Constant-fold explode() into a ConstantArrayType when separator, string and limit are all constant

src/Command/AnalyseCommand.php

@@ -2,6 +2,7 @@
 
 namespace PHPStan\Command;
 
+use DateTimeImmutable;
 use OndraM\CiDetector\CiDetector;
 use Override;
 use PHPStan\Analyser\InternalError;
@@ -35,6 +36,7 @@
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Input\InputOption;
 use Symfony\Component\Console\Input\StringInput;
+use Symfony\Component\Console\Output\ConsoleOutputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Output\StreamOutput;
 use Throwable;
@@ -63,6 +65,7 @@
 use function stream_get_contents;
 use function strlen;
 use function substr;
+use function time;
 use const PATHINFO_BASENAME;
 use const PATHINFO_EXTENSION;
 
@@ -140,6 +143,34 @@ protected function initialize(InputInterface $input, OutputInterface $output): v
 	#[Override]
 	protected function execute(InputInterface $input, OutputInterface $output): int
 	{
+		if ($output instanceof ConsoleOutputInterface) {
+			$errorOutput = $output->getErrorOutput();
+			$errorOutput->writeln('');
+			$errorOutput->writeln("⚠️  You're running an old version of PHPStan.️");
+			$errorOutput->writeln('');
+			$errorOutput->writeln('The last release in the 1.12.x series with new features');
+
+			$lastRelease = new DateTimeImmutable('2025-07-17 00:00:00');
+			$daysSince = (time() - $lastRelease->getTimestamp()) / 60 / 60 / 24;
+			$errorOutput->writeln('and bugfixes was released on <fg=red>July 17th 2025</>,');
+			$errorOutput->writeln(sprintf('that\'s <fg=red>%d days ago.</>', (int) $daysSince));
+			$errorOutput->writeln('');
+
+			$errorOutput->writeln('Since then more than <fg=cyan>65 new PHPStan versions</> were released');
+			$errorOutput->writeln('with hundreds of new features, bugfixes, and other');
+			$errorOutput->writeln('quality of life improvements.');
+			$errorOutput->writeln('');
+
+			$errorOutput->writeln("To learn about what you're missing out on, check out");
+			$errorOutput->writeln('this blog with articles about the latest major releases:');
+			$errorOutput->writeln('<options=underscore>https://phpstan.org/blog</>');
+			$errorOutput->writeln('');
+
+			$errorOutput->writeln('Upgrade today to <fg=green>PHPStan 2.2 or newer</> by using');
+			$errorOutput->writeln('<fg=cyan>"phpstan/phpstan": "^2.2"</> in your <fg=cyan>composer.json</>.');
+			$errorOutput->writeln('');
+		}
+
 		$paths = $input->getArgument('paths');
 		$memoryLimit = $input->getOption('memory-limit');
 		$autoloadFile = $input->getOption('autoload-file');

src/Type/Php/ExplodeFunctionDynamicReturnTypeExtension.php

@@ -29,7 +29,9 @@
 use PHPStan\Type\TypeUtils;
 use PHPStan\Type\UnionType;
 use function count;
+use function explode;
 use function max;
+use const PHP_INT_MAX;
 
 #[AutowiredService]
 final class ExplodeFunctionDynamicReturnTypeExtension implements DynamicFunctionReturnTypeExtension
@@ -45,6 +47,12 @@ final class ExplodeFunctionDynamicReturnTypeExtension implements DynamicFunction
 		'str_ends_with',
 	];
 
+	/**
+	 * How many delimiter/string/limit combinations may be evaluated when
+	 * constant-folding the call before giving up on the exact result.
+	 */
+	private const CONSTANT_COMBINATION_LIMIT = 16;
+
 	public function __construct(private PhpVersion $phpVersion)
 	{
 	}
@@ -90,6 +98,12 @@ public function getTypeFromFunctionCall(
 		}
 
 		$limitType = isset($args[2]) ? $scope->getType($args[2]->value) : null;
+
+		$constantType = $this->createConstantSplitType($delimiterType, $stringType, $limitType);
+		if ($constantType !== null) {
+			return $constantType;
+		}
+
 		$delimiterGuaranteedPresent = $this->isDelimiterGuaranteedPresent($args, $scope);
 
 		if ($this->isSingleElementLimit($limitType)) {
@@ -144,6 +158,75 @@ private function isDelimiterGuaranteedPresent(array $args, Scope $scope): bool
 		return false;
 	}
 
+	/**
+	 * The exact result of the split when the delimiter, the string and the limit
+	 * are all known constants, or null when it cannot be computed.
+	 */
+	private function createConstantSplitType(Type $delimiterType, Type $stringType, ?Type $limitType): ?Type
+	{
+		$delimiters = [];
+		foreach ($delimiterType->getConstantStrings() as $delimiterString) {
+			$delimiterValue = $delimiterString->getValue();
+			if ($delimiterValue === '') {
+				// explode() does not split on an empty separator, it errors out
+				return null;
+			}
+
+			$delimiters[] = $delimiterValue;
+		}
+
+		if (count($delimiters) === 0) {
+			return null;
+		}
+
+		$strings = $stringType->getConstantStrings();
+		if (count($strings) === 0) {
+			return null;
+		}
+
+		if ($limitType === null) {
+			$limits = [PHP_INT_MAX];
+		} else {
+			$limits = [];
+			foreach ($limitType->getFiniteTypes() as $finiteType) {
+				if (!$finiteType instanceof ConstantIntegerType) {
+					return null;
+				}
+
+				$limits[] = $finiteType->getValue();
+			}
+
+			if (count($limits) === 0) {
+				return null;
+			}
+		}
+
+		if (count($delimiters) * count($strings) * count($limits) > self::CONSTANT_COMBINATION_LIMIT) {
+			return null;
+		}
+
+		$results = [];
+		foreach ($delimiters as $delimiter) {
+			foreach ($strings as $string) {
+				foreach ($limits as $limit) {
+					$items = explode($delimiter, $string->getValue(), $limit);
+					if (count($items) > ConstantArrayTypeBuilder::ARRAY_COUNT_LIMIT) {
+						return null;
+					}
+
+					$builder = ConstantArrayTypeBuilder::createEmpty();
+					foreach ($items as $i => $item) {
+						$builder->setOffsetValueType(new ConstantIntegerType($i), new ConstantStringType($item));
+					}
+
+					$results[] = $builder->getArray();
+				}
+			}
+		}
+
+		return TypeCombinator::union(...$results);
+	}
+
 	/**
 	 * A limit of 0 or 1 returns the whole string as the only element, without
 	 * splitting on the delimiter.

