bundle: introduce a --exact option

I have been wanting this options for a long time.

mercurial/commands.py

@@ -1484,6 +1484,13 b' def branches(ui, repo, active=False, clo'
 @command(
     b'bundle',
     [
+
+        (
+            b'',
+            b'exact',
+            None,
+            _(b'compute the base from the revision specified'),
+        ),
         (
             b'f',
             b'force',
@@ -1553,6 +1560,7 b' def bundle(ui, repo, fname, *dests, **op'
     Returns 0 on success, 1 if no changes found.
     """
     opts = pycompat.byteskwargs(opts)
+
     revs = None
     if b'rev' in opts:
         revstrings = opts[b'rev']
@@ -1586,7 +1594,19 b' def bundle(ui, repo, fname, *dests, **op'
             )
         if opts.get(b'base'):
             ui.warn(_(b"ignoring --base because --all was specified\n"))
+        if opts.get(b'exact'):
+            ui.warn(_(b"ignoring --exact because --all was specified\n"))
         base = [nullrev]
+    elif opts.get(b'exact'):
+        if dests:
+            raise error.InputError(
+                _(b"--exact is incompatible with specifying destinations")
+            )
+        if opts.get(b'base'):
+            ui.warn(_(b"ignoring --base because --exact was specified\n"))
+        base = repo.revs(b'parents(%ld) - %ld', revs, revs)
+        if not base:
+            base = [nullrev]
     else:
         base = logcmdutil.revrange(repo, opts.get(b'base'))
     if cgversion not in changegroup.supportedoutgoingversions(repo):

tests/test-bundle.t

@@ -718,7 +718,7 b' Unbundle incremental bundles into fresh '
   $ hg init empty
   $ hg -R test bundle --base null -r 0 ../0.hg
   1 changesets found
-  $ hg -R test bundle --base 0    -r 1 ../1.hg
+  $ hg -R test bundle --exact -r 1 ../1.hg
   1 changesets found
   $ hg -R empty unbundle -u ../0.hg ../1.hg
   adding changesets

tests/test-completion.t

@@ -261,7 +261,7 b' Show all commands + options'
   bookmarks: force, rev, delete, rename, inactive, list, template
   branch: force, clean, rev
   branches: active, closed, rev, template
-  bundle: force, rev, branch, base, all, type, ssh, remotecmd, insecure
+  bundle: exact, force, rev, branch, base, all, type, ssh, remotecmd, insecure
   cat: output, rev, decode, include, exclude, template
   clone: noupdate, updaterev, rev, branch, pull, uncompressed, stream, ssh, remotecmd, insecure
   commit: addremove, close-branch, amend, secret, edit, force-close-branch, interactive, include, exclude, message, logfile, date, user, subrepos