Stack overflow when writing a Nix parser #180

RossComputerGuy · 2024-10-17T05:39:35Z

RossComputerGuy
Oct 17, 2024

I am writing a Nix parser and I get a stack overflow error:

import 'package:petitparser/petitparser.dart';

class NixGrammar extends GrammarDefinition {
  Parser token(Object input) {
    if (input is Parser) {
      return input.token().trim(ref0(hiddenStuffWhitespace));
    } else if (input is String) {
      return token(input.toParser());
    }
    throw ArgumentError.value(input, 'Invalid token parser');
  }

  /* Tokens */

  Parser importToken() => ref1(token, 'import');
  Parser derivationToken() => ref1(token, 'derivation');
  Parser builtinsToken() => ref1(token, 'builtins');
  Parser letToken() => ref1(token, 'let');
  Parser inToken() => ref1(token, 'in');
  Parser withToken() => ref1(token, 'with');
  Parser inheritToken() => ref1(token, 'inherit');
  Parser ifToken() => ref1(token, 'if');
  Parser thenToken() => ref1(token, 'then');
  Parser elseToken() => ref1(token, 'else');

  Parser orToken() => ref1(token, 'or');
  Parser assetToken() => ref1(token, 'assert');
  Parser nullToken() => ref1(token, 'null');
  Parser trueToken() => ref1(token, 'true');
  Parser falseToken() => ref1(token, 'false');

  Parser numberLexicalToken() =>
      ref0(digitLexicalToken).plus() &
          ref0(numberOptFractionalPartLexicalToken) &
          ref0(numberOptIllegalEndLexicalToken) |
      char('.') &
          ref0(digitLexicalToken).plus() &
          ref0(numberOptIllegalEndLexicalToken);

  Parser numberOptFractionalPartLexicalToken() =>
      char('.') & ref0(digitLexicalToken).plus() | epsilon();

  Parser numberOptIllegalEndLexicalToken() => epsilon();

  Parser digitLexicalToken() => digit();

  Parser stringLexicalToken() =>
      ref0(multiLineStringLexicalToken) | ref0(singleLineStringLexicalToken);

  Parser multiLineStringLexicalToken() =>
      string("''") & any().starLazy(string("''")) & string("''");

  Parser singleLineStringLexicalToken() =>
      char('"') &
          ref0(stringContentDoubleQuotedLexicalToken).star() &
          char('"') |
      pattern('^"\n\r').star() & char('"');

  Parser stringContentDoubleQuotedLexicalToken() =>
      pattern('^\\"\n\r') | char('\\') & pattern('\n\r');

  Parser letterLexicalToken() => letter();

  Parser identifierLexicalToken() =>
      ref0(identifierStartLexicalToken) &
      ref0(identifierPartLexicalToken).star();

  Parser identifierStartLexicalToken() =>
      ref0(letterLexicalToken) | ref0(identifierExpressionLexicalToken);

  Parser identifierPartLexicalToken() =>
      ref0(letterLexicalToken) |
      ref0(identifierExpressionLexicalToken) |
      ref0(digitLexicalToken);

  Parser identifierExpressionLexicalToken() =>
      ref1(token, '\${') & ref0(expression) & ref1(token, '}');

  Parser pathToken() => ref0(pathTokenElement).plusSeparated(ref1(token, '/'));

  Parser pathTokenElement() =>
      ref1(token, '../') | ref1(token, './') | ref0(identifier);

  /* Expressions */

  @override
  Parser start() => ref0(expression).end();

  Parser expression() =>
      ref0(withExpression).star() &
      ref0(assertExpression).star() &
      ref0(simpleExpression);

  Parser simpleExpression() =>
      ref0(letInExpression) |
      ref0(derivationExpression) |
      ref0(hasAttrExpression) |
      ref0(ifElseExpression) |
      ref0(mathExpression) |
      ref0(importExpression) |
      ref0(orExpression) |
      ref0(funcExpression) |
      ref0(listExpression) |
      ref0(attrSetExpression) |
      ref0(identifierList) |
      ref0(literal);

  Parser letInExpression() =>
      ref0(letToken) &
      (ref0(inheritExpression) | ref0(simpleExpression))
          .plusSeparated(ref1(token, ';')) &
      ref0(inToken) &
      ref0(expression);

