Webklar.com/node_modules/next/dist/esm/build/webpack/loaders/next-barrel-loader.js

/**
 * ## Barrel Optimizations
 *
 * This loader is used to optimize the imports of "barrel" files that have many
 * re-exports. Currently, both Node.js and Webpack have to enter all of these
 * submodules even if we only need a few of them.
 *
 * For example, say a file `foo.js` with the following contents:
 *
 *   export { a } from './a'
 *   export { b } from './b'
 *   export { c } from './c'
 *   ...
 *
 * If the user imports `a` only, this loader will accept the `names` option to
 * be `['a']`. Then, it request the "__barrel_transform__" SWC transform to load
 * `foo.js` and receive the following output:
 *
 *   export const __next_private_export_map__ = '[["a","./a","a"],["b","./b","b"],["c","./c","c"],...]'
 *
 *   format: '["<imported identifier>", "<import path>", "<exported name>"]'
 *   e.g.: import { a as b } from './module-a' => '["b", "./module-a", "a"]'
 *
 * The export map, generated by SWC, is a JSON that represents the exports of
 * that module, their original file, and their original name (since you can do
 * `export { a as b }`).
 *
 * Then, this loader can safely remove all the exports that are not needed and
 * re-export the ones from `names`:
 *
 *   export { a } from './a'
 *
 * That's the basic situation and also the happy path.
 *
 *
 *
 * ## Wildcard Exports
 *
 * For wildcard exports (e.g. `export * from './a'`), it becomes a bit more complicated.
 * Say `foo.js` with the following contents:
 *
 *   export * from './a'
 *   export * from './b'
 *   export * from './c'
 *   ...
 *
 * If the user imports `bar` from it, SWC can never know which files are going to be
 * exporting `bar`. So, we have to keep all the wildcard exports and do the same
 * process recursively. This loader will return the following output:
 *
 *   export * from '__barrel_optimize__?names=bar&wildcard!=!./a'
 *   export * from '__barrel_optimize__?names=bar&wildcard!=!./b'
 *   export * from '__barrel_optimize__?names=bar&wildcard!=!./c'
 *   ...
 *
 * The "!=!" tells Webpack to use the same loader to process './a', './b', and './c'.
 * After the recursive process, the "inner loaders" will either return an empty string
 * or:
 *
 *   export * from './target'
 *
 * Where `target` is the file that exports `bar`.
 *
 *
 *
 * ## Non-Barrel Files
 *
 * If the file is not a barrel, we can't apply any optimizations. That's because
 * we can't easily remove things from the file. For example, say `foo.js` with:
 *
 *   const v = 1
 *   export function b () {
 *     return v
 *   }
 *
 * If the user imports `b` only, we can't remove the `const v = 1` even though
 * the file is side-effect free. In these caes, this loader will simply re-export
 * `foo.js`:
 *
 *   export * from './foo'
 *
 * Besides these cases, this loader also carefully handles the module cache so
 * SWC won't analyze the same file twice, and no instance of the same file will
 * be accidentally created as different instances.
 */ const NextBarrelLoader = async function() {
    this.async();
    const { names, wildcard } = this.getOptions();
    const source = await new Promise((resolve, reject)=>{
        this.loadModule(`__barrel_transform__${wildcard ? "?wildcard" : ""}!=!${this.resourcePath}`, (err, src)=>{
            if (err) {
                reject(err);
            } else {
                resolve(src);
            }
        });
    });
    const matches = source.match(/^([^]*)export const __next_private_export_map__ = ('[^']+'|"[^"]+")/);
    if (!matches) {
        // This file isn't a barrel and we can't apply any optimizations. Let's re-export everything.
        // Since this loader accepts `names` and the request is keyed with `names`, we can't simply
        // return the original source here. That will create these imports with different names as
        // different modules instances.
        this.callback(null, `export * from ${JSON.stringify(this.resourcePath)}`);
        return;
    }
    const wildcardExports = [
        ...source.matchAll(/export \* from "([^"]+)"/g)
    ];
    // It needs to keep the prefix for comments and directives like "use client".
    const prefix = matches[1];
    const exportList = JSON.parse(matches[2].slice(1, -1));
    const exportMap = new Map();
    for (const [name, path, orig] of exportList){
        exportMap.set(name, [
            path,
            orig
        ]);
    }
    let output = prefix;
    let missedNames = [];
    for (const name of names){
        // If the name matches
        if (exportMap.has(name)) {
            const decl = exportMap.get(name);
            // In the wildcard case, if the value is exported from another file, we
            // redirect to that file (decl[0]). Otherwise, export from the current
            // file itself (this.resourcePath).
            if (wildcard && !decl[0]) {
                // E.g. the file contains `export const a = 1`
                decl[0] = this.resourcePath;
                decl[1] = name;
            }
            if (decl[1] === "*") {
                output += `\nexport * as ${name} from ${JSON.stringify(decl[0])}`;
            } else if (decl[1] === "default") {
                output += `\nexport { default as ${name} } from ${JSON.stringify(decl[0])}`;
            } else if (decl[1] === name) {
                output += `\nexport { ${name} } from ${JSON.stringify(decl[0])}`;
            } else {
                output += `\nexport { ${decl[1]} as ${name} } from ${JSON.stringify(decl[0])}`;
            }
        } else {
            missedNames.push(name);
        }
    }
    // These are from wildcard exports.
    if (missedNames.length > 0) {
        for (const match of wildcardExports){
            const path = match[1];
            output += `\nexport * from ${JSON.stringify(path.replace("__PLACEHOLDER__", missedNames.join(",") + "&wildcard"))}`;
        }
    }
    this.callback(null, output);
};
export default NextBarrelLoader;

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