tests/PHPStan/Analyser/nsrt/array-destructuring.php

@@ -129,10 +129,10 @@ function (\stdClass $obj) {
     assertType('non-empty-string', $secondStringArrayForeachList);
     assertType('non-empty-string', $thirdStringArrayForeachList);
     assertType('non-empty-string', $fourthStringArrayForeachList);
-    assertType('lowercase-string&uppercase-string', $dateArray['Y']);
-    assertType('lowercase-string&uppercase-string', $dateArray['m']);
+    assertType("'2018'", $dateArray['Y']);
+    assertType("'12'", $dateArray['m']);
     assertType('int', $dateArray['d']);
-    assertType('lowercase-string&uppercase-string', $intArrayForRewritingFirstElement[0]);
+    assertType("''", $intArrayForRewritingFirstElement[0]);
     assertType('int', $intArrayForRewritingFirstElement[1]);
     assertType('ArrayAccess&stdClass', $obj);
     assertType('stdClass', $newArray['newKey']);

tests/PHPStan/Analyser/nsrt/bug-15013.php

@@ -0,0 +1,16 @@
+<?php declare(strict_types = 1);
+
+namespace Bug15013;
+
+use function PHPStan\Testing\assertType;
+
+function () {
+	$string = 'App/Service::foo';
+
+	assertType("array{'App/Service::foo'}", explode(':::', $string));
+
+	[$first, $second] = explode(':::', $string);
+
+	assertType("'App/Service::foo'", $first);
+	assertType('*ERROR*', $second);
+};

tests/PHPStan/Analyser/nsrt/explode.php

@@ -27,3 +27,34 @@ function (string $delimiter, $mixed) {
 	assertType('non-empty-list<string>', $benevolentArrayOrFalse);
 
 };
+
+/**
+ * @param ','|';' $delimiterUnion
+ * @param 'a,b'|'x;y;z' $stringUnion
+ * @param 1|2 $limitUnion
+ * @param int<1, 3> $limitRange
+ * @param ''|',' $maybeEmptyDelimiter
+ */
+function constantSplit(string $delimiterUnion, string $stringUnion, int $limitUnion, int $limitRange, string $maybeEmptyDelimiter, string $unknown, int $unknownLimit): void
+{
+	assertType("array{'a', 'b', 'c'}", explode(',', 'a,b,c'));
+	assertType("array{'App/Service::foo'}", explode(':::', 'App/Service::foo'));
+	assertType("array{''}", explode(',', ''));
+	assertType("array{'a', 'b,c'}", explode(',', 'a,b,c', 2));
+	assertType("array{'a,b,c'}", explode(',', 'a,b,c', 0));
+	assertType("array{'a,b,c'}", explode(',', 'a,b,c', 1));
+	assertType("array{'a', 'b'}", explode(',', 'a,b,c', -1));
+	assertType('array{}', explode(',', 'a,b', -5));
+
+	assertType("array{'a', 'b'}|array{'a,b'}|array{'x', 'y', 'z'}|array{'x;y;z'}", explode($delimiterUnion, $stringUnion));
+	assertType("array{'a', 'b'}|array{'x;y;z'}", explode(',', $stringUnion));
+	assertType("array{'a', 'b,c'}|array{'a,b,c'}", explode(',', 'a,b,c', $limitUnion));
+	assertType("array{'a', 'b', 'c'}|array{'a', 'b,c'}|array{'a,b,c'}", explode(',', 'a,b,c', $limitRange));
+
+	// the delimiter may be an empty string, which is not a valid split
+	assertType('non-empty-list<lowercase-string>', explode($maybeEmptyDelimiter, 'a,b'));
+
+	assertType('non-empty-list<lowercase-string>', explode($unknown, 'a,b'));
+	assertType('non-empty-list<string>', explode(',', $unknown));
+	assertType('list<lowercase-string>', explode(',', 'a,b,c', $unknownLimit));
+}

tests/PHPStan/Rules/Arrays/ArrayDestructuringRuleTest.php

@@ -102,6 +102,16 @@ public function testBug8075(): void
 		]);
 	}
 
+	public function testBug15013(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-15013.php'], [
+			[
+				'Offset 1 does not exist on array{\'App/Service::foo\'}.',
+				8,
+			],
+		]);
+	}
+
 	#[RequiresPhp('>= 8.0.0')]
 	public function testRuleWithNullsafeVariant(): void
 	{

tests/PHPStan/Rules/Arrays/data/bug-15013.php

@@ -0,0 +1,15 @@
+<?php declare(strict_types = 1);
+
+namespace Bug15013RuleTest;
+
+function () {
+	$string = 'App/Service::foo';
+
+	[$first, $second] = explode(':::', $string);
+};
+
+function () {
+	$string = 'App/Service::foo';
+
+	[$first, $second] = explode('::', $string);
+};