dir.c: refactor is_excluded_from_list()

The excluded function uses a new helper function called
last_exclude_matching_from_list() to perform the inner loop over all of
the exclude patterns.  The helper just tells us whether the path is
included, excluded, or undecided.

However, it may be useful to know _which_ pattern was triggered.  So
let's pass out the entire exclude match, which contains the status
information we were already passing out.

Further patches can make use of this.

This is a modified forward port of a patch from 2009 by Jeff King:
http://article.gmane.org/gmane.comp.version-control.git/108815

Signed-off-by: Adam Spiers <git@adamspiers.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

dir.c

@@ -602,22 +602,26 @@ int match_pathname(const char *pathname, int pathlen,
 	return fnmatch_icase(pattern, name, FNM_PATHNAME) == 0;
 }
 
-/* Scan the list and let the last match determine the fate.
- * Return 1 for exclude, 0 for include and -1 for undecided.
+/*
+ * Scan the given exclude list in reverse to see whether pathname
+ * should be ignored.  The first match (i.e. the last on the list), if
+ * any, determines the fate.  Returns the exclude_list element which
+ * matched, or NULL for undecided.
  */
-int is_excluded_from_list(const char *pathname,
-			  int pathlen, const char *basename, int *dtype,
-			  struct exclude_list *el)
+static struct exclude *last_exclude_matching_from_list(const char *pathname,
+						       int pathlen,
+						       const char *basename,
+						       int *dtype,
+						       struct exclude_list *el)
 {
 	int i;
 
 	if (!el->nr)
-		return -1;	/* undefined */
+		return NULL;	/* undefined */
 
 	for (i = el->nr - 1; 0 <= i; i--) {
 		struct exclude *x = el->excludes[i];
 		const char *exclude = x->pattern;
-		int to_exclude = x->flags & EXC_FLAG_NEGATIVE ? 0 : 1;
 		int prefix = x->nowildcardlen;
 
 		if (x->flags & EXC_FLAG_MUSTBEDIR) {
@@ -632,16 +636,31 @@ int is_excluded_from_list(const char *pathname,
 					   pathlen - (basename - pathname),
 					   exclude, prefix, x->patternlen,
 					   x->flags))
-				return to_exclude;
+				return x;
 			continue;
 		}
 
 		assert(x->baselen == 0 || x->base[x->baselen - 1] == '/');
 		if (match_pathname(pathname, pathlen,
 				   x->base, x->baselen ? x->baselen - 1 : 0,
 				   exclude, prefix, x->patternlen, x->flags))
-			return to_exclude;
+			return x;
 	}
+	return NULL; /* undecided */
+}
+
+/*
+ * Scan the list and let the last match determine the fate.
+ * Return 1 for exclude, 0 for include and -1 for undecided.
+ */
+int is_excluded_from_list(const char *pathname,
+			  int pathlen, const char *basename, int *dtype,
+			  struct exclude_list *el)
+{
+	struct exclude *exclude;
+	exclude = last_exclude_matching_from_list(pathname, pathlen, basename, dtype, el);
+	if (exclude)
+		return exclude->flags & EXC_FLAG_NEGATIVE ? 0 : 1;
 	return -1; /* undecided */
 }