`lexer.conditions[K].rules` grows with each call to parse

[ericprud]

The lexer code in setInput switches the .rules to 1-indexed:

for (var k in conditions) {
  var spec = conditions[k];
  var rule_ids = spec.rules;
  var len = rule_ids.length;
  var rule_regexes = new Array(len + 1); // slot 0 is unused; we use a 1-based index approach here to keep the hottest code in `lexer_next()` fast and simple! 
  var rule_new_ids = new Array(len + 1);

  for (var i = 0; i < len; i++) {
    var idx = rule_ids[i];
    var rule_re = rules[idx];
    rule_regexes[i + 1] = rule_re;
    rule_new_ids[i + 1] = idx;
  }

  spec.rules = rule_new_ids;
  spec.__rule_regexes = rule_regexes;
  spec.__rule_count = len;
}

If you generate a parser and use it a second time, .rules ends up with an undefined at index [1]. For some reason "foo".match(undefined) matches so you end up an in endless look where undefined matches but doesn't advance the cursor.

I found a terrible and a maybe-not-so-bad work-around.

terrible - ignore leading undefines

      for (var i = 1; i <= len; i++) {
        tempMatch = regexes[i] ? this._input.match(regexes[i]) : null;

pros: one line to change cons: it grows by one undefined on each iteration

maybe-no-so-bad - s/len \+ 1/len/ and unshift into the rules

        for (var k in conditions) {
          var spec = conditions[k];
          var rule_ids = spec.rules;
          var len = rule_ids.length;
          var rule_regexes = new Array(len);             // slot 0 is unused; we use a 1-based index approach here to keep the hottest code in `lexer_next()` fast and simple! 
          var rule_new_ids = new Array(len);

          for (var i = 0; i < len; i++) {
            var idx = rule_ids[i];
            var rule_re = rules[idx];
            rule_regexes[i] = rule_re;
            rule_new_ids[i] = idx;
          }

          spec.rules = rule_new_ids;
          spec.__rule_regexes = rule_regexes;
          spec.__rule_count = len;
        }

and in the constructor, prefix each rules block with an undefined:

Object.keys(lexer.conditions).forEach(c => lexer.conditions[c].rules.unshift(null))

I did this just after

    conditions: {
      'INITIAL': {
        rules: [...]

and was able to use the parser a zillion times (well, north of 2000, at least).

[GerHobbelt]

Good catch. Hm. Better to fix this in the code generator itself so that my (already hacky ;-) ) shift-by-1 in there is not needed any more.

[ericprud]

What, you don't like my terrible solution?!

Yeah, I considered diving into the generator but thought I'd need your guidance in order to make it reasonably productive.

[ericprud]

/me politely pestering

[GerHobbelt]

:-) pestering is ok

Will be busy with other matters this week. I have looked at this and want to do this as part of a new jison release, which will take some time as the road I had taken for further jison development is wrong and I need to get jison back on the road. Long story there, bottom line: this will take several weeks to get done.

The alternative is doing a kind of hotfix patch release earlier, but I was hoping I could do without that if you can wait that long. Otherwise it's gotta be a hotfix patch next week or something...

On Mon, Nov 25, 2019, 10:31 ericprud notifications@github.com wrote:

/me politely pestering

— You are receiving this because you were assigned. Reply to this email directly, view it on GitHub https://github.com/GerHobbelt/jison/issues/52?email_source=notifications&email_token=AADCIHRXSIKA4VZB244HSTTQVOLQNA5CNFSM4I54AYX2YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEFBXKBQ#issuecomment-558068998, or unsubscribe https://github.com/notifications/unsubscribe-auth/AADCIHTEJGRMZSQWIFPU6C3QVOLQNANCNFSM4I54AYXQ .

[ericprud]

here's another friendly pester in case the holidays bring a little time to pick through backlogs...

if you want someone to pair with, i won't be a ton of help at first but i'm keenly interested in the product.

[ericprud]

another pester to remind you that you have a fan base excited to use your parser

[GerHobbelt]

This should be fixed in the upcoming 0.7.0 release, as the lexer kernel code has been fixed by checking if the lexer decompression work has already been done (the this.__decompressed flag...):

    setInput: function lexer_setInput(input, yy) {
        this.yy = yy || this.yy || {};

        // also check if we've fully initialized the lexer instance,
        // including expansion work to be done to go from a loaded
        // lexer to a usable lexer:
        if (!this.__decompressed) {
          // step 1: decompress the regex list:
            let rules = this.rules;
            for (var i = 0, len = rules.length; i < len; i++) {
                var rule_re = rules[i];

            // compression: is the RE an xref to another RE slot in the rules[] table?
                if (typeof rule_re === 'number') {
                    rules[i] = rules[rule_re];
                }
            }

          // step 2: unfold the conditions[] set to make these ready for use:
            let conditions = this.conditions;
            for (let k in conditions) {
                let spec = conditions[k];

                let rule_ids = spec.rules;

                var len = rule_ids.length;
                let rule_regexes = new Array(len + 1);            // slot 0 is unused; we use a 1-based index approach here to keep the hottest code in `lexer_next()` fast and simple!
                let rule_new_ids = new Array(len + 1);

                for (var i = 0; i < len; i++) {
                    let idx = rule_ids[i];
                    var rule_re = rules[idx];
                    rule_regexes[i + 1] = rule_re;
                    rule_new_ids[i + 1] = idx;
                }

                spec.rules = rule_new_ids;
                spec.__rule_regexes = rule_regexes;
                spec.__rule_count = len;
            }

            this.__decompressed = true;
        }