Add array_is_list(array $array) function

This function tests if an array contains only sequential integer keys. While
list isn't an official type, this usage is consistent with the community usage
of "list" as an annotation type, cf.
https://psalm.dev/docs/annotating_code/type_syntax/array_types/#lists

Rebased and modified version of #4886

- Use .stub.php files
- Add opcache constant evaluation when argument is a constant
- Change from is_list(mixed $value) to array_is_list(array $array)

RFC: https://wiki.php.net/rfc/is_list

Co-Authored-By: Tyson Andre <tysonandre775@hotmail.com>
Co-Authored-By: Dusk <dusk@woofle.net>

Closes GH-6070

7 files changed, 151 insertions, 23 deletions

diff --git a/Zend/zend_hash.h b/Zend/zend_hash.h
index e339345a32..64a9220573 100644
--- a/Zend/zend_hash.h
+++ b/Zend/zend_hash.h
@@ -1188,6 +1188,33 @@ static zend_always_inline void *zend_hash_get_current_data_ptr_ex(HashTable *ht,
 		ZEND_HASH_FILL_FINISH(); \
 	} while (0)
 
+/* Check if an array is a list */
+static zend_always_inline zend_bool zend_array_is_list(zend_array *array)
+{
+	zend_long expected_idx = 0;
+	zend_long num_idx;
+	zend_string* str_idx;
+	/* Empty arrays are lists */
+	if (zend_hash_num_elements(array) == 0) {
+		return 1;
+	}
+
+	/* Packed arrays are lists */
+	if (HT_IS_PACKED(array) && HT_IS_WITHOUT_HOLES(array)) {
+		return 1;
+	}
+
+	/* Check if the list could theoretically be repacked */
+	ZEND_HASH_FOREACH_KEY(array, num_idx, str_idx) {
+		if (str_idx != NULL || num_idx != expected_idx++) {
+			return 0;
+		}
+	} ZEND_HASH_FOREACH_END();
+
+	return 1;
+}
+
+
 static zend_always_inline zval *_zend_hash_append_ex(HashTable *ht, zend_string *key, zval *zv, bool interned)
 {
 	uint32_t idx = ht->nNumUsed++;
diff --git a/ext/json/json_encoder.c b/ext/json/json_encoder.c
index 92e4a10933..f608936349 100644
--- a/ext/json/json_encoder.c
+++ b/ext/json/json_encoder.c
@@ -36,29 +36,10 @@ static int php_json_escape_string(
 
 static int php_json_determine_array_type(zval *val) /* {{{ */
 {
-	int i;
-	HashTable *myht = Z_ARRVAL_P(val);
-
-	i = myht ? zend_hash_num_elements(myht) : 0;
-	if (i > 0) {
-		zend_string *key;
-		zend_ulong index, idx;
+	zend_array *myht = Z_ARRVAL_P(val);
 
-		if (HT_IS_PACKED(myht) && HT_IS_WITHOUT_HOLES(myht)) {
-			return PHP_JSON_OUTPUT_ARRAY;
-		}
-
-		idx = 0;
-		ZEND_HASH_FOREACH_KEY(myht, index, key) {
-			if (key) {
-				return PHP_JSON_OUTPUT_OBJECT;
-			} else {
-				if (index != idx) {
-					return PHP_JSON_OUTPUT_OBJECT;
-				}
-			}
-			idx++;
-		} ZEND_HASH_FOREACH_END();
+	if (myht) {
+		return zend_array_is_list(myht) ? PHP_JSON_OUTPUT_ARRAY : PHP_JSON_OUTPUT_OBJECT;
 	}
 
