From 24640d93e975f2974443e05c8dece9b7f911705c Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Sat, 8 Nov 2025 10:52:37 +0100
Subject: [PATCH 1/6] Infer non-empty-array after array_key_first/last()

---
 src/Analyser/TypeSpecifier.php            | 15 +++++++++
 tests/PHPStan/Analyser/nsrt/bug-13546.php | 37 +++++++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100644 tests/PHPStan/Analyser/nsrt/bug-13546.php

diff --git a/src/Analyser/TypeSpecifier.php b/src/Analyser/TypeSpecifier.php
index 6698a8a800..bd08d4f364 100644
--- a/src/Analyser/TypeSpecifier.php
+++ b/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()
diff --git a/tests/PHPStan/Analyser/nsrt/bug-13546.php b/tests/PHPStan/Analyser/nsrt/bug-13546.php
new file mode 100644
index 0000000000..47beb71390
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-13546.php
@@ -0,0 +1,37 @@
+<?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);
+}

From e4b9e606574d6af38432f42c37bb48d7ae8fa4b9 Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Sat, 8 Nov 2025 10:56:15 +0100
Subject: [PATCH 2/6] Update bug-13546.php

---
 tests/PHPStan/Analyser/nsrt/bug-13546.php | 26 +++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/tests/PHPStan/Analyser/nsrt/bug-13546.php b/tests/PHPStan/Analyser/nsrt/bug-13546.php
index 47beb71390..17d221d495 100644
--- a/tests/PHPStan/Analyser/nsrt/bug-13546.php
+++ b/tests/PHPStan/Analyser/nsrt/bug-13546.php
@@ -35,3 +35,29 @@ function last(array $array): void
 	}
 	assertType('array<int>', $array);
 }
+
+function maybeArray(array $array, mixed $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 $mixed): void
+{
+	if (is_array($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);
+}

From 28f6ee14ea91888949acd157f8672b49694da1fa Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Sat, 8 Nov 2025 15:30:54 +0100
Subject: [PATCH 3/6] add test

---
 tests/PHPStan/Analyser/nsrt/bug-13546.php | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tests/PHPStan/Analyser/nsrt/bug-13546.php b/tests/PHPStan/Analyser/nsrt/bug-13546.php
index 17d221d495..588e90d162 100644
--- a/tests/PHPStan/Analyser/nsrt/bug-13546.php
+++ b/tests/PHPStan/Analyser/nsrt/bug-13546.php
@@ -61,3 +61,14 @@ function mixedLast(mixed $mixed): void
 	}
 	assertType('mixed~array<mixed, mixed>', $mixed);
 }
+
+/** @param list<string> $array */
+function firstInCondition(array $array): mixed
+{
+	if (($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;
+}

From 4196932a079319c556ccac6cdd00fb046f18ba78 Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Sat, 8 Nov 2025 15:33:51 +0100
Subject: [PATCH 4/6] test maybe null

---
 tests/PHPStan/Analyser/nsrt/bug-13546.php | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tests/PHPStan/Analyser/nsrt/bug-13546.php b/tests/PHPStan/Analyser/nsrt/bug-13546.php
index 588e90d162..c390b717d0 100644
--- a/tests/PHPStan/Analyser/nsrt/bug-13546.php
+++ b/tests/PHPStan/Analyser/nsrt/bug-13546.php
@@ -72,3 +72,15 @@ function firstInCondition(array $array): mixed
 	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);
+}

From f2252dc0a5d129276c774922ad3ff0e92954b4b0 Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Sat, 8 Nov 2025 15:37:54 +0100
Subject: [PATCH 5/6] fix php 7.4 compat

---
 tests/PHPStan/Analyser/nsrt/bug-13546.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/PHPStan/Analyser/nsrt/bug-13546.php b/tests/PHPStan/Analyser/nsrt/bug-13546.php
index c390b717d0..cfa4dd9aba 100644
--- a/tests/PHPStan/Analyser/nsrt/bug-13546.php
+++ b/tests/PHPStan/Analyser/nsrt/bug-13546.php
@@ -63,7 +63,7 @@ function mixedLast(mixed $mixed): void
 }
 
 /** @param list<string> $array */
-function firstInCondition(array $array): mixed
+function firstInCondition(array $array)
 {
 	if (($key = array_key_first($array)) !== null) {
 		assertType('list<string>', $array); // could be 'non-empty-list<string>'

From be0c368c197405508e9df8c4f50e79faceebcbd5 Mon Sep 17 00:00:00 2001
From: Markus Staab <maggus.staab@googlemail.com>
Date: Sat, 8 Nov 2025 15:52:51 +0100
Subject: [PATCH 6/6] Update bug-13546.php

---
 tests/PHPStan/Analyser/nsrt/bug-13546.php | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/PHPStan/Analyser/nsrt/bug-13546.php b/tests/PHPStan/Analyser/nsrt/bug-13546.php
index cfa4dd9aba..63eb5ee889 100644
--- a/tests/PHPStan/Analyser/nsrt/bug-13546.php
+++ b/tests/PHPStan/Analyser/nsrt/bug-13546.php
@@ -36,7 +36,7 @@ function last(array $array): void
 	assertType('array<int>', $array);
 }
 
-function maybeArray(array $array, mixed $mixed): void
+function maybeArray(array $array, $mixed): void
 {
 	$arrayOrMixed = rand(0, 1) ? $array : $mixed;
 
@@ -48,7 +48,7 @@ function maybeArray(array $array, mixed $mixed): void
 	assertType('mixed', $arrayOrMixed);
 }
 
-function mixedLast(mixed $mixed): void
+function mixedLast($mixed): void
 {
 	if (is_array($mixed)) {
 		return;