  Parser derivationExpression() =>
      ref0(derivationToken) &
      ref1(token, '{') &
      ref0(attrSetList).optional() &
      ref1(token, '}');

  Parser inheritExpression() =>
      ref0(inheritToken) &
      ((ref1(token, '(') & ref0(identifierList) & ref1(token, ')')) |
          ref0(identifier));

  Parser hasAttrExpression() =>
      ref0(identifier) & ref1(token, '?') & ref0(identifierList);

  Parser ifElseExpression() =>
      ref0(ifToken) &
      ref0(expression) &
      ref0(thenToken) &
      ref0(expression) &
      ref0(elseToken) &
      ref0(expression);

  Parser mathExpression() =>
      ref0(expression) &
      (ref1(token, '+') | ref1(token, '-') | ref1(token, '*') | ref1(token, '/')) &
      ref0(expression);

  Parser importExpression() => ref0(importToken) & ref0(expression).star();

  Parser orExpression() =>
      ref0(identifierList) & ref0(orToken) & ref0(expression);

  Parser assertExpression() =>
      ref0(assertExpression) & ref0(expression) & ref1(token, ';');

  Parser withExpression() =>
      ref0(withToken) & ref0(expression) & ref1(token, ';');

  Parser funcExpression() => ref0(funcArguments) & ref0(expression);

  Parser funcArguments() =>
      ref0(funcArgumentsElement).plusSeparated(ref1(token, ':'));

  Parser funcArgumentsElement() => ref0(identifier) | ref0(attrSetExpression);

  Parser mergeListExpression() =>
      ref0(mergeListExpressionSide) &
      ref1(token, '++') &
      ref0(mergeListExpressionSide);

  Parser mergeListExpressionSide() =>
      ref0(listExpression) | ref0(identifierList) | ref0(literal);

  Parser listExpression() =>
      ref1(token, '[') & ref0(listElement).star() & ref1(token, ']');

  Parser listElement() =>
      ref0(listExpression) |
      ref0(attrSetExpression) |
      ref0(identifierList) |
      ref0(literal);

  Parser mergeAttrExpression() =>
      ref0(mergeAttrExpressionSide) &
      ref1(token, '//') &
      ref0(mergeAttrExpressionSide);

  Parser mergeAttrExpressionSide() =>
      ref0(attrSetExpression) | ref0(identifierList) | ref0(literal);

  Parser attrSetExpression() =>
      ref1(token, '{') & ref0(attrSetList).optional() & ref1(token, '}');

  Parser attrSetList() =>
      ref0(attrSetListElement).plusSeparated(ref1(token, ','));

  Parser attrSetListElement() =>
      (ref0(identifier) & ref0(attrSetListElementValue)) |
      ref0(inheritExpression);

  Parser attrSetListElementValue() =>
      ref0(attrSetListElementValueOptional) |
      ref0(attrSetListElementValueAssignment);

  Parser attrSetListElementValueOptional() =>
      ref1(token, '?') & ref0(expression);

  Parser attrSetListElementValueAssignment() =>
      ref1(token, '=') & ref0(expression);

  Parser literal() => ref1(
      token,
      ref0(nullToken) |
          ref0(trueToken) |
          ref0(falseToken) |
          ref0(numberLexicalToken) |
          ref0(stringLexicalToken) |
          ref0(pathToken));

  Parser identifier() => ref1(token, ref0(identifierLexicalToken));

  Parser identifierList() => ref0(identifier).plusSeparated(ref1(token, '.'));

  /* Whitespace & newlines */

  Parser newlineLexicalToken() => pattern('\n\r');

  Parser hiddenWhitespace() => ref0(hiddenStuffWhitespace).plus();

  Parser hiddenStuffWhitespace() =>
      ref0(visibleWhitespace) |
      ref0(singleLineComment) |
      ref0(multiLineComment);

  Parser visibleWhitespace() => whitespace();

  Parser singleLineComment() =>
      string('#') &
      ref0(newlineLexicalToken).neg().star() &
      ref0(newlineLexicalToken).optional();

  Parser multiLineComment() =>
      string('/*') &
      (ref0(multiLineComment) | string('*/').neg()).star() &
      string('*/');
}

void main() {
  final grammar = NixGrammar();
  final parser = grammar.build();
  print(parser.parse('''
    import nixpkgs {
      system = "aarch64-linux";
    }
  '''));
}

Any ideas as how to solve this?

renggli · 2024-10-17T10:46:14Z

renggli
Oct 17, 2024
Maintainer

There are at least two examples of left-recursion in your grammar:

assertExpression -> assertExpression directly refers to itself, and
expression -> mathExpression -> simpleExpression -> expression indirectly refers to itself.

