chevrotain/src/parse/errors_public.ts

Chevrotain is a high performance fault tolerant javascript parsing DSL for building recursive decent parsers

import { hasTokenLabel, tokenLabel } from "../scan/tokens_public.js";
import { first, map, reduce } from "lodash-es";
import {
  Alternation,
  getProductionDslName,
  NonTerminal,
  Rule,
  Terminal,
} from "@chevrotain/gast";
import {
  IParserErrorMessageProvider,
  IProductionWithOccurrence,
  TokenType,
} from "@chevrotain/types";
import {
  IGrammarResolverErrorMessageProvider,
  IGrammarValidatorErrorMessageProvider,
} from "./grammar/types.js";

export const defaultParserErrorProvider: IParserErrorMessageProvider = {
  buildMismatchTokenMessage({ expected, actual, previous, ruleName }): string {
    const hasLabel = hasTokenLabel(expected);
    const expectedMsg = hasLabel
      ? `--> ${tokenLabel(expected)} <--`
      : `token of type --> ${expected.name} <--`;

    const msg = `Expecting ${expectedMsg} but found --> '${actual.image}' <--`;

    return msg;
  },

  buildNotAllInputParsedMessage({ firstRedundant, ruleName }): string {
    return "Redundant input, expecting EOF but found: " + firstRedundant.image;
  },

  buildNoViableAltMessage({
    expectedPathsPerAlt,
    actual,
    previous,
    customUserDescription,
    ruleName,
  }): string {
    const errPrefix = "Expecting: ";
    // TODO: issue: No Viable Alternative Error may have incomplete details. #502
    const actualText = first(actual)!.image;
    const errSuffix = "\nbut found: '" + actualText + "'";

    if (customUserDescription) {
      return errPrefix + customUserDescription + errSuffix;
    } else {
      const allLookAheadPaths = reduce(
        expectedPathsPerAlt,
        (result, currAltPaths) => result.concat(currAltPaths),
        [] as TokenType[][],
      );
      const nextValidTokenSequences = map(
        allLookAheadPaths,
        (currPath) =>
          `[${map(currPath, (currTokenType) => tokenLabel(currTokenType)).join(
            ", ",
          )}]`,
      );
      const nextValidSequenceItems = map(
        nextValidTokenSequences,
        (itemMsg, idx) => `  ${idx + 1}. ${itemMsg}`,
      );
      const calculatedDescription = `one of these possible Token sequences:\n${nextValidSequenceItems.join(
        "\n",
      )}`;

      return errPrefix + calculatedDescription + errSuffix;
    }
  },

  buildEarlyExitMessage({
    expectedIterationPaths,
    actual,
    customUserDescription,
    ruleName,
  }): string {
    const errPrefix = "Expecting: ";
    // TODO: issue: No Viable Alternative Error may have incomplete details. #502
    const actualText = first(actual)!.image;
    const errSuffix = "\nbut found: '" + actualText + "'";

    if (customUserDescription) {
      return errPrefix + customUserDescription + errSuffix;
    } else {
      const nextValidTokenSequences = map(
        expectedIterationPaths,
        (currPath) =>
          `[${map(currPath, (currTokenType) => tokenLabel(currTokenType)).join(
            ",",
          )}]`,
      );
      const calculatedDescription =
        `expecting at least one iteration which starts with one of these possible Token sequences::\n  ` +
        `<${nextValidTokenSequences.join(" ,")}>`;

      return errPrefix + calculatedDescription + errSuffix;
    }
  },
};

Object.freeze(defaultParserErrorProvider);

export const defaultGrammarResolverErrorProvider: IGrammarResolverErrorMessageProvider =
  {
    buildRuleNotFoundError(
      topLevelRule: Rule,
      undefinedRule: NonTerminal,
    ): string {
      const msg =
        "Invalid grammar, reference to a rule which is not defined: ->" +
        undefinedRule.nonTerminalName +
        "<-\n" +
        "inside top level rule: ->" +
        topLevelRule.name +
        "<-";
      return msg;
    },
  };

export const defaultGrammarValidatorErrorProvider: IGrammarValidatorErrorMessageProvider =
  {
    buildDuplicateFoundError(
      topLevelRule: Rule,
      duplicateProds: IProductionWithOccurrence[],
    ): string {
      function getExtraProductionArgument(
        prod: IProductionWithOccurrence,
      ): string {
        if (prod instanceof Terminal) {
          return prod.terminalType.name;
        } else if (prod instanceof NonTerminal) {
          return prod.nonTerminalName;
        } else {
          return "";
        }
      }

      const topLevelName = topLevelRule.name;
      const duplicateProd = first(duplicateProds)!;
      const index = duplicateProd.idx;
      const dslName = getProductionDslName(duplicateProd);
      const extraArgument = getExtraProductionArgument(duplicateProd);

      const hasExplicitIndex = index > 0;
      let msg = `->${dslName}${hasExplicitIndex ? index : ""}<- ${
        extraArgument ? `with argument: ->${extraArgument}<-` : ""
      }
                  appears more than once (${
                    duplicateProds.length
                  } times) in the top level rule: ->${topLevelName}<-.                  
                  For further details see: https://chevrotain.io/docs/FAQ.html#NUMERICAL_SUFFIXES 
                  `;

