remapping.mjs

import { traceSegment, decodedMappings, presortedDecodedMap, TraceMap, encodedMappings } from '@jridgewell/trace-mapping';

/**
 * A "leaf" node in the sourcemap tree, representing an original, unmodified
 * source file. Recursive segment tracing ends at the `OriginalSource`.
 */
class OriginalSource {
    constructor(source, content) {
        this.source = source;
        this.content = content;
    }
    /**
     * Tracing a `SourceMapSegment` ends when we get to an `OriginalSource`,
     * meaning this line/column location originated from this source file.
     */
    originalPositionFor(line, column, name) {
        return { column, line, name, source: this.source, content: this.content };
    }
}

/**
 * Puts `key` into the backing array, if it is not already present. Returns
 * the index of the `key` in the backing array.
 */
let put;
/**
 * FastStringArray acts like a `Set` (allowing only one occurrence of a string
 * `key`), but provides the index of the `key` in the backing array.
 *
 * This is designed to allow synchronizing a second array with the contents of
 * the backing array, like how `sourcesContent[i]` is the source content
 * associated with `source[i]`, and there are never duplicates.
 */
class FastStringArray {
    constructor() {
        this.indexes = Object.create(null);
        this.array = [];
    }
}
(() => {
    put = (strarr, key) => {
        const { array, indexes } = strarr;
        // The key may or may not be present. If it is present, it's a number.
        let index = indexes[key];
        // If it's not yet present, we need to insert it and track the index in the
        // indexes.
        if (index === undefined) {
            index = indexes[key] = array.length;
            array.push(key);
        }
        return index;
    };
})();

const INVALID_MAPPING = undefined;
const SOURCELESS_MAPPING = null;
/**
 * traceMappings is only called on the root level SourceMapTree, and begins the process of
 * resolving each mapping in terms of the original source files.
 */
let traceMappings;
/**
 * SourceMapTree represents a single sourcemap, with the ability to trace
 * mappings into its child nodes (which may themselves be SourceMapTrees).
 */
class SourceMapTree {
    constructor(map, sources) {
        this.map = map;
        this.sources = sources;
    }
    /**
     * originalPositionFor is only called on children SourceMapTrees. It recurses down
     * into its own child SourceMapTrees, until we find the original source map.
     */
    originalPositionFor(line, column, name) {
        const segment = traceSegment(this.map, line, column);
        // If we couldn't find a segment, then this doesn't exist in the sourcemap.
        if (segment == null)
            return INVALID_MAPPING;
        // 1-length segments only move the current generated column, there's no source information
        // to gather from it.
        if (segment.length === 1)
            return SOURCELESS_MAPPING;
        const source = this.sources[segment[1]];
        return source.originalPositionFor(segment[2], segment[3], segment.length === 5 ? this.map.names[segment[4]] : name);
    }
}
(() => {
    traceMappings = (tree) => {
        const mappings = [];
        const names = new FastStringArray();
        const sources = new FastStringArray();
        const sourcesContent = [];
        const { sources: rootSources, map } = tree;
        const rootNames = map.names;
        const rootMappings = decodedMappings(map);
        let lastLineWithSegment = -1;
        for (let i = 0; i < rootMappings.length; i++) {
            const segments = rootMappings[i];
            const tracedSegments = [];
            let lastSourcesIndex = -1;
            let lastSourceLine = -1;
            let lastSourceColumn = -1;
            for (let j = 0; j < segments.length; j++) {
                const segment = segments[j];
                let traced = SOURCELESS_MAPPING;
                // 1-length segments only move the current generated column, there's no source information
                // to gather from it.
                if (segment.length !== 1) {
                    const source = rootSources[segment[1]];
                    traced = source.originalPositionFor(segment[2], segment[3], segment.length === 5 ? rootNames[segment[4]] : '');
                    // If the trace is invalid, then the trace ran into a sourcemap that doesn't contain a
                    // respective segment into an original source.
                    if (traced === INVALID_MAPPING)
                        continue;
                }
                const genCol = segment[0];
                if (traced === SOURCELESS_MAPPING) {
                    if (lastSourcesIndex === -1) {
                        // This is a consecutive source-less segment, which doesn't carry any new information.
                        continue;
                    }
                    lastSourcesIndex = lastSourceLine = lastSourceColumn = -1;
                    tracedSegments.push([genCol]);
                    continue;
                }
                // So we traced a segment down into its original source file. Now push a
                // new segment pointing to this location.
                const { column, line, name, content, source } = traced;
                // Store the source location, and ensure we keep sourcesContent up to
                // date with the sources array.
                const sourcesIndex = put(sources, source);
                sourcesContent[sourcesIndex] = content;
                if (lastSourcesIndex === sourcesIndex &&
                    lastSourceLine === line &&
                    lastSourceColumn === column) {
                    // This is a duplicate mapping pointing at the exact same starting point in the source
                    // file. It doesn't carry any new information, and only bloats the sourcemap.
                    continue;
                }
                lastLineWithSegment = i;
                lastSourcesIndex = sourcesIndex;
                lastSourceLine = line;
                lastSourceColumn = column;
                // This looks like unnecessary duplication, but it noticeably increases performance. If we
                // were to push the nameIndex onto length-4 array, v8 would internally allocate 22 slots!
                // That's 68 wasted bytes! Array literals have the same capacity as their length, saving
                // memory.
                tracedSegments.push(name
                    ? [genCol, sourcesIndex, line, column, put(names, name)]
                    : [genCol, sourcesIndex, line, column]);
            }
            mappings.push(tracedSegments);
        }
        if (mappings.length > lastLineWithSegment + 1) {
            mappings.length = lastLineWithSegment + 1;
        }
        return presortedDecodedMap(Object.assign({}, tree.map, {
            mappings,
            // TODO: Make all sources relative to the sourceRoot.
            sourceRoot: undefined,
            names: names.array,
            sources: sources.array,
            sourcesContent,
        }));
    };
})();

