Add warning and convert to exception in string offset assignment:

Convert the empty string assignment to an Error as per RFC [1]
Add a warning that only the first byte will be assigned to the offset if provided
a needle that is longer than one byte.

[1] https://wiki.php.net/rfc/engine_warnings

Closes GH-5063

Author: Girgias

Zend/tests/bug71572.phpt

@@ -4,22 +4,31 @@ Bug #71572: String offset assignment from an empty string inserts null byte
 <?php
 
 $str = "abc";
-var_dump($str[0] = "");
-var_dump($str[1] = "");
-var_dump($str[3] = "");
-var_dump($str[10] = "");
+try {
+    var_dump($str[0] = "");
+} catch (\Error $e) {
+    echo $e->getMessage() . \PHP_EOL;
+}
+try {
+    var_dump($str[1] = "");
+} catch (\Error $e) {
+    echo $e->getMessage() . \PHP_EOL;
+}
+try {
+    var_dump($str[3] = "");
+} catch (\Error $e) {
+    echo $e->getMessage() . \PHP_EOL;
+}
+try {
+    var_dump($str[10] = "");
+} catch (\Error $e) {
+    echo $e->getMessage() . \PHP_EOL;
+}
 var_dump($str);
 ?>
---EXPECTF--
-Warning: Cannot assign an empty string to a string offset in %s on line %d
-NULL
-
-Warning: Cannot assign an empty string to a string offset in %s on line %d
-NULL
-
-Warning: Cannot assign an empty string to a string offset in %s on line %d
-NULL
-
-Warning: Cannot assign an empty string to a string offset in %s on line %d
-NULL
+--EXPECT--
+Cannot assign an empty string to a string offset
+Cannot assign an empty string to a string offset
+Cannot assign an empty string to a string offset
+Cannot assign an empty string to a string offset
 string(3) "abc"

Zend/tests/indexing_001.phpt

@@ -51,8 +51,6 @@ foreach ($testvalues as $testvalue) {
     var_dump ($testvalue);
 }
 
-
-echo "\nDone";
 ?>
 --EXPECTF--
 *** Indexing - Testing value assignment with key ***
@@ -80,11 +78,15 @@ array(1) {
 Warning: Illegal string offset 'foo' in %s on line %d
 
 Warning: Array to string conversion in %s on line %d
+
+Warning: Only the first byte will be assigned to the string offset in %s on line %d
 string(1) "A"
 
 Warning: Illegal string offset 'foo' in %s on line %d
 
 Warning: Array to string conversion in %s on line %d
+
+Warning: Only the first byte will be assigned to the string offset in %s on line %d
 string(1) "A"
 Cannot use a scalar value as an array
 float(0.1)
@@ -187,5 +189,3 @@ array(1) {
     int(1)
   }
 }
-
-Done

Zend/tests/str_offset_004.phpt

@@ -45,5 +45,7 @@ Warning: Illegal string offset:  -20 in %sstr_offset_004.php on line %d
 string(15) "abCZefghijPQmno"
 string(15) "AbCZefghijPQmno"
 string(21) "AbCZefghijPQmno     N"
+
+Warning: Only the first byte will be assigned to the string offset in %s on line %d
 string(21) "AbCZefghijPQmno    UN"
 string(21) "AbCZefghijPQmno   nUN"

Zend/zend_execute.c

@@ -1597,14 +1597,18 @@ static zend_never_inline void zend_assign_to_string_offset(zval *str, zval *dim,
 		string_len = Z_STRLEN_P(value);
 		c = (zend_uchar)Z_STRVAL_P(value)[0];
 	}
-
-	if (string_len == 0) {
-		/* Error on empty input string */
-		zend_error(E_WARNING, "Cannot assign an empty string to a string offset");
-		if (UNEXPECTED(RETURN_VALUE_USED(opline))) {
-			ZVAL_NULL(EX_VAR(opline->result.var));
+	
+	if (string_len != 1) {
+		if (string_len == 0) {
+			/* Error on empty input string */
+			zend_throw_error(NULL, "Cannot assign an empty string to a string offset");
+			if (UNEXPECTED(RETURN_VALUE_USED(opline))) {
+				ZVAL_NULL(EX_VAR(opline->result.var));
+			}
+			return;
 		}
-		return;
+
+		zend_error(E_WARNING, "Only the first byte will be assigned to the string offset");
 	}
 
 	if (offset < 0) { /* Handle negative offset */

ext/opcache/jit/zend_jit_helpers.c

@@ -895,13 +895,18 @@ static zend_never_inline void zend_assign_to_string_offset(zval *str, zval *dim,
 		c = (zend_uchar)Z_STRVAL_P(value)[0];
 	}
 
-	if (string_len == 0) {
-		/* Error on empty input string */
-		zend_error(E_WARNING, "Cannot assign an empty string to a string offset");
-		if (result) {
-			ZVAL_NULL(result);
+
+	if (string_len != 1) {
+		if (string_len == 0) {
+			/* Error on empty input string */
+			zend_throw_error(NULL, "Cannot assign an empty string to a string offset");
+			if (result) {
+				ZVAL_NULL(result);
+			}
+			return;
 		}
-		return;
+
+		zend_error(E_WARNING, "Only the first byte will be assigned to the string offset");
 	}
 
 	if (offset < 0) { /* Handle negative offset */

tests/lang/bug22592.phpt

@@ -39,9 +39,11 @@ var_dump($result);
 string(5) "* *-*"
 string(7) "* *-* *"
 string(7) "*4*-* *"
+[Only the first byte will be assigned to the string offset]
 string(7) "*4*s* *"
 string(8) "*4*s* *0"
 string(8) "*-*-* *0"
+[Only the first byte will be assigned to the string offset]
 string(8) "*-*s*s*0"
 string(8) "4-4s4s*0"
 string(9) "4-4s4s505"