PEST Parser does not recognise comments

Question

I'm trying to write a parser with PEST the Rust parser generator. I'm having trouble with a fairly simple grammar. file is the top level rule in the grammar. It contains the SOI and EOI rules.

// example.pest

WHITESPACE = _ { "\n" | " " }
COMMENT = _{ "(*" ~ ANY* ~ "*)" }

KEYWORD = { ^"keyword" }

file = _{ SOI ~ KEYWORD ~ EOI }

Here is the contents of the file I'm trying to parse:

(*
*)
keyword

The generated parser cannot parse this file. The error looks like this:

1 | (*␊
  | ^---
  |
  = expected KEYWORD

The built in COMMENT rule should handle this situation. Is whitespace handled differently inside comments?

How to properly write a grammar with comments?

Answer 1

There is actually an error in the logic of the grammar as given here. This rule in the grammar will match everything to the end of the file.

COMMENT = _{ "(*" ~ ANY* ~ "*)" }

The rule should be

COMMENT = _{ "(*" ~ (!"*)" ~ ANY)* ~ "*)" }

This means that any number of characters will be matched, but not anything that looks like *). Once *) is encountered, the next part of the sequence is reached and *) is matched and the whole rule is fulfilled.