[PATCH v2 1/2] Lib-ify fmt-merge-msg

[Denton Liu <liu.denton@gmail.com>]

In builtin.h, there exists the distinctly "lib-ish" function
fmt_merge_msg(). This function can currently only be called by built-in
commands but, unlike most of the other functions in the header, it does
not make sense to impose this restriction as the functionality can be
logically reused in libgit.

Extract this function into fmt-merge-msg.c so that related definitions
can exist clearly in their own header file.

While we're at it, clean up #includes that are unused.

This patch is best viewed with --color-moved.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
---
 Makefile                |   1 +
 builtin.h               |  11 -
 builtin/fmt-merge-msg.c | 655 +---------------------------------------
 fmt-merge-msg.c         | 653 +++++++++++++++++++++++++++++++++++++++
 fmt-merge-msg.h         |  13 +
 5 files changed, 668 insertions(+), 665 deletions(-)
 create mode 100644 fmt-merge-msg.c

diff --git a/Makefile b/Makefile
index 9804a0758b..04e3cc179e 100644
--- a/Makefile
+++ b/Makefile
@@ -886,6 +886,7 @@ LIB_OBJS += ewah/ewah_rlw.o
 LIB_OBJS += exec-cmd.o
 LIB_OBJS += fetch-negotiator.o
 LIB_OBJS += fetch-pack.o
+LIB_OBJS += fmt-merge-msg.o
 LIB_OBJS += fsck.o
 LIB_OBJS += fsmonitor.o
 LIB_OBJS += gettext.o
diff --git a/builtin.h b/builtin.h
index 2b25a80cde..6101d98661 100644
--- a/builtin.h
+++ b/builtin.h
@@ -94,8 +94,6 @@
  * command.
  */
 
-#define DEFAULT_MERGE_LOG_LEN 20
-
 extern const char git_usage_string[];
 extern const char git_more_info_string[];
 
@@ -104,15 +102,6 @@ extern const char git_more_info_string[];
 
 void prune_packed_objects(int);
 
-struct fmt_merge_msg_opts {
-	unsigned add_title:1,
-		credit_people:1;
-	int shortlog_len;
-};
-
-int fmt_merge_msg(struct strbuf *in, struct strbuf *out,
-		  struct fmt_merge_msg_opts *);
-
 /**
  * If a built-in has DELAY_PAGER_CONFIG set, the built-in should call this early
  * when it wishes to respect the `pager.foo`-config. The `cmd` is the name of
diff --git a/builtin/fmt-merge-msg.c b/builtin/fmt-merge-msg.c
index 736f666f64..48a8699de7 100644
--- a/builtin/fmt-merge-msg.c
+++ b/builtin/fmt-merge-msg.c
@@ -1,666 +1,13 @@
 #include "builtin.h"
-#include "cache.h"
 #include "config.h"
-#include "refs.h"
-#include "object-store.h"
-#include "commit.h"
-#include "diff.h"
-#include "revision.h"
-#include "tag.h"
-#include "string-list.h"
-#include "branch.h"
 #include "fmt-merge-msg.h"
-#include "gpg-interface.h"
-#include "repository.h"
-#include "commit-reach.h"
+#include "parse-options.h"
 
 static const char * const fmt_merge_msg_usage[] = {
 	N_("git fmt-merge-msg [-m <message>] [--log[=<n>] | --no-log] [--file <file>]"),
 	NULL
 };
 
-static int use_branch_desc;
-
-int fmt_merge_msg_config(const char *key, const char *value, void *cb)
-{
-	if (!strcmp(key, "merge.log") || !strcmp(key, "merge.summary")) {
-		int is_bool;
-		merge_log_config = git_config_bool_or_int(key, value, &is_bool);
-		if (!is_bool && merge_log_config < 0)
-			return error("%s: negative length %s", key, value);
-		if (is_bool && merge_log_config)
-			merge_log_config = DEFAULT_MERGE_LOG_LEN;
-	} else if (!strcmp(key, "merge.branchdesc")) {
-		use_branch_desc = git_config_bool(key, value);
-	} else {
-		return git_default_config(key, value, cb);
-	}
-	return 0;
-}
-
-/* merge data per repository where the merged tips came from */
-struct src_data {
-	struct string_list branch, tag, r_branch, generic;
-	int head_status;
-};
-
-struct origin_data {
-	struct object_id oid;
-	unsigned is_local_branch:1;
-};
-
-static void init_src_data(struct src_data *data)
-{
-	data->branch.strdup_strings = 1;
-	data->tag.strdup_strings = 1;
-	data->r_branch.strdup_strings = 1;
-	data->generic.strdup_strings = 1;
-}
-
-static struct string_list srcs = STRING_LIST_INIT_DUP;
-static struct string_list origins = STRING_LIST_INIT_DUP;
-
-struct merge_parents {
-	int alloc, nr;
-	struct merge_parent {
-		struct object_id given;
-		struct object_id commit;
-		unsigned char used;
-	} *item;
-};
-
-/*
- * I know, I know, this is inefficient, but you won't be pulling and merging
- * hundreds of heads at a time anyway.
