query.ungram

// Un-Grammar for the tracing query filter language.
// 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.
//
// 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

// This grammar as-is has problems differentiating the filtering of events and
// of spans themselves; this comes from only thinking about filtering the output
// of fmtlayer and not the data model itself. As such, it needs rethinking and
// a proper redesign.

Filter = queries:(Directive (',' Directive)*)* ,?

Directive = '(' query:Query ')' ('=' level:LevelFilter)?

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

Query =
  | select:Select
  | union:(Query '|' Query)
  | intersect:(Query '&' Query)
  | difference:(Query? '-' Query)
  | '(' query:Query? ')' ('=' level:LevelFilter)?

Select =
  | target:Name
  | target:Name? span:Span
  | target:Name? event:Event

Span = '?' name:Name fields:Fields? (('>' child:Span) | descendant:Span)?
Event = fields:Fields

Fields = '{' (Field ',')* Field? '}'
Field =
  | name:Name
  | name:Name '=' fields:Fields
  | name:Name '=' value:String
  | name:Name cmp:('=','<','<=','>','>=') value:Number
  | name:Name '=' value:('true' | 'false')

Name = '/([^[:punct:][:space:]]|[_:])+/' | String
String = '/(#*)".*?"\1/'
Number = '/[0-9]+(\.[0-9]+)?([eE][0-9]+)?/'
_Whitespace = '/[[:space:]]+/'

// [[:punct:]
//     !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
// [[:space:]]
//     \t\n\v\f\r\x20