Adding only a single recovery rule for now.
The API is now:
* throwOnError parser option must be disabled.
* List of Errors is available through $parser->getErrors(). This
method is available either way.
* If no recovery is possible $parser->parse() will return null.
(Obviously only if throwOnError is disabled).
* Don't assign to attribute stack on reduce - why was that there
in the first place?
* Assign attributes to the position in the stack where the first
token of the production is, instead of one position earlier.
* Add a comment to clarify why we also assign attributes on read,
instead of just on shift.
Minor performance improvement for parsing, also allows to access
attributes with higher granulity in the parser, though this is not
currently done.
* #n can now be used to access the stack position of a token. $n
is the same as $this->semStack[#n]. (Post-translate $n will
actually be the stack position.)
* $attributeStack is now $this->startAttributeStack and
$endAttributes is now $this->endAttributes.
* Attributes for a node are now computed inside the individual
reduction methods, instead of being passed as a parameter.
Accessible through the attributes() macro.
This adds an additional "returnType" subnode to Stmt\Function_,
Stmt\ClassMethod and Expr\Closure, as well as the corresponding
support in the name resolver and pretty printer.
And improve the code a tad bit in general.
I left YY2TBLSTATES and YYNLSTATES around, because I don't fully
understand their role in the action double indexing.
The end attributes previously were always assigned from the last read token,
which does not necessarily correspond to the last token in the reduced rule.
In particular this occurs if the parser read a new token and based on that
lookahead decided to reduce a rule. The behavior was only correct if the
newly read token was first shifted and then the rule was reduced.
This is fixed by buffering the endAttributes of the new token in a temporary
variable and only assigning them once the token is shifted.