function asArray(value) {
    if (Array.isArray(value))
        return value;
    return [value];
}
/**
 * Recursively builds a tree structure out of sourcemap files, with each node
 * being either an `OriginalSource` "leaf" or a `SourceMapTree` composed of
 * `OriginalSource`s and `SourceMapTree`s.
 *
 * Every sourcemap is composed of a collection of source files and mappings
 * into locations of those source files. When we generate a `SourceMapTree` for
 * the sourcemap, we attempt to load each source file's own sourcemap. If it
 * does not have an associated sourcemap, it is considered an original,
 * unmodified source file.
 */
function buildSourceMapTree(input, loader) {
    const maps = asArray(input).map((m) => new TraceMap(m, ''));
    const map = maps.pop();
    for (let i = 0; i < maps.length; i++) {
        if (maps[i].sources.length > 1) {
            throw new Error(`Transformation map ${i} must have exactly one source file.\n` +
                'Did you specify these with the most recent transformation maps first?');
        }
    }
    let tree = build(map, loader, '', 0);
    for (let i = maps.length - 1; i >= 0; i--) {
        tree = new SourceMapTree(maps[i], [tree]);
    }
    return tree;
}
function build(map, loader, importer, importerDepth) {
    const { resolvedSources, sourcesContent } = map;
    const depth = importerDepth + 1;
    const children = resolvedSources.map((sourceFile, i) => {
        // The loading context gives the loader more information about why this file is being loaded
        // (eg, from which importer). It also allows the loader to override the location of the loaded
        // sourcemap/original source, or to override the content in the sourcesContent field if it's
        // an unmodified source file.
        const ctx = {
            importer,
            depth,
            source: sourceFile || '',
            content: undefined,
        };
        // Use the provided loader callback to retrieve the file's sourcemap.
        // TODO: We should eventually support async loading of sourcemap files.
        const sourceMap = loader(ctx.source, ctx);
        const { source, content } = ctx;
        // If there is no sourcemap, then it is an unmodified source file.
        if (!sourceMap) {
            // The contents of this unmodified source file can be overridden via the loader context,
            // allowing it to be explicitly null or a string. If it remains undefined, we fall back to
            // the importing sourcemap's `sourcesContent` field.
            const sourceContent = content !== undefined ? content : sourcesContent ? sourcesContent[i] : null;
            return new OriginalSource(source, sourceContent);
        }
        // Else, it's a real sourcemap, and we need to recurse into it to load its
        // source files.
        return build(new TraceMap(sourceMap, source), loader, source, depth);
    });
    return new SourceMapTree(map, children);
}

/**
 * A SourceMap v3 compatible sourcemap, which only includes fields that were
 * provided to it.
 */
class SourceMap {
    constructor(map, options) {
        this.version = 3; // SourceMap spec says this should be first.
        this.file = map.file;
        this.mappings = options.decodedMappings ? decodedMappings(map) : encodedMappings(map);
        this.names = map.names;
        this.sourceRoot = map.sourceRoot;
        this.sources = map.sources;
        if (!options.excludeContent && 'sourcesContent' in map) {
            this.sourcesContent = map.sourcesContent;
        }
    }
    toString() {
        return JSON.stringify(this);
    }
}

/**
 * Traces through all the mappings in the root sourcemap, through the sources
 * (and their sourcemaps), all the way back to the original source location.
 *
 * `loader` will be called every time we encounter a source file. If it returns
 * a sourcemap, we will recurse into that sourcemap to continue the trace. If
 * it returns a falsey value, that source file is treated as an original,
 * unmodified source file.
 *
 * Pass `excludeContent` to exclude any self-containing source file content
 * from the output sourcemap.
 *
 * Pass `decodedMappings` to receive a SourceMap with decoded (instead of
 * VLQ encoded) mappings.
 */
function remapping(input, loader, options) {
    const opts = typeof options === 'object' ? options : { excludeContent: !!options, decodedMappings: false };
    const tree = buildSourceMapTree(input, loader);
    return new SourceMap(traceMappings(tree), opts);
}

export { remapping as default };
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