Complains about "object is possibly 'undefined'" when it should not

[boris-petrov]

import Component from '@glimmer/component';

export default class GlimmerComponent extends Component {
  public foo?: { bar: any };
}

{{#if this.foo.bar}}
{{/if}}

This leads to:

Object is possibly 'undefined'.typed-templates

Which is kind of useless - HBS supports getting properties on undefined objects - that's a feature, not a bug.

There is another case worth mentioning:

{{some-helper-that-accepts-undefined this.foo.bar}}
{{some-helper-that-does-NOT-accept-undefined this.foo.bar}}

The first line should be fine but the second one should err if possible.

[boris-petrov]

Third example:

public arr?: readonly string[];

{{#each this.arr as |value index|}}
{{/each}}

Again complains about the possibility arr to be undefined.

[lifeart]

Likely it should be an warning, not error

[lifeart]

this errors now warnings (4.0.6)

[boris-petrov]

@lifeart - thanks for all the quick fixes and changes! However, in this case, I disagree with what you've done. As I mentioned in my first post, HBS' handling of undefined is actually a feature. So having this.foo.bar.baz.qux, when any of the parts could return undefined, the type of the whole thing should also include undefined (in addition to what type qux has) and that should definitely be neither an error, nor a warning. Or at least provide an option for that - but again, this is a feature of HBS so most people are likely depending on it. So please do not err or warn for that. 😄

[boris-petrov]

Also, the third example I gave still errs - #each works fine with undefined as a first parameter (and is expected to, as it even has an else clause because of that) but els-addon-typed-templates complains about it.

[lifeart]

@boris-petrov I'm getting your points accroding to handlebars undefined handing feature, but I'm not shure we have to follow it in typed way, we could ask question in emberjs/rfcs#591 and in related typescript chatter in discord (https://discord.com/channels/480462759797063690/484421406659182603) to agree on path forward for given case.

[lifeart]

conversation: https://discord.com/channels/480462759797063690/484421406659182603/808348456045379584

as I get:
we have to use optional chaining, but, all invocable items should be defined

[lifeart]

@boris-petrov could you check els-addon-typed-templates@4.1.0?

[boris-petrov]

@lifeart - I think this version broke a bunch of other things:

public get columns(): readonly string[] {
  return [];
}

@action
public onClick(): void {
}

{{#each this.columns as |column|}}
{{/each}}

<button type="button" {{on "click" this.onClick}}>
</button>

These give the following two errors:

Type 'readonly string[] | undefined' is not assignable to type 'ArrayLike<string>'.
  Type 'undefined' is not assignable to type 'ArrayLike<string>'.typed-templates

Type '(() => void) | undefined' is not assignable to type 'Function'.
  Type 'undefined' is not assignable to type 'Function'.typed-templates

[lifeart]

ya, that’s I’m talking about, both issue could be fixed as typing updates, but it will produce less maintainable and checkable code, looks like we need to refigure out how to handle it

[lifeart]

@boris-petrov for now I'm rolling back changes in 4.2.0
issue for context-related paths created - #57