Support bool as template type bound

src/Rules/Generics/TemplateTypeCheck.php

@@ -7,6 +7,7 @@
 use PHPStan\Rules\ClassCaseSensitivityCheck;
 use PHPStan\Rules\ClassNameNodePair;
 use PHPStan\Rules\RuleErrorBuilder;
+use PHPStan\Type\BooleanType;
 use PHPStan\Type\Generic\GenericObjectType;
 use PHPStan\Type\Generic\TemplateType;
 use PHPStan\Type\Generic\TemplateTypeScope;
@@ -110,6 +111,7 @@ public function check(
 					$boundClass === MixedType::class
 					|| $boundClass === StringType::class
 					|| $boundClass === IntegerType::class
+					|| $boundClass === BooleanType::class
 					|| $boundClass === ObjectWithoutClassType::class
 					|| $boundClass === ObjectType::class
 					|| $boundClass === GenericObjectType::class

src/Type/Generic/TemplateBooleanType.php

@@ -0,0 +1,54 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Generic;
+
+use PHPStan\Type\BooleanType;
+use PHPStan\Type\Traits\UndecidedComparisonCompoundTypeTrait;
+use PHPStan\Type\Type;
+
+/** @api */
+final class TemplateBooleanType extends BooleanType implements TemplateType
+{
+
+	/** @use TemplateTypeTrait<BooleanType> */
+	use TemplateTypeTrait;
+	use UndecidedComparisonCompoundTypeTrait;
+
+	public function __construct(
+		TemplateTypeScope $scope,
+		TemplateTypeStrategy $templateTypeStrategy,
+		TemplateTypeVariance $templateTypeVariance,
+		string $name,
+		BooleanType $bound
+	)
+	{
+		parent::__construct();
+		$this->scope = $scope;
+		$this->strategy = $templateTypeStrategy;
+		$this->variance = $templateTypeVariance;
+		$this->name = $name;
+		$this->bound = $bound;
+	}
+
+	public function traverse(callable $cb): Type
+	{
+		$newBound = $cb($this->getBound());
+		if ($this->getBound() !== $newBound && $newBound instanceof BooleanType) {
+			return new self(
+				$this->scope,
+				$this->strategy,
+				$this->variance,
+				$this->name,
+				$newBound
+			);
+		}
+
+		return $this;
+	}
+
+	protected function shouldGeneralizeInferredType(): bool
+	{
+		return false;
+	}
+
+}

src/Type/Generic/TemplateTypeFactory.php

@@ -4,6 +4,7 @@
 
 use PHPStan\PhpDoc\Tag\TemplateTag;
 use PHPStan\Type\BenevolentUnionType;
+use PHPStan\Type\BooleanType;
 use PHPStan\Type\IntegerType;
 use PHPStan\Type\MixedType;
 use PHPStan\Type\ObjectType;
@@ -44,6 +45,10 @@ public static function create(TemplateTypeScope $scope, string $name, ?Type $bou
 			return new TemplateIntegerType($scope, $strategy, $variance, $name, $bound);
 		}
 
+		if ($bound instanceof BooleanType && ($boundClass === BooleanType::class || $bound instanceof TemplateType)) {
+			return new TemplateBooleanType($scope, $strategy, $variance, $name, $bound);
+		}
+
 		if ($bound instanceof MixedType && ($boundClass === MixedType::class || $bound instanceof TemplateType)) {
 			return new TemplateMixedType($scope, $strategy, $variance, $name, $bound);
 		}

tests/PHPStan/Analyser/data/generics.php

@@ -1405,3 +1405,20 @@ function (): void {
 	$array = ['a' => 1, 'b' => 2];
 	assertType('array(\'a\' => int, \'b\' => int)', a($array));
 };
+
+
+/**
+ * @template T of bool
+ * @param T $b
+ * @return T
+ */
+function boolBound(bool $b): bool
+{
+	return $b;
+}
+
+function (bool $b): void {
+	assertType('true', boolBound(true));
+	assertType('false', boolBound(false));
+	assertType('bool', boolBound($b));
+};

tests/PHPStan/Rules/Generics/data/function-template.php

@@ -33,3 +33,9 @@ function lorem()
 {
 
 }
+
+/** @template T of bool */
+function ipsum()
+{
+
+}