Invalid return type of "DebugElement.query"

[stefanchrobot]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[x] Bug report
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request

Current behavior

DebugElement.query declares DebugElement as the return type.

Expected behavior

DebugElement.query declares DebugElement | null as the return type.

Minimal reproduction of the problem with instructions

let debugElement: DebugElement = ...;
let el = debugElement.query(By.CSS('not existent')).nativeElement;  // explodes

What is the motivation / use case for changing the behavior?

The result of DebugElement.query can actually be null.

The error should be caught by the compiler since the programmer should assert that the element was found. This is especially true for By.CSS predicate as it seems that the likelihood of typos and mistakes is pretty high.

The reason why this compiles without errors is that the return type of array indexing is T, not T | undefined. This seems to be the intended behaviour of the TypeScript compiler.

Environment

Angular version: latest
Browser: all

[mhevery]

Would you be awesome and create a PR for us?

[lacolaco]

I can follow this up.

[adam-marshall]

what is the status of this issue? noticed the PR was cancelled and we are now over 4 years on.

it causes an issue when trying to use the lint rule 'no unnecessary condition' - i.e. the user may know that query() may return null, but if they try and use optional chaining this contravenes the lint rule.

really the recommended advice should not be to deliberately throw, exceptions should be exceptional surely?

[rbirkgit]

We encountered issues with this in our unit tests. strict checking complains. Is this hard to fix? It feels like we just need to add | null as return type?

[JeanMeche]

I just checked, debugElement.query is called 664 times alone in the angular repo.

A fixing of the type would require a migration schematics at least.

I might give it a try since have I done a similar one for #48039.

[lazarljubenovic]

Why does this have only 7 upvotes? Apparently only seven Angular users are writing tests properly 😩 Six years with no response from the team, and there's a pretty damn good PR, with a schematic even! 🥇

Apparently all discussion is moved to the mentioned PR. Hopefully we see this landing in 2024.