reformat informational commit message

When committing, we print a message like:

  Created [DETACHED commit] <hash> (<subject>) on <branch>

The most useful bit of information there (besides the
detached status, if it is present) is which branch you made
the commit on. However,  it is sometimes hard to see because
the subject dominates the line.

Instead, let's put the most useful information (detached
status and commit branch) on the far left, with the subject
(which is least likely to be interesting) on the far right.

We'll use brackets to offset the branch name so the line is
not mistaken for an error line of the form "program: some
sort of error". E.g.,:

  [jk/bikeshed] created bd8098f: "reformat informational commit message"
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

builtin-commit.c

@@ -878,35 +878,13 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	return commitable ? 0 : 1;
 }
 
-static char *get_commit_format_string(void)
-{
-	unsigned char sha[20];
-	const char *head = resolve_ref("HEAD", sha, 0, NULL);
-	struct strbuf buf = STRBUF_INIT;
-
-	/* use shouty-caps if we're on detached HEAD */
-	strbuf_addf(&buf, "format:%s", strcmp("HEAD", head) ? "" : "DETACHED commit");
-	strbuf_addstr(&buf, "%h (%s)");
-
-	if (!prefixcmp(head, "refs/heads/")) {
-		const char *cp;
-		strbuf_addstr(&buf, " on ");
-		for (cp = head + 11; *cp; cp++) {
-			if (*cp == '%')
-				strbuf_addstr(&buf, "%x25");
-			else
-				strbuf_addch(&buf, *cp);
-		}
-	}
-
-	return strbuf_detach(&buf, NULL);
-}
-
 static void print_summary(const char *prefix, const unsigned char *sha1)
 {
 	struct rev_info rev;
 	struct commit *commit;
-	char *format = get_commit_format_string();
+	static const char *format = "format:%h: \"%s\"";
+	unsigned char junk_sha1[20];
+	const char *head = resolve_ref("HEAD", junk_sha1, 0, NULL);
 
 	commit = lookup_commit(sha1);
 	if (!commit)
@@ -931,7 +909,13 @@ static void print_summary(const char *prefix, const unsigned char *sha1)
 	rev.diffopt.break_opt = 0;
 	diff_setup_done(&rev.diffopt);
 
-	printf("Created %s", initial_commit ? "root-commit " : "");
+	printf("[%s%s]: created ",
+		!prefixcmp(head, "refs/heads/") ?
+			head + 11 :
+			!strcmp(head, "HEAD") ?
+				"detached HEAD" :
+				head,
+		initial_commit ? " (root-commit)" : "");
 
 	if (!log_tree_commit(&rev, commit)) {
 		struct strbuf buf = STRBUF_INIT;
@@ -939,7 +923,6 @@ static void print_summary(const char *prefix, const unsigned char *sha1)
 		printf("%s\n", buf.buf);
 		strbuf_release(&buf);
 	}
-	free(format);
 }
 
 static int git_commit_config(const char *k, const char *v, void *cb)