Fix callable array intersection type offset narrowing

src/Type/IntersectionType.php

@@ -943,7 +943,17 @@
 			}
 		}
 
-		return $this->intersectResults(static fn (Type $type): TrinaryLogic => $type->hasOffsetValueType($offsetType));
+		$result = $this->intersectResults(static fn (Type $type): TrinaryLogic => $type->hasOffsetValueType($offsetType));
+
+		if (!$result->yes() && $this->isCallable()->yes() && $this->isArray()->yes()) {
+			$arrayKeyOffsetType = $offsetType->toArrayKey();
+			$callableArrayOffsetType = new UnionType([new ConstantIntegerType(0), new ConstantIntegerType(1)]);
+			if ($callableArrayOffsetType->isSuperTypeOf($arrayKeyOffsetType)->yes()) {
+				return TrinaryLogic::createYes();
+			}
+		}
+
+		return $result;
 	}
 
 	public function getOffsetValueType(Type $offsetType): Type
@@ -953,6 +963,21 @@
 			return TypeUtils::toBenevolentUnion($result);
 		}
 
+		if ($this->isCallable()->yes() && $this->isArray()->yes()) {
+			$arrayKeyOffsetType = $offsetType->toArrayKey();
+			$callableArrayOffsetType = new UnionType([new ConstantIntegerType(0), new ConstantIntegerType(1)]);
+			if ($callableArrayOffsetType->isSuperTypeOf($arrayKeyOffsetType)->yes()) {
+				if ((new ConstantIntegerType(0))->isSuperTypeOf($arrayKeyOffsetType)->yes()) {
+					$narrowedType = new UnionType([new ClassStringType(), new ObjectWithoutClassType()]);
+				} elseif ((new ConstantIntegerType(1))->isSuperTypeOf($arrayKeyOffsetType)->yes()) {
+					$narrowedType = new StringType();
+				} else {
+					$narrowedType = new UnionType([new StringType(), new ObjectWithoutClassType()]);
+				}
+				$result = TypeCombinator::intersect($result, $narrowedType);
+			}
+		}
+
 		return $result;
 	}
 

tests/PHPStan/Analyser/nsrt/bug-3842.php

@@ -0,0 +1,62 @@
+<?php declare(strict_types = 1);
+
+namespace Bug3842;
+
+use function PHPStan\Testing\assertType;
+
+class ClassA
+{
+	public static function callback(): void
+	{
+	}
+}
+
+class ClassB
+{
+	public function callback(): void
+	{
+	}
+}
+
+function testIsArrayOnCallable(callable $value): void {
+	if (is_array($value)) {
+		assertType('array<mixed, mixed>&callable(): mixed', $value);
+		assertType('class-string|object', $value[0]);
+		assertType('string', $value[1]);
+	}
+}
+
+/** @param callable-array $value */
+function testCallableArrayPhpDoc(array $value): void {
+	assertType('array&callable(): mixed', $value);
+	assertType('class-string|object', $value[0]);
+	assertType('string', $value[1]);
+}
+
+function testIsStringOnCallable(callable $value): void {
+	if (is_string($value)) {
+		assertType('callable-string', $value);
+	}
+}
+
+/** @param array{string|object, string} $values */
+function check(array $values): void {
+}
+
+/** @param array{class-string|object, string} $values */
+function checkClassString(array $values): void {
+}
+
+/** @param 0|1 $offset */
+function testCallableArrayUnionOffset(callable $value, int $offset): void {
+	if (is_array($value)) {
+		assertType('object|string', $value[$offset]);
+	}
+}
+
+function testPassCallableArray(callable $value): void {
+	if (is_array($value)) {
+		check($value);
+		checkClassString($value);
+	}
+}

tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php

@@ -2866,4 +2866,9 @@ public function testBug13643(): void
 		$this->analyse([__DIR__ . '/data/bug-13643.php'], []);
 	}
 
+	public function testBug3842(): void
+	{
+		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-3842.php'], []);
+	}
+
 }