Request: Strict/complete proto2 compliance

[jhugard]

Froto appears to only parse a subset of the proto2 language, and allows a looser syntax. Requesting the parser be tightened up to match the official protoc compiler: handle the complete syntax and produce errors in the same cases, in order to provide better compatibility.

• Support enum as a top-level construct (outside any message)
• Support "group" keyword in a message
• Support "one of" keyword in a message
• Support "map" keyword in a message
• Support "extensions" keyword in a message
• Support "reserved" keyword in a message
• Support options on enum, enumItem
• Support alternate option syntax; e.g. option (myOpt) = { fieldA : 1, fieldB: "test" };
• Tighten up intLit to support proto2 octal (code uses pint32, which parses "0o77", but not "077")
• Same thing for strLit; can't recall the specifics, but don't think Froto handles all proto2 escape sequences
• Parse out strong literal types for constants (intLit, floatLit, boolLit, and strLit), rather than parsing all of those as string values.
• Tighten up identifier parser; can't recall the specifics, but IIRC Froto allows invalid identifiers

I've been hacking my own F#/FParsec parser and am almost done: have support for all the above w/tests, and only a few productions remaining (iirc, "service" and "extends"). Using this as a learning experience. Once I've implemented proto3 syntax (using an FParsec state and rejection of invalid items when in proto3 mode), I should probably circle back and fork Froto to help implement the above, if you're open to contributions :-).

[ctaggart]

I'm totally open to contributions! In fact, I was just cleaning stuff up to tackle this. I'm glad you beat me to it.