dandv•2mo ago

Deno check/lint doesn't warn against obvious bugs

type Point = {
  [key: string]: number
};

function processPoints(points: Point[]): string[] {
  // Should error on Object.keys(number), TS2345: Argument of type 'number' is not assignable to parameter of type 'object'.
  // Should warn on points[3] possibly being undefined
  return Object.keys(points[3].foo);
}

console.log(processPoints([ { bar: 2 } ]));

type Point = {
  [key: string]: number
};

function processPoints(points: Point[]): string[] {
  // Should error on Object.keys(number), TS2345: Argument of type 'number' is not assignable to parameter of type 'object'.
  // Should warn on points[3] possibly being undefined
  return Object.keys(points[3].foo);
}

console.log(processPoints([ { bar: 2 } ]));

I've run deno lint --rules-tags=recommended but it doesn't detect anything. This is quite worrying. PS: should there be a Lint tag when posting here, now that we have lint plugins?

7 Replies

marvinh.•2mo ago

You might be looking for deno check instead. At the moment deno lint does no type checking whereas deno check does. In either way there wouldn't be a type error in the code posted. Calling Object.keys() on a number always yields an empty array and an empty array is a valid string[]

dandvOP•2mo ago

@marvinh. deno check was my first line of defense, but it doesn't output anything about this code. tsc does:

$ cat warnme.ts 
type Point = {
  [key: string]: number
};

function processPoints(points: Point[]): string[] {
  // Should error on Object.keys(number), TS2345: Argument of type 'number' is not assignable to parameter of type 'object'.
  // Should warn on points[3] possibly being undefined
  return Object.keys(points[3].foo);
}

console.log(processPoints([ { bar: 2 } ]));

$ deno check warnme.ts 

$ tsc warnme.ts 
warnme.ts:8:22 - error TS2345: Argument of type 'number' is not assignable to parameter of type 'object'.

8   return Object.keys(points[3].foo);
                       ~~~~~~~~~~~~~


Found 1 error in warnme.ts:8

$ cat warnme.ts 
type Point = {
  [key: string]: number
};

function processPoints(points: Point[]): string[] {
  // Should error on Object.keys(number), TS2345: Argument of type 'number' is not assignable to parameter of type 'object'.
  // Should warn on points[3] possibly being undefined
  return Object.keys(points[3].foo);
}

console.log(processPoints([ { bar: 2 } ]));

$ deno check warnme.ts 

$ tsc warnme.ts 
warnme.ts:8:22 - error TS2345: Argument of type 'number' is not assignable to parameter of type 'object'.

8   return Object.keys(points[3].foo);
                       ~~~~~~~~~~~~~


Found 1 error in warnme.ts:8

marvinh.•2mo ago

I see, that sounds like a bug. Can you file an issue for that at https://github.com/denoland/deno/issues ?

CodyC•2mo ago

It looks like Object.keys() is overloaded: Did an issue get opened for this? I can add this there if so.

CodyC•2mo ago

Didn't find it. Created one: https://github.com/denoland/deno/issues/28433

GitHub

deno check != tsc w.r.t. Object.keys() · Issue #28433 · denol...

Version: deno 2.2.3+0ef3f6b (canary, release, x86_64-pc-windows-msvc) v8 13.4.114.11-rusty typescript 5.7.3 Originally reported on Discord type Point = { [key: string]: number }; function processPo...

CodyC•2mo ago

As for:

// Should warn on points[3] possibly being undefined

Unfortunately, even typescript "strict" mode doesn't enable this check. There is a LOT of code that just assumes your indexes are in-bounds. It can become tedious to check undefined for all cases. If you want that check, you have to enable: https://www.typescriptlang.org/tsconfig/#noUncheckedIndexedAccess

dsherret•5w ago

just a note that this isn't a bug in Deno. The code does not error with tsc either when targeting ESNext https://github.com/denoland/deno/issues/28433#issuecomment-2721404946

Deno check/lint doesn't warn against obvious bugs

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