use get_commit_buffer everywhere

Each of these sites assumes that commit->buffer is valid.
Since they would segfault if this was not the case, they are
likely to be correct in practice. However, we can
future-proof them by using get_commit_buffer.

And as a side effect, we abstract away the final bare uses
of commit->buffer.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fast-export.c

@@ -279,6 +279,7 @@ static const char *find_encoding(const char *begin, const char *end)
 static void handle_commit(struct commit *commit, struct rev_info *rev)
 {
 	int saved_output_format = rev->diffopt.output_format;
+	const char *commit_buffer;
 	const char *author, *author_end, *committer, *committer_end;
 	const char *encoding, *message;
 	char *reencoded = NULL;
@@ -288,7 +289,8 @@ static void handle_commit(struct commit *commit, struct rev_info *rev)
 	rev->diffopt.output_format = DIFF_FORMAT_CALLBACK;
 
 	parse_commit_or_die(commit);
-	author = strstr(commit->buffer, "\nauthor ");
+	commit_buffer = get_commit_buffer(commit);
+	author = strstr(commit_buffer, "\nauthor ");
 	if (!author)
 		die ("Could not find author in commit %s",
 		     sha1_to_hex(commit->object.sha1));
@@ -335,6 +337,7 @@ static void handle_commit(struct commit *commit, struct rev_info *rev)
 			  ? strlen(message) : 0),
 	       reencoded ? reencoded : message ? message : "");
 	free(reencoded);
+	unuse_commit_buffer(commit, commit_buffer);
 
 	for (i = 0, p = commit->parents; p; p = p->next) {
 		int mark = get_object_mark(&p->item->object);

builtin/fmt-merge-msg.c

@@ -230,12 +230,14 @@ static void add_branch_desc(struct strbuf *out, const char *name)
 static void record_person(int which, struct string_list *people,
 			  struct commit *commit)
 {
+	const char *buffer;
 	char *name_buf, *name, *name_end;
 	struct string_list_item *elem;
 	const char *field;
 
 	field = (which == 'a') ? "\nauthor " : "\ncommitter ";
-	name = strstr(commit->buffer, field);
+	buffer = get_commit_buffer(commit);
+	name = strstr(buffer, field);
 	if (!name)
 		return;
 	name += strlen(field);
@@ -247,6 +249,7 @@ static void record_person(int which, struct string_list *people,
 	if (name_end < name)
 		return;
 	name_buf = xmemdupz(name, name_end - name + 1);
+	unuse_commit_buffer(commit, buffer);
 
 	elem = string_list_lookup(people, name_buf);
 	if (!elem) {

builtin/log.c

@@ -918,9 +918,12 @@ static void make_cover_letter(struct rev_info *rev, int use_stdout,
 	log_write_email_headers(rev, head, &pp.subject, &pp.after_subject,
 				&need_8bit_cte);
 
-	for (i = 0; !need_8bit_cte && i < nr; i++)
-		if (has_non_ascii(list[i]->buffer))
+	for (i = 0; !need_8bit_cte && i < nr; i++) {
+		const char *buf = get_commit_buffer(list[i]);
+		if (has_non_ascii(buf))
 			need_8bit_cte = 1;
+		unuse_commit_buffer(list[i], buf);
+	}
 
 	if (!branch_name)
 		branch_name = find_branch_name(rev);

fsck.c

@@ -276,9 +276,10 @@ static int fsck_ident(const char **ident, struct object *obj, fsck_error error_f
 	return 0;
 }
 
-static int fsck_commit(struct commit *commit, fsck_error error_func)
+static int fsck_commit_buffer(struct commit *commit, const char *buffer,
+			      fsck_error error_func)
 {
-	const char *buffer = commit->buffer, *tmp;
+	const char *tmp;
 	unsigned char tree_sha1[20], sha1[20];
 	struct commit_graft *graft;
 	int parents = 0;
@@ -336,6 +337,14 @@ static int fsck_commit(struct commit *commit, fsck_error error_func)
 	return 0;
 }
 
+static int fsck_commit(struct commit *commit, fsck_error error_func)
+{
+	const char *buffer = get_commit_buffer(commit);
+	int ret = fsck_commit_buffer(commit, buffer, error_func);
+	unuse_commit_buffer(commit, buffer);
+	return ret;
+}
+
 static int fsck_tag(struct tag *tag, fsck_error error_func)
 {
 	struct object *tagged = tag->tagged;

merge-recursive.c

@@ -190,9 +190,11 @@ static void output_commit_title(struct merge_options *o, struct commit *commit)
 			printf(_("(bad commit)\n"));
 		else {
 			const char *title;
-			int len = find_commit_subject(commit->buffer, &title);
+			const char *msg = get_commit_buffer(commit);
+			int len = find_commit_subject(msg, &title);
 			if (len)
 				printf("%.*s\n", len, title);
+			unuse_commit_buffer(commit, msg);
 		}
 	}
 }

notes-merge.c

@@ -672,7 +672,8 @@ int notes_merge_commit(struct notes_merge_options *o,
 	DIR *dir;
 	struct dirent *e;
 	struct strbuf path = STRBUF_INIT;
-	char *msg = strstr(partial_commit->buffer, "\n\n");
+	const char *buffer = get_commit_buffer(partial_commit);
+	const char *msg = strstr(buffer, "\n\n");
 	int baselen;
 
 	strbuf_addstr(&path, git_path(NOTES_MERGE_WORKTREE));
@@ -721,6 +722,7 @@ int notes_merge_commit(struct notes_merge_options *o,
 
 	create_notes_commit(partial_tree, partial_commit->parents,
 			    msg, strlen(msg), result_sha1);
+	unuse_commit_buffer(partial_commit, buffer);
 	if (o->verbosity >= 4)
 		printf("Finalized notes merge commit: %s\n",
 			sha1_to_hex(result_sha1));

sequencer.c

@@ -662,10 +662,12 @@ static int format_todo(struct strbuf *buf, struct commit_list *todo_list,
 	int subject_len;
 
 	for (cur = todo_list; cur; cur = cur->next) {
+		const char *commit_buffer = get_commit_buffer(cur->item);
 		sha1_abbrev = find_unique_abbrev(cur->item->object.sha1, DEFAULT_ABBREV);
-		subject_len = find_commit_subject(cur->item->buffer, &subject);
+		subject_len = find_commit_subject(commit_buffer, &subject);
 		strbuf_addf(buf, "%s %s %.*s\n", action_str, sha1_abbrev,
 			subject_len, subject);
+		unuse_commit_buffer(cur->item, commit_buffer);
 	}
 	return 0;
 }