Add exceptional case for DateInterval::format return type inference

Difference in days might behave differently when the DateInterval is created from scratch or from a diff.

- Extend returned type information for DateInterval::format method
- Exceptional case's type should form a Union with others

Author: adamturcsan

src/Type/Php/DateIntervalFormatDynamicReturnTypeExtension.php

@@ -3,6 +3,7 @@
 namespace PHPStan\Type\Php;
 
 use DateInterval;
+use DateTimeImmutable;
 use PhpParser\Node\Expr\MethodCall;
 use PHPStan\Analyser\Scope;
 use PHPStan\DependencyInjection\AutowiredService;
@@ -12,11 +13,13 @@
 use PHPStan\Type\Accessory\AccessoryNonFalsyStringType;
 use PHPStan\Type\Accessory\AccessoryNumericStringType;
 use PHPStan\Type\Accessory\AccessoryUppercaseStringType;
+use PHPStan\Type\Constant\ConstantStringType;
 use PHPStan\Type\DynamicMethodReturnTypeExtension;
 use PHPStan\Type\IntersectionType;
 use PHPStan\Type\StringType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
+use PHPStan\Type\UnionType;
 use function count;
 use function is_numeric;
 use function strtolower;
@@ -55,12 +58,12 @@ public function getTypeFromMethodCall(MethodReflection $methodReflection, Method
 			return null;
 		}
 
-		// The worst case scenario for the non-falsy-string check is that every number is 0.
-		$dateInterval = new DateInterval('P0D');
+		$dateInterval = $this->referenceDateInterval();
 
 		$possibleReturnTypes = [];
 		foreach ($constantStrings as $string) {
-			$value = $dateInterval->format($string->getValue());
+			$formatString = $string->getValue();
+			$value = $dateInterval->format($formatString);
 
 			$accessories = [];
 			if (is_numeric($value)) {
@@ -77,15 +80,42 @@ public function getTypeFromMethodCall(MethodReflection $methodReflection, Method
 			if (strtoupper($value) === $value) {
 				$accessories[] = new AccessoryUppercaseStringType();
 			}
+			$diffInDaysType = $this->diffInDaysTypes($formatString);
 
-			if (count($accessories) === 0) {
+			if (count($accessories) === 0 && $diffInDaysType === null) {
 				return null;
 			}
 
-			$possibleReturnTypes[] = new IntersectionType([new StringType(), ...$accessories]);
+			$intersectionType = new IntersectionType([
+				new StringType(),
+				...$accessories,
+			]);
+			$possibleReturnTypes[] = $diffInDaysType === null
+				? $intersectionType
+				: new UnionType([$diffInDaysType, $intersectionType]);
 		}
 
 		return TypeCombinator::union(...$possibleReturnTypes);
 	}
 
+	/**
+	 * The worst case scenario for the non-falsy-string check is that every number is 0.
+	 * We create an interval from a difference of two DateTime instances due to the different behavior for %a
+	 *
+	 * @see https://www.php.net/manual/en/dateinterval.format.php
+	 *
+	 * @return DateInterval
+	 */
+	private function referenceDateInterval(): DateInterval
+	{
+		return (new DateTimeImmutable('@0'))->diff((new DateTimeImmutable('@0')));
+	}
+
+	private function diffInDaysTypes(string $formatString): ?ConstantStringType
+	{
+		return $formatString === '%a'
+			? new ConstantStringType('(unknown)')
+			: null;
+	}
+
 }

tests/PHPStan/Analyser/nsrt/bug-1452.php

@@ -6,5 +6,7 @@
 
 $dateInterval = (new \DateTimeImmutable('now -60 minutes'))->diff(new \DateTimeImmutable('now'));
 
-// Could be lowercase-string&non-falsy-string&numeric-string&uppercase-string
-assertType('lowercase-string&non-falsy-string', $dateInterval->format('%a'));
+assertType(
+    "'(unknown)'|(lowercase-string&non-empty-string&numeric-string&uppercase-string)",
+    $dateInterval->format('%a')
+);