@fastly/js-compute/dist/compiler-steps/composeSourcemaps.js

JavaScript SDK and CLI for building JavaScript applications on [Fastly Compute](https://www.fastly.com/products/edge-compute/serverless).

import { readFile, writeFile } from 'node:fs/promises';
import { resolve } from 'node:path';
import remapping from '@jridgewell/remapping';
import { TraceMap } from '@jridgewell/trace-mapping';
import picomatch from 'picomatch';
// Compiler Step - Compose Sourcemaps
// This step usually runs at the end.
// This step composes all the source maps up to this point into a single
// source map, and injects it into the bundle.
// Be careful: Do not run any steps after this step. Such steps will not be
// reflected in downstream source maps.
export const composeSourcemapsStep = {
    outFilename: '__fastly_bundle_with_sourcemaps.js',
    async fn(ctx) {
        // Compose source maps
        const replaceSourceMapToken = '__FINAL_SOURCE_MAP__';
        let excludePatterns = [
            'forbid-entry:/**',
            'node_modules/**',
        ];
        if (ctx.excludeSources) {
            excludePatterns = [() => true];
        }
        const composed = await composeSourcemaps(ctx.sourceMaps, excludePatterns);
        const postBundleContent = await readFile(ctx.inFilepath, {
            encoding: 'utf-8',
        });
        const outputWithSourcemapsContent = postBundleContent.replace(replaceSourceMapToken, () => JSON.stringify(composed));
        await writeFile(ctx.outFilepath, outputWithSourcemapsContent);
        if (ctx.debugIntermediateFilesDir != null) {
            await writeFile(resolve(ctx.debugIntermediateFilesDir, 'fastly_sourcemaps.json'), composed);
        }
    },
};
async function readSourcemap(e) {
    const sourceMapJson = await readFile(e.s, { encoding: 'utf-8' });
    return JSON.parse(sourceMapJson);
}
export async function composeSourcemaps(sourceMaps, excludePatterns = []) {
    const topSourceMap = sourceMaps.pop();
    if (topSourceMap == null) {
        throw new Error('Unexpected: composeSourcemaps received empty sourceMaps array.');
    }
    const top = new TraceMap(await readSourcemap(topSourceMap));
    const priors = {};
    for (const sourceMap of sourceMaps) {
        priors[sourceMap.f] = await readSourcemap(sourceMap);
    }
    // Loader: given a source name from mapXZ, return a TraceMap for that source (if any).
    const loader = (source) => {
        const m = priors[source];
        if (!m)
            return null; // no earlier map for this source
        return new TraceMap(m);
    };
    const raw = JSON.parse(remapping(top, loader, false).toString());
    return JSON.stringify(stripSourcesContent(raw, excludePatterns));
}
function stripSourcesContent(map, excludes) {
    if (map.sourcesContent == null) {
        return map;
    }
    const matchers = excludes.map((p) => typeof p === 'string' ? picomatch(p) : p);
    for (let i = 0; i < map.sources.length; i++) {
        const src = map.sources[i];
        // [Windows] normalize slashes
        const normalized = src?.replace(/\\/g, '/');
        if (normalized == null || matchers.some((fn) => fn(normalized))) {
            map.sourcesContent[i] = null;
        }
    }
    return map;
}