- */
-static struct merge_parent *find_merge_parent(struct merge_parents *table,
-					      struct object_id *given,
-					      struct object_id *commit)
-{
-	int i;
-	for (i = 0; i < table->nr; i++) {
-		if (given && !oideq(&table->item[i].given, given))
-			continue;
-		if (commit && !oideq(&table->item[i].commit, commit))
-			continue;
-		return &table->item[i];
-	}
-	return NULL;
-}
-
-static void add_merge_parent(struct merge_parents *table,
-			     struct object_id *given,
-			     struct object_id *commit)
-{
-	if (table->nr && find_merge_parent(table, given, commit))
-		return;
-	ALLOC_GROW(table->item, table->nr + 1, table->alloc);
-	oidcpy(&table->item[table->nr].given, given);
-	oidcpy(&table->item[table->nr].commit, commit);
-	table->item[table->nr].used = 0;
-	table->nr++;
-}
-
-static int handle_line(char *line, struct merge_parents *merge_parents)
-{
-	int i, len = strlen(line);
-	struct origin_data *origin_data;
-	char *src;
-	const char *origin, *tag_name;
-	struct src_data *src_data;
-	struct string_list_item *item;
-	int pulling_head = 0;
-	struct object_id oid;
-	const unsigned hexsz = the_hash_algo->hexsz;
-
-	if (len < hexsz + 3 || line[hexsz] != '\t')
-		return 1;
-
-	if (starts_with(line + hexsz + 1, "not-for-merge"))
-		return 0;
-
-	if (line[hexsz + 1] != '\t')
-		return 2;
-
-	i = get_oid_hex(line, &oid);
-	if (i)
-		return 3;
-
-	if (!find_merge_parent(merge_parents, &oid, NULL))
-		return 0; /* subsumed by other parents */
-
-	origin_data = xcalloc(1, sizeof(struct origin_data));
-	oidcpy(&origin_data->oid, &oid);
-
-	if (line[len - 1] == '\n')
-		line[len - 1] = 0;
-	line += hexsz + 2;
-
-	/*
-	 * At this point, line points at the beginning of comment e.g.
-	 * "branch 'frotz' of git://that/repository.git".
-	 * Find the repository name and point it with src.
-	 */
-	src = strstr(line, " of ");
-	if (src) {
-		*src = 0;
-		src += 4;
-		pulling_head = 0;
-	} else {
-		src = line;
-		pulling_head = 1;
-	}
-
-	item = unsorted_string_list_lookup(&srcs, src);
-	if (!item) {
-		item = string_list_append(&srcs, src);
-		item->util = xcalloc(1, sizeof(struct src_data));
-		init_src_data(item->util);
-	}
-	src_data = item->util;
-
-	if (pulling_head) {
-		origin = src;
-		src_data->head_status |= 1;
-	} else if (skip_prefix(line, "branch ", &origin)) {
-		origin_data->is_local_branch = 1;
-		string_list_append(&src_data->branch, origin);
-		src_data->head_status |= 2;
-	} else if (skip_prefix(line, "tag ", &tag_name)) {
-		origin = line;
-		string_list_append(&src_data->tag, tag_name);
-		src_data->head_status |= 2;
-	} else if (skip_prefix(line, "remote-tracking branch ", &origin)) {
-		string_list_append(&src_data->r_branch, origin);
-		src_data->head_status |= 2;
-	} else {
-		origin = src;
-		string_list_append(&src_data->generic, line);
-		src_data->head_status |= 2;
-	}
-
-	if (!strcmp(".", src) || !strcmp(src, origin)) {
-		int len = strlen(origin);
-		if (origin[0] == '\'' && origin[len - 1] == '\'')
-			origin = xmemdupz(origin + 1, len - 2);
-	} else
-		origin = xstrfmt("%s of %s", origin, src);
-	if (strcmp(".", src))
-		origin_data->is_local_branch = 0;
-	string_list_append(&origins, origin)->util = origin_data;
-	return 0;
-}
-
-static void print_joined(const char *singular, const char *plural,
-		struct string_list *list, struct strbuf *out)
-{
-	if (list->nr == 0)
-		return;
-	if (list->nr == 1) {
-		strbuf_addf(out, "%s%s", singular, list->items[0].string);
-	} else {
-		int i;
-		strbuf_addstr(out, plural);
-		for (i = 0; i < list->nr - 1; i++)
-			strbuf_addf(out, "%s%s", i > 0 ? ", " : "",
-				    list->items[i].string);
-		strbuf_addf(out, " and %s", list->items[list->nr - 1].string);
-	}
-}
-
-static void add_branch_desc(struct strbuf *out, const char *name)
-{
-	struct strbuf desc = STRBUF_INIT;
-
-	if (!read_branch_desc(&desc, name)) {
-		const char *bp = desc.buf;
-		while (*bp) {
-			const char *ep = strchrnul(bp, '\n');
-			if (*ep)
-				ep++;
-			strbuf_addf(out, "  : %.*s", (int)(ep - bp), bp);
-			bp = ep;
-		}
-		strbuf_complete_line(out);
-	}
-	strbuf_release(&desc);
-}
-
-#define util_as_integral(elem) ((intptr_t)((elem)->util))
-
-static void record_person_from_buf(int which, struct string_list *people,
-				   const char *buffer)
-{
-	char *name_buf, *name, *name_end;
-	struct string_list_item *elem;
-	const char *field;
-
-	field = (which == 'a') ? "\nauthor " : "\ncommitter ";
-	name = strstr(buffer, field);
-	if (!name)
-		return;
-	name += strlen(field);
-	name_end = strchrnul(name, '<');
-	if (*name_end)
-		name_end--;
-	while (isspace(*name_end) && name <= name_end)
-		name_end--;
-	if (name_end < name)
-		return;
-	name_buf = xmemdupz(name, name_end - name + 1);
-
-	elem = string_list_lookup(people, name_buf);
-	if (!elem) {
-		elem = string_list_insert(people, name_buf);
-		elem->util = (void *)0;
-	}
-	elem->util = (void*)(util_as_integral(elem) + 1);
