Rule for disallowing implicit array creation

rules.neon

@@ -13,6 +13,7 @@ rules:
 	- PHPStan\Rules\BooleansInConditions\BooleanInIfConditionRule
 	- PHPStan\Rules\BooleansInConditions\BooleanInTernaryOperatorRule
 	- PHPStan\Rules\DisallowedConstructs\DisallowedEmptyRule
+	- PHPStan\Rules\DisallowedConstructs\DisallowedImplicitArrayCreationRule
 	- PHPStan\Rules\Methods\WrongCaseOfInheritedMethodRule
 	- PHPStan\Rules\StrictCalls\DynamicCallOnStaticMethodsRule
 	- PHPStan\Rules\StrictCalls\StrictFunctionCallsRule

src/Rules/DisallowedConstructs/DisallowedImplicitArrayCreationRule.php

@@ -0,0 +1,53 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\DisallowedConstructs;
+
+use PHPStan\Analyser\Scope;
+
+class DisallowedImplicitArrayCreationRule implements \PHPStan\Rules\Rule
+{
+
+	public function getNodeType(): string
+	{
+		return \PhpParser\Node\Expr\Assign::class;
+	}
+
+	/**
+	 * @param \PhpParser\Node\Expr\Assign $node
+	 * @param \PHPStan\Analyser\Scope $scope
+	 * @return string[]
+	 */
+	public function processNode(\PhpParser\Node $node, Scope $scope): array
+	{
+		if (!$node->var instanceof \PhpParser\Node\Expr\ArrayDimFetch) {
+			return [];
+		}
+
+		$node = $node->var;
+		while ($node instanceof \PhpParser\Node\Expr\ArrayDimFetch) {
+			$node = $node->var;
+		}
+
+		if (!$node instanceof \PhpParser\Node\Expr\Variable) {
+			return [];
+		}
+
+		if (!is_string($node->name)) {
+			return [];
+		}
+
+		$certainty = $scope->hasVariableType($node->name);
+		if ($certainty->no()) {
+			return [
+				sprintf('Implicit array creation is not allowed - variable $%s does not exist.', $node->name),
+			];
+		} elseif ($certainty->maybe()) {
+			return [
+				sprintf('Implicit array creation is not allowed - variable $%s might not exist.', $node->name),
+			];
+		}
+
+		return [];
+	}
+
+}

tests/Rules/DisallowedConstructs/DisallowedImplicitArrayCreationRuleTest.php

@@ -0,0 +1,33 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\DisallowedConstructs;
+
+use PHPStan\Rules\Rule;
+
+class DisallowedImplicitArrayCreationRuleTest extends \PHPStan\Testing\RuleTestCase
+{
+
+	protected function getRule(): Rule
+	{
+		return new DisallowedImplicitArrayCreationRule();
+	}
+
+	public function testRule(): void
+	{
+		$this->analyse([__DIR__ . '/data/array-creation.php'], [
+			[
+				'Implicit array creation is not allowed - variable $b does not exist.',
+				11,
+			],
+			[
+				'Implicit array creation is not allowed - variable $c might not exist.',
+				17,
+			],
+			[
+				'Implicit array creation is not allowed - variable $d does not exist.',
+				18,
+			],
+		]);
+	}
+
+}

tests/Rules/DisallowedConstructs/data/array-creation.php

@@ -0,0 +1,21 @@
+<?php declare(strict_types = 1);
+
+namespace ImplicitArrayCreation;
+
+class Foo
+{
+
+	public function doFoo($a)
+	{
+		$a['foo'] = 'test';
+		$b[] = 'test';
+
+		if (doFoo()) {
+			$c = [];
+		}
+
+		$c['foo'] = 'test';
+		$d[][] = 'blabla';
+	}
+
+}