Typescript: API: incorrect declarations in types.ts

[ajafff]

The --strictNullChecks PR changed some declarations in types.ts to avoid frequent assertions in the compiler's code. Unfortunately these changes make it really unsafe for API users because they no longer contain the actually nullable types: https://github.com/Microsoft/TypeScript/pull/22088#discussion_r184149465 https://github.com/Microsoft/TypeScript/pull/22088#discussion_r184155027

• ts.Node#parent is no longer optional (which is definitely wrong for SourceFile)
• ts.Symbol#declarations and ts.Symbol.valueDeclaration are no longer optional, but can still be undefined
• ts.Type#symbol is no longer optional, but I guess this comment is still up to date: // Symbol associated with type (if any)

These changes should either be reverted or replaced in the published declaration files.
/cc @andy-ms @weswigham

[weswigham]

I agree. I mentioned it on the PR. Now that we've done the bulk of the changes, we should fix one at a time and introduce helpers to help the pain.

[ajafff]

@RyanCavanaugh Do you plan to fix this in the near future? It's a real PITA for me as I use TypeScript's API a lot.
Is there anything I can do to help? Would you accept PRs to fix the issues listed above (probably one at a time to keep the diff small)?

[mike-north]

repro case for ts.Symbol.valueDeclaration being undefined

// src/index.ts
export type NumberDict = { [k: string]: number };

// analyze.js
const ts = require('typescript');

const program = ts.createProgram(['src/index.ts'], {
  target: ts.ScriptTarget.ES2015,
  noEmit: true,
  strict: true
});

const checker = program.getTypeChecker();
// get the file
const [indexFile] = program.getSourceFiles().filter(f => !f.isDeclarationFile);

// file's symbol
const indexFileSymbol = checker.getSymbolAtLocation(indexFile);

// file's exports
const { exports: exportSymbols } = indexFileSymbol;

// first exported symbol from the file
const firstExport = exportSymbols.values().next().value;

console.log(
  'First symbol has type of',
  checker.typeToString(checker.getDeclaredTypeOfSymbol(firstExport)),
  'and it has a valueDeclaration of',
  firstExport.valueDeclaration
);

Result: of node analyze.js

First symbol has type of NumberDict and it has a valueDeclaration of undefined

[bradzacher]

We just ran into this bug in @typescript-eslint. One of our rules assumed the typing was correct, causing a bug for an end user.
As an API consumer, we rely on the types to help us ensure we catch bugs at compile time, and it's counter-intuitive to handle cases that are contrary to the types.

Related issues:
https://github.com/typescript-eslint/typescript-eslint/issues/498
https://github.com/typescript-eslint/typescript-eslint/issues/496

[ayazhafiz]

@weswigham @RyanCavanaugh will you accept changes fixing this?