-	free(name_buf);
-}
-
-
-static void record_person(int which, struct string_list *people,
-			  struct commit *commit)
-{
-	const char *buffer = get_commit_buffer(commit, NULL);
-	record_person_from_buf(which, people, buffer);
-	unuse_commit_buffer(commit, buffer);
-}
-
-static int cmp_string_list_util_as_integral(const void *a_, const void *b_)
-{
-	const struct string_list_item *a = a_, *b = b_;
-	return util_as_integral(b) - util_as_integral(a);
-}
-
-static void add_people_count(struct strbuf *out, struct string_list *people)
-{
-	if (people->nr == 1)
-		strbuf_addstr(out, people->items[0].string);
-	else if (people->nr == 2)
-		strbuf_addf(out, "%s (%d) and %s (%d)",
-			    people->items[0].string,
-			    (int)util_as_integral(&people->items[0]),
-			    people->items[1].string,
-			    (int)util_as_integral(&people->items[1]));
-	else if (people->nr)
-		strbuf_addf(out, "%s (%d) and others",
-			    people->items[0].string,
-			    (int)util_as_integral(&people->items[0]));
-}
-
-static void credit_people(struct strbuf *out,
-			  struct string_list *them,
-			  int kind)
-{
-	const char *label;
-	const char *me;
-
-	if (kind == 'a') {
-		label = "By";
-		me = git_author_info(IDENT_NO_DATE);
-	} else {
-		label = "Via";
-		me = git_committer_info(IDENT_NO_DATE);
-	}
-
-	if (!them->nr ||
-	    (them->nr == 1 &&
-	     me &&
-	     skip_prefix(me, them->items->string, &me) &&
-	     starts_with(me, " <")))
-		return;
-	strbuf_addf(out, "\n%c %s ", comment_line_char, label);
-	add_people_count(out, them);
-}
-
-static void add_people_info(struct strbuf *out,
-			    struct string_list *authors,
-			    struct string_list *committers)
-{
-	QSORT(authors->items, authors->nr,
-	      cmp_string_list_util_as_integral);
-	QSORT(committers->items, committers->nr,
-	      cmp_string_list_util_as_integral);
-
-	credit_people(out, authors, 'a');
-	credit_people(out, committers, 'c');
-}
-
-static void shortlog(const char *name,
-		     struct origin_data *origin_data,
-		     struct commit *head,
-		     struct rev_info *rev,
-		     struct fmt_merge_msg_opts *opts,
-		     struct strbuf *out)
-{
-	int i, count = 0;
-	struct commit *commit;
-	struct object *branch;
-	struct string_list subjects = STRING_LIST_INIT_DUP;
-	struct string_list authors = STRING_LIST_INIT_DUP;
-	struct string_list committers = STRING_LIST_INIT_DUP;
-	int flags = UNINTERESTING | TREESAME | SEEN | SHOWN | ADDED;
-	struct strbuf sb = STRBUF_INIT;
-	const struct object_id *oid = &origin_data->oid;
-	int limit = opts->shortlog_len;
-
-	branch = deref_tag(the_repository, parse_object(the_repository, oid),
-			   oid_to_hex(oid),
-			   the_hash_algo->hexsz);
-	if (!branch || branch->type != OBJ_COMMIT)
-		return;
-
-	setup_revisions(0, NULL, rev, NULL);
-	add_pending_object(rev, branch, name);
-	add_pending_object(rev, &head->object, "^HEAD");
-	head->object.flags |= UNINTERESTING;
-	if (prepare_revision_walk(rev))
-		die("revision walk setup failed");
-	while ((commit = get_revision(rev)) != NULL) {
-		struct pretty_print_context ctx = {0};
-
-		if (commit->parents && commit->parents->next) {
-			/* do not list a merge but count committer */
-			if (opts->credit_people)
-				record_person('c', &committers, commit);
-			continue;
-		}
-		if (!count && opts->credit_people)
-			/* the 'tip' committer */
-			record_person('c', &committers, commit);
-		if (opts->credit_people)
-			record_person('a', &authors, commit);
-		count++;
-		if (subjects.nr > limit)
-			continue;
-
-		format_commit_message(commit, "%s", &sb, &ctx);
-		strbuf_ltrim(&sb);
-
-		if (!sb.len)
-			string_list_append(&subjects,
-					   oid_to_hex(&commit->object.oid));
-		else
-			string_list_append_nodup(&subjects,
-						 strbuf_detach(&sb, NULL));
-	}
-
-	if (opts->credit_people)
-		add_people_info(out, &authors, &committers);
-	if (count > limit)
-		strbuf_addf(out, "\n* %s: (%d commits)\n", name, count);
-	else
-		strbuf_addf(out, "\n* %s:\n", name);
-
-	if (origin_data->is_local_branch && use_branch_desc)
-		add_branch_desc(out, name);
-
-	for (i = 0; i < subjects.nr; i++)
-		if (i >= limit)
-			strbuf_addstr(out, "  ...\n");
-		else
-			strbuf_addf(out, "  %s\n", subjects.items[i].string);
-
-	clear_commit_marks((struct commit *)branch, flags);
-	clear_commit_marks(head, flags);
-	free_commit_list(rev->commits);
-	rev->commits = NULL;
-	rev->pending.nr = 0;
-
-	string_list_clear(&authors, 0);
-	string_list_clear(&committers, 0);
-	string_list_clear(&subjects, 0);
-}
-
-static void fmt_merge_msg_title(struct strbuf *out,
-				const char *current_branch)
-{
-	int i = 0;
-	char *sep = "";
-
-	strbuf_addstr(out, "Merge ");
-	for (i = 0; i < srcs.nr; i++) {
-		struct src_data *src_data = srcs.items[i].util;
-		const char *subsep = "";
-
-		strbuf_addstr(out, sep);
-		sep = "; ";
-
-		if (src_data->head_status == 1) {
-			strbuf_addstr(out, srcs.items[i].string);
