psalm/docs/supported_annotations.md

Supported docblock annotations

Psalm supports a wide range of docblock annotations.

PHPDoc tags

Psalm uses the following PHPDoc tags to understand your code:

• @var Used for specifying the types of properties and variables
• @return Used for specifying the return types of functions, methods and closures
• @param Used for specifying types of parameters passed to functions, methods and closures
• @property Used to specify what properties can be accessed on an object that uses __get and __set
• @property-read Used to specify what properties can be read on object that uses __get
• @property-write Used to specify what properties can be written on object that uses __set
• @deprecated Used to mark functions, methods, classes and interfaces as being deprecated

Off-label usage of the @var tag

The @var tag is supposed to only be used for properties. Psalm, taking a lead from PHPStorm and other static analysis tools, allows its use inline in the form @var Type [VariableReference].

If VariableReference is provided, it should be of the form $variable or $variable->property. If used above an assignment, Psalm checks whether the VariableReference matches the variable being assigned. If they differ, Psalm will assign the Type to VariableReference and use it in the expression below.

If no VariableReference is given, the annotation tells Psalm that the right hand side of the expression, whether an assignment or a return, is of type Type.

/** @var string */
$a = $_GET['foo'];

/** @var string $b */
$b = $_GET['bar'];

function bat(): string {
    /** @var string */
    return $_GET['bat'];
}

Psalm-specific tags

There are a number of custom tags that determine how Psalm treats your code.

@param-out

This is used to specify that a by-ref type is different from the one that entered. In the function below the first param can be null, but once the function has executed the by-ref value is not null.

/**
 * @param-out string $s
 */
function addFoo(?string &$s) : void {
    if ($s === null) {
        $s = "hello";
    }
    $s .= "foo";
}

@psalm-var, @psalm-param and @psalm-return

When specifying types in a format not supported phpDocumentor (but supported by Psalm) you may wish to prepend @psalm- to the PHPDoc tag, so as to avoid confusing your IDE. If a @psalm-prefixed tag is given, Psalm will use it in place of its non-prefixed counterpart.

@psalm-suppress SomeIssueName

This annotation is used to suppress issues. It can be used in function docblocks, class docblocks and also inline, applying to the following statement.

Function docblock example:

/**
 * @psalm-suppress PossiblyNullOperand
 */
function addString(?string $s) {
    echo "hello " . $s;
}

Inline example:

function addString(?string $s) {
    /** @psalm-suppress PossiblyNullOperand */
    echo "hello " . $s;
}

@psalm-assert, @psalm-assert-if-true and @psalm-assert-if-false

These annotations allow you to specify very basic facts about how a class of functions operate.

For example, if you have a class that verified its input is an array of strings, you can make that clear to Psalm:

/** @psalm-assert string[] $arr */
function validateStringArray(array $arr) : void {
    foreach ($arr as $s) {
        if (!is_string($s)) {
          throw new UnexpectedValueException('Invalid value ' . gettype($s));
        }
    }
}

This enables you to call the validateStringArray function on some data and have Psalm understand that the given data must be an array of strings:

function takesString(string $s) : void {}
function takesInt(int $s) : void {}

function takesArray(array $arr) : void {
    takesInt($arr[0]); // this is fine

    validateStringArray($arr);

    takesInt($arr[0]); // this is an error

    foreach ($arr as $a) {
        takesString($a); // this is fine
    }
}

Similarly, @psalm-assert-if-true and @psalm-assert-if-false will filter input if the function/method returns true and false respectively:

class A {
    public function isValid() : bool {
        return (bool) rand(0, 1);
    }
}
class B extends A {
    public function bar() : void {}
}

/**
 * @psalm-assert-if-true B $a
 */
function isValidB(A $a) : bool {
    return $a instanceof B && $a->isValid();
}

/**
 * @psalm-assert-if-false B $a
 */
function isInvalidB(A $a) : bool {
    return $a instanceof B || !$a->isValid();
}

function takesA(A $a) : void {
    if (isValidB($a)) {
        $a->bar();
    }

    if (isInvalidB($a)) {
        // do something
    } else {
        $a->bar();
    }

    $a->bar(); //error
}

As well as getting Psalm to understand that the given data must be a certain type, you can also show that a variable must be not null:

/**
 * @psalm-assert !null $value
 */
function assertNotNull($value): void {
  // Some check that will mean the method will only complete if $value is not null.
}

And you can check on null values:

/**
 * @psalm-assert-if-true null $value
 */
function isNull($value): bool {
  return ($value === null);
}

@psalm-ignore-nullable-return

This can be used to tell Psalm not to worry if a function/method returns null. It’s a bit of a hack, but occasionally useful for scenarios where you either have a very high confidence of a non-null value, or some other function guarantees a non-null value for that particular code path.

class Foo {}
function takesFoo(Foo $f): void {}

/** @psalm-ignore-nullable-return */
function getFoo(): ?Foo {
  return rand(0, 10000) > 1 ? new Foo() : null;
}

takesFoo(getFoo());

@psalm-ignore-falsable-return

This provides the same, but for false. Psalm uses this internally for functions like preg_replace, which can return false if the given input has encoding errors, but where 99.9% of the time the function operates as expected.

