generate-sourcemap.js

"use strict";

const os = require("os");
const convertSourceMap = require("convert-source-map");
const SourceMapConsumer = require("source-map").SourceMapConsumer;
const SourceMapGenerator = require("source-map").SourceMapGenerator;
const stableSort = require("stable");

function SourceMapper(src, nodePositions, fragments, inFile, sourceRoot) {
    this.generator = new SourceMapGenerator({ sourceRoot: sourceRoot });
    this.src = src;
    // stableSort does not mutate input array so no need to copy it
    this.nodePositions = stableSort(nodePositions, compareLoc);
    this.fragments = stableSort(fragments, function(a, b) { return a.start - b.start });
    this.inFile = inFile;

    this.generator.setSourceContent(this.inFile, src);
}

SourceMapper.prototype.calculateMappings = function() {
    const self = this;

    // These offsets represent the difference in coordinates between a node in the source
    // and the corresponding position in the output.
    let lineOffset = 0;
    let columnOffset = 0;

    // Since the column position resets to zero after each newline, we have to keep track
    // of the current line that columnOffset refers to in order to know whether to reset it
    let currentLine = 0;

    let frag = 0;
    let pos = 0;

    while (pos < self.nodePositions.length) {
        while (frag < self.fragments.length &&
            compareLoc(self.fragments[frag].loc.start, self.nodePositions[pos]) < 1) {

            const fragmentLines = self.fragments[frag].str.split("\n");
            const addedNewlines = fragmentLines.length - 1;

            const replacedLines = self.fragments[frag].loc.end.line - self.fragments[frag].loc.start.line;
            const replacedColumns = self.fragments[frag].loc.end.column - self.fragments[frag].loc.start.column;

            // If there were any lines added by the fragment string, the line offset should increase;
            // If there were any lines removed by the fragment replacement then the line offset should decrease
            lineOffset = lineOffset + addedNewlines - replacedLines;

            // The column position needs to reset after each newline.  So if the fragment added any
            // newlines then the column offset is the difference between the column of the last line of
            // the fragment, and the column of the end of the replaced section of the source.
            // Otherwise we increment or decrement the column offset just like how the line offset works.
            // Note that "replacedColumns" might be negative in some cases (if the beginning of the source
            // was further right than the end due to a newline); the math still works out.
            columnOffset = fragmentLines.length > 1 ?
                fragmentLines[fragmentLines.length - 1].length - self.fragments[frag].loc.end.column :
                columnOffset + self.fragments[frag].str.length - replacedColumns;

            currentLine = self.fragments[frag].loc.end.line;

            // Skip creating mappings for any source nodes that were replaced by this fragment (and are thus
            // no longer a part of the output)
            while (pos < self.nodePositions.length &&
                compareLoc(self.fragments[frag].loc.end, self.nodePositions[pos]) > 0) {
                ++pos;
            }

            ++frag;
        }

        if (pos < self.nodePositions.length) {
            if (currentLine < self.nodePositions[pos].line)
                columnOffset = 0;
            self.addMapping(self.nodePositions[pos], {
                line: self.nodePositions[pos].line + lineOffset,
                column: self.nodePositions[pos].column + columnOffset
            });
            ++pos;
        }
    }
}

SourceMapper.prototype.addMapping = function(input, output) {
    this.generator.addMapping({
        source: this.inFile,
        original: input,
        generated: output
    });
}

SourceMapper.prototype.applySourceMap = function (consumer) {
    this.generator.applySourceMap(consumer);
}

SourceMapper.prototype.generate = function () {
    return this.generator.toString();
}

function compareLoc(a, b) {
    return (a.line - b.line) || (a.column - b.column);
}

module.exports = function generateSourcemap(result, src, nodePositions, fragments, mapOpts) {
    const existingMap = convertSourceMap.fromSource(src);
    const existingMapObject = existingMap && existingMap.toObject();
    const inFile = (existingMapObject && existingMapObject.file) || mapOpts.inFile || "source.js";
    const sourceRoot = (existingMapObject && existingMapObject.sourceRoot) || mapOpts.sourceRoot;
    src = convertSourceMap.removeMapFileComments(src);

    const mapper = new SourceMapper(src, nodePositions, fragments, inFile, sourceRoot);
    mapper.calculateMappings();

    if (mapOpts.inline) {
        if (existingMapObject)
            mapper.applySourceMap(new SourceMapConsumer(existingMapObject));

        result.src = convertSourceMap.removeMapFileComments(result.src) +
            os.EOL +
            convertSourceMap.fromJSON(mapper.generate()).toComment();
    } else {
        result.map = mapper.generate();
    }
}