Support for compound expressions

[mhitza]

I have a compound expression as seen in the following example

ERROR: PossiblyNullReference - src/Workflow/Assessment.php:38:86 - Cannot call method getAttributeRoot on possibly null value
        if (is_null($project->getAssessment()) || is_null($project->getAssessment()->getAttributeRoot())) {

I would expect psalm to be able to infer that if these two checks pass (I throw an exception in the if block), those returns cannot be null afterwards.

While this isn't supported yet, is there a way for me to rewrite the code as to have psalm be able to infer everything is safe without just suppressing the PossiblyNullReference?

[weirdan]

It's a bit longer, but yes, you can rewrite the code using intermediate variables so there's no need to memoize the method call results:

<?php
  class Assessment {
     public function getAttributeRoot(): ?string {
       return rand(0, 1) ? 'root' : null;
     }
  }
  class Project {
     public function getAssessment(): ?Assessment {
       return rand(0, 1) ? new Assessment : null;
     }
  }

function f(Project $project): int {
  $assessment = $project->getAssessment();
  if (is_null($assessment)) {
    throw new RuntimeException('no assessment');
  }
  
  $attributeRoot = $assessment->getAttributeRoot();
  if (is_null($attributeRoot)) {
    throw new RuntimeException('no attribute root');
  }
  
  return strlen($attributeRoot);
}

https://psalm.dev/r/1efae3f536

[muglug]

This should definitely work:

<?php
class Assessment {
    private ?string $root = null;
  
    /** @psalm-mutation-free */
    public function getRoot(): ?string {
        return $this->root;
    }
}

class Project {
    private ?Assessment $assessment = null;
  
    /** @psalm-mutation-free */
    public function getAssessment(): ?Assessment {
        return $this->assessment;
    }
}

function f(Project $project): int {
    if (($project->getAssessment() === null)
        || ($project->getAssessment()->getRoot() !== null)
    ) {
        throw new RuntimeException('no assessment');
    }
  
    return strlen($project->getAssessment()->getRoot());
}

https://psalm.dev/r/531c4ad15b

[mhitza]

@muglug you're awesome, I can confirm it works with the latest master version and the @psalm-mutation-free annotation