chevrotain/src/parse/parser/traits/perf_tracer.ts

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

import { IParserConfig } from "../../../../api"
import { has, timer } from "../../../utils/utils"
import { MixedInParser } from "./parser_traits"
import { DEFAULT_PARSER_CONFIG } from "../parser"

/**
 * Trait responsible for runtime parsing errors.
 */
export class PerformanceTracer {
  traceInitPerf: boolean | number
  traceInitMaxIdent: number
  traceInitIndent: number

  initPerformanceTracer(config: IParserConfig) {
    if (has(config, "traceInitPerf")) {
      const userTraceInitPerf = config.traceInitPerf
      const traceIsNumber = typeof userTraceInitPerf === "number"
      this.traceInitMaxIdent = traceIsNumber
        ? <number>userTraceInitPerf
        : Infinity
      this.traceInitPerf = traceIsNumber
        ? userTraceInitPerf > 0
        : userTraceInitPerf
    } else {
      this.traceInitMaxIdent = 0
      this.traceInitPerf = DEFAULT_PARSER_CONFIG.traceInitPerf
    }

    this.traceInitIndent = -1
  }

  TRACE_INIT<T>(this: MixedInParser, phaseDesc: string, phaseImpl: () => T): T {
    // No need to optimize this using NOOP pattern because
    // It is not called in a hot spot...
    if (this.traceInitPerf === true) {
      this.traceInitIndent++
      const indent = new Array(this.traceInitIndent + 1).join("\t")
      if (this.traceInitIndent < this.traceInitMaxIdent) {
        console.log(`${indent}--> <${phaseDesc}>`)
      }
      const { time, value } = timer(phaseImpl)
      /* istanbul ignore next - Difficult to reproduce specific performance behavior (>10ms) in tests */
      const traceMethod = time > 10 ? console.warn : console.log
      if (this.traceInitIndent < this.traceInitMaxIdent) {
        traceMethod(`${indent}<-- <${phaseDesc}> time: ${time}ms`)
      }
      this.traceInitIndent--
      return value
    } else {
      return phaseImpl()
    }
  }
}