Fix rewrite_diff() name quoting.

This moves the logic to quote two paths (prefix + path) in
C-style introduced in the previous commit from the
dump_quoted_path() in combine-diff.c to quote.c, and uses it to
fix rewrite_diff() that never C-quoted the pathnames correctly.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

combine-diff.c

@@ -656,16 +656,7 @@ static void dump_quoted_path(const char *head,
 	strbuf_reset(&buf);
 	strbuf_addstr(&buf, c_meta);
 	strbuf_addstr(&buf, head);
-	if (quote_c_style(prefix, NULL, NULL, 0) ||
-	    quote_c_style(path, NULL, NULL, 0)) {
-		strbuf_addch(&buf, '"');
-		quote_c_style(prefix, &buf, NULL, 1);
-		quote_c_style(path, &buf, NULL, 1);
-		strbuf_addch(&buf, '"');
-	} else {
-		strbuf_addstr(&buf, prefix);
-		strbuf_addstr(&buf, path);
-	}
+	quote_two_c_style(&buf, prefix, path, 0);
 	strbuf_addstr(&buf, c_reset);
 	puts(buf.buf);
 }

diff.c

@@ -300,19 +300,25 @@ static void emit_rewrite_diff(const char *name_a,
 	const char *old = diff_get_color(color_diff, DIFF_FILE_OLD);
 	const char *new = diff_get_color(color_diff, DIFF_FILE_NEW);
 	const char *reset = diff_get_color(color_diff, DIFF_RESET);
+	static struct strbuf a_name = STRBUF_INIT, b_name = STRBUF_INIT;
 
 	name_a += (*name_a == '/');
 	name_b += (*name_b == '/');
 	name_a_tab = strchr(name_a, ' ') ? "\t" : "";
 	name_b_tab = strchr(name_b, ' ') ? "\t" : "";
 
+	strbuf_reset(&a_name);
+	strbuf_reset(&b_name);
+	quote_two_c_style(&a_name, o->a_prefix, name_a, 0);
+	quote_two_c_style(&b_name, o->b_prefix, name_b, 0);
+
 	diff_populate_filespec(one, 0);
 	diff_populate_filespec(two, 0);
 	lc_a = count_lines(one->data, one->size);
 	lc_b = count_lines(two->data, two->size);
-	printf("%s--- %s%s%s%s\n%s+++ %s%s%s%s\n%s@@ -",
-	       metainfo, o->a_prefix, name_a, name_a_tab, reset,
-	       metainfo, o->b_prefix, name_b, name_b_tab, reset, fraginfo);
+	printf("%s--- %s%s%s\n%s+++ %s%s%s\n%s@@ -",
+	       metainfo, a_name.buf, name_a_tab, reset,
+	       metainfo, b_name.buf, name_b_tab, reset, fraginfo);
 	print_line_count(lc_a);
 	printf(" +");
 	print_line_count(lc_b);

quote.c

@@ -213,6 +213,22 @@ size_t quote_c_style(const char *name, struct strbuf *sb, FILE *fp, int nodq)
 	return quote_c_style_counted(name, -1, sb, fp, nodq);
 }
 
+void quote_two_c_style(struct strbuf *sb, const char *prefix, const char *path, int nodq)
+{
+	if (quote_c_style(prefix, NULL, NULL, 0) ||
+	    quote_c_style(path, NULL, NULL, 0)) {
+		if (!nodq)
+			strbuf_addch(sb, '"');
+		quote_c_style(prefix, sb, NULL, 1);
+		quote_c_style(path, sb, NULL, 1);
+		if (!nodq)
+			strbuf_addch(sb, '"');
+	} else {
+		strbuf_addstr(sb, prefix);
+		strbuf_addstr(sb, path);
+	}
+}
+
 void write_name_quoted(const char *name, FILE *fp, int terminator)
 {
 	if (terminator) {

quote.h

@@ -41,6 +41,7 @@ extern char *sq_dequote(char *);
 
 extern int unquote_c_style(struct strbuf *, const char *quoted, const char **endp);
 extern size_t quote_c_style(const char *name, struct strbuf *, FILE *, int no_dq);
+extern void quote_two_c_style(struct strbuf *, const char *, const char *, int);
 
 extern void write_name_quoted(const char *name, FILE *, int terminator);
 extern void write_name_quotedpfx(const char *pfx, size_t pfxlen,