[PATCH v5 4/4] merge: add support for merging from upstream by default

[Jared Hance <jaredhance@gmail.com>]

Add the option merge.defaultupstream to add support for merging from
the upstream branch by default. The upstream branch is found using
branch.[name].merge.

Signed-off-by: Jared Hance <jaredhance@gmail.com>
---
 Documentation/config.txt |    6 ++++++
 builtin/merge.c          |   32 +++++++++++++++++++++++---------
 2 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index c5e1835..4415691 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1389,6 +1389,12 @@ man.<tool>.path::
 
 include::merge-config.txt[]
 
+merge.defaultUpstream::
+	If merge is called without any ref arguments, merge from the branch
+	specified in branch.<current branch>.merge, which is considered to be
+	the upstream branch for the current branch, possibly set by --track or
+	--set-upstream.
+
 mergetool.<tool>.path::
 	Override the path for the given tool.  This is useful in case
 	your tool is not in the PATH.
diff --git a/builtin/merge.c b/builtin/merge.c
index 71b392d..a3ca6a0 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -37,7 +37,7 @@ struct strategy {
 };
 
 static const char * const builtin_merge_usage[] = {
-	"git merge [options] <branch>...",
+	"git merge [options] [<branch>...]",
 	"git merge [options] <msg> HEAD <branch>",
 	NULL
 };
@@ -58,6 +58,8 @@ static int option_renormalize;
 static int verbosity;
 static int allow_rerere_auto;
 static int abort_current_merge;
+static int default_upstream;
+static const char *upstream_branch;
 
 static struct strategy all_strategy[] = {
 	{ "recursive",  DEFAULT_TWOHEAD | NO_TRIVIAL },
@@ -524,7 +526,8 @@ static int per_branch_config(const char *k, const char *v, void *cb)
 		free(buf);
 
 		return 0;
-	}
+	} else if (!strcmp(variable, ".merge"))
+		return git_config_string(&upstream_branch, k, v);
 
 	return 1; /* not what I handle */
 }
@@ -536,7 +539,9 @@ static int git_merge_config(const char *k, const char *v, void *cb)
 	if (status <= 0)
 		return status;
 
-	if (!strcmp(k, "merge.diffstat") || !strcmp(k, "merge.stat"))
+	if (!strcmp(k, "merge.defaultupstream"))
+		default_upstream = git_config_bool(k, v);
+	else if (!strcmp(k, "merge.diffstat") || !strcmp(k, "merge.stat"))
 		show_diffstat = git_config_bool(k, v);
 	else if (!strcmp(k, "pull.twohead"))
 		return git_config_string(&pull_twohead, k, v);
@@ -1017,9 +1022,13 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	if (!allow_fast_forward && fast_forward_only)
 		die("You cannot combine --no-ff with --ff-only.");
 
-	if (!argc)
-		usage_with_options(builtin_merge_usage,
-			builtin_merge_options);
+	if (!argc) {
+		if (!default_upstream || !upstream_branch)
+			usage_with_options(builtin_merge_usage,
+					builtin_merge_options);
+
+		setup_merge_commit(&buf, &remotes, upstream_branch);
+	}
 
 	/*
 	 * This could be traditional "merge <msg> HEAD <commit>..."  and
@@ -1082,9 +1091,14 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		}
 	}
 
-	if (head_invalid || !argc)
-		usage_with_options(builtin_merge_usage,
-			builtin_merge_options);
+	if (head_invalid)
+		usage_msg_opt("cannot use old-style invocation from an unborn"
+				"branch", 
+				builtin_merge_usage, builtin_merge_options);
+
+	if (!argc && !(default_upstream && upstream_branch))
+		usage_msg_opt("no commit to merge specified",
+				builtin_merge_usage, builtin_merge_options);
 
 	strbuf_addstr(&buf, "merge");
 	for (i = 0; i < argc; i++)
-- 
1.7.4