3 files changed, 24 insertions, 25 deletions

diff --git a/builtin/branch.c b/builtin/branch.c
index e6c2655af6..7c20e049a2 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -366,17 +366,8 @@ static const char *quote_literal_for_format(const char *s)
 	static struct strbuf buf = STRBUF_INIT;
 
 	strbuf_reset(&buf);
-	while (*s) {
-		const char *ep = strchrnul(s, '%');
-		if (s < ep)
-			strbuf_add(&buf, s, ep - s);
-		if (*ep == '%') {
-			strbuf_addstr(&buf, "%%");
-			s = ep + 1;
-		} else {
-			s = ep;
-		}
-	}
+	while (strbuf_expand_step(&buf, &s))
+		strbuf_addstr(&buf, "%%");
 	return buf.buf;
 }
 
diff --git a/strbuf.c b/strbuf.c
index 08eec8f1d8..a90b597da1 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -415,19 +415,24 @@ void strbuf_vaddf(struct strbuf *sb, const char *fmt, va_list ap)
 	strbuf_setlen(sb, sb->len + len);
 }
 
+int strbuf_expand_step(struct strbuf *sb, const char **formatp)
+{
+	const char *format = *formatp;
+	const char *percent = strchrnul(format, '%');
+
+	strbuf_add(sb, format, percent - format);
+	if (!*percent)
+		return 0;
+	*formatp = percent + 1;
+	return 1;
+}
+
 void strbuf_expand(struct strbuf *sb, const char *format, expand_fn_t fn,
 		   void *context)
 {
-	for (;;) {
-		const char *percent;
+	while (strbuf_expand_step(sb, &format)) {
 		size_t consumed;
 
-		percent = strchrnul(format, '%');
-		strbuf_add(sb, format, percent - format);
-		if (!*percent)
-			break;
-		format = percent + 1;
-
 		if (*format == '%') {
 			strbuf_addch(sb, '%');
 			format++;
@@ -1022,12 +1027,7 @@ void strbuf_addftime(struct strbuf *sb, const char *fmt, const struct tm *tm,
 	 * we want for %z, but the computation for %s has to convert to number
 	 * of seconds.
 	 */
-	for (;;) {
-		const char *percent = strchrnul(fmt, '%');
-		strbuf_add(&munged_fmt, fmt, percent - fmt);
-		if (!*percent)
-			break;
-		fmt = percent + 1;
+	while (strbuf_expand_step(&munged_fmt, &fmt)) {
 		switch (*fmt) {
 		case '%':
 			strbuf_addstr(&munged_fmt, "%%");
diff --git a/strbuf.h b/strbuf.h
index 3dfeadb44c..a189f12b84 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -372,6 +372,14 @@ size_t strbuf_expand_dict_cb(struct strbuf *sb,
 			     void *context);
 
 /**
+ * If the string pointed to by `formatp` contains a percent sign ("%"),
+ * advance it to point to the character following the next one and
+ * return 1, otherwise return 0.  Append the substring before that
+ * percent sign to `sb`, or the whole string if there is none.
+ */
+int strbuf_expand_step(struct strbuf *sb, const char **formatp);
+
+/**
  * Append the contents of one strbuf to another, quoting any
  * percent signs ("%") into double-percents ("%%") in the
  * destination. This is useful for literal data to be fed to either