implement gettype() inference in TypeSpecifier

src/Analyser/TypeSpecifier.php

@@ -30,6 +30,7 @@
 use PHPStan\Type\Accessory\HasOffsetType;
 use PHPStan\Type\Accessory\HasPropertyType;
 use PHPStan\Type\Accessory\NonEmptyArrayType;
+use PHPStan\Type\ArrayType;
 use PHPStan\Type\BooleanType;
 use PHPStan\Type\ConditionalTypeForParameter;
 use PHPStan\Type\Constant\ConstantArrayType;
@@ -52,6 +53,7 @@
 use PHPStan\Type\NullType;
 use PHPStan\Type\ObjectType;
 use PHPStan\Type\ObjectWithoutClassType;
+use PHPStan\Type\ResourceType;
 use PHPStan\Type\StaticMethodTypeSpecifyingExtension;
 use PHPStan\Type\StaticType;
 use PHPStan\Type\StaticTypeFactory;
@@ -490,6 +492,62 @@ public function specifyTypesInCondition(
 				);
 			}
 
+			$getttypeType = static function (ConstantStringType $constantStringType) {
+				$type = null;
+				if ($constantStringType->getValue() === 'string') {
+					$type = new StringType();
+				}
+				if ($constantStringType->getValue() === 'array') {
+					$type = new ArrayType(new MixedType(), new MixedType());
+				}
+				if ($constantStringType->getValue() === 'boolean') {
+					$type = new BooleanType();
+				}
+				if ($constantStringType->getValue() === 'resource' || $constantStringType->getValue() === 'resource (closed)') {
+					$type = new ResourceType();
+				}
+				if ($constantStringType->getValue() === 'integer') {
+					$type = new IntegerType();
+				}
+				if ($constantStringType->getValue() === 'double') {
+					$type = new FloatType();
+				}
+				if ($constantStringType->getValue() === 'NULL') {
+					$type = new NullType();
+				}
+				if ($constantStringType->getValue() === 'object') {
+					$type = new ObjectWithoutClassType();
+				}
+				return $type;
+			};
+
+			if (
+				$expr->left instanceof FuncCall
+				&& $expr->left->name instanceof Name
+				&& strtolower($expr->left->name->toString()) === 'gettype'
+				&& isset($expr->left->getArgs()[0])
+				&& $rightType instanceof ConstantStringType
+			) {
+				$type = $getttypeType($rightType);
+
+				if ($type !== null) {
+					return $this->create($expr->left->getArgs()[0]->value, $type, $context, false, $scope, $rootExpr);
+				}
+			}
+			if (
+				$expr->right instanceof FuncCall
+				&& $expr->right->name instanceof Name
+				&& strtolower($expr->right->name->toString()) === 'gettype'
+				&& isset($expr->right->getArgs()[0])
+				&& $leftType instanceof ConstantStringType
+			) {
+				$type = $getttypeType($leftType);
+
+				if ($type !== null) {
+					return $this->create($expr->right->getArgs()[0]->value, $type, $context, false, $scope, $rootExpr);
+				}
+			}
+
 			$stringType = new StringType();
 			$integerType = new IntegerType();
 			$floatType = new FloatType();

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -969,6 +969,7 @@ public function dataFileAsserts(): iterable
 		yield from $this->gatherAssertTypes(__DIR__ . '/../Rules/Variables/data/bug-7417.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/../Rules/Arrays/data/bug-7469.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/../Rules/Variables/data/bug-3391.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6901.php');
 	}
 
 	/**

tests/PHPStan/Analyser/data/bug-6901.php

@@ -0,0 +1,57 @@
+<?php
+
+namespace Bug6901;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param integer|string|array<string>|bool $y
+ * @return integer
+ */
+function foo($y)
+{
+	switch (gettype($y)) {
+		case "integer":
+			assertType('int', $y);
+			break;
+		case "string":
+			assertType('string', $y);
+			break;
+		case "boolean":
+			assertType('bool', $y);
+			break;
+		case "array":
+			assertType('array<string>', $y);
+			break;
+		default:
+			assertType('*NEVER*', $y);
+	}
+	assertType('array<string>|bool|int|string', $y);
+	return 0;
+}
+
+/**
+ * @param object|float|null|resource $y
+ * @return integer
+ */
+function bar($y)
+{
+	switch (gettype($y)) {
+		case "object":
+			assertType('object', $y);
+			break;
+		case "double":
+			assertType('float', $y);
+			break;
+		case "NULL":
+			assertType('null', $y);
+			break;
+		case "resource":
+			assertType('resource', $y);
+			break;
+		default:
+			assertType('*NEVER*', $y);
+	}
+	assertType('float|object|resource|null', $y);
+	return 0;
+}