type projections: enhance template type resolution

ondrejmirtes · Sep 18, 2023 · Jul 21, 2023 · Jun 23, 2023 · Jun 23, 2023 · Jun 23, 2023
commit 01131e8f2208b00cf72ec0f66f18ea75aacf97a6
diff --git a/src/Type/Generic/TemplateTypeHelper.php b/src/Type/Generic/TemplateTypeHelper.php
@@ -3,32 +3,53 @@
 namespace PHPStan\Type\Generic;
 
 use PHPStan\Type\ErrorType;
+use PHPStan\Type\NonAcceptingNeverType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeTraverser;
+use PHPStan\Type\VarianceAwareTypeTraverser;
 
 class TemplateTypeHelper
 {
 
 	/**
 	 * Replaces template types with standin types
 	 */
-	public static function resolveTemplateTypes(Type $type, TemplateTypeMap $standins, bool $keepErrorTypes = false): Type
+	public static function resolveTemplateTypes(
+		Type $type,
+		TemplateTypeMap $standins,
+		TemplateTypeVarianceMap $callSiteVariances,
+		TemplateTypeVariance $positionVariance,
+		bool $keepErrorTypes = false,
+	): Type
 	{
-		return TypeTraverser::map($type, static function (Type $type, callable $traverse) use ($standins, $keepErrorTypes): Type {
+		return VarianceAwareTypeTraverser::map($type, $positionVariance, static function (Type $type, TemplateTypeVariance $variance, callable $traverse) use ($standins, $callSiteVariances, $keepErrorTypes): Type {
 			if ($type instanceof TemplateType && !$type->isArgument()) {
 				$newType = $standins->getType($type->getName());
 				if ($newType === null) {
-					return $traverse($type);
+					return $traverse($type, $variance);
 				}
 
 				if ($newType instanceof ErrorType && !$keepErrorTypes) {
-					return $traverse($type->getBound());
+					return $traverse($type->getBound(), $variance);
+				}
+
+				$callSiteVariance = $callSiteVariances->getVariance($type->getName());
+				if ($callSiteVariance === null || $callSiteVariance->invariant()) {
+					return $newType;
+				}
+
+				if (!$callSiteVariance->covariant() && $variance->covariant()) {
+					return $traverse($type->getBound(), $variance);
+				}
+
+				if (!$callSiteVariance->contravariant() && $variance->contravariant()) {
+					return new NonAcceptingNeverType();
 				}
 
 				return $newType;
 			}
 
-			return $traverse($type);
+			return $traverse($type, $variance);
 		});
 	}
 

diff --git a/src/Type/Type.php b/src/Type/Type.php
@@ -326,6 +326,13 @@ public function traverse(callable $cb): Type;
 	 */
 	public function traverseSimultaneously(Type $right, callable $cb): Type;
 
+	/**
+	 * Traverses inner types while composing their positional variance.
+	 *
+	 * @param callable(Type $type, TemplateTypeVariance $variance): Type $cb
+	 */
+	public function traverseWithVariance(TemplateTypeVariance $variance, callable $cb): Type;
+
 	public function toPhpDocNode(): TypeNode;
 
 	/**

diff --git a/src/Type/VarianceAwareTypeTraverser.php b/src/Type/VarianceAwareTypeTraverser.php
@@ -0,0 +1,46 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type;
+
+use PHPStan\Type\Generic\TemplateTypeVariance;
+
+/**
+ * @phpstan-type Callback callable(Type $type, TemplateTypeVariance $variance, callable(Type, TemplateTypeVariance): Type $traverse): Type
+ */
+class VarianceAwareTypeTraverser
+{
+
+	/** @var Callback */
+	private $cb;
+
+	/**
+	 * @param Callback $cb
+	 */
+	public static function map(Type $type, TemplateTypeVariance $variance, callable $cb): Type
+	{
+		$self = new self($cb);
+
+		return $self->mapInternal($type, $variance);
+	}
+
+	/**
+	 * @param Callback $cb
+	 */
+	private function __construct(callable $cb)
+	{
+		$this->cb = $cb;
+	}
+
+	/** @internal */
+	public function mapInternal(Type $type, TemplateTypeVariance $variance): Type
+	{
+		return ($this->cb)($type, $variance, [$this, 'traverseInternal']);
+	}
+
+	/** @internal */
+	public function traverseInternal(Type $type, TemplateTypeVariance $variance): Type
+	{
+		return $type->traverseWithVariance($variance, [$this, 'mapInternal']);
+	}
+
+}