Added ImplodeFunctionRule

conf/config.level0.neon

@@ -55,6 +55,7 @@ rules:
 	- PHPStan\Rules\Functions\ExistingClassesInTypehintsRule
 	- PHPStan\Rules\Functions\FunctionAttributesRule
 	- PHPStan\Rules\Functions\InnerFunctionRule
+	- PHPStan\Rules\Functions\ImplodeFunctionRule
 	- PHPStan\Rules\Functions\ParamAttributesRule
 	- PHPStan\Rules\Functions\PrintfParametersRule
 	- PHPStan\Rules\Functions\ReturnNullsafeByRefRule

src/Rules/Functions/ImplodeFunctionRule.php

@@ -0,0 +1,64 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Functions;
+
+use PhpParser\Node;
+use PhpParser\Node\Expr\FuncCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Php\PhpVersion;
+use PHPStan\Rules\RuleErrorBuilder;
+use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
+use PHPStan\Type\ErrorType;
+use PHPStan\Type\TypeUtils;
+use PHPStan\Type\UnionType;
+
+/**
+ * @implements \PHPStan\Rules\Rule<\PhpParser\Node\Expr\FuncCall>
+ */
+class ImplodeFunctionRule implements \PHPStan\Rules\Rule
+{
+	public function getNodeType(): string
+	{
+		return FuncCall::class;
+	}
+
+	public function processNode(Node $node, Scope $scope): array
+	{
+		if (!($node->name instanceof \PhpParser\Node\Name)) {
+			return [];
+		}
+
+		$name = strtolower((string) $node->name);
+		if ($name !== 'implode') {
+			return [];
+		}
+
+		$args = $node->getArgs();
+		if (count($args) !== 2) {
+			return [];
+		}
+
+		$arrayType = $scope->getType($args[1]->value);
+		if ($arrayType->getIterableValueType()->isArray()->yes()) {
+			return [
+				RuleErrorBuilder::message(
+					'Call to implode with invalid nested array argument.',
+				)->build()
+			];
+		}
+		if ($arrayType->getIterableValueType() instanceof UnionType) {
+			foreach ($arrayType->getIterableValueType()->getTypes() as $subType) {
+				if ($subType->isArray()->yes()) {
+					return [
+						RuleErrorBuilder::message(
+							'Call to implode with invalid nested array argument in union type.',
+						)->build()
+					];
+				}
+			}
+		}
+
+		return [];
+	}
+
+}

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -510,6 +510,8 @@ public function dataFileAsserts(): iterable
 
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/eval-implicit-throw.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-5628.php');
+
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/implode.php');
 	}
 
 	/**

tests/PHPStan/Rules/Functions/ImplodeFunctionRuleTest.php

@@ -0,0 +1,33 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Functions;
+
+use PHPStan\Php\PhpVersion;
+use const PHP_VERSION_ID;
+
+/**
+ * @extends \PHPStan\Testing\RuleTestCase<ImplodeFunctionRule>
+ */
+class ImplodeFunctionRuleTest extends \PHPStan\Testing\RuleTestCase
+{
+
+	protected function getRule(): \PHPStan\Rules\Rule
+	{
+		return new ImplodeFunctionRule();
+	}
+
+	public function testFile(): void
+	{
+		$this->analyse([__DIR__ . '/data/implode.php'], [
+			[
+				'Call to implode with invalid nested array argument in union type.',
+				9,
+			],
+			[
+				'Call to implode with invalid nested array argument.',
+				10,
+			],
+		]);
+	}
+
+}

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

@@ -0,0 +1,16 @@
+<?php declare(strict_types = 1);
+
+namespace ImplodeFunction;
+
+class Foo
+{
+	public function invalidArgs(): void
+	{
+		implode('', ['12', '123', ['1234', '12345']]);
+		implode('', [['1234', '12345']]);
+	}
+
+	public function valid() {
+		implode('', ['12', '345']);
+	}
+}