You can find such problems with the linter:

final grammar = NixGrammar();
final parser = grammar.build();
print(linter(parser).join('\n\n'));

To see how to avoid left-recursion in expression grammars have a look at the examples in the tutorial: https://github.com/petitparser/dart-petitparser?tab=readme-ov-file#writing-a-more-complicated-grammar

1 reply

RossComputerGuy Oct 17, 2024
Author

To see how to avoid left-recursion in expression grammars have a look at the examples in the tutorial

So it looks like I need to ref0 some stuff? I don't quite understand.

renggli · 2024-10-17T17:28:32Z

renggli
Oct 17, 2024
Maintainer

That's probably a typo and you rather want ref1(token, 'assert') instead of ref0(assertExpression), but if you write

Parser assertExpression() => ref0(assertExpression) & ref0(expression) & ...

then at parse-time when trying to read an assertions the assertion-parser immediately calls itself. This leads to the infinite recursion that you observe with the stack overflow.

A similar, albeit less obvious case, you have with expressions. The wikipedia link about left-recursion has an in-depth explanation of why it happens and how to solve it (with the example of an expression parser). The PetitParser tutorial also gives various examples of expression grammars that do not have this problem.

2 replies

RossComputerGuy Oct 17, 2024
Author

Thanks, I didn't catch that one heh. Now I just need to fix these:

LinterIssue(type: LinterType.error, title: Left recursion, parser: LabelParser<dynamic>[innerExpression], description: The parsers directly or indirectly refers to itself without consuming input:
 1: LabelParser<dynamic>[innerExpression]
 2: ChoiceParser<dynamic>
 3: LabelParser<dynamic>[logicalExpression]
 4: ChoiceParser<dynamic>
 5: LabelParser<List<dynamic>>[mathExpression]
 6: SequenceParser<dynamic>
This causes an infinite loop when parsing.)

LinterIssue(type: LinterType.error, title: Left recursion, parser: ChoiceParser<dynamic>, description: The parsers directly or indirectly refers to itself without consuming input:
 1: LabelParser<dynamic>[innerExpression]
 2: ChoiceParser<dynamic>
 3: LabelParser<dynamic>[logicalExpression]
 4: ChoiceParser<dynamic>
 5: LabelParser<List<dynamic>>[mathExpression]
 6: SequenceParser<dynamic>
This causes an infinite loop when parsing.)

LinterIssue(type: LinterType.error, title: Left recursion, parser: LabelParser<dynamic>[logicalExpression], description: The parsers directly or indirectly refers to itself without consuming input:
 1: LabelParser<dynamic>[innerExpression]
 2: ChoiceParser<dynamic>
 3: LabelParser<dynamic>[logicalExpression]
 4: ChoiceParser<dynamic>
 5: LabelParser<List<dynamic>>[mathExpression]
 6: SequenceParser<dynamic>
This causes an infinite loop when parsing.)

LinterIssue(type: LinterType.error, title: Left recursion, parser: ChoiceParser<dynamic>, description: The parsers directly or indirectly refers to itself without consuming input:
 1: LabelParser<dynamic>[innerExpression]
 2: ChoiceParser<dynamic>
 3: LabelParser<dynamic>[logicalExpression]
 4: ChoiceParser<dynamic>
 5: LabelParser<List<dynamic>>[mathExpression]
 6: SequenceParser<dynamic>
This causes an infinite loop when parsing.)

LinterIssue(type: LinterType.error, title: Left recursion, parser: LabelParser<List<dynamic>>[mathExpression], description: The parsers directly or indirectly refers to itself without consuming input:
 1: LabelParser<dynamic>[innerExpression]
 2: ChoiceParser<dynamic>
 3: LabelParser<dynamic>[logicalExpression]
 4: ChoiceParser<dynamic>
 5: LabelParser<List<dynamic>>[mathExpression]
 6: SequenceParser<dynamic>
This causes an infinite loop when parsing.)

