Infer non-empty-array after array_key_first/last()

src/Analyser/TypeSpecifier.php

@@ -2346,6 +2346,21 @@ public function resolveIdentical(Expr\BinaryOp\Identical $expr, Scope $scope, Ty
 			}
 		}
 
+		// array_key_first($a) !== null
+		// array_key_last($a) !== null
+		if (
+			$unwrappedLeftExpr instanceof FuncCall
+			&& $unwrappedLeftExpr->name instanceof Name
+			&& in_array($unwrappedLeftExpr->name->toLowerString(), ['array_key_first', 'array_key_last'], true)
+			&& isset($unwrappedLeftExpr->getArgs()[0])
+			&& $rightType->isNull()->yes()
+		) {
+			$argType = $scope->getType($unwrappedLeftExpr->getArgs()[0]->value);
+			if ($argType->isArray()->yes()) {
+				return $this->create($unwrappedLeftExpr->getArgs()[0]->value, new NonEmptyArrayType(), $context->negate(), $scope)->setRootExpr($expr);
+			}
+		}
+
 		// preg_match($a) === $b
 		if (
 			$context->true()

tests/PHPStan/Analyser/nsrt/bug-13546.php

@@ -0,0 +1,86 @@
+<?php
+namespace Bug13546;
+
+use function PHPStan\Testing\assertType;
+
+/** @param array<int> $array */
+function first(array $array): void
+{
+	if (array_key_first($array) !== null) {
+		assertType('non-empty-array<int>', $array);
+	} else {
+		assertType('array{}', $array);
+	}
+	assertType('array<int>', $array);
+}
+
+/** @param array<int> $array */
+function firstReversed(array $array): void
+{
+	if (null !== array_key_first($array)) {
+		assertType('non-empty-array<int>', $array);
+	} else {
+		assertType('array{}', $array);
+	}
+	assertType('array<int>', $array);
+}
+
+/** @param array<int> $array */
+function last(array $array): void
+{
+	if (array_key_last($array) !== null) {
+		assertType('non-empty-array<int>', $array);
+	} else {
+		assertType('array{}', $array);
+	}
+	assertType('array<int>', $array);
+}
+
+function maybeArray(array $array, $mixed): void
+{
+	$arrayOrMixed = rand(0, 1) ? $array : $mixed;
+
+	if (array_key_last($arrayOrMixed) !== null) {
+		assertType('mixed', $arrayOrMixed);
+	} else {
+		assertType('mixed', $arrayOrMixed);
+	}
+	assertType('mixed', $arrayOrMixed);
+}
+
+function mixedLast($mixed): void
+{
+	if (is_array($mixed)) {
+		return;
+	}
+
+	if (array_key_last($mixed) !== null) {
+		assertType('mixed~array<mixed, mixed>', $mixed);
+	} else {
+		assertType('mixed~array<mixed, mixed>', $mixed);
+	}
+	assertType('mixed~array<mixed, mixed>', $mixed);
+}
+
+/** @param list<string> $array */
+function firstInCondition(array $array)
+{
+	if (($key = array_key_first($array)) !== null) {
+		assertType('list<string>', $array); // could be 'non-empty-list<string>'
+		return $array[$key];
+	}
+	assertType('list<string>', $array);
+	return null;
+}
+
+/** @param list<string> $array */
+function maybeNull(array $array, ?int $nullOrInt, ?string $nullOrString): void
+{
+	if (array_key_first($array) !== $nullOrInt) {
+		assertType('list<string>', $array);
+	}
+	if (array_key_first($array) !== $nullOrString) {
+		assertType('list<string>', $array);
+	}
+	assertType('list<string>', $array);
+}