Function bfsPrefetch

runtime/src/prefetch.js:45–174

(rootSrc, exports, lockfile, ctx)

}

export async function bfsPrefetch(rootSrc, exports, lockfile, ctx) {
    const { fetchedSources, knownMissing, importsMap, mainThreadSpecs } = ctx;
    const visited = new Set();
    const queue = [];
    // Module specs that never registered; thrown together at the end so the user sees a clear cause.
    const failures = [];
    // Bare-name -> target spec. Seeded from importsMap (defaults + user); physical packages.json merge in as discovered.
    const table = { ...(importsMap || {}) };
    // Bare names scanned before a manifest declared them; retried after each manifest merge.
    const pendingBare = new Map(); // name -> importer dirs, for relative targets

    const writeBytes = (bytes) => {
        const ptr = exports.wasm_alloc(Math.max(1, bytes.length));
        new Uint8Array(exports.memory.buffer, ptr, bytes.length).set(bytes);
        return ptr;
    };
    const enqueueManifestSibling = (forSpec) => {
        const m = dirOf(forSpec) + 'packages.json';
        if (!knownMissing.has(m)) queue.push(m);
    };

    /* A scanned import contributes at most one fetch target: quoted is direct, bare resolves via the table. */
    const enqueueImport = (imp, dir) => {
        if (!imp.bare) { queue.push(joinRel(dir, imp.spec)); return; }
        const target = table[imp.spec];
        if (target !== undefined) queue.push(joinRel(dir, target));
        else { const ds = pendingBare.get(imp.spec); ds ? ds.push(dir) : pendingBare.set(imp.spec, [dir]); } // a later manifest may declare it
    };
    const retryPending = () => {
        for (const [name, dirs] of [...pendingBare]) {
            const target = table[name];
            if (target !== undefined) { for (const dir of dirs) queue.push(joinRel(dir, target)); pendingBare.delete(name); }
        }
    };

    // Synthetic root packages.json so the COMPILER resolves bare names at parse time the same way.
    if (Object.keys(table).length > 0) {
        fetchedSources.set('packages.json', TE.encode(JSON.stringify({ imports: table })));
        knownMissing.delete('packages.json');
    }

    for (const imp of scanImports(rootSrc, exports)) enqueueImport(imp, '');
    if (!knownMissing.has('packages.json')) queue.push('packages.json');

    while (queue.length) {
        const spec = queue.shift();
        if (visited.has(spec)) continue;
        visited.add(spec);

        // Eager host (programmatic object) already registered before prefetch; nothing to fetch.
        if (mainThreadSpecs && mainThreadSpecs.has(spec)) continue;

        // Lazy host: ask the page to load the ESM, then register its exports as `mt:<name>` stubs.
        if (spec.startsWith('mt:')) {
            const name = spec.slice(3);
            let exportNames;
            try { exportNames = await ctx.loadHost(name); }
            catch (e) { failures.push(`host '${name}' failed to load: ${e?.message ?? e}`); continue; }