Type-check utils (#491)

* Type-check utils

* Improve test coverage

src/tokenizer/index.js

@@ -809,6 +809,7 @@ export default class Tokenizer extends LocationParser {
 
         ++this.state.pos;
         const esc = this.readCodePoint(true);
+        // $FlowFixMe (thinks esc may be null, but throwOnInvalid is true)
         if (!(first ? isIdentifierStart : isIdentifierChar)(esc, true)) {
           this.raise(escStart, "Invalid Unicode escape");
         }

src/util/identifier.js

@@ -1,5 +1,7 @@
 /* eslint max-len: 0 */
 
+// @flow
+
 // This is a trick taken from Esprima. It turns out that, on
 // non-Chrome browsers, to check whether a string is in a set, a
 // predicate containing a big ugly `switch` statement is faster than
@@ -9,17 +11,17 @@
 //
 // It starts by sorting the words by length.
 
-function makePredicate(words) {
-  words = words.split(" ");
+function makePredicate(words: string): (str: string) => boolean {
+  const wordsArr = words.split(" ");
   return function (str) {
-    return words.indexOf(str) >= 0;
+    return wordsArr.indexOf(str) >= 0;
   };
 }
 
 // Reserved word lists for various dialects of the language
 
 export const reservedWords = {
-  6: makePredicate("enum await"),
+  "6": makePredicate("enum await"),
   strict: makePredicate("implements interface let package private protected public static yield"),
   strictBind: makePredicate("eval arguments")
 };
@@ -57,7 +59,7 @@ const astralIdentifierCodes = [509,0,227,0,150,4,294,9,1368,2,2,1,6,3,41,2,5,0,1
 // This has a complexity linear to the value of the code. The
 // assumption is that looking up astral identifier characters is
 // rare.
-function isInAstralSet(code, set) {
+function isInAstralSet(code: number, set: $ReadOnlyArray<number>): boolean {
   let pos = 0x10000;
   for (let i = 0; i < set.length; i += 2) {
     pos += set[i];
@@ -66,11 +68,12 @@ function isInAstralSet(code, set) {
     pos += set[i + 1];
     if (pos >= code) return true;
   }
+  return false;
 }
 
 // Test whether a given character code starts an identifier.
 
-export function isIdentifierStart(code) {
+export function isIdentifierStart(code: number): boolean {
   if (code < 65) return code === 36;
   if (code < 91) return true;
   if (code < 97) return code === 95;
@@ -81,7 +84,7 @@ export function isIdentifierStart(code) {
 
 // Test whether a given character is part of an identifier.
 
-export function isIdentifierChar(code) {
+export function isIdentifierChar(code: number): boolean {
   if (code < 48) return code === 36;
   if (code < 58) return true;
   if (code < 65) return false;

src/util/location.js

@@ -1,9 +1,18 @@
+// @flow
+
 import { lineBreakG } from "./whitespace";
 
+export type Pos = {
+  start: number;
+}
+
 // These are used when `options.locations` is on, for the
 // `startLoc` and `endLoc` properties.
 
 export class Position {
+  line: number;
+  column: number;
+
   constructor(line: number, col: number) {
     this.line = line;
     this.column = col;
@@ -11,8 +20,13 @@ export class Position {
 }
 
 export class SourceLocation {
+  start: Position;
+  end: Position;
+  filename: string;
+
   constructor(start: Position, end?: Position) {
     this.start = start;
+    // $FlowIgnore (may start as null, but initialized later)
     this.end = end;
   }
 }
@@ -23,7 +37,7 @@ export class SourceLocation {
 // offset. `input` should be the code string that the offset refers
 // into.
 
-export function getLineInfo(input, offset) {
+export function getLineInfo(input: string, offset: number): Position {
   for (let line = 1, cur = 0; ;) {
     lineBreakG.lastIndex = cur;
     const match = lineBreakG.exec(input);
@@ -34,4 +48,6 @@ export function getLineInfo(input, offset) {
       return new Position(line, offset - cur);
     }
   }
+  // istanbul ignore next
+  throw new Error("Unreachable");
 }

src/util/whitespace.js

@@ -1,3 +1,5 @@
+// @flow
+
 // Matches a whole line break (where CRLF is considered a single
 // line break). Used to count lines.