-			continue;
-		}
-		if (src_data->head_status == 3) {
-			subsep = ", ";
-			strbuf_addstr(out, "HEAD");
-		}
-		if (src_data->branch.nr) {
-			strbuf_addstr(out, subsep);
-			subsep = ", ";
-			print_joined("branch ", "branches ", &src_data->branch,
-					out);
-		}
-		if (src_data->r_branch.nr) {
-			strbuf_addstr(out, subsep);
-			subsep = ", ";
-			print_joined("remote-tracking branch ", "remote-tracking branches ",
-					&src_data->r_branch, out);
-		}
-		if (src_data->tag.nr) {
-			strbuf_addstr(out, subsep);
-			subsep = ", ";
-			print_joined("tag ", "tags ", &src_data->tag, out);
-		}
-		if (src_data->generic.nr) {
-			strbuf_addstr(out, subsep);
-			print_joined("commit ", "commits ", &src_data->generic,
-					out);
-		}
-		if (strcmp(".", srcs.items[i].string))
-			strbuf_addf(out, " of %s", srcs.items[i].string);
-	}
-
-	if (!strcmp("master", current_branch))
-		strbuf_addch(out, '\n');
-	else
-		strbuf_addf(out, " into %s\n", current_branch);
-}
-
-static void fmt_tag_signature(struct strbuf *tagbuf,
-			      struct strbuf *sig,
-			      const char *buf,
-			      unsigned long len)
-{
-	const char *tag_body = strstr(buf, "\n\n");
-	if (tag_body) {
-		tag_body += 2;
-		strbuf_add(tagbuf, tag_body, buf + len - tag_body);
-	}
-	strbuf_complete_line(tagbuf);
-	if (sig->len) {
-		strbuf_addch(tagbuf, '\n');
-		strbuf_add_commented_lines(tagbuf, sig->buf, sig->len);
-	}
-}
-
-static void fmt_merge_msg_sigs(struct strbuf *out)
-{
-	int i, tag_number = 0, first_tag = 0;
-	struct strbuf tagbuf = STRBUF_INIT;
-
-	for (i = 0; i < origins.nr; i++) {
-		struct object_id *oid = origins.items[i].util;
-		enum object_type type;
-		unsigned long size, len;
-		char *buf = read_object_file(oid, &type, &size);
-		struct strbuf sig = STRBUF_INIT;
-
-		if (!buf || type != OBJ_TAG)
-			goto next;
-		len = parse_signature(buf, size);
-
-		if (size == len)
-			; /* merely annotated */
-		else if (verify_signed_buffer(buf, len, buf + len, size - len, &sig, NULL)) {
-			if (!sig.len)
-				strbuf_addstr(&sig, "gpg verification failed.\n");
-		}
-
-		if (!tag_number++) {
-			fmt_tag_signature(&tagbuf, &sig, buf, len);
-			first_tag = i;
-		} else {
-			if (tag_number == 2) {
-				struct strbuf tagline = STRBUF_INIT;
-				strbuf_addch(&tagline, '\n');
-				strbuf_add_commented_lines(&tagline,
-						origins.items[first_tag].string,
-						strlen(origins.items[first_tag].string));
-				strbuf_insert(&tagbuf, 0, tagline.buf,
-					      tagline.len);
-				strbuf_release(&tagline);
-			}
-			strbuf_addch(&tagbuf, '\n');
-			strbuf_add_commented_lines(&tagbuf,
-					origins.items[i].string,
-					strlen(origins.items[i].string));
-			fmt_tag_signature(&tagbuf, &sig, buf, len);
-		}
-		strbuf_release(&sig);
-	next:
-		free(buf);
-	}
-	if (tagbuf.len) {
-		strbuf_addch(out, '\n');
-		strbuf_addbuf(out, &tagbuf);
-	}
-	strbuf_release(&tagbuf);
-}
-
-static void find_merge_parents(struct merge_parents *result,
-			       struct strbuf *in, struct object_id *head)
-{
-	struct commit_list *parents;
-	struct commit *head_commit;
-	int pos = 0, i, j;
-
-	parents = NULL;
-	while (pos < in->len) {
-		int len;
-		char *p = in->buf + pos;
-		char *newline = strchr(p, '\n');
-		const char *q;
-		struct object_id oid;
-		struct commit *parent;
-		struct object *obj;
-
-		len = newline ? newline - p : strlen(p);
-		pos += len + !!newline;
-
-		if (parse_oid_hex(p, &oid, &q) ||
-		    q[0] != '\t' ||
-		    q[1] != '\t')
-			continue; /* skip not-for-merge */
-		/*
-		 * Do not use get_merge_parent() here; we do not have
-		 * "name" here and we do not want to contaminate its
-		 * util field yet.
-		 */
-		obj = parse_object(the_repository, &oid);
-		parent = (struct commit *)peel_to_type(NULL, 0, obj, OBJ_COMMIT);
-		if (!parent)
-			continue;
-		commit_list_insert(parent, &parents);
-		add_merge_parent(result, &obj->oid, &parent->object.oid);
-	}
-	head_commit = lookup_commit(the_repository, head);
-	if (head_commit)
-		commit_list_insert(head_commit, &parents);
-	reduce_heads_replace(&parents);
-
-	while (parents) {
-		struct commit *cmit = pop_commit(&parents);
-		for (i = 0; i < result->nr; i++)
-			if (oideq(&result->item[i].commit, &cmit->object.oid))
-				result->item[i].used = 1;
-	}
-
-	for (i = j = 0; i < result->nr; i++) {
-		if (result->item[i].used) {
-			if (i != j)
-				result->item[j] = result->item[i];
-			j++;
-		}
-	}
-	result->nr = j;
-}
-
-int fmt_merge_msg(struct strbuf *in, struct strbuf *out,
-		  struct fmt_merge_msg_opts *opts)
-{
-	int i = 0, pos = 0;
-	struct object_id head_oid;
-	const char *current_branch;
-	void *current_branch_to_free;
-	struct merge_parents merge_parents;
-
-	memset(&merge_parents, 0, sizeof(merge_parents));
-
-	/* get current branch */
-	current_branch = current_branch_to_free =
-		resolve_refdup("HEAD", RESOLVE_REF_READING, &head_oid, NULL);
-	if (!current_branch)
-		die("No current branch");
