From an engine perspective, named parameters mainly add three
concepts:
* The SEND_* opcodes now accept a CONST op2, which is the
argument name. For now, it is looked up by linear scan and
runtime cached.
* This may leave UNDEF arguments on the stack. To avoid having
to deal with them in other places, a CHECK_UNDEF_ARGS opcode
is used to either replace them with defaults, or error.
* For variadic functions, EX(extra_named_params) are collected
and need to be freed based on ZEND_CALL_HAS_EXTRA_NAMED_PARAMS.
RFC: https://wiki.php.net/rfc/named_params
Closes GH-5357.
Currently, unexpected tokens in the parser are shown as the text
found, plus the internal token name, including the notorious
"unexpected '::' (T_PAAMAYIM_NEKUDOTAYIM)".
This commit replaces that with a more user-friendly format, with
two main types of token:
* Tokens which always represent the same text are shown like
'unexpected token "::"' and 'expected "::"'
* Tokens which have variable text are given a user-friendly
name, and show like 'unexpected identifier "foo"', and
'expected identifer'.
A few tokens have special cases:
* unexpected token """ -> unexpected double-quote mark
* unexpected quoted string "'foo'" -> unexpected single-quoted
string "foo"
* unexpected quoted string ""foo"" -> unexpected double-quoted
string "foo"
* unexpected illegal character "_" -> unexpected character 0xNN
(where _ is almost certainly a control character, and NN is the
hexadecimal value of the byte)
The \ token has a special case in the implementation just to stop
bison making a mess of escaping it and it coming out as \\
