[PATCHv2 1/2] merge: Add '--continue' option as a synonym for 'git commit'

[Chris Packham <judge.packham@gmail.com>]

Teach 'git merge' the --continue option which allows 'continuing' a
merge by completing it. The traditional way of completing a merge after
resolving conflicts is to use 'git commit'. Now with commands like 'git
rebase' and 'git cherry-pick' having a '--continue' option adding such
an option to 'git merge' presents a consistent UI.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
---

Notes:
    Changes in v2:
    - add --continue to builtin_merge_usage
    - verify that no other arguments are present when --continue is used.
    - add basic test

 Documentation/git-merge.txt | 13 ++++++++++++-
 builtin/merge.c             | 22 +++++++++++++++++++++-
 t/t7600-merge.sh            |  8 ++++++++
 3 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/Documentation/git-merge.txt b/Documentation/git-merge.txt
index b758d5556..765b0f26e 100644
--- a/Documentation/git-merge.txt
+++ b/Documentation/git-merge.txt
@@ -15,6 +15,7 @@ SYNOPSIS
 	[--[no-]rerere-autoupdate] [-m <msg>] [<commit>...]
 'git merge' <msg> HEAD <commit>...
 'git merge' --abort
+'git merge' --continue
 
 DESCRIPTION
 -----------
@@ -61,6 +62,9 @@ reconstruct the original (pre-merge) changes. Therefore:
 discouraged: while possible, it may leave you in a state that is hard to
 back out of in the case of a conflict.
 
+The fourth syntax ("`git merge --continue`") can only be run after the
+merge has resulted in conflicts. 'git merge --continue' will take the
+currently staged changes and complete the merge.
 
 OPTIONS
 -------
@@ -99,6 +103,12 @@ commit or stash your changes before running 'git merge'.
 'git merge --abort' is equivalent to 'git reset --merge' when
 `MERGE_HEAD` is present.
 
+--continue::
+	Take the currently staged changes and complete the merge.
++
+'git merge --continue' is equivalent to 'git commit' when
+`MERGE_HEAD` is present.
+
 <commit>...::
 	Commits, usually other branch heads, to merge into our branch.
 	Specifying more than one commit will create a merge with
@@ -277,7 +287,8 @@ After seeing a conflict, you can do two things:
 
  * Resolve the conflicts.  Git will mark the conflicts in
    the working tree.  Edit the files into shape and
-   'git add' them to the index.  Use 'git commit' to seal the deal.
+   'git add' them to the index.  Use 'git merge --continue' to seal the
+   deal.
 
 You can work through the conflict with a number of tools:
 
diff --git a/builtin/merge.c b/builtin/merge.c
index b65eeaa87..379685223 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -46,6 +46,7 @@ static const char * const builtin_merge_usage[] = {
 	N_("git merge [<options>] [<commit>...]"),
 	N_("git merge [<options>] <msg> HEAD <commit>"),
 	N_("git merge --abort"),
+	N_("git merge --continue"),
 	NULL
 };
 
@@ -65,6 +66,7 @@ static int option_renormalize;
 static int verbosity;
 static int allow_rerere_auto;
 static int abort_current_merge;
+static int continue_current_merge;
 static int allow_unrelated_histories;
 static int show_progress = -1;
 static int default_to_upstream = 1;
@@ -223,6 +225,8 @@ static struct option builtin_merge_options[] = {
 	OPT__VERBOSITY(&verbosity),
 	OPT_BOOL(0, "abort", &abort_current_merge,
 		N_("abort the current in-progress merge")),
+	OPT_BOOL(0, "continue", &continue_current_merge,
+		N_("continue the current in-progress merge")),
 	OPT_BOOL(0, "allow-unrelated-histories", &allow_unrelated_histories,
 		 N_("allow merging unrelated histories")),
 	OPT_SET_INT(0, "progress", &show_progress, N_("force progress reporting"), 1),
@@ -739,7 +743,7 @@ static void abort_commit(struct commit_list *remoteheads, const char *err_msg)
 	if (err_msg)
 		error("%s", err_msg);
 	fprintf(stderr,
-		_("Not committing merge; use 'git commit' to complete the merge.\n"));
+		_("Not committing merge; use 'git merge --continue' to complete the merge.\n"));
 	write_merge_state(remoteheads);
 	exit(1);
 }
@@ -1166,6 +1170,22 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		goto done;
 	}
 
+	if (continue_current_merge) {
+		int nargc = 1;
+		const char *nargv[] = {"commit", NULL};
+
+		if (argc)
+			usage_msg_opt("--continue expects no arguments",
+			      builtin_merge_usage, builtin_merge_options);
+
+		if (!file_exists(git_path_merge_head()))
+			die(_("There is no merge in progress (MERGE_HEAD missing)."));
+
+		/* Invoke 'git commit' */
+		ret = cmd_commit(nargc, nargv, prefix);
+		goto done;
+	}
+
 	if (read_cache_unmerged())
 		die_resolve_conflict("merge");
 
diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh
index 85248a14b..44b34ef3a 100755
--- a/t/t7600-merge.sh
+++ b/t/t7600-merge.sh
@@ -154,6 +154,7 @@ test_expect_success 'test option parsing' '
 	test_must_fail git merge -s foobar c1 &&
 	test_must_fail git merge -s=foobar c1 &&
 	test_must_fail git merge -m &&
+	test_must_fail git merge --continue foobar &&
 	test_must_fail git merge
 '
 
@@ -763,4 +764,11 @@ test_expect_success 'merge nothing into void' '
 	)
 '
 
+test_expect_success 'merge can be completed with --continue' '
+	git reset --hard c0 &&
+	git merge --no-ff --no-commit c1 &&
+	git merge --continue &&
+	verify_parents $c0 $c1
+'
+
 test_done
-- 
2.11.0.24.ge6920cf