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chevrotain

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

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import { forEach, has } from "lodash-es"; import { DEFAULT_PARSER_CONFIG } from "../parser.js"; import { ILookaheadStrategy, IParserConfig, OptionalProductionType, } from "@chevrotain/types"; import { AT_LEAST_ONE_IDX, AT_LEAST_ONE_SEP_IDX, getKeyForAutomaticLookahead, MANY_IDX, MANY_SEP_IDX, OPTION_IDX, OR_IDX, } from "../../grammar/keys.js"; import { MixedInParser } from "./parser_traits.js"; import { Alternation, GAstVisitor, getProductionDslName, Option, Repetition, RepetitionMandatory, RepetitionMandatoryWithSeparator, RepetitionWithSeparator, Rule, } from "@chevrotain/gast"; import { LLkLookaheadStrategy } from "../../grammar/llk_lookahead.js"; /** * Trait responsible for the lookahead related utilities and optimizations. */ export class LooksAhead { maxLookahead: number; lookAheadFuncsCache: any; dynamicTokensEnabled: boolean; lookaheadStrategy: ILookaheadStrategy; initLooksAhead(config: IParserConfig) { this.dynamicTokensEnabled = has(config, "dynamicTokensEnabled") ? (config.dynamicTokensEnabled as boolean) // assumes end user provides the correct config value/type : DEFAULT_PARSER_CONFIG.dynamicTokensEnabled; this.maxLookahead = has(config, "maxLookahead") ? (config.maxLookahead as number) // assumes end user provides the correct config value/type : DEFAULT_PARSER_CONFIG.maxLookahead; this.lookaheadStrategy = has(config, "lookaheadStrategy") ? (config.lookaheadStrategy as ILookaheadStrategy) // assumes end user provides the correct config value/type : new LLkLookaheadStrategy({ maxLookahead: this.maxLookahead }); this.lookAheadFuncsCache = new Map(); } preComputeLookaheadFunctions(this: MixedInParser, rules: Rule[]): void { forEach(rules, (currRule) => { this.TRACE_INIT(`${currRule.name} Rule Lookahead`, () => { const { alternation, repetition, option, repetitionMandatory, repetitionMandatoryWithSeparator, repetitionWithSeparator, } = collectMethods(currRule); forEach(alternation, (currProd) => { const prodIdx = currProd.idx === 0 ? "" : currProd.idx; this.TRACE_INIT(`${getProductionDslName(currProd)}${prodIdx}`, () => { const laFunc = this.lookaheadStrategy.buildLookaheadForAlternation({ prodOccurrence: currProd.idx, rule: currRule, maxLookahead: currProd.maxLookahead || this.maxLookahead, hasPredicates: currProd.hasPredicates, dynamicTokensEnabled: this.dynamicTokensEnabled, }); const key = getKeyForAutomaticLookahead( this.fullRuleNameToShort[currRule.name], OR_IDX, currProd.idx, ); this.setLaFuncCache(key, laFunc); }); }); forEach(repetition, (currProd) => { this.computeLookaheadFunc( currRule, currProd.idx, MANY_IDX, "Repetition", currProd.maxLookahead, getProductionDslName(currProd), ); }); forEach(option, (currProd) => { this.computeLookaheadFunc( currRule, currProd.idx, OPTION_IDX, "Option", currProd.maxLookahead, getProductionDslName(currProd), ); }); forEach(repetitionMandatory, (currProd) => { this.computeLookaheadFunc( currRule, currProd.idx, AT_LEAST_ONE_IDX, "RepetitionMandatory", currProd.maxLookahead, getProductionDslName(currProd), ); }); forEach(repetitionMandatoryWithSeparator, (currProd) => { this.computeLookaheadFunc( currRule, currProd.idx, AT_LEAST_ONE_SEP_IDX, "RepetitionMandatoryWithSeparator", currProd.maxLookahead, getProductionDslName(currProd), ); }); forEach(repetitionWithSeparator, (currProd) => { this.computeLookaheadFunc( currRule, currProd.idx, MANY_SEP_IDX, "RepetitionWithSeparator", currProd.maxLookahead, getProductionDslName(currProd), ); }); }); }); } computeLookaheadFunc( this: MixedInParser, rule: Rule, prodOccurrence: number, prodKey: number, prodType: OptionalProductionType, prodMaxLookahead: number | undefined, dslMethodName: string, ): void { this.TRACE_INIT( `${dslMethodName}${prodOccurrence === 0 ? "" : prodOccurrence}`, () => { const laFunc = this.lookaheadStrategy.buildLookaheadForOptional({ prodOccurrence, rule, maxLookahead: prodMaxLookahead || this.maxLookahead, dynamicTokensEnabled: this.dynamicTokensEnabled, prodType, }); const key = getKeyForAutomaticLookahead( this.fullRuleNameToShort[rule.name], prodKey, prodOccurrence, ); this.setLaFuncCache(key, laFunc); }, ); } // this actually returns a number, but it is always used as a string (object prop key) getKeyForAutomaticLookahead( this: MixedInParser, dslMethodIdx: number, occurrence: number, ): number { const currRuleShortName: any = this.getLastExplicitRuleShortName(); return getKeyForAutomaticLookahead( currRuleShortName, dslMethodIdx, occurrence, ); } getLaFuncFromCache(this: MixedInParser, key: number): Function { return this.lookAheadFuncsCache.get(key); } /* istanbul ignore next */ setLaFuncCache(this: MixedInParser, key: number, value: Function): void { this.lookAheadFuncsCache.set(key, value); } } class DslMethodsCollectorVisitor extends GAstVisitor { public dslMethods: { option: Option[]; alternation: Alternation[]; repetition: Repetition[]; repetitionWithSeparator: RepetitionWithSeparator[]; repetitionMandatory: RepetitionMandatory[]; repetitionMandatoryWithSeparator: RepetitionMandatoryWithSeparator[]; } = { option: [], alternation: [], repetition: [], repetitionWithSeparator: [], repetitionMandatory: [], repetitionMandatoryWithSeparator: [], }; reset() { this.dslMethods = { option: [], alternation: [], repetition: [], repetitionWithSeparator: [], repetitionMandatory: [], repetitionMandatoryWithSeparator: [], }; } public visitOption(option: Option): void { this.dslMethods.option.push(option); } public visitRepetitionWithSeparator(manySep: RepetitionWithSeparator): void { this.dslMethods.repetitionWithSeparator.push(manySep); } public visitRepetitionMandatory(atLeastOne: RepetitionMandatory): void { this.dslMethods.repetitionMandatory.push(atLeastOne); } public visitRepetitionMandatoryWithSeparator( atLeastOneSep: RepetitionMandatoryWithSeparator, ): void { this.dslMethods.repetitionMandatoryWithSeparator.push(atLeastOneSep); } public visitRepetition(many: Repetition): void { this.dslMethods.repetition.push(many); } public visitAlternation(or: Alternation): void { this.dslMethods.alternation.push(or); } } const collectorVisitor = new DslMethodsCollectorVisitor(); export function collectMethods(rule: Rule): { option: Option[]; alternation: Alternation[]; repetition: Repetition[]; repetitionWithSeparator: RepetitionWithSeparator[]; repetitionMandatory: RepetitionMandatory[]; repetitionMandatoryWithSeparator: RepetitionMandatoryWithSeparator[]; } { collectorVisitor.reset(); rule.accept(collectorVisitor); const dslMethods = collectorVisitor.dslMethods; // avoid uncleaned references collectorVisitor.reset(); return <any>dslMethods; }