Date format return type extensions

conf/config.neon

@@ -1068,6 +1068,16 @@ services:
 		tags:
 			- phpstan.broker.dynamicFunctionReturnTypeExtension
 
+	-
+		class: PHPStan\Type\Php\DateFormatFunctionReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicFunctionReturnTypeExtension
+
+	-
+		class: PHPStan\Type\Php\DateFormatMethodReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicMethodReturnTypeExtension
+
 	-
 		class: PHPStan\Type\Php\DateFunctionReturnTypeExtension
 		tags:

src/Type/Php/DateFormatFunctionReturnTypeExtension.php

@@ -0,0 +1,39 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use PhpParser\Node\Expr\FuncCall;
+use PhpParser\Node\Name\FullyQualified;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\DynamicFunctionReturnTypeExtension;
+use PHPStan\Type\StringType;
+use PHPStan\Type\Type;
+use function count;
+
+class DateFormatFunctionReturnTypeExtension implements DynamicFunctionReturnTypeExtension
+{
+
+	public function isFunctionSupported(FunctionReflection $functionReflection): bool
+	{
+		return $functionReflection->getName() === 'date_format';
+	}
+
+	public function getTypeFromFunctionCall(
+		FunctionReflection $functionReflection,
+		FuncCall $functionCall,
+		Scope $scope,
+	): Type
+	{
+		if (count($functionCall->getArgs()) < 2) {
+			return new StringType();
+		}
+
+		return $scope->getType(
+			new FuncCall(new FullyQualified('date'), [
+				$functionCall->getArgs()[1],
+			]),
+		);
+	}
+
+}

src/Type/Php/DateFormatMethodReturnTypeExtension.php

@@ -0,0 +1,42 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use DateTimeInterface;
+use PhpParser\Node\Expr\FuncCall;
+use PhpParser\Node\Expr\MethodCall;
+use PhpParser\Node\Name\FullyQualified;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\MethodReflection;
+use PHPStan\Type\DynamicMethodReturnTypeExtension;
+use PHPStan\Type\StringType;
+use PHPStan\Type\Type;
+use function count;
+
+class DateFormatMethodReturnTypeExtension implements DynamicMethodReturnTypeExtension
+{
+
+	public function getClass(): string
+	{
+		return DateTimeInterface::class;
+	}
+
+	public function isMethodSupported(MethodReflection $methodReflection): bool
+	{
+		return $methodReflection->getName() === 'format';
+	}
+
+	public function getTypeFromMethodCall(MethodReflection $methodReflection, MethodCall $methodCall, Scope $scope): Type
+	{
+		if (count($methodCall->getArgs()) === 0) {
+			return new StringType();
+		}
+
+		return $scope->getType(
+			new FuncCall(new FullyQualified('date'), [
+				$methodCall->getArgs()[0],
+			]),
+		);
+	}
+
+}

src/Type/Php/DateFunctionReturnTypeExtension.php

@@ -5,17 +5,19 @@
 use PhpParser\Node\Expr\FuncCall;
 use PHPStan\Analyser\Scope;
 use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
 use PHPStan\Type\Accessory\AccessoryNumericStringType;
 use PHPStan\Type\Constant\ConstantStringType;
+use PHPStan\Type\ConstantTypeHelper;
 use PHPStan\Type\DynamicFunctionReturnTypeExtension;
 use PHPStan\Type\IntersectionType;
 use PHPStan\Type\StringType;
 use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
 use PHPStan\Type\TypeUtils;
 use PHPStan\Type\UnionType;
 use function count;
 use function date;
-use function is_numeric;
 use function sprintf;
 
 class DateFunctionReturnTypeExtension implements DynamicFunctionReturnTypeExtension
@@ -76,17 +78,31 @@ public function getTypeFromFunctionCall(
 			}
 		}
 
+		$types = [];
 		foreach ($constantStrings as $constantString) {
-			$formattedDate = date($constantString->getValue());
-			if (!is_numeric($formattedDate)) {
-				return new StringType();
-			}
+			$types[] = ConstantTypeHelper::getTypeFromValue(date($constantString->getValue()));
+		}
+
+		$type = TypeCombinator::union(...$types);
+		if ($type->isNumericString()->yes()) {
+			return new IntersectionType([
+				new StringType(),
+				new AccessoryNumericStringType(),
+			]);
+		}
+
+		if ($type->isNonEmptyString()->yes()) {
+			return new IntersectionType([
+				new StringType(),
+				new AccessoryNonEmptyStringType(),
+			]);
+		}
+
+		if ($type->isNonEmptyString()->no()) {
+			return new ConstantStringType('');
 		}
 
-		return new IntersectionType([
-			new StringType(),
-			new AccessoryNumericStringType(),
-		]);
+		return new StringType();
 	}
 
 	private function buildNumericRangeType(int $min, int $max, bool $zeroPad): Type

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -736,6 +736,7 @@ public function dataFileAsserts(): iterable
 		}
 
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6698.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/date-format.php');
 	}
 
 	/**

tests/PHPStan/Analyser/data/bug-2899.php

@@ -10,7 +10,7 @@ class Foo
 	public function doFoo(string $s, $mixed)
 	{
 		assertType('numeric-string', date('Y'));
-		assertType('string', date('Y.m.d'));
+		assertType('non-empty-string', date('Y.m.d'));
 		assertType('string', date($s));
 		assertType('string', date($mixed));
 	}

tests/PHPStan/Analyser/data/date-format.php

@@ -0,0 +1,45 @@
+<?php
+
+namespace DateFormatReturnType;
+
+use function PHPStan\Testing\assertType;
+
+function (string $s): void {
+	assertType('\'\'', date(''));
+	assertType('string', date($s));
+	assertType('non-empty-string', date('D'));
+	assertType('numeric-string', date('Y'));
+	assertType('numeric-string', date('Ghi'));
+};
+
+function (\DateTime $dt, string $s): void {
+	assertType('\'\'', date_format($dt, ''));
+	assertType('string', date_format($dt, $s));
+	assertType('non-empty-string', date_format($dt, 'D'));
+	assertType('numeric-string', date_format($dt, 'Y'));
+	assertType('numeric-string', date_format($dt, 'Ghi'));
+};
+
+function (\DateTimeInterface $dt, string $s): void {
+	assertType('\'\'', $dt->format(''));
+	assertType('string', $dt->format($s));
+	assertType('non-empty-string', $dt->format('D'));
+	assertType('numeric-string', $dt->format('Y'));
+	assertType('numeric-string', $dt->format('Ghi'));
+};
+
+function (\DateTime $dt, string $s): void {
+	assertType('\'\'', $dt->format(''));
+	assertType('string', $dt->format($s));
+	assertType('non-empty-string', $dt->format('D'));
+	assertType('numeric-string', $dt->format('Y'));
+	assertType('numeric-string', $dt->format('Ghi'));
+};
+
+function (\DateTimeImmutable $dt, string $s): void {
+	assertType('\'\'', $dt->format(''));
+	assertType('string', $dt->format($s));
+	assertType('non-empty-string', $dt->format('D'));
+	assertType('numeric-string', $dt->format('Y'));
+	assertType('numeric-string', $dt->format('Ghi'));
+};