Fix crash in MakeString.EndsWith()

Bug: 226974242
Test: go test
Change-Id: I21ff26d00ed7be145ae2c1175f1438b6e7d60834

androidmk/parser/make_strings.go

@@ -279,7 +279,7 @@ func (ms *MakeString) TrimRightOne() {
 
 func (ms *MakeString) EndsWith(ch rune) bool {
 	s := ms.Strings[len(ms.Strings)-1]
-	return s[len(s)-1] == uint8(ch)
+	return len(s) > 0 && s[len(s)-1] == uint8(ch)
 }
 
 func (ms *MakeString) ReplaceLiteral(input string, output string) {

androidmk/parser/make_strings_test.go

@@ -217,6 +217,36 @@ func TestMakeStringWords(t *testing.T) {
 	}
 }
 
+var endsWithTestCases = []struct {
+	in       *MakeString
+	endsWith rune
+	expected bool
+}{
+	{
+		in:       genMakeString("foo", "X", "bar ="),
+		endsWith: '=',
+		expected: true,
+	},
+	{
+		in:       genMakeString("foo", "X", "bar ="),
+		endsWith: ':',
+		expected: false,
+	},
+	{
+		in:       genMakeString("foo", "X", ""),
+		endsWith: '=',
+		expected: false,
+	},
+}
+
+func TestMakeStringEndsWith(t *testing.T) {
+	for _, test := range endsWithTestCases {
+		if test.in.EndsWith(test.endsWith) != test.expected {
+			t.Errorf("with:\n%q\nexpected:\n%t\ngot:\n%t", test.in.Dump(), test.expected, !test.expected)
+		}
+	}
+}
+
 func dumpArray(a []*MakeString) string {
 	ret := make([]string, len(a))