-	if (starts_with(current_branch, "refs/heads/"))
-		current_branch += 11;
-
-	find_merge_parents(&merge_parents, in, &head_oid);
-
-	/* get a line */
-	while (pos < in->len) {
-		int len;
-		char *newline, *p = in->buf + pos;
-
-		newline = strchr(p, '\n');
-		len = newline ? newline - p : strlen(p);
-		pos += len + !!newline;
-		i++;
-		p[len] = 0;
-		if (handle_line(p, &merge_parents))
-			die("error in line %d: %.*s", i, len, p);
-	}
-
-	if (opts->add_title && srcs.nr)
-		fmt_merge_msg_title(out, current_branch);
-
-	if (origins.nr)
-		fmt_merge_msg_sigs(out);
-
-	if (opts->shortlog_len) {
-		struct commit *head;
-		struct rev_info rev;
-
-		head = lookup_commit_or_die(&head_oid, "HEAD");
-		repo_init_revisions(the_repository, &rev, NULL);
-		rev.commit_format = CMIT_FMT_ONELINE;
-		rev.ignore_merges = 1;
-		rev.limited = 1;
-
-		strbuf_complete_line(out);
-
-		for (i = 0; i < origins.nr; i++)
-			shortlog(origins.items[i].string,
-				 origins.items[i].util,
-				 head, &rev, opts, out);
-	}
-
-	strbuf_complete_line(out);
-	free(current_branch_to_free);
-	free(merge_parents.item);
-	return 0;
-}
-
 int cmd_fmt_merge_msg(int argc, const char **argv, const char *prefix)
 {
 	const char *inpath = NULL;
diff --git a/fmt-merge-msg.c b/fmt-merge-msg.c
new file mode 100644
index 0000000000..5bcd4fd1c6
--- /dev/null
+++ b/fmt-merge-msg.c
@@ -0,0 +1,653 @@
+#include "config.h"
+#include "refs.h"
+#include "object-store.h"
+#include "diff.h"
+#include "revision.h"
+#include "tag.h"
+#include "string-list.h"
+#include "branch.h"
+#include "fmt-merge-msg.h"
+#include "commit-reach.h"
+
+static int use_branch_desc;
+
+int fmt_merge_msg_config(const char *key, const char *value, void *cb)
+{
+	if (!strcmp(key, "merge.log") || !strcmp(key, "merge.summary")) {
+		int is_bool;
+		merge_log_config = git_config_bool_or_int(key, value, &is_bool);
+		if (!is_bool && merge_log_config < 0)
+			return error("%s: negative length %s", key, value);
+		if (is_bool && merge_log_config)
+			merge_log_config = DEFAULT_MERGE_LOG_LEN;
+	} else if (!strcmp(key, "merge.branchdesc")) {
+		use_branch_desc = git_config_bool(key, value);
+	} else {
+		return git_default_config(key, value, cb);
+	}
+	return 0;
+}
+
+/* merge data per repository where the merged tips came from */
+struct src_data {
+	struct string_list branch, tag, r_branch, generic;
+	int head_status;
+};
+
+struct origin_data {
+	struct object_id oid;
+	unsigned is_local_branch:1;
+};
+
+static void init_src_data(struct src_data *data)
+{
+	data->branch.strdup_strings = 1;
+	data->tag.strdup_strings = 1;
+	data->r_branch.strdup_strings = 1;
+	data->generic.strdup_strings = 1;
+}
+
+static struct string_list srcs = STRING_LIST_INIT_DUP;
+static struct string_list origins = STRING_LIST_INIT_DUP;
+
+struct merge_parents {
+	int alloc, nr;
+	struct merge_parent {
+		struct object_id given;
+		struct object_id commit;
+		unsigned char used;
+	} *item;
+};
+
+/*
+ * I know, I know, this is inefficient, but you won't be pulling and merging
+ * hundreds of heads at a time anyway.
+ */
+static struct merge_parent *find_merge_parent(struct merge_parents *table,
+					      struct object_id *given,
+					      struct object_id *commit)
+{
+	int i;
+	for (i = 0; i < table->nr; i++) {
+		if (given && !oideq(&table->item[i].given, given))
+			continue;
+		if (commit && !oideq(&table->item[i].commit, commit))
+			continue;
+		return &table->item[i];
+	}
+	return NULL;
+}
+
+static void add_merge_parent(struct merge_parents *table,
+			     struct object_id *given,
+			     struct object_id *commit)
+{
+	if (table->nr && find_merge_parent(table, given, commit))
+		return;
+	ALLOC_GROW(table->item, table->nr + 1, table->alloc);
+	oidcpy(&table->item[table->nr].given, given);
+	oidcpy(&table->item[table->nr].commit, commit);
+	table->item[table->nr].used = 0;
+	table->nr++;
+}
+
+static int handle_line(char *line, struct merge_parents *merge_parents)
+{
+	int i, len = strlen(line);
+	struct origin_data *origin_data;
+	char *src;
+	const char *origin, *tag_name;
+	struct src_data *src_data;
+	struct string_list_item *item;
+	int pulling_head = 0;
+	struct object_id oid;
+	const unsigned hexsz = the_hash_algo->hexsz;
+
+	if (len < hexsz + 3 || line[hexsz] != '\t')
+		return 1;
+
+	if (starts_with(line + hexsz + 1, "not-for-merge"))
+		return 0;
+
+	if (line[hexsz + 1] != '\t')
+		return 2;
+
+	i = get_oid_hex(line, &oid);
+	if (i)
+		return 3;
+
+	if (!find_merge_parent(merge_parents, &oid, NULL))
+		return 0; /* subsumed by other parents */
+
+	origin_data = xcalloc(1, sizeof(struct origin_data));
+	oidcpy(&origin_data->oid, &oid);
+
+	if (line[len - 1] == '\n')
+		line[len - 1] = 0;
+	line += hexsz + 2;
+
+	/*
+	 * At this point, line points at the beginning of comment e.g.
+	 * "branch 'frotz' of git://that/repository.git".
+	 * Find the repository name and point it with src.
