Linter

[Aloso]

Is your feature request related to a problem? Please describe.

These days, many languages have top-notch tooling to help the developer write idiomatic, easy-to-understand code. Pomsky should be no exception.

Describe the solution you'd like

A linter, part of pomsky-bin and the VS code extension, which gives the developer useful suggestions.

Lints that I'd like to have:

• Unreachable alternative: ('ab' | 'abc')
  • Since the first alternative always matches when the second would also match, the second alternative is never reached and therefore useless
• Empty expression: let x = ; or ()
  • Also detects when the input is completely empty, or contains only let bindings
• Unnecessary modifier: 'a'? lazy or enable greedy; 'a' greedy
• Unnecessary parentheses: ('ab')?
• Unnecessary repetition: ('x'?)? or 'x'{1}
• Unnecessary repetition chain: 'a'{2}{5}
  • Could be written with a single repetition
• Impossible forward reference: ::1 :('x')
  • Since the reference is not in a repeated group together with the referenced expression, it can never match successfully
• Too lazy repetition: C* or 'x'* C
  • The lazy repetition is not followed by a "terminator"; a terminator is an expression that is not a subset of the repeated expression. For example, C is not a terminator for 'x'?, because it always matches when 'x' would match
  • This should not trigger the lint
    • 'x'* C 'y'
    • ('x'* C) 'y'
• Exponential backtracking
  • This might be difficult to detect correctly in all situations, but a solution with many false negatives and few false positives is better than nothing
• Too many numbered capturing groups: :('a') :('a') :('a') :('a') :('a') :('a') :('a') :('a') :('a') :('a') :('a') :('a')
  • Threshold should be configurable