round(): Validate the rounding mode (#12252)

NEWS

@@ -15,5 +15,6 @@ Standard:
   . Implement GH-12188 (Indication for the int size in phpinfo()). (timwolla)
   . Partly fix GH-12143 (Incorrect round() result for 0.49999999999999994).
     (timwolla)
+  . Fix GH-12252 (round(): Validate the rounding mode). (timwolla)
 
 <<< NOTE: Insert NEWS from last stable release here prior to actual release! >>>

UPGRADING

@@ -58,6 +58,9 @@ PHP 8.4 UPGRADE NOTES
     would have resulted in 1.0 instead of the correct result 0.0. Additional
     inputs might also be affected and result in different outputs compared to
     earlier PHP versions.
+  . round() now validates the value of the $mode parameter and throws a ValueError
+    for invalid modes. Previously invalid modes would have been interpreted as
+    PHP_ROUND_HALF_UP.
 
 ========================================
 6. New Functions

ext/standard/math.c

@@ -335,6 +335,17 @@ PHP_FUNCTION(round)
 		}
 	}
 
+	switch (mode) {
+		case PHP_ROUND_HALF_UP:
+		case PHP_ROUND_HALF_DOWN:
+		case PHP_ROUND_HALF_EVEN:
+		case PHP_ROUND_HALF_ODD:
+			break;
+		default:
+			zend_argument_value_error(3, "must be a valid rounding mode (PHP_ROUND_*)");
+			RETURN_THROWS();
+	}
+
 	switch (Z_TYPE_P(value)) {
 		case IS_LONG:
 			/* Simple case - long that doesn't need to be rounded. */

ext/standard/tests/math/round_valid_rounding_mode.phpt

@@ -0,0 +1,12 @@
+--TEST--
+round() rejects invalid rounding modes.
+--FILE--
+<?php
+try {
+    var_dump(round(1.5, mode: 1234));
+} catch (ValueError $e) {
+    echo $e->getMessage(), PHP_EOL;
+}
+?>
+--EXPECT--
+round(): Argument #3 ($mode) must be a valid rounding mode (PHP_ROUND_*)