About Psalm

Psalm is a static analysis tool that attempts to dig into your program and find as many type-related bugs as possible.

It has a few features that go further than other similar tools:

• Mixed type warnings If Psalm cannot infer a type for an expression then it uses a mixed placeholder type. mixed types can sometimes mask bugs, so keeping track of them helps you avoid a number of common pitfalls.

• Intelligent logic checks Psalm keeps track of logical assertions made about your code, so if ($a && $a) {} and if ($a && !$a) {} are both treated as issues. Psalm also keeps track of logical assertions made in prior code paths, preventing issues like if ($a) {} elseif ($a) {}.

• Property initialisation checks Psalm checks that all properties of a given object have values after the constructor is called.

• Taint analysis Psalm can detect security vulnerabilities in your code.

• Language Server Psalm has a Language Server that’s compatible with a range of different IDEs.

• Automatic fixes Psalm can fix many of the issues it finds automatically.

• Automatic refactoring Psalm can also perform simple refactors from the command line.

Example output

Given a file implode_strings.php:

<?php
$a = ['foo', 'bar'];
echo implode($a, ' ');

> ./vendor/bin/psalm implode_strings.php
ERROR: InvalidArgument - somefile.php:3:14 - Argument 1 of implode expects `string`, `array` provided (see https://psalm.dev/004)

Inspirations

There are two main inspirations for Psalm:

• Etsy's Phan, which uses nikic's php-ast extension to create an abstract syntax tree
• Facebook's Hack, a PHP-like language that supports many advanced typing features natively, so docblocks aren't necessary.

Index

• Running Psalm:
  • Installation
  • Configuration
  • Plugins
    • Using plugins
    • Authoring plugins
    • How Psalm represents types
  • Command line usage
  • IDE support
  • Handling errors:
    • Dealing with code issues
    • Issue Types
  • Checking non-PHP files
• Annotating code:
  • Typing in Psalm
  • Supported Annotations
  • Template Annotations
• Manipulating code:
  • Fixing code
  • Refactoring code