Implement the negative_array_index RFC

Author: pmmaga

UPGRADING

@@ -39,6 +39,9 @@ PHP 8.0 UPGRADE NOTES
   . Removed each(). foreach or ArrayIterator should be used instead.
   . Removed ability to unbind $this from closures that were created from a
     method, using Closure::fromCallable() or ReflectionMethod::getClosure().
+  . Any array that has a number n as its first numeric key will use n+1 for
+    its next implicit key. Even if n is negative.
+    RFC: https://wiki.php.net/rfc/negative_array_index
 
 - Date:
   . mktime() and gmmktime() now require at least one argument. time() can be

Zend/zend_hash.c

@@ -220,7 +220,7 @@ static zend_always_inline void _zend_hash_init_int(HashTable *ht, uint32_t nSize
 	ht->nNumUsed = 0;
 	ht->nNumOfElements = 0;
 	ht->nInternalPointer = 0;
-	ht->nNextFreeElement = 0;
+	ht->nNextFreeElement = ZEND_LONG_MIN;
 	ht->pDestructor = pDestructor;
 	ht->nTableSize = zend_hash_check_size(nSize);
 }
@@ -935,6 +935,10 @@ static zend_always_inline zval *_zend_hash_index_add_or_update_i(HashTable *ht,
 	IS_CONSISTENT(ht);
 	HT_ASSERT_RC1(ht);
 
+	if (h == ZEND_LONG_MIN && (flag & HASH_ADD_NEXT)) {
+		h = 0;
+	}
+
 	if (HT_FLAGS(ht) & HASH_FLAG_PACKED) {
 		if (h < ht->nNumUsed) {
 			p = ht->arData + h;
@@ -998,8 +1002,8 @@ static zend_always_inline zval *_zend_hash_index_add_or_update_i(HashTable *ht,
 	p = ht->arData + idx;
 	Z_NEXT(p->val) = HT_HASH(ht, nIndex);
 	HT_HASH(ht, nIndex) = HT_IDX_TO_HASH(idx);
-	if ((zend_long)h >= (zend_long)ht->nNextFreeElement) {
-		ht->nNextFreeElement = h < ZEND_LONG_MAX ? h + 1 : ZEND_LONG_MAX;
+	if ((zend_long)h >= ht->nNextFreeElement) {
+		ht->nNextFreeElement = (zend_long)h < ZEND_LONG_MAX ? h + 1 : ZEND_LONG_MAX;
 	}
 add:
 	ht->nNumOfElements++;
@@ -1665,7 +1669,7 @@ ZEND_API void ZEND_FASTCALL zend_hash_clean(HashTable *ht)
 	}
 	ht->nNumUsed = 0;
 	ht->nNumOfElements = 0;
-	ht->nNextFreeElement = 0;
+	ht->nNextFreeElement = ZEND_LONG_MIN;
 	ht->nInternalPointer = 0;
 }
 
@@ -1704,7 +1708,7 @@ ZEND_API void ZEND_FASTCALL zend_symtable_clean(HashTable *ht)
 	}
 	ht->nNumUsed = 0;
 	ht->nNumOfElements = 0;
-	ht->nNextFreeElement = 0;
+	ht->nNextFreeElement = ZEND_LONG_MIN;
 	ht->nInternalPointer = 0;
 }
 
@@ -2018,7 +2022,7 @@ ZEND_API HashTable* ZEND_FASTCALL zend_array_dup(HashTable *source)
 		target->nTableMask = HT_MIN_MASK;
 		target->nNumUsed = 0;
 		target->nNumOfElements = 0;
-		target->nNextFreeElement = 0;
+		target->nNextFreeElement = ZEND_LONG_MIN;
 		target->nInternalPointer = 0;
 		target->nTableSize = HT_MIN_SIZE;
 		HT_SET_DATA_ADDR(target, &uninitialized_bucket);

ext/standard/array.c

@@ -3228,7 +3228,7 @@ PHP_FUNCTION(array_pop)
 	}
 	ZVAL_COPY_DEREF(return_value, val);
 
-	if (!p->key && Z_ARRVAL_P(stack)->nNextFreeElement > 0 && p->h >= (zend_ulong)(Z_ARRVAL_P(stack)->nNextFreeElement - 1)) {
+	if (!p->key && (zend_long)p->h == (Z_ARRVAL_P(stack)->nNextFreeElement - 1)) {
 		Z_ARRVAL_P(stack)->nNextFreeElement = Z_ARRVAL_P(stack)->nNextFreeElement - 1;
 	}
 

ext/standard/tests/array/bug67693.phpt

@@ -16,9 +16,9 @@ echo"\nDone";
 ?>
 --EXPECT--
 array(2) {
-  [0]=>
+  [-1]=>
   int(0)
-  [1]=>
+  [0]=>
   int(0)
 }
 

ext/standard/tests/array/negative_index.phpt

@@ -0,0 +1,31 @@
+--TEST--
+Test arrays starting with negative indices
+--FILE--
+<?php
+
+$a = array_fill(-2, 3, true);
+$b = [-2 => true, true, true];
+$c = ["string" => true, -2 => true, true, true];
+unset($c["string"]);
+$d[-2] = true;
+$d[] = true;
+$d[] = true;
+$e = [-2 => false];
+array_pop($e);
+$e[] = true;
+$e[] = true;
+$e[] = true;
+
+var_dump($a === $b && $b === $c && $c === $d && $d == $e);
+var_dump($a);
+?>
+--EXPECT--
+bool(true)
+array(3) {
+  [-2]=>
+  bool(true)
+  [-1]=>
+  bool(true)
+  [0]=>
+  bool(true)
+}