Switch/case with class instantiation from variable can result in unexpected errors

[kevinquinnyo]

Bug report

Sorry for the bad title. This one is hard for me to explain, but the snippet should help clear it up.

Object instantiation from a class name stored in a variable within a switch/case statement produces an error under the following conditions:

• if there exists some kind of validation code (or any code) above the switch/case that allows phpstan to determine/guess what the $className variable contains.
• one of the possible class names in the switch/case requires constructor arguments and the other does not.

You can reproduce this using level 1.

The errors presented are:

• Class B does not have a constructor and must be instantiated without any parameters.
• Class A constructor invoked with 0 parameters, 1 required.

Some additional observations:

• Errors go away if instead of doing new $className... we do new A() explicitly for instance, which is probably a better way to write the code anyway.
• Errors go away if the swicth/case is replaced with an equivalent if/else.
• This is admittedly a strange factory pattern, and probably an edge-case that isn't encountered very often, so I assume this is not a high priority bug at first glance.

Code snippet that reproduces the problem

https://phpstan.org/r/bf1178c0-5ca0-4a52-a4c4-93b126344900

Expected output

I expected that phpstan would assume $className could be something like A|B and infer from the case statements which one it must be at the time it's initialized.

Did PHPStan help you today? Did it make you happy in any way?

yes!

[phpstan-bot]

@kevinquinnyo After the latest commit in dev-master, PHPStan now reports different result with your code snippet:

@@ @@
-30: Class B does not have a constructor and must be instantiated without any parameters.
-32: Class A constructor invoked with 0 parameters, 1 required.
+No errors

[github-actions]

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