revert: Eliminate global "commit" variable

Functions which act on commits currently rely on a file-scope static
variable to be set before they're called.  Consequently, the API and
corresponding callsites are ugly and unclear.  Remove this variable
and change their API to accept the commit to act on as additional
argument so that the callsites change from looking like

  commit = prepare_a_commit();
  act_on_commit();

to looking like

  commit = prepare_a_commit();
  act_on_commit(commit);

This change is also in line with our long-term goal of exposing some
of these functions through a public API.

Inspired-by: Christian Couder <chriscool@tuxfamily.org>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/revert.c

@@ -37,7 +37,6 @@ static const char * const cherry_pick_usage[] = {
 
 static int edit, record_origin, no_commit, mainline, signoff, allow_ff;
 static enum { REVERT, CHERRY_PICK } action;
-static struct commit *commit;
 static int commit_argc;
 static const char **commit_argv;
 static int allow_rerere_auto;
@@ -116,25 +115,25 @@ struct commit_message {
 	const char *message;
 };
 
-static int get_message(const char *raw_message, struct commit_message *out)
+static int get_message(struct commit *commit, struct commit_message *out)
 {
 	const char *encoding;
 	const char *abbrev, *subject;
 	int abbrev_len, subject_len;
 	char *q;
 
-	if (!raw_message)
+	if (!commit->buffer)
 		return -1;
-	encoding = get_encoding(raw_message);
+	encoding = get_encoding(commit->buffer);
 	if (!encoding)
 		encoding = "UTF-8";
 	if (!git_commit_encoding)
 		git_commit_encoding = "UTF-8";
 
 	out->reencoded_message = NULL;
-	out->message = raw_message;
+	out->message = commit->buffer;
 	if (strcmp(encoding, git_commit_encoding))
-		out->reencoded_message = reencode_string(raw_message,
+		out->reencoded_message = reencode_string(commit->buffer,
 					git_commit_encoding, encoding);
 	if (out->reencoded_message)
 		out->message = out->reencoded_message;
@@ -182,7 +181,7 @@ static char *get_encoding(const char *message)
 	return NULL;
 }
 
-static void write_cherry_pick_head(void)
+static void write_cherry_pick_head(struct commit *commit)
 {
 	int fd;
 	struct strbuf buf = STRBUF_INIT;
@@ -355,7 +354,7 @@ static int run_git_commit(const char *defmsg)
 	return run_command_v_opt(args, RUN_GIT_CMD);
 }
 
-static int do_pick_commit(void)
+static int do_pick_commit(struct commit *commit)
 {
 	unsigned char head[20];
 	struct commit *base, *next, *parent;
@@ -417,7 +416,7 @@ static int do_pick_commit(void)
 		die(_("%s: cannot parse parent commit %s"),
 		    me, sha1_to_hex(parent->object.sha1));
 
-	if (get_message(commit->buffer, &msg) != 0)
+	if (get_message(commit, &msg) != 0)
 		die(_("Cannot get commit message for %s"),
 				sha1_to_hex(commit->object.sha1));
 
@@ -470,7 +469,7 @@ static int do_pick_commit(void)
 			strbuf_addstr(&msgbuf, ")\n");
 		}
 		if (!no_commit)
-			write_cherry_pick_head();
+			write_cherry_pick_head(commit);
 	}
 
 	if (!strategy || !strcmp(strategy, "recursive") || action == REVERT) {
@@ -548,6 +547,7 @@ static void read_and_refresh_cache(const char *me)
 static int revert_or_cherry_pick(int argc, const char **argv)
 {
 	struct rev_info revs;
+	struct commit *commit;
 
 	git_config(git_default_config, NULL);
 	me = action == REVERT ? "revert" : "cherry-pick";
@@ -570,7 +570,7 @@ static int revert_or_cherry_pick(int argc, const char **argv)
 	prepare_revs(&revs);
 
 	while ((commit = get_revision(&revs))) {
-		int res = do_pick_commit();
+		int res = do_pick_commit(commit);
 		if (res)
 			return res;
 	}