Implement stateful parser

[emcfarlane]

This is an alternative stateful parser implementation. It main method is parsePathTemplate which takes the route config and returns pathSegments and pathVariables. This removes the logic to recompute the variable capture in the router whilst still keeping the parser clean.

[jhump]

This lexer seems overly complicated. You basically have repeated the grammar in both the lexing phase and the parse phase, which leads to code bloat. I think it's overkill since lexical analysis for this language does not need that kind of context. The only place that benefits is distinguishing path literals from identifiers, but that's easy enough to handle in the parser by accepting a sequence of tokens (identifiers and non-identifiers) as a single literal.

I also notice that your implementation accepts wildcards in the middle of path elements, which seems highly error-prone for users, since it means a literal asterisk and is not interpreted as a wildcard. Is that lifted from grpc-gateway?

[emcfarlane]

@jhump I don't understand the complexity argument. It's around the same loc and helps reduce the logic needed in the parser.

It doesn't accept wildcards in the middle of path elements.

[jhump]

It's around the same loc and helps reduce the logic needed in the parser.

LOC is not complexity (simpler code can be more verbose). This doesn't reduce the logic: it still needs to enforce the grammar rules, but now it also tracks more state in order to produce a flattened model. The added state and logic is what I mean by increasing complexity -- it is "complecting" additional concerns into the parse operation. Perhaps by "simplify" you mean removing the recursive quality?

It doesn't accept wildcards in the middle of path elements.

My bad, I misinterpreted this line (which I see you've now removed).

[emcfarlane]

Closing, might be worth revisiting as a lexerless parser but not needed.