bind: correctly lowercasing all caps names

Fixes golang/go#13031

Change-Id: I6cae8e303d0d929e26c44cbdf1c243e98dabb766
Reviewed-on: https://go-review.googlesource.com/16270
Reviewed-by: David Crawshaw <crawshaw@golang.org>

bind/bind_test.go

@@ -212,3 +212,23 @@ func TestCustomPrefix(t *testing.T) {
 		}
 	}
 }
+
+func TestLowerFirst(t *testing.T) {
+	testCases := []struct {
+		in, want string
+	}{
+		{"", ""},
+		{"Hello", "hello"},
+		{"HelloGopher", "helloGopher"},
+		{"hello", "hello"},
+		{"ID", "id"},
+		{"IDOrName", "idOrName"},
+		{"ΓειαΣας", "γειαΣας"},
+	}
+
+	for _, tc := range testCases {
+		if got := lowerFirst(tc.in); got != tc.want {
+			t.Errorf("lowerFirst(%q) = %q; want %q", tc.in, got, tc.want)
+		}
+	}
+}

bind/genobjc.go

@@ -1006,6 +1006,18 @@ func lowerFirst(s string) string {
 	if s == "" {
 		return ""
 	}
-	r, n := utf8.DecodeRuneInString(s)
-	return string(unicode.ToLower(r)) + s[n:]
+
+	var conv []rune
+	for len(s) > 0 {
+		r, n := utf8.DecodeRuneInString(s)
+		if !unicode.IsUpper(r) {
+			if l := len(conv); l > 1 {
+				conv[l-1] = unicode.ToUpper(conv[l-1])
+			}
+			return string(conv) + s
+		}
+		conv = append(conv, unicode.ToLower(r))
+		s = s[n:]
+	}
+	return string(conv)
 }