coccicheck: make transformation for strbuf_addf(sb, "...") more precise

We can replace strbuf_addf() calls that just add a simple string with
calls to strbuf_addstr() to make the intent clearer.  We need to be
careful if that string contains printf format specifications like %%,
though, as a simple replacement would change the output.

Add checks to the semantic patch to make sure we only perform the
transformation if the second argument is a string constant (possibly
translated) that doesn't contain any percent signs.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/coccinelle/strbuf.cocci

@@ -1,8 +1,31 @@
+@ strbuf_addf_with_format_only @
+expression E;
+constant fmt;
 @@
-expression E1, E2;
+  strbuf_addf(E,
+(
+  fmt
+|
+  _(fmt)
+)
+  );
+
+@ script:python @
+fmt << strbuf_addf_with_format_only.fmt;
 @@
-- strbuf_addf(E1, E2);
+cocci.include_match("%" not in fmt)
-+ strbuf_addstr(E1, E2);
+
+@ extends strbuf_addf_with_format_only @
+@@
+- strbuf_addf
++ strbuf_addstr
+  (E,
+(
+  fmt
+|
+  _(fmt)
+)
+  );
 
 @@
 expression E1, E2;