Fix disallow arrays in action creators

[chrisguttandin]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

I think it is debatable whether this is a bugfix or a feature.

[-] Bugfix
[-] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

I noticed that the new createAction() function has a clever type definition which prevents it from being used with a props object shaped like this { type: any }. Since an array is also an object in JavaScript it can still be used like this:

const myAction = createAction('MY_ACTION_TYPE', (x: string) => [ x ]);
const myOtherAction = createAction('MY_ACTION_TYPE', props<[ string ]>());

Of course this becomes a little odd when the resulting function is used to create an actual action:

myAction('hello');

TypeScript thinks it has the type string[] & TypedAction<"MY_ACTION_TYPE"> but in reality it is an object with the following shape: { 0: hello, type: 'MY_ACTION_TYPE' }.

What is the new behavior?

A similar technique to the one which prevents { type: any } is used to prevent arrays which means createAction('MY_ACTION_TYPE', props<[]>()) will not compile anymore.

Does this PR introduce a breaking change?

Technically this is a breaking change. But it will only break code which used createAction() in an unintended way.

[ -] Yes
[ -] No

Other information

Please let me know if there is anything I need to change before this can be merged. And in case you think this is not necessary at all feel free to close it.

I also cleaned up the test suite of the action creator a little bit by removing an unused line of code and by inserting a missing blank line and a missing quote. Please let me know if I should better exclude those changes from this pull request.

[ngrxbot]

Preview docs changes for aef4dba at https://previews.ngrx.io/pr2155-aef4dba/

[alex-okrushko]

Nice. Interesting use case. Thanks for adjusting it.