+	 */
+	src = strstr(line, " of ");
+	if (src) {
+		*src = 0;
+		src += 4;
+		pulling_head = 0;
+	} else {
+		src = line;
+		pulling_head = 1;
+	}
+
+	item = unsorted_string_list_lookup(&srcs, src);
+	if (!item) {
+		item = string_list_append(&srcs, src);
+		item->util = xcalloc(1, sizeof(struct src_data));
+		init_src_data(item->util);
+	}
+	src_data = item->util;
+
+	if (pulling_head) {
+		origin = src;
+		src_data->head_status |= 1;
+	} else if (skip_prefix(line, "branch ", &origin)) {
+		origin_data->is_local_branch = 1;
+		string_list_append(&src_data->branch, origin);
+		src_data->head_status |= 2;
+	} else if (skip_prefix(line, "tag ", &tag_name)) {
+		origin = line;
+		string_list_append(&src_data->tag, tag_name);
+		src_data->head_status |= 2;
+	} else if (skip_prefix(line, "remote-tracking branch ", &origin)) {
+		string_list_append(&src_data->r_branch, origin);
+		src_data->head_status |= 2;
+	} else {
+		origin = src;
+		string_list_append(&src_data->generic, line);
+		src_data->head_status |= 2;
+	}
+
+	if (!strcmp(".", src) || !strcmp(src, origin)) {
+		int len = strlen(origin);
+		if (origin[0] == '\'' && origin[len - 1] == '\'')
+			origin = xmemdupz(origin + 1, len - 2);
+	} else
+		origin = xstrfmt("%s of %s", origin, src);
+	if (strcmp(".", src))
+		origin_data->is_local_branch = 0;
+	string_list_append(&origins, origin)->util = origin_data;
+	return 0;
+}
+
+static void print_joined(const char *singular, const char *plural,
+		struct string_list *list, struct strbuf *out)
+{
+	if (list->nr == 0)
+		return;
+	if (list->nr == 1) {
+		strbuf_addf(out, "%s%s", singular, list->items[0].string);
+	} else {
+		int i;
+		strbuf_addstr(out, plural);
+		for (i = 0; i < list->nr - 1; i++)
+			strbuf_addf(out, "%s%s", i > 0 ? ", " : "",
+				    list->items[i].string);
+		strbuf_addf(out, " and %s", list->items[list->nr - 1].string);
+	}
+}
+
+static void add_branch_desc(struct strbuf *out, const char *name)
+{
+	struct strbuf desc = STRBUF_INIT;
+
+	if (!read_branch_desc(&desc, name)) {
+		const char *bp = desc.buf;
+		while (*bp) {
+			const char *ep = strchrnul(bp, '\n');
+			if (*ep)
+				ep++;
+			strbuf_addf(out, "  : %.*s", (int)(ep - bp), bp);
+			bp = ep;
+		}
+		strbuf_complete_line(out);
+	}
+	strbuf_release(&desc);
+}
+
+#define util_as_integral(elem) ((intptr_t)((elem)->util))
+
+static void record_person_from_buf(int which, struct string_list *people,
+				   const char *buffer)
+{
+	char *name_buf, *name, *name_end;
+	struct string_list_item *elem;
+	const char *field;
+
+	field = (which == 'a') ? "\nauthor " : "\ncommitter ";
+	name = strstr(buffer, field);
+	if (!name)
+		return;
+	name += strlen(field);
+	name_end = strchrnul(name, '<');
+	if (*name_end)
+		name_end--;
+	while (isspace(*name_end) && name <= name_end)
+		name_end--;
+	if (name_end < name)
+		return;
+	name_buf = xmemdupz(name, name_end - name + 1);
+
+	elem = string_list_lookup(people, name_buf);
+	if (!elem) {
+		elem = string_list_insert(people, name_buf);
+		elem->util = (void *)0;
+	}
+	elem->util = (void*)(util_as_integral(elem) + 1);
+	free(name_buf);
+}
+
+
+static void record_person(int which, struct string_list *people,
+			  struct commit *commit)
+{
+	const char *buffer = get_commit_buffer(commit, NULL);
+	record_person_from_buf(which, people, buffer);
+	unuse_commit_buffer(commit, buffer);
+}
+
+static int cmp_string_list_util_as_integral(const void *a_, const void *b_)
+{
+	const struct string_list_item *a = a_, *b = b_;
+	return util_as_integral(b) - util_as_integral(a);
+}
+
+static void add_people_count(struct strbuf *out, struct string_list *people)
+{
+	if (people->nr == 1)
+		strbuf_addstr(out, people->items[0].string);
+	else if (people->nr == 2)
+		strbuf_addf(out, "%s (%d) and %s (%d)",
+			    people->items[0].string,
+			    (int)util_as_integral(&people->items[0]),
+			    people->items[1].string,
+			    (int)util_as_integral(&people->items[1]));
+	else if (people->nr)
+		strbuf_addf(out, "%s (%d) and others",
+			    people->items[0].string,
+			    (int)util_as_integral(&people->items[0]));
+}
+
+static void credit_people(struct strbuf *out,
+			  struct string_list *them,
+			  int kind)
+{
+	const char *label;
+	const char *me;
+
+	if (kind == 'a') {
+		label = "By";
+		me = git_author_info(IDENT_NO_DATE);
+	} else {
+		label = "Via";
+		me = git_committer_info(IDENT_NO_DATE);
+	}
+
+	if (!them->nr ||
+	    (them->nr == 1 &&
+	     me &&
+	     skip_prefix(me, them->items->string, &me) &&
+	     starts_with(me, " <")))
+		return;
+	strbuf_addf(out, "\n%c %s ", comment_line_char, label);
+	add_people_count(out, them);
+}
+
+static void add_people_info(struct strbuf *out,
+			    struct string_list *authors,
+			    struct string_list *committers)
+{
+	QSORT(authors->items, authors->nr,
+	      cmp_string_list_util_as_integral);
+	QSORT(committers->items, committers->nr,
