record: check that we are not committing a merge before patch selection

It might sound like a good idea to use record to filter changes when merging.
If someone attemps this, it's better to tell her "no" right ahead, before the
patch generation/line selection, so she does not spend time doing it just to
receive a red light after that (sometimes rather long) process.

hgext/record.py

@@ -379,7 +379,9 def record(ui, repo, *pats, **opts):
       a - record all changes to all remaining files
       q - quit, recording no changes
 
-      ? - display help'''
+      ? - display help
+
+    This command is not available when committing a merge.'''
 
     dorecord(ui, repo, commands.commit, *pats, **opts)
 
@@ -422,6 +424,11 def dorecord(ui, repo, commitfunc, *pats
         left in place, so the user can continue his work.
         """
 
+        merge = len(repo[None].parents()) > 1
+        if merge:
+            raise util.Abort(_('cannot partially commit a merge '
+                               '(use hg commit instead)'))
+
         changes = repo.status(match=match)[:3]
         diffopts = mdiff.diffopts(git=True, nodates=True)
         chunks = patch.diff(repo, changes=changes, opts=diffopts)

tests/test-record

@@ -297,9 +297,20 y
 EOF
 echo; hg tip --config diff.git=True -p
 
+cd ..
+
+echo % abort early when a merge is in progress
+hg up 4
+touch iwillmergethat
+hg add iwillmergethat
+hg branch thatbranch
+hg ci -m'new head'
+hg up default
+hg merge thatbranch
+echo; hg record -m'will abort'
+hg up -C
 
 echo % with win32ext
-cd ..
 echo '[extensions]' >> .hg/hgrc
 echo 'win32text = ' >> .hg/hgrc
 echo '[decode]' >> .hg/hgrc

tests/test-record.out

@@ -24,6 +24,8 interactively select changes to commit
 
       ? - display help
 
+    This command is not available when committing a merge.
+
 options:
 
  -A --addremove     mark new/missing files as added/removed before committing
@@ -569,6 +571,16 new mode 100644
  b
 +c
 
+% abort early when a merge is in progress
+1 files updated, 0 files merged, 5 files removed, 0 files unresolved
+marked working directory as branch thatbranch
+created new head
+5 files updated, 0 files merged, 2 files removed, 0 files unresolved
+1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+(branch merge, don't forget to commit)
+
+abort: cannot partially commit a merge (use hg commit instead)
+0 files updated, 0 files merged, 1 files removed, 0 files unresolved
 % with win32ext
 diff --git a/subdir/f1 b/subdir/f1
 1 hunks, 1 lines changed
@@ -578,8 +590,9 examine changes to 'subdir/f1'? [Ynsfdaq
  c
 +d
 record this change to 'subdir/f1'? [Ynsfdaq?] 
-changeset:   25:5bacc1f6e9cf
+changeset:   26:5bacc1f6e9cf
 tag:         tip
+parent:      24:1460f6e47966
 user:        test
 date:        Thu Jan 01 00:00:23 1970 +0000
 summary:     w1