 
+
+Test conflict*() revsets
+
+# Bad usage
+  $ hg log -r 'conflictlocal(foo)'
+  hg: parse error: conflictlocal takes no arguments
+  [255]
+  $ hg log -r 'conflictother(foo)'
+  hg: parse error: conflictother takes no arguments
+  [255]
+  $ hg co -C .
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+# No merge parents when not merging
+  $ hg log -r 'conflictlocal() + conflictother()'
+# No merge parents when there is no conflict
+  $ hg merge 1
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ hg log -r 'conflictlocal() + conflictother()'
+  $ hg co -C .
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ echo conflict > b
+  $ hg ci -Aqm 'conflicting change to b'
+  $ hg merge 1
+  merging b
+  warning: conflicts while merging b! (edit, then use 'hg resolve --mark')
+  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
+  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
+  [1]
+# Shows merge parents when there is a conflict
+  $ hg log -r 'conflictlocal()' -T '{rev} {desc}\n'
+  3 conflicting change to b
+  $ hg log -r 'conflictother()' -T '{rev} {desc}\n'
+  1 commit #1