+	      cmp_string_list_util_as_integral);
+
+	credit_people(out, authors, 'a');
+	credit_people(out, committers, 'c');
+}
+
+static void shortlog(const char *name,
+		     struct origin_data *origin_data,
+		     struct commit *head,
+		     struct rev_info *rev,
+		     struct fmt_merge_msg_opts *opts,
+		     struct strbuf *out)
+{
+	int i, count = 0;
+	struct commit *commit;
+	struct object *branch;
+	struct string_list subjects = STRING_LIST_INIT_DUP;
+	struct string_list authors = STRING_LIST_INIT_DUP;
+	struct string_list committers = STRING_LIST_INIT_DUP;
+	int flags = UNINTERESTING | TREESAME | SEEN | SHOWN | ADDED;
+	struct strbuf sb = STRBUF_INIT;
+	const struct object_id *oid = &origin_data->oid;
+	int limit = opts->shortlog_len;
+
+	branch = deref_tag(the_repository, parse_object(the_repository, oid),
+			   oid_to_hex(oid),
+			   the_hash_algo->hexsz);
+	if (!branch || branch->type != OBJ_COMMIT)
+		return;
+
+	setup_revisions(0, NULL, rev, NULL);
+	add_pending_object(rev, branch, name);
+	add_pending_object(rev, &head->object, "^HEAD");
+	head->object.flags |= UNINTERESTING;
+	if (prepare_revision_walk(rev))
+		die("revision walk setup failed");
+	while ((commit = get_revision(rev)) != NULL) {
+		struct pretty_print_context ctx = {0};
+
+		if (commit->parents && commit->parents->next) {
+			/* do not list a merge but count committer */
+			if (opts->credit_people)
+				record_person('c', &committers, commit);
+			continue;
+		}
+		if (!count && opts->credit_people)
+			/* the 'tip' committer */
+			record_person('c', &committers, commit);
+		if (opts->credit_people)
+			record_person('a', &authors, commit);
+		count++;
+		if (subjects.nr > limit)
+			continue;
+
+		format_commit_message(commit, "%s", &sb, &ctx);
+		strbuf_ltrim(&sb);
+
+		if (!sb.len)
+			string_list_append(&subjects,
+					   oid_to_hex(&commit->object.oid));
+		else
+			string_list_append_nodup(&subjects,
+						 strbuf_detach(&sb, NULL));
+	}
+
+	if (opts->credit_people)
+		add_people_info(out, &authors, &committers);
+	if (count > limit)
+		strbuf_addf(out, "\n* %s: (%d commits)\n", name, count);
+	else
+		strbuf_addf(out, "\n* %s:\n", name);
+
+	if (origin_data->is_local_branch && use_branch_desc)
+		add_branch_desc(out, name);
+
+	for (i = 0; i < subjects.nr; i++)
+		if (i >= limit)
+			strbuf_addstr(out, "  ...\n");
+		else
+			strbuf_addf(out, "  %s\n", subjects.items[i].string);
+
+	clear_commit_marks((struct commit *)branch, flags);
+	clear_commit_marks(head, flags);
+	free_commit_list(rev->commits);
+	rev->commits = NULL;
+	rev->pending.nr = 0;
+
+	string_list_clear(&authors, 0);
+	string_list_clear(&committers, 0);
+	string_list_clear(&subjects, 0);
+}
+
+static void fmt_merge_msg_title(struct strbuf *out,
+				const char *current_branch)
+{
+	int i = 0;
+	char *sep = "";
+
+	strbuf_addstr(out, "Merge ");
+	for (i = 0; i < srcs.nr; i++) {
+		struct src_data *src_data = srcs.items[i].util;
+		const char *subsep = "";
+
+		strbuf_addstr(out, sep);
+		sep = "; ";
+
+		if (src_data->head_status == 1) {
+			strbuf_addstr(out, srcs.items[i].string);
+			continue;
+		}
+		if (src_data->head_status == 3) {
+			subsep = ", ";
+			strbuf_addstr(out, "HEAD");
+		}
+		if (src_data->branch.nr) {
+			strbuf_addstr(out, subsep);
+			subsep = ", ";
+			print_joined("branch ", "branches ", &src_data->branch,
+					out);
+		}
+		if (src_data->r_branch.nr) {
+			strbuf_addstr(out, subsep);
+			subsep = ", ";
+			print_joined("remote-tracking branch ", "remote-tracking branches ",
+					&src_data->r_branch, out);
+		}
+		if (src_data->tag.nr) {
+			strbuf_addstr(out, subsep);
+			subsep = ", ";
+			print_joined("tag ", "tags ", &src_data->tag, out);
+		}
+		if (src_data->generic.nr) {
+			strbuf_addstr(out, subsep);
+			print_joined("commit ", "commits ", &src_data->generic,
+					out);
+		}
+		if (strcmp(".", srcs.items[i].string))
+			strbuf_addf(out, " of %s", srcs.items[i].string);
+	}
+
+	if (!strcmp("master", current_branch))
+		strbuf_addch(out, '\n');
+	else
+		strbuf_addf(out, " into %s\n", current_branch);
+}
+
+static void fmt_tag_signature(struct strbuf *tagbuf,
+			      struct strbuf *sig,
+			      const char *buf,
+			      unsigned long len)
+{
+	const char *tag_body = strstr(buf, "\n\n");
+	if (tag_body) {
+		tag_body += 2;
+		strbuf_add(tagbuf, tag_body, buf + len - tag_body);
+	}
+	strbuf_complete_line(tagbuf);
+	if (sig->len) {
+		strbuf_addch(tagbuf, '\n');
+		strbuf_add_commented_lines(tagbuf, sig->buf, sig->len);
+	}
+}
+
+static void fmt_merge_msg_sigs(struct strbuf *out)
+{
+	int i, tag_number = 0, first_tag = 0;
+	struct strbuf tagbuf = STRBUF_INIT;
+
+	for (i = 0; i < origins.nr; i++) {
+		struct object_id *oid = origins.items[i].util;
+		enum object_type type;
+		unsigned long size, len;
+		char *buf = read_object_file(oid, &type, &size);
+		struct strbuf sig = STRBUF_INIT;
