Add rule checking arguments to unset (#2605)

src/Rules/Functions/UnsetRule.php

@@ -0,0 +1,69 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Functions;
+
+use PhpParser\Node;
+use PHPStan\Analyser\Scope;
+use PHPStan\Rules\RuleErrorBuilder;
+use PHPStan\Type\VerbosityLevel;
+
+/**
+ * @implements \PHPStan\Rules\Rule<\PhpParser\Node\Stmt\Unset_>
+ */
+class UnsetRule implements \PHPStan\Rules\Rule
+{
+
+	public function getNodeType(): string
+	{
+		return Node\Stmt\Unset_::class;
+	}
+
+	public function processNode(Node $node, Scope $scope): array
+	{
+		$functionArguments = $node->vars;
+		$messages = [];
+
+		foreach ($functionArguments as $argument) {
+			$message = $this->canBeUnset($argument, $scope);
+
+			if (!$message) {
+				continue;
+			}
+
+			$messages[] = $message;
+		}
+
+		return $messages;
+	}
+
+	private function canBeUnset(Node $node, Scope $scope): ?string
+	{
+		if ($node instanceof Node\Expr\Variable && is_string($node->name)) {
+			$scopeHasVariable = $scope->hasVariableType($node->name);
+
+			if ($scopeHasVariable->no()) {
+				return RuleErrorBuilder::message(
+					sprintf('Call to function unset() contains undefined variable $%s.', $node->name)
+				)->line($node->getLine())->build()->getMessage();
+			}
+		} elseif ($node instanceof Node\Expr\ArrayDimFetch && $node->dim !== null) {
+			$type = $scope->getType($node->var);
+			$dimType = $scope->getType($node->dim);
+
+			$isOffsetAccessible = !$type->isOffsetAccessible()->no() && $type->getIterableKeyType()->isSuperTypeOf($dimType)->no();
+
+			if ($isOffsetAccessible || $type->hasOffsetValueType($dimType)->no()) {
+				return RuleErrorBuilder::message(
+					sprintf(
+						'Cannot unset offset %s on %s.',
+						$dimType->describe(VerbosityLevel::value()),
+						$type->describe(VerbosityLevel::value())
+					)
+				)->line($node->getLine())->build()->getMessage();
+			}
+		}
+
+		return null;
+	}
+
+}

tests/PHPStan/Rules/Functions/UnsetRuleTest.php

@@ -0,0 +1,47 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Functions;
+
+/**
+ * @extends \PHPStan\Testing\RuleTestCase<UnsetRule>
+ */
+class UnsetRuleTest extends \PHPStan\Testing\RuleTestCase
+{
+
+	protected function getRule(): \PHPStan\Rules\Rule
+	{
+		return new UnsetRule();
+	}
+
+	public function testUnsetRule(): void
+	{
+		require_once __DIR__ . '/data/unset.php';
+		$this->analyse([__DIR__ . '/data/unset.php'], [
+			[
+				'Call to function unset() contains undefined variable $notSetVariable.',
+				6,
+			],
+			[
+				'Cannot unset offset \'a\' on 3.',
+				10,
+			],
+			[
+				'Cannot unset offset \'b\' on 1.',
+				14,
+			],
+			[
+				'Cannot unset offset \'c\' on 1.',
+				18,
+			],
+			[
+				'Cannot unset offset \'b\' on 1.',
+				18,
+			],
+			[
+				'Cannot unset offset \'string\' on iterable<int, int>.',
+				31,
+			],
+		]);
+	}
+
+}

tests/PHPStan/Rules/Functions/data/unset.php

@@ -0,0 +1,32 @@
+<?php
+
+function unsetInaccessible ()
+{
+
+	unset($notSetVariable);
+
+	$scalar = 3;
+
+	unset($scalar['a']);
+
+	$singleDimArray = ['a' => 1];
+
+	unset($singleDimArray['a']['b']);
+
+	$multiDimArray = ['a' => ['b' => 1]];
+
+	unset($multiDimArray['a']['b']['c'], $scalar, $singleDimArray['a']['b']);
+
+}
+
+/** @param iterable<int> $iterable */
+function unsetOnMaybeIterable(iterable $iterable)
+{
+	unset($iterable['string']);
+}
+
+/** @param iterable<int, int> $iterable */
+function unsetOnYesIterable(iterable $iterable)
+{
+	unset($iterable['string']);
+}