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
  ...

Documentation/git-fmt-merge-msg.txt

@@ -9,8 +9,8 @@ git-fmt-merge-msg - Produce a merge commit message
 SYNOPSIS
 --------
 [verse]
-'git fmt-merge-msg' [--log | --no-log] <$GIT_DIR/FETCH_HEAD
-'git fmt-merge-msg' [--log | --no-log] -F <file>
+'git fmt-merge-msg' [-m <message>] [--log | --no-log] <$GIT_DIR/FETCH_HEAD
+'git fmt-merge-msg' [-m <message>] [--log | --no-log] -F <file>
 
 DESCRIPTION
 -----------
@@ -38,6 +38,11 @@ OPTIONS
 	Synonyms to --log and --no-log; these are deprecated and will be
 	removed in the future.
 
+-m <message>::
+--message <message>::
+	Use <message> instead of the branch names for the first line
+	of the log message.  For use with `--log`.
+
 -F <file>::
 --file <file>::
 	Take the list of merged objects from <file> instead of

Documentation/git-merge-base.txt

@@ -8,7 +8,9 @@ git-merge-base - Find as good common ancestors as possible for a merge
 
 SYNOPSIS
 --------
-'git merge-base' [-a|--all] <commit> <commit>...
+[verse]
+'git merge-base' [-a|--all] [--octopus] <commit> <commit>...
+'git merge-base' --independent <commit>...
 
 DESCRIPTION
 -----------
@@ -20,12 +22,12 @@ that does not have any better common ancestor is a 'best common
 ancestor', i.e. a 'merge base'.  Note that there can be more than one
 merge base for a pair of commits.
 
-Among the two commits to compute the merge base from, one is specified by
-the first commit argument on the command line; the other commit is a
-(possibly hypothetical) commit that is a merge across all the remaining
-commits on the command line.  As the most common special case, specifying only
-two commits on the command line means computing the merge base between
-the given two commits.
+Unless `--octopus` is given, among the two commits to compute the merge
+base from, one is specified by the first commit argument on the command
+line; the other commit is a (possibly hypothetical) commit that is a merge
+across all the remaining commits on the command line.  As the most common
+special case, specifying only two commits on the command line means
+computing the merge base between the given two commits.
 
 As a consequence, the 'merge base' is not necessarily contained in each of the
 commit arguments if more than two commits are specified. This is different
@@ -37,6 +39,18 @@ OPTIONS
 --all::
 	Output all merge bases for the commits, instead of just one.
 
+--octopus::
+	Compute the best common ancestors of all supplied commits,
+	in preparation for an n-way merge.  This mimics the behavior
+	of 'git show-branch --merge-base'.
+
+--independent::
+	Instead of printing merge bases, print a minimal subset of
+	the supplied commits with the same ancestors.  In other words,
+	among the commits given, list those which cannot be reached
+	from any other.  This mimics the behavior of 'git show-branch
+	--independent'.
+
 DISCUSSION
 ----------
 
@@ -96,6 +110,12 @@ Documentation
 --------------
 Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>.
 
+See also
+--------
+linkgit:git-rev-list[1],
+linkgit:git-show-branch[1],
+linkgit:git-merge[1]
+
 GIT
 ---
 Part of the linkgit:git[1] suite

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);

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++);

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),