      // white space trimming time! better to trim afterwards as it allows to use WELL formatted multi line template strings...
      msg = msg.replace(/[ \t]+/g, " ");
      msg = msg.replace(/\s\s+/g, "\n");

      return msg;
    },

    buildNamespaceConflictError(rule: Rule): string {
      const errMsg =
        `Namespace conflict found in grammar.\n` +
        `The grammar has both a Terminal(Token) and a Non-Terminal(Rule) named: <${rule.name}>.\n` +
        `To resolve this make sure each Terminal and Non-Terminal names are unique\n` +
        `This is easy to accomplish by using the convention that Terminal names start with an uppercase letter\n` +
        `and Non-Terminal names start with a lower case letter.`;

      return errMsg;
    },

    buildAlternationPrefixAmbiguityError(options: {
      topLevelRule: Rule;
      prefixPath: TokenType[];
      ambiguityIndices: number[];
      alternation: Alternation;
    }): string {
      const pathMsg = map(options.prefixPath, (currTok) =>
        tokenLabel(currTok),
      ).join(", ");
      const occurrence =
        options.alternation.idx === 0 ? "" : options.alternation.idx;
      const errMsg =
        `Ambiguous alternatives: <${options.ambiguityIndices.join(
          " ,",
        )}> due to common lookahead prefix\n` +
        `in <OR${occurrence}> inside <${options.topLevelRule.name}> Rule,\n` +
        `<${pathMsg}> may appears as a prefix path in all these alternatives.\n` +
        `See: https://chevrotain.io/docs/guide/resolving_grammar_errors.html#COMMON_PREFIX\n` +
        `For Further details.`;

      return errMsg;
    },

    buildAlternationAmbiguityError(options: {
      topLevelRule: Rule;
      prefixPath: TokenType[];
      ambiguityIndices: number[];
      alternation: Alternation;
    }): string {
      const pathMsg = map(options.prefixPath, (currtok) =>
        tokenLabel(currtok),
      ).join(", ");
      const occurrence =
        options.alternation.idx === 0 ? "" : options.alternation.idx;
      let currMessage =
        `Ambiguous Alternatives Detected: <${options.ambiguityIndices.join(
          " ,",
        )}> in <OR${occurrence}>` +
        ` inside <${options.topLevelRule.name}> Rule,\n` +
        `<${pathMsg}> may appears as a prefix path in all these alternatives.\n`;

      currMessage =
        currMessage +
        `See: https://chevrotain.io/docs/guide/resolving_grammar_errors.html#AMBIGUOUS_ALTERNATIVES\n` +
        `For Further details.`;
      return currMessage;
    },

    buildEmptyRepetitionError(options: {
      topLevelRule: Rule;
      repetition: IProductionWithOccurrence;
    }): string {
      let dslName = getProductionDslName(options.repetition);
      if (options.repetition.idx !== 0) {
        dslName += options.repetition.idx;
      }

      const errMsg =
        `The repetition <${dslName}> within Rule <${options.topLevelRule.name}> can never consume any tokens.\n` +
        `This could lead to an infinite loop.`;

      return errMsg;
    },

    // TODO: remove - `errors_public` from nyc.config.js exclude
    //       once this method is fully removed from this file
    buildTokenNameError(options: {
      tokenType: TokenType;
      expectedPattern: RegExp;
    }): string {
      /* istanbul ignore next */
      return "deprecated";
    },

    buildEmptyAlternationError(options: {
      topLevelRule: Rule;
      alternation: Alternation;
      emptyChoiceIdx: number;
    }): string {
      const errMsg =
        `Ambiguous empty alternative: <${options.emptyChoiceIdx + 1}>` +
        ` in <OR${options.alternation.idx}> inside <${options.topLevelRule.name}> Rule.\n` +
        `Only the last alternative may be an empty alternative.`;

      return errMsg;
    },

    buildTooManyAlternativesError(options: {
      topLevelRule: Rule;
      alternation: Alternation;
    }): string {
      const errMsg =
        `An Alternation cannot have more than 256 alternatives:\n` +
        `<OR${options.alternation.idx}> inside <${
          options.topLevelRule.name
        }> Rule.\n has ${
          options.alternation.definition.length + 1
        } alternatives.`;

      return errMsg;
    },

    buildLeftRecursionError(options: {
      topLevelRule: Rule;
      leftRecursionPath: Rule[];
    }): string {
      const ruleName = options.topLevelRule.name;
      const pathNames = map(
        options.leftRecursionPath,
        (currRule) => currRule.name,
      );
      const leftRecursivePath = `${ruleName} --> ${pathNames
        .concat([ruleName])
        .join(" --> ")}`;
      const errMsg =
        `Left Recursion found in grammar.\n` +
        `rule: <${ruleName}> can be invoked from itself (directly or indirectly)\n` +
        `without consuming any Tokens. The grammar path that causes this is: \n ${leftRecursivePath}\n` +
        ` To fix this refactor your grammar to remove the left recursion.\n` +
        `see: https://en.wikipedia.org/wiki/LL_parser#Left_factoring.`;

      return errMsg;
    },

    // TODO: remove - `errors_public` from nyc.config.js exclude
    //       once this method is fully removed from this file
    buildInvalidRuleNameError(options: {
      topLevelRule: Rule;
      expectedPattern: RegExp;
    }): string {
      /* istanbul ignore next */
      return "deprecated";
    },

    buildDuplicateRuleNameError(options: {
      topLevelRule: Rule | string;
      grammarName: string;
    }): string {
      let ruleName;
      if (options.topLevelRule instanceof Rule) {
        ruleName = options.topLevelRule.name;
      } else {
        ruleName = options.topLevelRule;
      }

      const errMsg = `Duplicate definition, rule: ->${ruleName}<- is already defined in the grammar: ->${options.grammarName}<-`;

      return errMsg;
    },
  };