Check datetime instantiation

conf/config.level0.neon

@@ -55,6 +55,7 @@ rules:
 	- PHPStan\Rules\Properties\AccessStaticPropertiesInAssignRule
 	- PHPStan\Rules\Properties\PropertyAttributesRule
 	- PHPStan\Rules\Variables\UnsetRule
+	- PHPStan\Rules\DateTimeInstantiationRule
 
 services:
 	-

src/Rules/DateTimeInstantiationRule.php

@@ -0,0 +1,65 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules;
+
+use DateTime;
+use DateTimeImmutable;
+use PhpParser\Node;
+use PhpParser\Node\Expr\New_;
+use PHPStan\Analyser\Scope;
+use PHPStan\Type\Constant\ConstantStringType;
+
+/**
+ * @implements \PHPStan\Rules\Rule<\PhpParser\Node\Expr\New_>
+ */
+class DateTimeInstantiationRule implements \PHPStan\Rules\Rule
+{
+
+	public function getNodeType(): string
+	{
+		return New_::class;
+	}
+
+	/**
+	 * @param New_ $node
+	 */
+	public function processNode(Node $node, Scope $scope): array
+	{
+		if (
+			!($node->class instanceof \PhpParser\Node\Name)
+			|| !\in_array((string) $node->class, [DateTime::class, DateTimeImmutable::class], true)
+			|| \count($node->args) === 0
+			|| !($arg = $scope->getType($node->args[0]->value)) instanceof ConstantStringType
+		) {
+			return [];
+		}
+
+		$errors = [];
+		$dateString = $arg->getValue();
+		try {
+			new DateTime($dateString);
+		} catch (\Throwable $e) {
+			// an exception is thrown for errors only but we want to catch warnings too
+		}
+		$result = DateTime::getLastErrors();
+		foreach ($result['warnings'] as $warning) {
+			$errors[] = RuleErrorBuilder::message(sprintf(
+				'Instantiating %s with %s produces a warning: %s',
+				(string) $node->class,
+				$dateString,
+				$warning
+			))->build();
+		}
+		foreach ($result['errors'] as $error) {
+			$errors[] = RuleErrorBuilder::message(sprintf(
+				'Instantiating %s with %s produces an error: %s',
+				(string) $node->class,
+				$dateString,
+				$error
+			))->build();
+		}
+
+		return $errors;
+	}
+
+}

tests/PHPStan/Rules/DateTimeConstructorRuleTest.php

@@ -0,0 +1,34 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules;
+
+/**
+ * @extends \PHPStan\Testing\RuleTestCase<DateTimeInstantiationRule>
+ */
+class DateTimeConstructorRuleTest extends \PHPStan\Testing\RuleTestCase
+{
+
+	protected function getRule(): \PHPStan\Rules\Rule
+	{
+		return new DateTimeInstantiationRule();
+	}
+
+	public function test(): void
+	{
+		$this->analyse(
+			[__DIR__ . '/data/datetime-instantiation.php'],
+			[
+				['Instantiating DateTime with 2020.11.17 produces an error: Double time specification', 3],
+				['Instantiating DateTimeImmutable with asdfasdf produces a warning: Double timezone specification', 5],
+				[
+					'Instantiating DateTimeImmutable with asdfasdf produces an error: The timezone could not be found in the database',
+					5,
+				],
+				['Instantiating DateTimeImmutable with 2020.11.17 produces an error: Double time specification', 10],
+				['Instantiating DateTimeImmutable with 2020.11.18 produces an error: Double time specification', 17],
+				['Instantiating DateTime with 2020-04-31 produces a warning: The parsed date was invalid', 20],
+			]
+		);
+	}
+
+}

tests/PHPStan/Rules/data/datetime-instantiation.php

@@ -0,0 +1,20 @@
+<?php
+
+new DateTime('2020.11.17');
+
+new DateTimeImmutable('asdfasdf');
+
+new DateTime('');
+
+$test = '2020.11.17';
+new DateTimeImmutable($test);
+
+/**
+ * @param '2020.11.18' $date2
+ */
+function foo(string $date, string $date2): void {
+	new DateTime($date);
+	new DateTimeImmutable($date2);
+}
+
+new DateTime('2020-04-31');