Add android.Expand
Add android.Expand to expand $() variables in properties.
Test: expand_test
Bug: 31948427
Change-Id: Id30856a1d21d02e8997fcf2358e4a5feeede05be
diff --git a/android/expand.go b/android/expand.go
new file mode 100644
index 0000000..dafb2b6
--- /dev/null
+++ b/android/expand.go
@@ -0,0 +1,72 @@
+// Copyright 2016 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package android
+
+import (
+ "fmt"
+ "strings"
+ "unicode"
+)
+
+// Expand substitutes $() variables in a string
+// $(var) is passed to Expander(var)
+// $$ is converted to $
+func Expand(s string, mapping func(string) (string, error)) (string, error) {
+ // based on os.Expand
+ buf := make([]byte, 0, 2*len(s))
+ i := 0
+ for j := 0; j < len(s); j++ {
+ if s[j] == '$' {
+ if j+1 >= len(s) {
+ return "", fmt.Errorf("expected character after '$'")
+ }
+ buf = append(buf, s[i:j]...)
+ value, w, err := getMapping(s[j+1:], mapping)
+ if err != nil {
+ return "", err
+ }
+ buf = append(buf, value...)
+ j += w
+ i = j + 1
+ }
+ }
+ return string(buf) + s[i:], nil
+}
+
+func getMapping(s string, mapping func(string) (string, error)) (string, int, error) {
+ switch s[0] {
+ case '(':
+ // Scan to closing brace
+ for i := 1; i < len(s); i++ {
+ if s[i] == ')' {
+ ret, err := mapping(strings.TrimSpace(s[1:i]))
+ return ret, i + 1, err
+ }
+ }
+ return "", len(s), fmt.Errorf("missing )")
+ case '$':
+ return s[0:1], 1, nil
+ default:
+ i := strings.IndexFunc(s, func(c rune) bool {
+ return !(unicode.IsLetter(c) || unicode.IsNumber(c) || c == '_' || c == '.' || c == '-')
+ })
+ if i == 0 {
+ return "", 0, fmt.Errorf("unexpected character '%c' after '$'", s[0])
+ } else if i == -1 {
+ i = len(s)
+ }
+ return "", 0, fmt.Errorf("expected '(' after '$', did you mean $(%s)?", s[:i])
+ }
+}