Merge branch 'jn/update-contrib-example-merge'

* jn/update-contrib-example-merge: (24 commits)
  merge script: learn --[no-]rerere-autoupdate
  merge script: notice @{-1} shorthand
  merge script: handle --no-ff --no-commit correctly
  merge script: --ff-only to disallow true merge
  merge script: handle many-way octopus
  merge script: handle -m --log correctly
  merge script: forbid merge -s index
  merge script: allow custom strategies
  merge script: merge -X<option>
  merge script: improve log message subject
  merge script: refuse to merge during merge
  merge script: tweak unmerged files message to match builtin
  merge script: --squash, --ff from unborn branch are errors
  fmt-merge-msg -m to override merge title
  merge-base --independent to print reduced parent list in a merge
  merge-base --octopus to mimic show-branch --merge-base
  Documentation: add a SEE ALSO section for merge-base
  t6200 (fmt-merge-msg): style nitpicks
  t6010 (merge-base): modernize style
  t7600 (merge): test merge from branch yet to be born
  ...

3 files changed, 58 insertions, 6 deletions

diff --git a/builtin/fmt-merge-msg.c b/builtin/fmt-merge-msg.c
index a76cd4e9d1..e7e12eea25 100644
--- a/builtin/fmt-merge-msg.c
+++ b/builtin/fmt-merge-msg.c
@@ -7,7 +7,7 @@
 #include "string-list.h"
 
 static const char * const fmt_merge_msg_usage[] = {
-	"git fmt-merge-msg [--log|--no-log] [--file <file>]",
+	"git fmt-merge-msg [-m <message>] [--log|--no-log] [--file <file>]",
 	NULL
 };
 
@@ -319,11 +319,14 @@ int fmt_merge_msg_shortlog(struct strbuf *in, struct strbuf *out) {
 int cmd_fmt_merge_msg(int argc, const char **argv, const char *prefix)
 {
 	const char *inpath = NULL;
+	const char *message = NULL;
 	struct option options[] = {
 		OPT_BOOLEAN(0, "log",     &merge_summary, "populate log with the shortlog"),
 		{ OPTION_BOOLEAN, 0, "summary", &merge_summary, NULL,
 		  "alias for --log (deprecated)",
 		  PARSE_OPT_NOARG | PARSE_OPT_HIDDEN },
+		OPT_STRING('m', "message", &message, "text",
+			"use <text> as start of message"),
 		OPT_FILENAME('F', "file", &inpath, "file to read from"),
 		OPT_END()
 	};
@@ -337,6 +340,12 @@ int cmd_fmt_merge_msg(int argc, const char **argv, const char *prefix)
 			     0);
 	if (argc > 0)
 		usage_with_options(fmt_merge_msg_usage, options);
+	if (message && !merge_summary) {
+		char nl = '\n';
+		write_in_full(STDOUT_FILENO, message, strlen(message));
+		write_in_full(STDOUT_FILENO, &nl, 1);
+		return 0;
+	}
 
 	if (inpath && strcmp(inpath, "-")) {
 		in = fopen(inpath, "r");
@@ -346,7 +355,12 @@ int cmd_fmt_merge_msg(int argc, const char **argv, const char *prefix)
 
 	if (strbuf_read(&input, fileno(in), 0) < 0)
 		die_errno("could not read input file");
-	ret = fmt_merge_msg(merge_summary, &input, &output);
+	if (message) {
+		strbuf_addstr(&output, message);
+		ret = fmt_merge_msg_shortlog(&input, &output);
+	} else {
+		ret = fmt_merge_msg(merge_summary, &input, &output);
+	}
 	if (ret)
 		return ret;
 	write_in_full(STDOUT_FILENO, output.buf, output.len);
diff --git a/builtin/merge-base.c b/builtin/merge-base.c
index 54e7ec2237..96dd160731 100644
--- a/builtin/merge-base.c
+++ b/builtin/merge-base.c
@@ -23,7 +23,8 @@ static int show_merge_base(struct commit **rev, int rev_nr, int show_all)
 }
 
 static const char * const merge_base_usage[] = {
-	"git merge-base [-a|--all] <commit> <commit>...",
+	"git merge-base [-a|--all] [--octopus] <commit> <commit>...",
+	"git merge-base --independent <commit>...",
 	NULL
 };
 
@@ -41,21 +42,58 @@ static struct commit *get_commit_reference(const char *arg)
 	return r;
 }
 
+static int handle_octopus(int count, const char **args, int reduce, int show_all)
+{
+	struct commit_list *revs = NULL;
+	struct commit_list *result;
+	int i;
+
+	if (reduce)
+		show_all = 1;
+
+	for (i = count - 1; i >= 0; i--)
+		commit_list_insert(get_commit_reference(args[i]), &revs);
+
+	result = reduce ? reduce_heads(revs) : get_octopus_merge_bases(revs);
+
+	if (!result)
+		return 1;
+
+	while (result) {
+		printf("%s\n", sha1_to_hex(result->item->object.sha1));
+		if (!show_all)
+			return 0;
+		result = result->next;
+	}
+
+	return 0;
+}
+
 int cmd_merge_base(int argc, const char **argv, const char *prefix)
 {
 	struct commit **rev;
 	int rev_nr = 0;
 	int show_all = 0;
+	int octopus = 0;
+	int reduce = 0;
 
 	struct option options[] = {
-		OPT_BOOLEAN('a', "all", &show_all, "outputs all common ancestors"),
+		OPT_BOOLEAN('a', "all", &show_all, "output all common ancestors"),
+		OPT_BOOLEAN(0, "octopus", &octopus, "find ancestors for a single n-way merge"),
+		OPT_BOOLEAN(0, "independent", &reduce, "list revs not reachable from others"),
 		OPT_END()
 	};
 
 	git_config(git_default_config, NULL);
 	argc = parse_options(argc, argv, prefix, options, merge_base_usage, 0);
-	if (argc < 2)
+	if (!octopus && !reduce && argc < 2)
 		usage_with_options(merge_base_usage, options);
+	if (reduce && (show_all || octopus))
+		die("--independent cannot be used with other options");
+
+	if (octopus || reduce)
+		return handle_octopus(argc, argv, reduce, show_all);
+
 	rev = xmalloc(argc * sizeof(*rev));
 	while (argc-- > 0)
 		rev[rev_nr++] = get_commit_reference(*argv++);
diff --git a/builtin/merge.c b/builtin/merge.c
index da26cd629a..576e81f145 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -438,7 +438,7 @@ static void merge_name(const char *remote, struct strbuf *msg)
 		strbuf_addstr(&truname, "refs/heads/");
 		strbuf_addstr(&truname, remote);
 		strbuf_setlen(&truname, truname.len - len);
-		if (resolve_ref(truname.buf, buf_sha, 0, NULL)) {
+		if (resolve_ref(truname.buf, buf_sha, 1, NULL)) {
 			strbuf_addf(msg,
 				    "%s\t\tbranch '%s'%s of .\n",
 				    sha1_to_hex(remote_head->sha1),