subtree: push: allow specifying a local rev other than HEAD

'git subtree split' lets you specify a rev other than HEAD.  'git push'
lets you specify a mapping between a local thing and a remot ref.  So
smash those together, and have 'git subtree push' let you specify which
local thing to run split on and push the result of that split to the
remote ref.

Signed-off-by: Luke Shumaker <lukeshu@datawire.io>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/subtree/git-subtree.sh

@@ -27,7 +27,7 @@ git subtree add   --prefix=<prefix> <repository> <ref>
 git subtree merge --prefix=<prefix> <commit>
 git subtree split --prefix=<prefix> [<commit>]
 git subtree pull  --prefix=<prefix> <repository> <ref>
-git subtree push  --prefix=<prefix> <repository> <ref>
+git subtree push  --prefix=<prefix> <repository> <refspec>
 --
 h,help        show the help
 q             quiet
@@ -952,20 +952,30 @@ cmd_pull () {
 	cmd_merge FETCH_HEAD
 }
 
-# Usage: cmd_push REPOSITORY REMOTEREF
+# Usage: cmd_push REPOSITORY [+][LOCALREV:]REMOTEREF
 cmd_push () {
 	if test $# -ne 2
 	then
-		die "You must provide <repository> <ref>"
+		die "You must provide <repository> <refspec>"
 	fi
-	ensure_valid_ref_format "$2"
 	if test -e "$dir"
 	then
 		repository=$1
-		refspec=$2
+		refspec=${2#+}
+		remoteref=${refspec#*:}
+		if test "$remoteref" = "$refspec"
+		then
+			localrevname_presplit=HEAD
+		else
+			localrevname_presplit=${refspec%%:*}
+		fi
+		ensure_valid_ref_format "$remoteref"
+		localrev_presplit=$(git rev-parse -q --verify "$localrevname_presplit^{commit}") ||
+			die "'$localrevname_presplit' does not refer to a commit"
+
 		echo "git push using: " "$repository" "$refspec"
-		localrev=$(cmd_split) || die
-		git push "$repository" "$localrev":"refs/heads/$refspec"
+		localrev=$(cmd_split "$localrev_presplit") || die
+		git push "$repository" "$localrev":"refs/heads/$remoteref"
 	else
 		die "'$dir' must already exist. Try 'git subtree add'."
 	fi

contrib/subtree/git-subtree.txt

@@ -16,7 +16,7 @@ SYNOPSIS
 
 [verse]
 'git subtree' [<options>] -P <prefix> pull <repository> <remote-ref>
-'git subtree' [<options>] -P <prefix> push <repository> <remote-ref>
+'git subtree' [<options>] -P <prefix> push <repository> <refspec>
 
 DESCRIPTION
 -----------
@@ -115,11 +115,13 @@ pull <repository> <remote-ref>::
 	it fetches the given ref from the specified remote
 	repository.
 
-push <repository> <remote-ref>::
-	Does a 'split' using the <prefix> subtree of HEAD and then
-	does a 'git push' to push the result to the <repository> and
-	<remote-ref>.  This can be used to push your subtree to
-	different branches of the remote repository.
+push <repository> [+][<local-commit>:]<remote-ref>::
+	Does a 'split' using the <prefix> subtree of <local-commit>
+	and then does a 'git push' to push the result to the
+	<repository> and <remote-ref>.  This can be used to push your
+	subtree to different branches of the remote repository.  Just
+	as with 'split', if no <local-commit> is given, then HEAD is
+	used.  The optional leading '+' is ignored.
 
 OPTIONS FOR ALL COMMANDS
 ------------------------

contrib/subtree/t/t7900-subtree.sh

@@ -820,6 +820,28 @@ test_expect_success 'push "sub dir"/ with --branch for an incompatible branch' '
 	)
 '
 
+test_expect_success 'push "sub dir"/ with a local rev' '
+	subtree_test_create_repo "$test_count" &&
+	subtree_test_create_repo "$test_count/sub proj" &&
+	test_create_commit "$test_count" main1 &&
+	test_create_commit "$test_count/sub proj" sub1 &&
+	(
+		cd "$test_count" &&
+		git fetch ./"sub proj" HEAD &&
+		git subtree add --prefix="sub dir" FETCH_HEAD
+	) &&
+	test_create_commit "$test_count" "sub dir"/main-sub1 &&
+	test_create_commit "$test_count" "sub dir"/main-sub2 &&
+	(
+		cd "$test_count" &&
+		bad_tree=$(git rev-parse --verify HEAD:"sub dir") &&
+		good_tree=$(git rev-parse --verify HEAD^:"sub dir") &&
+		git subtree push --prefix="sub dir" --annotate="*" ./"sub proj" HEAD^:from-mainline &&
+		split_tree=$(git -C "sub proj" rev-parse --verify refs/heads/from-mainline:) &&
+		test "$split_tree" = "$good_tree"
+	)
+'
+
 #
 # Validity checking
 #