Check index types (google#116)

Before it would just crash

interpreter.go

@@ -362,16 +362,26 @@ func (i *interpreter) evaluate(a ast.Node) (value, error) {
 			return nil, err
 		}
 		switch target := targetValue.(type) {
-		// TODO(sbarzowski) better error handling if bad index type
 		case valueObject:
-			indexString := index.(*valueString).getString()
-			return target.index(e, indexString)
+			indexString, err := e.getString(index)
+			if err != nil {
+				return nil, err
+			}
+			return target.index(e, indexString.getString())
 		case *valueArray:
-			indexInt := int(index.(*valueNumber).value)
-			return e.evaluate(target.elements[indexInt])
+			indexInt, err := e.getNumber(index)
+			if err != nil {
+				return nil, err
+			}
+			// TODO(https://github.com/google/jsonnet/issues/377): non-integer indexes should be an error
+			return e.evaluate(target.elements[int(indexInt.value)])
 		case *valueString:
-			indexInt := int(index.(*valueNumber).value)
-			return target.index(e, indexInt)
+			indexInt, err := e.getNumber(index)
+			if err != nil {
+				return nil, err
+			}
+			// TODO(https://github.com/google/jsonnet/issues/377): non-integer indexes should be an error
+			return target.index(e, int(indexInt.value))
 		}
 
 		return nil, e.Error(fmt.Sprintf("Value non indexable: %v", reflect.TypeOf(targetValue)))

testdata/bad_index_array.golden

@@ -0,0 +1,10 @@
+RUNTIME ERROR: Unexpected type string, expected number
+-------------------------------------------------
+	testdata/bad_index_array:1:1-10	$
+
+[]["xxx"]
+
+-------------------------------------------------
+	During evaluation	
+
+

testdata/bad_index_array.jsonnet

@@ -0,0 +1 @@
+[]["xxx"]

testdata/bad_index_object.golden

@@ -0,0 +1,10 @@
+RUNTIME ERROR: Unexpected type number, expected string
+-------------------------------------------------
+	testdata/bad_index_object:1:1-7	$
+
+{}[42]
+
+-------------------------------------------------
+	During evaluation	
+
+

testdata/bad_index_object.jsonnet

@@ -0,0 +1 @@
+{}[42]

testdata/bad_index_string.golden

@@ -0,0 +1,10 @@
+RUNTIME ERROR: Unexpected type string, expected number
+-------------------------------------------------
+	testdata/bad_index_string:1:2-13	$
+
+"xxx"["xxx"]
+
+-------------------------------------------------
+	During evaluation	
+
+

testdata/bad_index_string.jsonnet

@@ -0,0 +1 @@
+"xxx"["xxx"]