LinterIssue(type: LinterType.error, title: Left recursion, parser: SequenceParser<dynamic>, description: The parsers directly or indirectly refers to itself without consuming input:
 1: LabelParser<dynamic>[innerExpression]
 2: ChoiceParser<dynamic>
 3: LabelParser<dynamic>[logicalExpression]
 4: ChoiceParser<dynamic>
 5: LabelParser<List<dynamic>>[mathExpression]
 6: SequenceParser<dynamic>
This causes an infinite loop when parsing.)

RossComputerGuy Oct 17, 2024
Author

Oh, this works.

import 'package:petitparser/petitparser.dart';

class NixGrammar extends GrammarDefinition {
  Parser token(Object input) {
    if (input is Parser) {
      return input.token().trim(ref0(hiddenStuffWhitespace));
    } else if (input is String) {
      return token(input.toParser()).labeled(input);
    }
    throw ArgumentError.value(input, 'Invalid token parser');
  }

  /* Tokens */

  Parser importToken() => ref1(token, 'import');
  Parser derivationToken() => ref1(token, 'derivation');
  Parser builtinsToken() => ref1(token, 'builtins');
  Parser letToken() => ref1(token, 'let');
  Parser inToken() => ref1(token, 'in');
  Parser withToken() => ref1(token, 'with');
  Parser inheritToken() => ref1(token, 'inherit');
  Parser ifToken() => ref1(token, 'if');
  Parser thenToken() => ref1(token, 'then');
  Parser elseToken() => ref1(token, 'else');
  Parser recToken() => ref1(token, 'rec');

  Parser orToken() => ref1(token, 'or');
  Parser assetToken() => ref1(token, 'assert');
  Parser<Null> nullToken() => ref1(token, 'null').trim().map((_) => null);
  Parser<bool> trueToken() => ref1(token, 'true').trim().map((_) => true);
  Parser<bool> falseToken() => ref1(token, 'false').trim().map((_) => true);

  Parser numberLexicalToken() => (ref1(token, '-').optional() &
          (ref0(digitLexicalToken).plus() &
                  ref0(numberOptFractionalPartLexicalToken) &
                  ref0(numberOptIllegalEndLexicalToken) |
              char('.') &
                  ref0(digitLexicalToken).plus() &
                  ref0(numberOptIllegalEndLexicalToken)))
      .labeled('numberLexicalToken');

  Parser numberOptFractionalPartLexicalToken() =>
      (char('.') & ref0(digitLexicalToken).plus() | epsilon())
          .labeled('numberOptFractionalPartLexicalToken');

  Parser numberOptIllegalEndLexicalToken() => epsilon();

  Parser digitLexicalToken() => digit();

  Parser stringLexicalToken() =>
      (ref0(multiLineStringLexicalToken) | ref0(singleLineStringLexicalToken))
          .labeled('stringLexicalToken');

  Parser multiLineStringLexicalToken() =>
      string("''") & any().starLazy(string("''")) & string("''");

  Parser singleLineStringLexicalToken() =>
      char('"') &
          ref0(stringContentDoubleQuotedLexicalToken).star() &
          char('"') |
      pattern('^"\n\r').star() & char('"');

  Parser stringContentDoubleQuotedLexicalToken() =>
      pattern('^\\"\n\r') | char('\\') & pattern('\n\r');

  Parser letterLexicalToken() => letter();

  Parser identifierLexicalToken() => (ref0(identifierStartLexicalToken) &
          ref0(identifierPartLexicalToken).star())
      .flatten()
      .labeled('identifierLexicalToken');

  Parser identifierStartLexicalToken() =>
      (ref0(letterLexicalToken) | ref0(identifierExpressionLexicalToken))
          .labeled('identifierStartLexicalToken');

  Parser identifierPartLexicalToken() => (ref0(letterLexicalToken) |
          ref0(identifierExpressionLexicalToken) |
          ref0(digitLexicalToken))
      .labeled('identifierPartLexicalToken');

  Parser identifierExpressionLexicalToken() =>
      (ref1(token, '\${') & ref0(expression) & ref1(token, '}'))
          .labeled('identifierExpressionLexicalToken');