 	return PHP_JSON_OUTPUT_ARRAY;
diff --git a/ext/opcache/Optimizer/sccp.c b/ext/opcache/Optimizer/sccp.c
index 7f9bdbdbb5..bc9dc38680 100644
--- a/ext/opcache/Optimizer/sccp.c
+++ b/ext/opcache/Optimizer/sccp.c
@@ -788,6 +788,7 @@ static bool can_ct_eval_func_call(zend_string *name, uint32_t num_args, zval **a
 		|| zend_string_equals_literal(name, "array_diff")
 		|| zend_string_equals_literal(name, "array_diff_assoc")
 		|| zend_string_equals_literal(name, "array_diff_key")
+		|| zend_string_equals_literal(name, "array_is_list")
 		|| zend_string_equals_literal(name, "array_key_exists")
 		|| zend_string_equals_literal(name, "array_keys")
 		|| zend_string_equals_literal(name, "array_merge")
diff --git a/ext/standard/basic_functions.stub.php b/ext/standard/basic_functions.stub.php
index b6597d262e..99d0d3c63d 100755
--- a/ext/standard/basic_functions.stub.php
+++ b/ext/standard/basic_functions.stub.php
@@ -248,6 +248,8 @@ function array_chunk(array $array, int $length, bool $preserve_keys = false): ar
 
 function array_combine(array $keys, array $values): array {}
 
+function array_is_list(array $array): bool {}
+
 /* base64.c */
 
 function base64_encode(string $string): string {}
diff --git a/ext/standard/basic_functions_arginfo.h b/ext/standard/basic_functions_arginfo.h
index e416fc5e27..5eafa59b50 100644
--- a/ext/standard/basic_functions_arginfo.h
+++ b/ext/standard/basic_functions_arginfo.h
@@ -1,5 +1,5 @@
 /* This is a generated file, edit the .stub.php file instead.
- * Stub hash: 4e471966d507762dd6fdd2fc4200c8430fac97f4 */
+ * Stub hash: 7540039937587f05584660bc1a1a8a80aa5ccbd1 */
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_set_time_limit, 0, 1, _IS_BOOL, 0)
 	ZEND_ARG_TYPE_INFO(0, seconds, IS_LONG, 0)
@@ -360,6 +360,10 @@ ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_array_combine, 0, 2, IS_ARRAY, 0
 	ZEND_ARG_TYPE_INFO(0, values, IS_ARRAY, 0)
 ZEND_END_ARG_INFO()
 
+ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_array_is_list, 0, 1, _IS_BOOL, 0)
+	ZEND_ARG_TYPE_INFO(0, array, IS_ARRAY, 0)
+ZEND_END_ARG_INFO()
+
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_base64_encode, 0, 1, IS_STRING, 0)
 	ZEND_ARG_TYPE_INFO(0, string, IS_STRING, 0)
 ZEND_END_ARG_INFO()
@@ -2309,6 +2313,7 @@ ZEND_FUNCTION(array_map);
 ZEND_FUNCTION(array_key_exists);
 ZEND_FUNCTION(array_chunk);
 ZEND_FUNCTION(array_combine);
+ZEND_FUNCTION(array_is_list);
 ZEND_FUNCTION(base64_encode);
 ZEND_FUNCTION(base64_decode);
 ZEND_FUNCTION(constant);
@@ -2933,6 +2938,7 @@ static const zend_function_entry ext_functions[] = {
 	ZEND_FALIAS(key_exists, array_key_exists, arginfo_key_exists)
 	ZEND_FE(array_chunk, arginfo_array_chunk)
 	ZEND_FE(array_combine, arginfo_array_combine)
+	ZEND_FE(array_is_list, arginfo_array_is_list)
 	ZEND_FE(base64_encode, arginfo_base64_encode)
 	ZEND_FE(base64_decode, arginfo_base64_decode)
 	ZEND_FE(constant, arginfo_constant)
diff --git a/ext/standard/tests/general_functions/array_is_list.phpt b/ext/standard/tests/general_functions/array_is_list.phpt
new file mode 100644
index 0000000000..1cc2886f96
--- /dev/null
+++ b/ext/standard/tests/general_functions/array_is_list.phpt
@@ -0,0 +1,98 @@
+--TEST--
+Test array_is_list() function
+--FILE--
+<?php
+
+function test_is_list(string $desc, $val) : void {
+    try {
+        printf("%s: %s\n", $desc, json_encode(array_is_list($val)));
+    } catch (TypeError $e) {
+        printf("%s: threw %s\n", $desc, $e->getMessage());
+    }
+}
+
+test_is_list("empty", []);
+test_is_list("one", [1]);
+test_is_list("two", [1,2]);
+test_is_list("three", [1,2,3]);
+test_is_list("four", [1,2,3,4]);
+test_is_list("ten", range(0, 10));
+
+test_is_list("null", null);
+test_is_list("int", 123);
+test_is_list("float", 1.23);
+test_is_list("string", "string");
+test_is_list("object", new stdClass());
+test_is_list("true", true);
+test_is_list("false", false);
+
+test_is_list("string key", ["a" => 1]);
+test_is_list("mixed keys", [0 => 0, "a" => 1]);
+test_is_list("ordered keys", [0 => 0, 1 => 1]);
+test_is_list("shuffled keys", [1 => 0, 0 => 1]);
+test_is_list("skipped keys", [0 => 0, 2 => 2]);
+
+$arr = [1, 2, 3];
+unset($arr[0]);
+test_is_list("unset first", $arr);
+
+$arr = [1, 2, 3];
+unset($arr[1]);
+test_is_list("unset middle", $arr);
+
+$arr = [1, 2, 3];
+unset($arr[2]);
+test_is_list("unset end", $arr);
+
+$arr = [1, "a" => "a", 2];
+unset($arr["a"]);
+test_is_list("unset string key", $arr);
+
+$arr = [1 => 1, 0 => 0];
+unset($arr[1]);
+test_is_list("unset into order", $arr);
+
+$arr = ["a" => 1];
+unset($arr["a"]);
+test_is_list("unset to empty", $arr);
+
+$arr = [1, 2, 3];
+$arr[] = 4;
+test_is_list("append implicit", $arr);
+
+$arr = [1, 2, 3];
+$arr[3] = 4;
+test_is_list("append explicit", $arr);
+
+$arr = [1, 2, 3];
+$arr[4] = 5;
+test_is_list("append with gap", $arr);
+
+--EXPECT--
+empty: true
+one: true
+two: true
+three: true
+four: true
+ten: true
+null: threw array_is_list(): Argument #1 ($array) must be of type array, null given
+int: threw array_is_list(): Argument #1 ($array) must be of type array, int given
+float: threw array_is_list(): Argument #1 ($array) must be of type array, float given
+string: threw array_is_list(): Argument #1 ($array) must be of type array, string given
+object: threw array_is_list(): Argument #1 ($array) must be of type array, stdClass given
+true: threw array_is_list(): Argument #1 ($array) must be of type array, bool given
+false: threw array_is_list(): Argument #1 ($array) must be of type array, bool given
+string key: false
+mixed keys: false
+ordered keys: true
+shuffled keys: false
+skipped keys: false
+unset first: false
+unset middle: false
+unset end: true
+unset string key: true
+unset into order: true
+unset to empty: true
+append implicit: true
+append explicit: true
+append with gap: false
\ No newline at end of file
diff --git a/ext/standard/type.c b/ext/standard/type.c
index afe0e7afc2..1036dd7d06 100644
--- a/ext/standard/type.c
+++ b/ext/standard/type.c
@@ -321,6 +321,19 @@ PHP_FUNCTION(is_array)
 }
 /* }}} */
 
+/* {{{ Returns true if $array is an array whose keys are all numeric, sequential, and start at 0 */
+PHP_FUNCTION(array_is_list)
+{
+	HashTable *array;
+
+	ZEND_PARSE_PARAMETERS_START(1, 1)
+		Z_PARAM_ARRAY_HT(array)
+	ZEND_PARSE_PARAMETERS_END();
+
+	RETURN_BOOL(zend_array_is_list(array));
+}
+/* }}} */
+
 /* {{{ Returns true if variable is an object
    Warning: This function is special-cased by zend_compile.c and so is usually bypassed */
 PHP_FUNCTION(is_object)