+
+		if (!buf || type != OBJ_TAG)
+			goto next;
+		len = parse_signature(buf, size);
+
+		if (size == len)
+			; /* merely annotated */
+		else if (verify_signed_buffer(buf, len, buf + len, size - len, &sig, NULL)) {
+			if (!sig.len)
+				strbuf_addstr(&sig, "gpg verification failed.\n");
+		}
+
+		if (!tag_number++) {
+			fmt_tag_signature(&tagbuf, &sig, buf, len);
+			first_tag = i;
+		} else {
+			if (tag_number == 2) {
+				struct strbuf tagline = STRBUF_INIT;
+				strbuf_addch(&tagline, '\n');
+				strbuf_add_commented_lines(&tagline,
+						origins.items[first_tag].string,
+						strlen(origins.items[first_tag].string));
+				strbuf_insert(&tagbuf, 0, tagline.buf,
+					      tagline.len);
+				strbuf_release(&tagline);
+			}
+			strbuf_addch(&tagbuf, '\n');
+			strbuf_add_commented_lines(&tagbuf,
+					origins.items[i].string,
+					strlen(origins.items[i].string));
+			fmt_tag_signature(&tagbuf, &sig, buf, len);
+		}
+		strbuf_release(&sig);
+	next:
+		free(buf);
+	}
+	if (tagbuf.len) {
+		strbuf_addch(out, '\n');
+		strbuf_addbuf(out, &tagbuf);
+	}
+	strbuf_release(&tagbuf);
+}
+
+static void find_merge_parents(struct merge_parents *result,
+			       struct strbuf *in, struct object_id *head)
+{
+	struct commit_list *parents;
+	struct commit *head_commit;
+	int pos = 0, i, j;
+
+	parents = NULL;
+	while (pos < in->len) {
+		int len;
+		char *p = in->buf + pos;
+		char *newline = strchr(p, '\n');
+		const char *q;
+		struct object_id oid;
+		struct commit *parent;
+		struct object *obj;
+
+		len = newline ? newline - p : strlen(p);
+		pos += len + !!newline;
+
+		if (parse_oid_hex(p, &oid, &q) ||
+		    q[0] != '\t' ||
+		    q[1] != '\t')
+			continue; /* skip not-for-merge */
+		/*
+		 * Do not use get_merge_parent() here; we do not have
+		 * "name" here and we do not want to contaminate its
+		 * util field yet.
+		 */
+		obj = parse_object(the_repository, &oid);
+		parent = (struct commit *)peel_to_type(NULL, 0, obj, OBJ_COMMIT);
+		if (!parent)
+			continue;
+		commit_list_insert(parent, &parents);
+		add_merge_parent(result, &obj->oid, &parent->object.oid);
+	}
+	head_commit = lookup_commit(the_repository, head);
+	if (head_commit)
+		commit_list_insert(head_commit, &parents);
+	reduce_heads_replace(&parents);
+
+	while (parents) {
+		struct commit *cmit = pop_commit(&parents);
+		for (i = 0; i < result->nr; i++)
+			if (oideq(&result->item[i].commit, &cmit->object.oid))
+				result->item[i].used = 1;
+	}
+
+	for (i = j = 0; i < result->nr; i++) {
+		if (result->item[i].used) {
+			if (i != j)
+				result->item[j] = result->item[i];
+			j++;
+		}
+	}
+	result->nr = j;
+}
+
+
+int fmt_merge_msg(struct strbuf *in, struct strbuf *out,
+		  struct fmt_merge_msg_opts *opts)
+{
+	int i = 0, pos = 0;
+	struct object_id head_oid;
+	const char *current_branch;
+	void *current_branch_to_free;
+	struct merge_parents merge_parents;
+
+	memset(&merge_parents, 0, sizeof(merge_parents));
+
+	/* get current branch */
+	current_branch = current_branch_to_free =
+		resolve_refdup("HEAD", RESOLVE_REF_READING, &head_oid, NULL);
+	if (!current_branch)
+		die("No current branch");
+	if (starts_with(current_branch, "refs/heads/"))
+		current_branch += 11;
+
+	find_merge_parents(&merge_parents, in, &head_oid);
+
+	/* get a line */
+	while (pos < in->len) {
+		int len;
+		char *newline, *p = in->buf + pos;
+
+		newline = strchr(p, '\n');
+		len = newline ? newline - p : strlen(p);
+		pos += len + !!newline;
+		i++;
+		p[len] = 0;
+		if (handle_line(p, &merge_parents))
+			die("error in line %d: %.*s", i, len, p);
+	}
+
+	if (opts->add_title && srcs.nr)
+		fmt_merge_msg_title(out, current_branch);
+
+	if (origins.nr)
+		fmt_merge_msg_sigs(out);
+
+	if (opts->shortlog_len) {
+		struct commit *head;
+		struct rev_info rev;
+
+		head = lookup_commit_or_die(&head_oid, "HEAD");
+		repo_init_revisions(the_repository, &rev, NULL);
+		rev.commit_format = CMIT_FMT_ONELINE;
+		rev.ignore_merges = 1;
+		rev.limited = 1;
+
+		strbuf_complete_line(out);
+
+		for (i = 0; i < origins.nr; i++)
+			shortlog(origins.items[i].string,
+				 origins.items[i].util,
+				 head, &rev, opts, out);
+	}
+
+	strbuf_complete_line(out);
+	free(current_branch_to_free);
+	free(merge_parents.item);
+	return 0;
+}
diff --git a/fmt-merge-msg.h b/fmt-merge-msg.h
index 01e3aa88c5..f2ab0e0085 100644
--- a/fmt-merge-msg.h
+++ b/fmt-merge-msg.h
@@ -1,7 +1,20 @@
 #ifndef FMT_MERGE_MSG_H
 #define FMT_MERGE_MSG_H
 
+#include "strbuf.h"
+
+#define DEFAULT_MERGE_LOG_LEN 20
+
+struct fmt_merge_msg_opts {
+	unsigned add_title:1,
+		credit_people:1;
+	int shortlog_len;
+};
+
 extern int merge_log_config;
 int fmt_merge_msg_config(const char *key, const char *value, void *cb);
+int fmt_merge_msg(struct strbuf *in, struct strbuf *out,
+		  struct fmt_merge_msg_opts *);
+
 
 #endif /* FMT_MERGE_MSG_H */
-- 
2.25.0.114.g5b0ca878e0