Add new annotation: @psalm-self-out

[olleharstedt]

This PR adds the annotation @param-self-out for methods, changing the type of $this.

Use-case is to be able to create your own typestates besides the ones already implicit in Psalm (resource, and closed-resource) in an object-oriented manner.

Typestates are mostly (only?) useful together with alias tracking or ownership inference, which is another discussion: #3614

[muglug]

This is a good start. I’d like Psalm to also be able to verify the integrity of @psalm-self-out just as it does for @param-out.

[olleharstedt]

This is a good start. I’d like Psalm to also be able to verify the integrity of @psalm-self-out just as it does for @param-out.

Agree.

[muglug]

This should be Foo&Bar, really - and could you add an exception if the function doesn’t do that?

[olleharstedt]

Yes, but maybe let's detail a little bit what we mean? Using the closed/open file as example:

interface ClosedFile {
  /**
   * @psalm-self-out File&OpenFile
   */
  public function open() {}
}
interface OpenFile {
  /**
   * @psalm-self-out File&ClosedFile
   */
  public function close() {}
  public function read() {}
}
class File implements OpenFile, ClosedFile {
  // ... function defs here
}

Then we define psalm-self-out as always requiring first part of the intersection type being the base-class, second part being the "next" state. This way, Psalm doesn't need to "remember" the base-class in a separate field.

[weirdan]

But in this case File is already File&OpenFile&ClosedFile, by virtue of implementing those interfaces, isn't it? Or do you propose to reuse the same syntax to achieve different effects?

[olleharstedt]

Oh, you're right. Hm, so maybe intersection types cannot be used.

Or do you propose to reuse the same syntax to achieve different effects?

No no no.

[olleharstedt]

Fun fact: In Smalltalk something similar is called become: https://gbracha.blogspot.com/2009/07/miracle-of-become.html

[olleharstedt]

@muglug Hm, how can I debug Circle CI without giving it access to absolutely everything on my account?

[olleharstedt]

Only thing left failing is taint tests, it seems.

[muglug]

Only thing left failing is taint tests, it seems.

Ignore that, but would you mind squashing these commits?

[olleharstedt]

Only thing left failing is taint tests, it seems.

Ignore that, but would you mind squashing these commits?

Can't do it without rebasing everthing. Can't you squash and merge instead if/when this PR gets accepted?

The tab "Files changed" contains all changes for all commits in this PR, if you want an overview.

[muglug]

Thanks!