TypeError: Cannot read property 'rules' of undefined

I get this error while reading the value of the message property of a MatchFailure.

Using a debugger, my understanding is that this is caused by pexprs.Apply.prototype.toFailure being called without a grammar argument.

Indeed in my case toFailure seems called without grammar being passed to it:

pexprs.Alt.prototype.toFailure = function(grammar) {
  var fs = this.terms.map(function(t) { return t.toFailure(); });

If I do not try to read the message property, I get no crash… but no help in fixing my grammar either.

I am willing to provide my grammar and test case, should that be of any help.

Regards, Olivier.

[pdubroy]

Hi! There was a problem with the latest version of npm — our repo structure caused npm publish to hang. It’s finally fixed now, and I just released version 15.0.0 of Ohm.

[melloc]

I’m seeing the same issue:

% node crash.js

TypeError: Cannot read property 'rules' of undefined
    at Apply.pexprs.Apply.toFailure (/home/cody/src/node-jiramark/node_modules/ohm-js/src/pexprs-toFailure.js:46:28)
    at /home/cody/src/node-jiramark/node_modules/ohm-js/src/pexprs-toFailure.js:59:50
    at Array.map (native)
    at Alt.pexprs.Alt.toFailure (/home/cody/src/node-jiramark/node_modules/ohm-js/src/pexprs-toFailure.js:59:23)
    at Not.pexprs.Not.toFailure (/home/cody/src/node-jiramark/node_modules/ohm-js/src/pexprs-toFailure.js:37:26)
    at Object.MatchState.processFailure (/home/cody/src/node-jiramark/node_modules/ohm-js/src/MatchState.js:176:31)
    at Not.pexprs.Not.eval (/home/cody/src/node-jiramark/node_modules/ohm-js/src/pexprs-eval.js:181:11)
    at Object.MatchState.eval (/home/cody/src/node-jiramark/node_modules/ohm-js/src/MatchState.js:310:20)
    at Seq.pexprs.Seq.eval (/home/cody/src/node-jiramark/node_modules/ohm-js/src/pexprs-eval.js:111:16)
    at Object.MatchState.eval (/home/cody/src/node-jiramark/node_modules/ohm-js/src/MatchState.js:310:20)

I managed to get my program down to this example:

var ohm = require('ohm-js');

var source = [
    'Crash {',
    '  Words = Word+',
    '',
    '  Word',
    '   = "[" ident+ "|" uri "]" -- link1',
    '   | ident',
    '',
    '  reserved = "{" | "}"',
    '',
    '  ident = regchar+',
    '',
    '  regchar = ~(space | reserved) any',
    '',
    '  uri = (alnum | "\u0023".."\u002F" | ":" | "_")+',
    '}'
].join('\n');

var grammar = ohm.grammar(source);

var contents = '[example|https://example.com]{'
var m = grammar.match(contents);
if (m.failed()) {
    console.log(m.shortMessage);
} else {
    console.log('Input matched grammar');
}