TypeScript: Cannot read property 'length' of undefined in v4 version

The issue happen with v4 version (tested on v4.0.3, v4.0.5 and the latest v4.1.2)

With the same config and code base it compile with no problem in v3.9

Expected behavior:

No such error! No failing at internal level! (Plus it works in v3.9 and not v4)

text should not come as undefined! Or should be handled without problem!

Actual behavior: In v3.9 the code compile with the same config with no problem! In v4 i get Cannot read property ‘length’ of undefined error! And internal failing!

Through the error stack! i get where the error happened and it was at the function computeLineStarts! text is coming undefined! i did some console logging! And i got what file was been treated! And what text node were printing! The file is all normal and correct! A comment at the end was the last thing which after it the code fail!

Then i added another instruction after it! (A variable assignment const someVar = '';) and the error went up! The last treated nodes before failing came more up! Here bellow the file at which my console.logging stopped at!

File on which the resolution failed at:

https://gist.github.com/MohamedLamineAllal/472cf2043a100cb03244de5fb1138034

When i added const someVar = ""; at the end! the last treated node was } from

export interface IWebSocketDriver {
  readonly protocol: string;
  readonly readyState: number;
  readonly url: string;
  binaryType: BinaryType;
  readonly CONNECTING: number;
  readonly OPEN: number;
  readonly CLOSING: number;
  readonly CLOSED: number;
  setGetStreamObj: (getStreamObj: () => WebSocket | IWebSocketDriver) => IWebSocketDriver;
  onInit: () => IWebSocketDriver;
  onopen: ((this: IWebSocketDriver, ev: Event) => any) | null;
  onmessage: ((this: IWebSocketDriver, ev: MessageEvent) => any) | null;
  onclose: ((this: IWebSocketDriver, ev: CloseEvent) => any) | null;
  onerror: ((this: IWebSocketDriver, ev: Event) => any) | null;
  close(code?: number, reason?: string): void;
  send(data: string | ArrayBufferLike | Blob | ArrayBufferView): void;
} // <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<!!!!!!!!!!!!!!! here the last treated element

/**
 * THINGS TO DO:
 * =============
 *
 *  decide and define the response output of all the functions
 *
 *  consider a design that add useful information that are exchange platform dependent
 *
 *
 *
 * STREAMS :
 * Need to precise what form the returned object should have
 *
 * ok dodo
 */
const someVar = ''; // <=== added this

How i debugged!?

in tsc.js

ts.stringToToken = stringToToken;
    function computeLineStarts(text) {
        console.log('text: ') // <<<==== here
        console.log(text)
        var result = new Array();
        var pos = 0;

And at

ts.getNonDecoratorTokenPosOfNode = getNonDecoratorTokenPosOfNode;
    function getSourceTextOfNodeFromSourceFile(sourceFile, node, includeTrivia) {
        console.log('Source file: ') // <<<<<<<<<<<<<<<<<<<<<<<<= here
        console.log(sourceFile.path)
        console.log('================+++>')
        if (includeTrivia === void 0) { includeTrivia = false; }
        return getTextOfNodeFromSourceText(sourceFile.text, node, includeTrivia);
    }

First Compilation execution (original file)

Without adding the last const someVar = '';

https://gist.github.com/MohamedLamineAllal/653fd4f597aa821f416a33e86d4514eb

Second compilation (after adding the last line)

https://gist.github.com/MohamedLamineAllal/022f6f285313aec30b82bb72238bcaeb

Always it fails at computeLineStarts() method! And because text is undefined.

Error stack

TypeError: Cannot read property 'length' of undefined
    at computeLineStarts (/home/coderhero/.nvm/versions/node/v15.0.1/lib/node_modules/typescript/lib/tsc.js:6528:27)
    at Object.getLineStarts (/home/coderhero/.nvm/versions/node/v15.0.1/lib/node_modules/typescript/lib/tsc.js:6581:60)
    at getCurrentLineMap (/home/coderhero/.nvm/versions/node/v15.0.1/lib/node_modules/typescript/lib/tsc.js:81810:59)
    at emitDetachedCommentsAndUpdateCommentsInfo (/home/coderhero/.nvm/versions/node/v15.0.1/lib/node_modules/typescript/lib/tsc.js:85144:94)
    at emitBodyWithDetachedComments (/home/coderhero/.nvm/versions/node/v15.0.1/lib/node_modules/typescript/lib/tsc.js:85007:17)
    at emitSourceFile (/home/coderhero/.nvm/versions/node/v15.0.1/lib/node_modules/typescript/lib/tsc.js:83873:21)
    at pipelineEmitWithHint (/home/coderhero/.nvm/versions/node/v15.0.1/lib/node_modules/typescript/lib/tsc.js:81887:24)
    at noEmitNotification (/home/coderhero/.nvm/versions/node/v15.0.1/lib/node_modules/typescript/lib/tsc.js:80586:9)
    at onEmitNode (/home/coderhero/.nvm/versions/node/v15.0.1/lib/node_modules/typescript/lib/tsc.js:70565:13)
    at onEmitNode (/home/coderhero/.nvm/versions/node/v15.0.1/lib/node_modules/typescript/lib/tsc.js:72333:13)

For the shared links i used typescript Version 4.1.2! Otherwise i tested with v4.0.3 and v4.0.5

tsconfig.json

{
  "compilerOptions": {
    "declaration": true,
    "declarationDir": "./dist",
    "module": "commonjs",
    "noImplicitAny": true,
    "lib": ["ESNext", "DOM"],
    "outDir": "./dist",
    "target": "es6",
    "moduleResolution": "node",
    "resolveJsonModule": true,
    "esModuleInterop": true
  },
  "typedocOptions": {
    "mode": "modules",
    "out": "docs"
  },
  "include": ["src/**/*.ts", "src/**/*.json", "test"],
  "exclude": ["node_modules", "dist", "src/**/*.spec.ts", "src/**/*.test.ts"]
}

Related Issues:

• https://github.com/microsoft/TypeScript/issues/40747
• https://github.com/microsoft/TypeScript/issues/35074