Fix #79908: json_decode decodes negative zero as positive zero

While the JSON standard knows only numbers (i.e. it doesn't distinguish
between int and float), and does not mention negative zero at all, PHP
makes that distinction, so a negative zero should be parsed as such,
even if the number is not otherwise designated as a float.

Author: cmb69

ext/json/json_scanner.re

@@ -170,8 +170,9 @@ std:
 		return PHP_JSON_T_FALSE;
 	}
 	<JS>INT                  {
-		zend_bool bigint = 0, negative = s->token[0] == '-';
+		zend_bool bigint = 0, negative = s->token[0] == '-', neg_zero;
 		size_t digits = (size_t) (s->cursor - s->token - negative);
+		neg_zero = negative && digits == 1 && s->token[1] == '0';
 		if (digits >= PHP_JSON_INT_MAX_LENGTH) {
 			if (digits == PHP_JSON_INT_MAX_LENGTH) {
 				int cmp = strncmp((char *) (s->token + negative), LONG_MIN_DIGITS, PHP_JSON_INT_MAX_LENGTH);
@@ -182,10 +183,10 @@ std:
 				bigint = 1;
 			}
 		}
-		if (!bigint) {
+		if (EXPECTED(!neg_zero) && !bigint) {
 			ZVAL_LONG(&s->value, ZEND_STRTOL((char *) s->token, NULL, 10));
 			return PHP_JSON_T_INT;
-		} else if (s->options & PHP_JSON_BIGINT_AS_STRING) {
+		} else if (EXPECTED(!neg_zero) && s->options & PHP_JSON_BIGINT_AS_STRING) {
 			ZVAL_STRINGL(&s->value, (char *) s->token, s->cursor - s->token);
 			return PHP_JSON_T_STRING;
 		} else {

ext/json/tests/bug79908.phpt

@@ -0,0 +1,12 @@
+--TEST--
+Bug #79908 (json_decode decodes negative zero as positive zero)
+--SKIPIF--
+<?php
+if (!extension_loaded('json')) die("skip json extension not available");
+?>
+--FILE--
+<?php
+var_dump(json_decode("-0"));
+?>
+--EXPECT--
+float(-0)