merge: add commands.merge.require-rev to require an argument to hg merge

This is related to commands.rebase.requiredest, commands.update.requiredest, and
commands.push.require-revs. Since it isn't really a "destination", I went with
require-rev to be similar to push's require-revs.

Differential Revision: https://phab.mercurial-scm.org/D7620

mercurial/commands.py

@@ -4888,6 +4888,13 b' def merge(ui, repo, node=None, **opts):'
         node = scmutil.revsingle(repo, node).node()
 
     if not node and not abort:
+        if ui.configbool(b'commands', b'merge.require-rev'):
+            raise error.Abort(
+                _(
+                    b'configuration requires specifying revision to merge '
+                    b'with'
+                )
+            )
         node = repo[destutil.destmerge(repo)].node()
 
     if opts.get(b'preview'):

mercurial/configitems.py

@@ -228,6 +228,9 b' coreconfigitem('
     b'commands', b'grep.all-files', default=False, experimental=True,
 )
 coreconfigitem(
+    b'commands', b'merge.require-rev', default=False,
+)
+coreconfigitem(
     b'commands', b'push.require-revs', default=False,
 )
 coreconfigitem(

mercurial/helptext/config.txt

@@ -442,6 +442,12 b' effect and style see :hg:`help color`.'
     Show status of files in the working directory after successful commit.
     (default: False)
 
+``merge.require-rev``
+    Require that the revision to merge the current commit with be specified on
+    the command line. If this is enabled and a revision is not specified, the
+    command aborts.
+    (default: False)
+
 ``push.require-revs``
     Require revisions to push be specified using one or more mechanisms such as
     specifying them positionally on the command line, using ``-r``, ``-b``,

tests/test-merge-default.t

@@ -44,9 +44,10 b' Should fail because > 2 heads:'
   (run 'hg heads .' to see heads, specify rev with -r)
   [255]
 
-Should succeed:
+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
+  $ 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
@@ -63,6 +64,13 b' Should succeed:'
   ]
   $ 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
+  [255]
+
 Should succeed - 2 heads:
 
   $ hg merge -P
@@ -88,6 +96,13 b' Should succeed - 2 heads:'
    }
   ]
 
+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
+  [255]
+
 Should fail because at tip:
 
   $ hg merge

tests/test-merge-tools.t

@@ -4,6 +4,8 b' test merge-tools configuration - mostly '
   $ cat >> $HGRCPATH << EOF
   > [ui]
   > merge=
+  > [commands]
+  > merge.require-rev=True
   > EOF
   $ hg init repo
   $ cd repo
@@ -1908,6 +1910,7 b' checked strictly.'
   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]
+(Testing that commands.merge.require-rev doesn't break --abort)
   $ hg merge --abort -q
 
 (for ui.merge, ignored unintentionally)