parjs/src/internal/trace-visualizer.ts

Library for building parsers using combinators.

/** @module parjs/trace */
import type { Trace } from "./result";

import { defaults } from "../utils";
import { padInt } from "./functions";
import type { ParjserBase } from "./parser";

/** A set of arguments for the trace visualizer. */
export interface TraceVisualizerArgs {
    lineNumbers: boolean;
    linesBefore: number;
}

/** A function that prints out a nice visualization of where a parser failed. */
export interface TraceVisualizer {
    (trace: Trace): string;
    configure(args: Partial<TraceVisualizerArgs>): TraceVisualizer;
}

const defaultArgs: TraceVisualizerArgs = {
    lineNumbers: true,
    linesBefore: 1
};

function newTraceVisualizer(pAgs: Partial<TraceVisualizerArgs>) {
    const args = defaults(pAgs, defaultArgs);
    const visualizer: TraceVisualizer = (trace: Trace) => {
        const rows = trace.input.split(/\r\n|\n|\r/g);
        const locRow = trace.location.line;
        const around = args.linesBefore;
        const firstRow = Math.max(0, locRow - around);
        let linesAround = rows.slice(firstRow, locRow + 1);

        let prefixLength = 0;
        if (args.lineNumbers) {
            const numLength = Math.floor(1 + Math.log(locRow + 1) / Math.log(10));
            const rowNumberPrefixer = (n: number) => `${padInt(firstRow + n, numLength, " ")} | `;
            prefixLength = numLength + 3;
            linesAround = linesAround.map((row, i) => `${rowNumberPrefixer(i + 1)}${row}`);
        }
        const errorMarked = `${" ".repeat(prefixLength + trace.location.column)}^${trace.reason}`;
        linesAround.push(errorMarked);
        const linesVisualization = linesAround.join("\n");

        const stack = trace.stackTrace
            .map(x => {
                const base = x as ParjserBase<unknown>;
                return `${base.expecting} (${x.type})`;
            })
            .filter(x => x)
            .join("\n");
        const fullVisualization = `${trace.kind} failure at Ln ${trace.location.line + 1} Col ${
            trace.location.column + 1
        }
${linesVisualization}

Stack:
${stack}
`;
        return fullVisualization;
    };
    visualizer.configure = newTraceVisualizer;
    return visualizer;
}

/** Visualizes a Parjs failure. */
export const visualizeTrace = newTraceVisualizer(defaultArgs);