Allow omitting @param type

doc/grammars/phpdoc-param.peg

@@ -1,5 +1,5 @@
 PhpDocParam
-  = AnnotationName Type IsReference? IsVariadic? ParameterName Description?
+  = AnnotationName Type? IsReference? IsVariadic? ParameterName Description?
 
 AnnotationName
   = '@param'

src/Ast/PhpDoc/PhpDocNode.php

@@ -76,6 +76,20 @@ static function (PhpDocTagValueNode $value): bool {
 	}
 
 
+	/**
+	 * @return TypelessParamTagValueNode[]
+	 */
+	public function getTypelessParamTagValues(string $tagName = '@param'): array
+	{
+		return array_filter(
+			array_column($this->getTagsByName($tagName), 'value'),
+			static function (PhpDocTagValueNode $value): bool {
+				return $value instanceof TypelessParamTagValueNode;
+			}
+		);
+	}
+
+
 	/**
 	 * @return TemplateTagValueNode[]
 	 */

src/Ast/PhpDoc/TypelessParamTagValueNode.php

@@ -0,0 +1,41 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\PhpDocParser\Ast\PhpDoc;
+
+use PHPStan\PhpDocParser\Ast\NodeAttributes;
+use function trim;
+
+class TypelessParamTagValueNode implements PhpDocTagValueNode
+{
+
+	use NodeAttributes;
+
+	/** @var bool */
+	public $isReference;
+
+	/** @var bool */
+	public $isVariadic;
+
+	/** @var string */
+	public $parameterName;
+
+	/** @var string (may be empty) */
+	public $description;
+
+	public function __construct(bool $isVariadic, string $parameterName, string $description, bool $isReference = false)
+	{
+		$this->isReference = $isReference;
+		$this->isVariadic = $isVariadic;
+		$this->parameterName = $parameterName;
+		$this->description = $description;
+	}
+
+
+	public function __toString(): string
+	{
+		$reference = $this->isReference ? '&' : '';
+		$variadic = $this->isVariadic ? '...' : '';
+		return trim("{$reference}{$variadic}{$this->parameterName} {$this->description}");
+	}
+
+}

src/Parser/PhpDocParser.php

@@ -230,14 +230,31 @@ public function parseTagValue(TokenIterator $tokens, string $tag): Ast\PhpDoc\Ph
 	}
 
 
-	private function parseParamTagValue(TokenIterator $tokens): Ast\PhpDoc\ParamTagValueNode
+	/**
+	 * @return Ast\PhpDoc\ParamTagValueNode|Ast\PhpDoc\TypelessParamTagValueNode
+	 */
+	private function parseParamTagValue(TokenIterator $tokens): Ast\PhpDoc\PhpDocTagValueNode
 	{
-		$type = $this->typeParser->parse($tokens);
+		if (
+			$tokens->isCurrentTokenType(Lexer::TOKEN_REFERENCE)
+			|| $tokens->isCurrentTokenType(Lexer::TOKEN_VARIADIC)
+			|| $tokens->isCurrentTokenType(Lexer::TOKEN_VARIABLE)
+		) {
+			$type = null;
+		} else {
+			$type = $this->typeParser->parse($tokens);
+		}
+
 		$isReference = $tokens->tryConsumeTokenType(Lexer::TOKEN_REFERENCE);
 		$isVariadic = $tokens->tryConsumeTokenType(Lexer::TOKEN_VARIADIC);
 		$parameterName = $this->parseRequiredVariableName($tokens);
 		$description = $this->parseOptionalDescription($tokens);
-		return new Ast\PhpDoc\ParamTagValueNode($type, $isVariadic, $parameterName, $description, $isReference);
+
+		if ($type !== null) {
+			return new Ast\PhpDoc\ParamTagValueNode($type, $isVariadic, $parameterName, $description, $isReference);
+		}
+
+		return new Ast\PhpDoc\TypelessParamTagValueNode($isVariadic, $parameterName, $description, $isReference);
 	}
 
 
@@ -463,7 +480,6 @@ private function parseRequiredVariableName(TokenIterator $tokens): string
 		return $parameterName;
 	}
 
-
 	private function parseOptionalDescription(TokenIterator $tokens, bool $limitStartToken = false): string
 	{
 		if ($limitStartToken) {

tests/PHPStan/Parser/PhpDocParserTest.php

@@ -27,6 +27,7 @@
 use PHPStan\PhpDocParser\Ast\PhpDoc\ThrowsTagValueNode;
 use PHPStan\PhpDocParser\Ast\PhpDoc\TypeAliasImportTagValueNode;
 use PHPStan\PhpDocParser\Ast\PhpDoc\TypeAliasTagValueNode;
+use PHPStan\PhpDocParser\Ast\PhpDoc\TypelessParamTagValueNode;
 use PHPStan\PhpDocParser\Ast\PhpDoc\UsesTagValueNode;
 use PHPStan\PhpDocParser\Ast\PhpDoc\VarTagValueNode;
 use PHPStan\PhpDocParser\Ast\Type\ArrayTypeNode;
@@ -64,6 +65,7 @@ protected function setUp(): void
 	/**
 	 * @dataProvider provideTagsWithNumbers
 	 * @dataProvider provideParamTagsData
+	 * @dataProvider provideTypelessParamTagsData
 	 * @dataProvider provideVarTagsData
 	 * @dataProvider provideReturnTagsData
 	 * @dataProvider provideThrowsTagsData
@@ -395,6 +397,86 @@ public function provideParamTagsData(): Iterator
 		];
 	}
 
+	public function provideTypelessParamTagsData(): Iterator
+	{
+		yield [
+			'OK',
+			'/** @param $foo description */',
+			new PhpDocNode([
+				new PhpDocTagNode(
+					'@param',
+					new TypelessParamTagValueNode(
+						false,
+						'$foo',
+						'description'
+					)
+				),
+			]),
+		];
+
+		yield [
+			'OK reference',
+			'/** @param &$foo description */',
+			new PhpDocNode([
+				new PhpDocTagNode(
+					'@param',
+					new TypelessParamTagValueNode(
+						false,
+						'$foo',
+						'description',
+						true
+					)
+				),
+			]),
+		];
+
+		yield [
+			'OK variadic',
+			'/** @param ...$foo description */',
+			new PhpDocNode([
+				new PhpDocTagNode(
+					'@param',
+					new TypelessParamTagValueNode(
+						true,
+						'$foo',
+						'description'
+					)
+				),
+			]),
+		];
+
+		yield [
+			'OK reference variadic',
+			'/** @param &...$foo description */',
+			new PhpDocNode([
+				new PhpDocTagNode(
+					'@param',
+					new TypelessParamTagValueNode(
+						true,
+						'$foo',
+						'description',
+						true
+					)
+				),
+			]),
+		];
+
+		yield [
+			'OK without type and description',
+			'/** @param $foo */',
+			new PhpDocNode([
+				new PhpDocTagNode(
+					'@param',
+					new TypelessParamTagValueNode(
+						false,
+						'$foo',
+						'',
+						false
+					)
+				),
+			]),
+		];
+	}
 
 	public function provideVarTagsData(): Iterator
 	{