@psalm-seal-properties

If you have a magic property getter/setter, you can use @psalm-seal-properties to instruct Psalm to disallow getting and setting any properties not contained in a list of @property (or @property-read/@property-write) annotations.

/**
 * @property string $foo
 * @psalm-seal-properties
 */
class A {
     public function __get(string $name): ?string {
          if ($name === "foo") {
               return "hello";
          }
     }

     public function __set(string $name, $value): void {}
}

$a = new A();
$a->bar = 5; // this call fails

Templating

@template

The @template tag allows classes and functions to implement type parameter-like functionality found in many other languages.

As a very simple example, this function returns whatever is passed in:

/** @template T
 * @psalm-param T $t
 * @return T
 */
function mirror($t) {
    return $t;
}

$a = 5;
$b = mirror(5); // Psalm knows the result is an int

Psalm also uses @template annotations in its stubbed versions of PHP array functions e.g.

/**
 * Takes one array with keys and another with values and combines them
 *
 * @template TKey
 * @template TValue
 *
 * @param array<mixed, TKey> $arr
 * @param array<mixed, TValue> $arr2
 * @return array<TKey, TValue>
 */
function array_combine(array $arr, array $arr2) {}

@param class-string<T>

Psalm also allows you to parameterise class types

/**
 * @template T
 * @psalm-param class-string<T> $class
 * @return T
 */
function instantiator(string $class) {
    return new $class();
}

class Foo {}

$a = instantiator(Foo::class); // Psalm knows the result is an object of type Foo

Template inheritance

Psalm allows you to extend templated classes with @extends/@template-extends:

/**
 * @template T
 */
class ParentClass {}

/**
 * @extends ParentClass<int>
 */
class ChildClass extends ParentClass {}

similarly you can implement interfaces with @implements/@template-implements

/**
 * @template T
 */
interface IFoo {}

/**
 * @implements IFoo<int>
 */
class Foo implements IFoo {}

and import traits with @use/@template-use

/**
 * @template T
 */
trait MyTrait {}

class Foo {
    /**
     * @use MyTrait<int>
     */
    use MyTrait;
}

You can also extend one templated class with another, e.g.

/**
 * @template T1
 */
class ParentClass {}

/**
 * @template T2
 * @extends ParentClass<T2>
 */
class ChildClass extends ParentClass {}

Template constraints

You can use @template of <type> to restrict input. For example, to restrict to a given class you can use

class Foo {}
class FooChild extends Foo {}

/**
 * @template T of Foo
 * @psalm-param T $class
 * @return array<int, T>
 */
function makeArray($t) {
    return [$t];
}
$a = makeArray(new Foo()); // typed as array<int, Foo>
$b = makeArray(new FooChild()); // typed as array<int, FooChild>
$c = makeArray(new stdClass()); // type error

Builtin templated classes and interfaces

Psalm has support for a number of builtin classes and interfaces that you can extend/implement in your own code.

• interface Traversable<TKey, TValue>

• interface ArrayAccess<TKey, TValue>

• interface IteratorAggregate<TKey, TValue> extends Traversable<TKey, TValue>

• interface Iterator<TKey, TValue> extends Traversable<TKey, TValue>

• interface SeekableIterator<TKey, TValue> extends Iterator<TKey, TValue>

• class Generator<TKey, TValue, TSend, TReturn> extends Traversable<TKey, TValue>

• class ArrayObject<TKey, TValue> implements IteratorAggregate<TKey, TValue>, ArrayAccess<TKey, TValue>

• class ArrayIterator<TKey of array-key, TValue> implements SeekableIterator<TKey, TValue>, ArrayAccess<TKey, TValue>

• class DOMNodeList<TNode of DOMNode> implements Traversable<int, TNode>

• class SplDoublyLinkedList<TKey, TValue> implements Iterator<TKey, TValue>, ArrayAccess<TKey, TValue>

• class SplQueue<TValue> extends SplDoublyLinkedList<int, TValue>

Type Syntax

Psalm supports PHPDoc’s type syntax, and also the proposed PHPDoc PSR type syntax.

A detailed write-up is found in Typing in Psalm