Allow using readonly as function name

Don't treat "readonly" as a keyword if followed by "(". This
allows using it as a global function name. In particular, this
function has been used by WordPress.

This does not allow other uses of "readonly", in particular it
cannot be used as a class name, unlike "enum". The reason is that
we'd still have to recognize it as a keyword when using in a type
position:

    class Test {
        public ReadOnly $foo;
    }

This should now be interpreted as a readonly property, not as a
read-write property with type `ReadOnly`. As such, a class with
name `ReadOnly`, while unambiguous in most other circumstances,
would not be usable as property or parameter type. For that
reason, we do not support it at all.

Author: nikic

Zend/tests/readonly_function.phpt

@@ -0,0 +1,16 @@
+--TEST--
+Can use readonly as a function name
+--FILE--
+<?php
+
+function readonly() {
+    echo "Hi!\n";
+}
+
+readonly();
+readonly ();
+
+?>
+--EXPECT--
+Hi!
+Hi!

Zend/zend_language_scanner.l

@@ -1718,6 +1718,12 @@ NEWLINE ("\r"|"\n"|"\r\n")
 	RETURN_TOKEN_WITH_IDENT(T_READONLY);
 }
 
+/* Don't treat "readonly(" as a keyword, to allow using it as a function name. */
+<ST_IN_SCRIPTING>"readonly"[ \n\r\t]*"(" {
+	yyless(strlen("readonly"));
+	RETURN_TOKEN_WITH_STR(T_STRING, 0);
+}
+
 <ST_IN_SCRIPTING>"unset" {
 	RETURN_TOKEN_WITH_IDENT(T_UNSET);
 }