Use a shared non-terminal for all class modifiers. This avoids conflicts when
adding modifiers that are only valid for certain targets. This change is
necessary for asymmetric visibility but might be useful for other future
additions.
Closes GH-9926
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 \\
Ilija Tovilo