simple.ungram

// Un-Grammar for the simple filter language. This should be identical to the
// grammar used for lib.rs/env_logger's filter; any deviation is a _bug_.
// https://rust-analyzer.github.io/blog/2020/10/24/introducing-ungrammar.html
//
// This does not specify parsing rules (ambiguities, precedence, etc).
// It is solely a human artifact intended as a communcation tool.
// Tokens are processed -- case insensitivity, etc is implied.
//
// Legend:
//
//   //          -- comment
//   Name =      -- non-terminal definition
//   'ident'     -- token (terminal)
//   A B         -- sequence
//   A | B       -- alternation
//   A*          -- zero or more repetition
//   A?          -- zero or one repetition
//   (A)         -- same as A
//   label:A     -- suggested name for field of AST node

Filter = directives:(Directive? (',' Directive?)*)* regex:('/' RegexFilter)?

Directive =
  |                         level:LevelFilter
  | target:TargetFilter
  | target:TargetFilter '=' level:LevelFilter

LevelFilter = 'OFF' | 'ERROR' | 'WARN' | 'INFO' | 'DEBUG' | 'TRACE'

TargetFilter = '/[^,/=]*/'

RegexFilter = '/[^/]*/'