  // FIXME: doesn't parse beyond the first
  Parser pathToken() => ref0(pathTokenElement)
      .plusSeparated(ref1(token, '/'))
      .labeled('pathToken');

  Parser pathTokenElement() =>
      (ref1(token, '../') | ref1(token, './') | ref0(identifier))
          .labeled('pathTokenElement');

  /* Expressions */

  @override
  Parser start() => ref0(expression).end();

  Parser expression() => (ref0(withExpression)
              .star()
              .labeled('sequence withExpression') &
          ref0(assertExpression).star().labeled('sequence assertExpression') &
          ref0(innerExpression))
      .labeled('expression');

  Parser parenExpression() =>
      (ref1(token, '(') & ref0(expression) & ref1(token, ')'))
          .labeled('parenExpression');

  Parser innerExpression() => (ref0(letInExpression) |
          ref0(derivationExpression) |
          ref0(ifElseExpression) |
          ref0(importExpression) |
          ref0(funcExpression) |
          ref0(listExpression) |
          ref0(attrSetExpression) |
          ref0(logicalExpression))
      .labeled('innerExpression');

  Parser logicalExpression() => (ref0(parenExpression) |
          ref0(hasAttrExpression) |
          ref0(orExpression) |
          ref0(mathExpression) |
          ref0(identifierList) |
          ref0(literal))
      .labeled('logicalExpression');

  Parser letInExpression() => (ref0(letToken) &
          (ref0(inheritExpression) |
                  (ref0(identifier) & ref1(token, '=') & ref0(expression)))
              .plusSeparated(ref1(token, ';').labeled('let field')) &
          ref0(inToken) &
          ref0(expression))
      .labeled('letInExpression');

  Parser derivationExpression() => (ref0(derivationToken) &
          ref1(token, '{') &
          ref0(attrSetList).optional() &
          ref1(token, '}'))
      .labeled('derivationExpression');

  Parser inheritExpression() => (ref0(inheritToken) &
          ((ref1(token, '(') & ref0(identifierList) & ref1(token, ')')) |
              ref0(identifier)))
      .labeled('inheritExpression');

  Parser hasAttrExpression() =>
      (ref0(identifier) & ref1(token, '?') & ref0(identifierList))
          .labeled('hasAttrExpression');

  Parser ifElseExpression() => (ref0(ifToken) &
          ref0(logicalExpression) &
          ref0(thenToken) &
          ref0(expression) &
          ref0(elseToken) &
          ref0(expression))
      .labeled('ifElseExpression');

  // FIXME: infinite recursion
  Parser mathExpression() =>
      (ref0(mathExpressionSide) & ref0(mathOperator) & ref0(mathExpressionSide))
          .labeled('mathExpression');

  Parser mathExpressionSide() =>
      ref0(parenExpression) |
      ref0(ifElseExpression) |
      ref0(importExpression) |
      ref0(hasAttrExpression) |
      ref0(orExpression) |
      ref0(identifierList) |
      ref0(literal);

  Parser mathOperator() => (ref1(token, '+') |
          ref1(token, '-') |
          ref1(token, '*') |
          ref1(token, '/') |
          ref1(token, '==') |
          ref1(token, '!=') |
          ref1(token, '>') |
          ref1(token, '<') |
          ref1(token, '>=') |
          ref1(token, '<='))
      .labeled('mathOperator');

  Parser importExpression() =>
      (ref0(importToken) & ref0(innerExpression).star())
          .labeled('importExpression');

  Parser orExpression() =>
      (ref0(identifierList) & ref0(orToken) & ref0(() => ref0(expression)))
          .labeled('orExpression');

  // FIXME: infinite recursion
  Parser assertExpression() =>
      (ref0(assetToken) & ref0(innerExpression) & ref1(token, ';'))
          .labeled('assertExpression');

  Parser withExpression() =>
      (ref0(withToken) & ref0(innerExpression) & ref1(token, ';'))
          .labeled('withExpression');

  Parser funcExpression() =>
      (ref0(funcArguments) & ref0(expression)).labeled('funcExpression');

  Parser funcArguments() => ref0(funcArgumentsElement)
      .plusSeparated(ref1(token, ':'))
      .labeled('funcArguments');

