path/filepath: Panic in Match when parsing invalid character range.

Fixes #5668.

R=golang-dev, rsc, r
CC=golang-dev
https://golang.org/cl/12001056

src/pkg/path/filepath/match.go

@@ -132,6 +132,12 @@ func matchChunk(chunk, s string) (rest string, ok bool, err error) {
 			r, n := utf8.DecodeRuneInString(s)
 			s = s[n:]
 			chunk = chunk[1:]
+			// We can't end right after '[', we're expecting at least
+			// a closing bracket and possibly a caret.
+			if len(chunk) == 0 {
+				err = ErrBadPattern
+				return
+			}
 			// possibly negated
 			negated := chunk[0] == '^'
 			if negated {

src/pkg/path/filepath/match_test.go

@@ -65,6 +65,11 @@ var matchTests = []MatchTest{
 	{"[-x]", "a", false, ErrBadPattern},
 	{"\\", "a", false, ErrBadPattern},
 	{"[a-b-c]", "a", false, ErrBadPattern},
+	{"[", "a", false, ErrBadPattern},
+	{"[^", "a", false, ErrBadPattern},
+	{"[^bc", "a", false, ErrBadPattern},
+	{"a[", "a", false, nil},
+	{"a[", "ab", false, ErrBadPattern},
 	{"*x", "xxx", true, nil},
 }
 

src/pkg/path/match_test.go

@@ -61,6 +61,11 @@ var matchTests = []MatchTest{
 	{"[-x]", "a", false, ErrBadPattern},
 	{"\\", "a", false, ErrBadPattern},
 	{"[a-b-c]", "a", false, ErrBadPattern},
+	{"[", "a", false, ErrBadPattern},
+	{"[^", "a", false, ErrBadPattern},
+	{"[^bc", "a", false, ErrBadPattern},
+	{"a[", "a", false, nil},
+	{"a[", "ab", false, ErrBadPattern},
 	{"*x", "xxx", true, nil},
 }