Fix allowed range of array indices

Author: thomastanck

src/utils/__tests__/__snapshots__/rttc.ts.snap

@@ -8606,7 +8606,7 @@ Object {
   "left": Array [
     2,
   ],
-  "right": 4294967296,
+  "right": 4294967295,
 }
 `;
 

src/utils/__tests__/rttc.ts

@@ -292,10 +292,10 @@ describe('Member expression type combinations:', () => {
   // Extra tests for array indices integral check.
   valid.push([arr, 0])
   valid.push([arr, 10])
-  valid.push([arr, 2 ** 32 - 1])
+  valid.push([arr, 2 ** 32 - 2])
   invalid.push([arr, -1])
   invalid.push([arr, 0.5])
-  invalid.push([arr, 2 ** 32])
+  invalid.push([arr, 2 ** 32 - 1])
 
   test('Valid type combinations are OK', () => {
     valid.forEach(([left, right]: [Value, Value]) => {

src/utils/rttc.ts

@@ -36,8 +36,9 @@ const typeOf = (v: Value) => {
 
 const isNumber = (v: Value) => typeOf(v) === 'number'
 // See section 4 of https://2ality.com/2012/12/arrays.html
+// v >>> 0 === v checks that v is a valid unsigned 32-bit int
 // tslint:disable-next-line:no-bitwise
-const isUint32 = (v: Value) => isNumber(v) && v >>> 0 === v
+const isArrayIndex = (v: Value) => isNumber(v) && v >>> 0 === v && v < 2 ** 32 - 1
 const isString = (v: Value) => typeOf(v) === 'string'
 const isBool = (v: Value) => typeOf(v) === 'boolean'
 const isObject = (v: Value) => typeOf(v) === 'object'
@@ -98,7 +99,7 @@ export const checkMemberAccess = (node: es.Node, obj: Value, prop: Value) => {
   if (isObject(obj)) {
     return isString(prop) ? undefined : new TypeError(node, ' as prop', 'string', typeOf(prop))
   } else if (isArray(obj)) {
-    return isUint32(prop) ? undefined : new TypeError(node, ' as prop', 'integer', typeOf(prop))
+    return isArrayIndex(prop) ? undefined : new TypeError(node, ' as prop', 'integer', typeOf(prop))
   } else {
     return new TypeError(node, '', 'object or array', typeOf(obj))
   }