commit: abort on merge with missing files

Here is a script illustrating the previous behaviour:

The merge brings a new file 'b' from remote
  $ hg merge 1 --debug
    searching for copies back to rev 1
    unmatched files in other:
     b
  resolving manifests
   overwrite: False, partial: False
   ancestor: 07f494440405, local: 540395c44225+, remote: 102a90ea7b4a
   b: remote created -> g
  updating: b 1/1 files (100.00%)
  getting b
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

Delete but do not remove b
  $ rm b
  $ hg st
  ! b

The commit succeeds
  $ hg commit -m merge
  $ hg parents --template "{rev} {desc|firstline} files: {files}\n"
  3 merge files:
  $ hg st
  ! b

b changes were ignored, but even b existence was ignored
  $ hg manifest
  a

This happens because localrepo.commitctx() checks the input ctx.files(), which
is empty for workingctx.files() only returns added, modified or removed
entries, and bypass files/manifest updates completely. So the committed
revision manifest is the same as its first parent one, not containing the 'b'
file.

This patch forces the commit to abort in presence of a merge and missing files.
test-merge4.t is modified accordingly as it was introduced to check hg was not
just terminating with a traceback (5e9e8b8d2629).

mercurial/localrepo.py

@@ -1147,6 +1147,9 b' class localrepository(repo.repository):'
                 and wctx.branch() == wctx.p1().branch()):
                 return None
 
+            if merge and changes[3]:
+                raise util.Abort(_("cannot commit merge with missing files"))
+
             ms = mergemod.mergestate(self)
             for f in changes[0]:
                 if f in ms and ms[f] == 'u':

tests/test-merge4.t

@@ -16,5 +16,10 b''
   (branch merge, don't forget to commit)
   $ rm b
   $ echo This is file c22 > c
+
+Test hg behaves when committing with a missing file added by a merge
+
   $ hg commit -m "commit #3"
+  abort: cannot commit merge with missing files
+  [255]