  Parser funcArgumentsElement() => (ref0(identifier) | ref0(attrSetExpression))
      .labeled('funcArgumentsElement');

  Parser mergeListExpression() => (ref0(mergeListExpressionSide) &
          ref1(token, '++') &
          ref0(mergeListExpressionSide))
      .labeled('mergeListExpression');

  Parser mergeListExpressionSide() =>
      (ref0(listExpression) | ref0(identifierList) | ref0(literal))
          .labeled('mergeListExpressionSide');

  Parser listExpression() =>
      (ref1(token, '[') & ref0(listElement).star() & ref1(token, ']'))
          .labeled('listExpression');

  Parser listElement() => (ref0(listExpression) |
          ref0(attrSetExpression) |
          ref0(identifierList) |
          ref0(literal))
      .labeled('listElement');

  Parser mergeAttrExpression() => (ref0(mergeAttrExpressionSide) &
          ref1(token, '//') &
          ref0(mergeAttrExpressionSide))
      .labeled('mergeAttrExpression');

  Parser mergeAttrExpressionSide() =>
      (ref0(attrSetExpression) | ref0(identifierList) | ref0(literal))
          .labeled('mergeAttrExpressionSide');

  Parser attrSetExpression() => (ref0(recToken).optional() &
          ref1(token, '{') &
          ref0(attrSetList).optional() &
          ref1(token, '}'))
      .labeled('attrSetExpression');

  Parser attrSetList() => ref0(attrSetListElement)
      .plusSeparated(ref1(token, ','))
      .labeled('attrSetList');

  Parser attrSetListElement() =>
      ((ref0(identifier) & ref0(attrSetListElementValue)) |
              ref0(inheritExpression))
          .labeled('attrSetListElement');

  Parser attrSetListElementValue() => (ref0(attrSetListElementValueOptional) |
          ref0(attrSetListElementValueAssignment))
      .labeled('attrSetListElementValue');

  Parser attrSetListElementValueOptional() =>
      (ref1(token, '?') & ref0(expression))
          .labeled('attrSetListElementValueOptional');

  Parser attrSetListElementValueAssignment() =>
      (ref1(token, '=') & ref0(() => ref0(expression)))
          .labeled('attrSetListElementValueAssignment');

  Parser literal() => ref1(
          token,
          (ref0(nullToken) |
                  ref0(trueToken) |
                  ref0(falseToken) |
                  ref0(pathToken) |
                  ref0(numberLexicalToken) |
                  ref0(stringLexicalToken))
              .labeled('literal value'))
      .labeled('literal');

  Parser identifier() =>
      ref1(token, ref0(identifierLexicalToken)).labeled('identifier');

  Parser identifierList() => ref0(identifier)
      .plusSeparated(ref1(token, '.'))
      .labeled('identifierList');

  /* Whitespace & newlines */

  Parser newlineLexicalToken() => pattern('\n\r');

  Parser hiddenWhitespace() => ref0(hiddenStuffWhitespace).plus();

  Parser hiddenStuffWhitespace() =>
      ref0(visibleWhitespace) |
      ref0(singleLineComment) |
      ref0(multiLineComment);

  Parser visibleWhitespace() => whitespace();

  Parser singleLineComment() =>
      string('#') &
      ref0(newlineLexicalToken).neg().star() &
      ref0(newlineLexicalToken).optional();

  Parser multiLineComment() =>
      string('/*') &
      (ref0(multiLineComment) | string('*/').neg()).star() &
      string('*/');
}

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Stack overflow when writing a Nix parser #180

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Stack overflow when writing a Nix parser #180

RossComputerGuy Oct 17, 2024

Replies: 2 comments · 3 replies

renggli Oct 17, 2024 Maintainer

RossComputerGuy Oct 17, 2024 Author

renggli Oct 17, 2024 Maintainer

RossComputerGuy Oct 17, 2024 Author

RossComputerGuy Oct 17, 2024 Author

RossComputerGuy
Oct 17, 2024

Replies: 2 comments 3 replies

renggli
Oct 17, 2024
Maintainer

RossComputerGuy Oct 17, 2024
Author

renggli
Oct 17, 2024
Maintainer

RossComputerGuy Oct 17, 2024
Author

RossComputerGuy Oct 17, 2024
Author