fix(core): QueryList first and last might be undefined

[PowerKiKi]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/main/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.io application / infrastructure changes
• Other... Please describe:

What is the current behavior?

It is possible that a QueryList has no results at all, and thus there is no first or last result.

Issue Number: N/A

What is the new behavior?

The typing now reflects that reality.

Does this PR introduce a breaking change?

• Yes
• No

if you are using TypeScript strict mode, you must now check for the existence of first and last before using them.

Other information

none

[JeanMeche]

Hi, this change was already tried to being landed a couples of year back, cf #43604.
Since this is a breaking change, it requires a migration.

There is little value to put the effort of landing this now that we have the signal view queries.

[PowerKiKi]

The CI is failing with many TypeError: Cannot read properties of null (reading 'ngModule') errors. I don't think it is related to my PR, but if it is, please help me understand what/where I should fix ?

[PowerKiKi]

I was not aware of the previous attempts, including yours 😞 ...

The way I see it this API is not deprecated, so improving it would still bring value to people who use it. And the fact that it is the third attempts to fix it seems to indicate that some people care.

I'll let you reject the PR if you think this is a dead end.

[dylhunn]

Hi @PowerKiKi. While I agree that the spirit of this change is great, the problem is that we would break a ton of code that relies on first and last and assumes they will never be undefined. We'd need to run a migration to fix all the user code, including inside of Google.

I think we're going to leave it alone, since we have replacement signals-based APIs anyway.

Thank you for your effort on this though, and sorry we cannot accept it!