Immutable unions

[danog]

This PR introduces fully immutable union types and some work towards immutable storages (I realized that while that's a good thing to have, the only thing we really need to avoid mutability bugs are immutable unions).

Marking this as draft due to the ~30 psalm issues I have to fix, plus a very nasty (set of) side-effects related to parent_nodes, which I'm currently trying to fix.

Basically, the trick here is to fix https://psalm.dev/r/eb9860a6c5, which is caused by src/Psalm/Internal/Analyzer/Statements/Block/IfElseAnalyzer.php:428 dropping all already-asserted info about $function_call_arg->value->items[0] and children, because src/Psalm/Internal/Analyzer/Statements/Expression/Fetch/InstancePropertyFetchAnalyzer.php:429 re-assigns some types after AtomicPropertyFetchAnalyzer::processTaints.

Technically, the behavior of IfElseAnalyzer is correct: when changing parent nodes ie due to a variable re-assignment (first part of the psalm.dev example), all known assertions about the variable and children should be dropped.
However, in this specific example in InstancePropertyFetchAnalyzer, originally the re-assignment is propagated to parent contexts, and I haven't figured out yet the proper way of replicating this.

[orklah]

should this change be included in this PR? Feels like it should be added for 4.x?

[danog]

I suppose this could be backported as well, just wanted to include it in this PR since I also introduced memoization for global types and wanted to avoid merge conflicts in this section of the VariableFetchAnalyzer.

[danog]

Though it would have to be changed a bit, here I re-use the string type for example, that can cause nasty issues in 4.x where unions aren't immutable

[orklah]

Seems like phpunit plugin broke :(

[danog]

Yep, this PR requires the other PR I sent to the phpunit plugin

[orklah]

Can you check there? We'll need to make a dedicated release for the phpunit plugin on version 5

[danog]

+, done!

[danog]

Also fixed the parent_nodes issues.

[orklah]

Not sure why, but composer install 0.16.1 of psalm's phpunit plugin, not 0.18.0...

[danog]

That's because in semver 0.x versions are treated as major, only 0.x.y versions are treated as minor.
I suggest pulling 0.18.0 and re-tagging 1.17.1, since there are no breaking changes.

[danog]

Nevermind, already updated ;)

[orklah]

0.18.1 doesn't seem to resolve the issue here

[danog]

Yeah, maybe it'll work after merging on master?
Or maybe I should add a version constant somewhere...

[orklah]

Oh! New error :)

[danog]

Yeah, sorry about this, psalm/psalm-plugin-phpunit#126 works for sure, just tested :)

[orklah]

I think this could be merged now. Can you cleanup some commits (or should I squish everything?). Please try to make sure every baseline addition is legit and it should be ok

[danog]

You can squash-merge, afaik all commit messages are retained when squash-merging, and yes I made sure all the baselined issues are pre-existing psalm bugs :P

[orklah]

Thanks a lot!

[danog]

YAY :D
Just fixed up #8395, that should be good to merge too :)