Basic moo/nearley parser for JS errors

error_parser.ne

@{%

const lexer = moo.states({
  error: {
    CausedBy: { match: /^\s*[cC]ause(?:d [bB]y)?:/, value: () => "Caused by:" },
    At: { match: /^[ \t]*at /, push: "frame", value: () => "at " },
    Space: /[ \t]+/,
    Newline: { match: "\n", lineBreaks: true },
    // Any line ending with file:line:col is a stack frame
    // file:line:col may be wrapped in parens, or may be the literal 'native'
    Text: /.+$/,
  },
  frame: {
    CN: ":",
    LP: "(",
    RP: ")",
    Number: { match: /\d+/, value: (str) => parseInt(str, 10)},
    NL: { match: "\n", lineBreaks: true, pop: true },
    Space: /[ \t]+/,
    FrameFragment: /[^(): \d\t\n]+/,
  },
});

%}

@lexer lexer

Error -> Message (NL Stack):? (NL CausedBy Error):? {% (d) => {
  const props = [{ message: d[0] }];
  if (d[1]) props.push({ stack: d[1][1] });
  if (d[2]) props.push({ cause: d[2][3] });
  return Object.assign({}, ...props);
}%}

Message -> Text (NL _ Text):* {% (d) => d[0] + stringFrom(d[1].flat())  %}

Text -> _Text:+ {% (d) => stringFrom(d[0]) %}

_Text -> %Text {% (d) => d[0].text %}

Stack -> Frame (NL Frame):* {% (d) => [d[0], ...(d[1] ? d[1].map(d => d[1]) : [])] %}

Frame -> At FrameFragments _ LP FrameFragments CN Number CN Number RP {% (d) => ({ function: d[1], file: d[4], line: d[6], col: d[8] }) %}
  | At FrameFragments CN Number CN Number {% (d) => ({ function: undefined, file: d[1], line: d[3], col: d[5] }) %}


FrameFragments -> (FrameFragment | Number | CN | LP | RP | _ ):* {% (d) => stringFrom(d[0].flat()) %}

FrameFragment -> %FrameFragment {% (d) => d[0].text %}

Number -> %Number {% (d) => d[0].value %}

At -> %At _:? {% () => null %}

CausedBy -> %CausedBy _ {% () => null %}

CN -> %CN {% (d) => d[0].text %} # Colon `:`

LP -> %LP {% (d) => d[0].text %} # Left paren `(`

RP -> %RP {% (d) => d[0].text %} # Right paren `)`

NL -> %NL {% (d) => d[0].text %} # Newline

_ -> %Space {% (d) => d[0].value  %}

@{%

function stringFrom(iterable) {
  let str = '';
  for (const f of iterable) {
    str += f;
  }
  return str;
}

%}