Fix array dim fetches with treatPhpDocTypesAsCertain: false

src/Analyser/MutatingScope.php

@@ -2039,6 +2039,17 @@ public function getNativeType(Expr $expr): Type
 			return $this->nativeExpressionTypes[$key];
 		}
 
+		if ($expr instanceof Expr\ArrayDimFetch && $expr->dim !== null) {
+			return $this->getNullsafeShortCircuitingType(
+				$expr->var,
+				$this->getTypeFromArrayDimFetch(
+					$expr,
+					$this->getNativeType($expr->dim),
+					$this->getNativeType($expr->var)
+				)
+			);
+		}
+
 		return $this->getType($expr);
 	}
 

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -10347,6 +10347,11 @@ public function dataIncDecInConditions(): array
 		return $this->gatherAssertTypes(__DIR__ . '/data/inc-dec-in-conditions.php');
 	}
 
+	public function dataBug4099(): array
+	{
+		return $this->gatherAssertTypes(__DIR__ . '/data/bug-4099.php');
+	}
+
 	/**
 	 * @param string $file
 	 * @return array<string, mixed[]>
@@ -10529,6 +10534,7 @@ private function gatherAssertTypes(string $file): array
 	 * @dataProvider dataComparisonOperators
 	 * @dataProvider dataBug3880
 	 * @dataProvider dataIncDecInConditions
+	 * @dataProvider dataBug4099
 	 * @param string $assertType
 	 * @param string $file
 	 * @param mixed ...$args

tests/PHPStan/Analyser/data/bug-4099.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace Bug4099;
+
+use function PHPStan\Analyser\assertNativeType;
+use function PHPStan\Analyser\assertType;
+
+class Foo
+{
+
+	/**
+	 * @param array{key: array{inner: mixed}} $arr
+	 */
+	function arrayHint(array $arr): void
+	{
+		assertType('array(\'key\' => array(\'inner\' => mixed))', $arr);
+		assertNativeType('array', $arr);
+
+		if (!array_key_exists('key', $arr)) {
+			assertType('*NEVER*', $arr);
+			assertNativeType('array', $arr);
+			throw new \Exception('no key "key" found.');
+		}
+		assertType('array(\'key\' => array(\'inner\' => mixed))', $arr);
+		assertNativeType('array&hasOffset(\'key\')', $arr);
+		assertType('array(\'inner\' => mixed)', $arr['key']);
+		assertNativeType('mixed', $arr['key']);
+
+		if (!array_key_exists('inner', $arr['key'])) {
+			assertType('array(\'key\' => *NEVER*)', $arr);
+			//assertNativeType('array(\'key\' => mixed)', $arr);
+			assertType('*NEVER*', $arr['key']);
+			//assertNativeType('mixed', $arr['key']);
+			throw new \Exception('need key.inner');
+		}
+
+		assertType('array(\'key\' => array(\'inner\' => mixed))', $arr);
+		assertNativeType('array(\'key\' => array(\'inner\' => mixed))', $arr);
+	}
+
+}