Implement #72918: negative offset inside a quoted string leads to par…

…se error

We allow negative numeric offsets for the simple syntax inside
double-quoted and heredoc strings.

UPGRADING

@@ -177,6 +177,8 @@ PHP 7.1 UPGRADE NOTES
     type declarations, and some internal functions. Both nullable type
     declarations (?int) and parameters with default values of null
     (int $foo = NULL) are considered to "accept null" for this purpose.
+  . The simple syntax for variable parsing inside of string literals now
+    supports negative offsets.
 
 ========================================
 3. Changes in SAPI modules

Zend/tests/bug72918.phpt

@@ -0,0 +1,22 @@
+--TEST--
+Bug #72918 (negative offset inside a quoted string leads to parse error)
+--FILE--
+<?php
+$array = [-3 => 'foo'];
+$string = 'abcde';
+
+echo "$array[-3]\n";
+echo "$string[-3]\n";
+echo <<<EOT
+$array[-3]
+$string[-3]
+
+EOT;
+?>
+===DONE===
+--EXPECT--
+foo
+c
+foo
+c
+===DONE===

Zend/zend_language_parser.y

@@ -1249,6 +1249,7 @@ encaps_var:
 encaps_var_offset:
 		T_STRING		{ $$ = $1; }
 	|	T_NUM_STRING	{ $$ = $1; }
+	|	'-' T_NUM_STRING { $$ = zend_ast_create(ZEND_AST_UNARY_MINUS, $2); }
 	|	T_VARIABLE		{ $$ = zend_ast_create(ZEND_AST_VAR, $1); }
 ;