256 lines
9.6 KiB
JavaScript
256 lines
9.6 KiB
JavaScript
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/**
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* ## Barrel Optimizations
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*
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* This loader is used to optimize the imports of "barrel" files that have many
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* re-exports. Currently, both Node.js and Webpack have to enter all of these
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* submodules even if we only need a few of them.
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*
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* For example, say a file `foo.js` with the following contents:
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*
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* export { a } from './a'
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* export { b } from './b'
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* export { c } from './c'
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* ...
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*
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* If the user imports `a` only, this loader will accept the `names` option to
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* be `['a']`. Then, it request the "__barrel_transform__" SWC transform to load
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* `foo.js` and receive the following output:
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*
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* export const __next_private_export_map__ = '[["a","./a","a"],["b","./b","b"],["c","./c","c"],...]'
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*
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* format: '["<imported identifier>", "<import path>", "<exported name>"]'
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* e.g.: import { a as b } from './module-a' => '["b", "./module-a", "a"]'
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*
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* The export map, generated by SWC, is a JSON that represents the exports of
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* that module, their original file, and their original name (since you can do
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* `export { a as b }`).
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*
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* Then, this loader can safely remove all the exports that are not needed and
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* re-export the ones from `names`:
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*
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* export { a } from './a'
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*
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* That's the basic situation and also the happy path.
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*
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*
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*
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* ## Wildcard Exports
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*
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* For wildcard exports (e.g. `export * from './a'`), it becomes a bit more complicated.
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* Say `foo.js` with the following contents:
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*
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* export * from './a'
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* export * from './b'
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* export * from './c'
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* ...
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*
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* If the user imports `bar` from it, SWC can never know which files are going to be
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* exporting `bar`. So, we have to keep all the wildcard exports and do the same
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* process recursively. This loader will return the following output:
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*
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* export * from '__barrel_optimize__?names=bar&wildcard!=!./a'
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* export * from '__barrel_optimize__?names=bar&wildcard!=!./b'
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* export * from '__barrel_optimize__?names=bar&wildcard!=!./c'
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* ...
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*
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* The "!=!" tells Webpack to use the same loader to process './a', './b', and './c'.
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* After the recursive process, the "inner loaders" will either return an empty string
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* or:
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*
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* export * from './target'
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*
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* Where `target` is the file that exports `bar`.
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*
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*
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*
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* ## Non-Barrel Files
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*
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* If the file is not a barrel, we can't apply any optimizations. That's because
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* we can't easily remove things from the file. For example, say `foo.js` with:
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*
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* const v = 1
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* export function b () {
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* return v
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* }
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*
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* If the user imports `b` only, we can't remove the `const v = 1` even though
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* the file is side-effect free. In these caes, this loader will simply re-export
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* `foo.js`:
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*
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* export * from './foo'
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*
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* Besides these cases, this loader also carefully handles the module cache so
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* SWC won't analyze the same file twice, and no instance of the same file will
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* be accidentally created as different instances.
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*/ "use strict";
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Object.defineProperty(exports, "__esModule", {
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value: true
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});
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Object.defineProperty(exports, "default", {
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enumerable: true,
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get: function() {
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return _default;
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}
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});
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const _path = /*#__PURE__*/ _interop_require_default(require("path"));
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const _swc = require("../../swc");
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function _interop_require_default(obj) {
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return obj && obj.__esModule ? obj : {
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default: obj
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};
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}
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// This is a in-memory cache for the mapping of barrel exports. This only applies
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// to the packages that we optimize. It will never change (e.g. upgrading packages)
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// during the lifetime of the server so we can safely cache it.
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// There is also no need to collect the cache for the same reason.
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const barrelTransformMappingCache = new Map();
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async function getBarrelMapping(resourcePath, swcCacheDir, resolve, fs) {
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if (barrelTransformMappingCache.has(resourcePath)) {
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return barrelTransformMappingCache.get(resourcePath);
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}
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// This is a SWC transform specifically for `optimizeBarrelExports`. We don't
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// care about other things but the export map only.
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async function transpileSource(filename, source, isWildcard) {
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const isTypeScript = filename.endsWith(".ts") || filename.endsWith(".tsx");
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return new Promise((res)=>(0, _swc.transform)(source, {
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filename,
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inputSourceMap: undefined,
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sourceFileName: filename,
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optimizeBarrelExports: {
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wildcard: isWildcard
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},
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jsc: {
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parser: {
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syntax: isTypeScript ? "typescript" : "ecmascript",
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[isTypeScript ? "tsx" : "jsx"]: true
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},
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experimental: {
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cacheRoot: swcCacheDir
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}
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}
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}).then((output)=>{
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res(output.code);
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}));
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}
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// Avoid circular `export *` dependencies
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const visited = new Set();
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async function getMatches(file, isWildcard) {
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if (visited.has(file)) {
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return null;
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}
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visited.add(file);
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const source = await new Promise((res, rej)=>{
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fs.readFile(file, (err, data)=>{
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if (err || data === undefined) {
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rej(err);
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} else {
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res(data.toString());
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}
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});
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});
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const output = await transpileSource(file, source, isWildcard);
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const matches = output.match(/^([^]*)export (const|var) __next_private_export_map__ = ('[^']+'|"[^"]+")/);
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if (!matches) {
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return null;
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}
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const prefix = matches[1];
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let exportList = JSON.parse(matches[3].slice(1, -1));
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const wildcardExports = [
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...output.matchAll(/export \* from "([^"]+)"/g)
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].map((match)=>match[1]);
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// In the wildcard case, if the value is exported from another file, we
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// redirect to that file (decl[0]). Otherwise, export from the current
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// file itself.
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if (isWildcard) {
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for (const decl of exportList){
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decl[1] = file;
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decl[2] = decl[0];
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}
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}
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// This recursively handles the wildcard exports (e.g. `export * from './a'`)
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if (wildcardExports.length) {
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await Promise.all(wildcardExports.map(async (req)=>{
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const targetPath = await resolve(_path.default.dirname(file), req.replace("__barrel_optimize__?names=__PLACEHOLDER__!=!", ""));
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const targetMatches = await getMatches(targetPath, true);
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if (targetMatches) {
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// Merge the export list
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exportList = exportList.concat(targetMatches.exportList);
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}
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}));
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}
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return {
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prefix,
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exportList,
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wildcardExports
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};
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}
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const res = await getMatches(resourcePath, false);
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barrelTransformMappingCache.set(resourcePath, res);
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return res;
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}
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const NextBarrelLoader = async function() {
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this.async();
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this.cacheable(true);
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const { names, swcCacheDir } = this.getOptions();
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// For barrel optimizations, we always prefer the "module" field over the
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// "main" field because ESM handling is more robust with better tree-shaking.
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const resolve = this.getResolve({
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mainFields: [
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"module",
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"main"
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]
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});
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const mapping = await getBarrelMapping(this.resourcePath, swcCacheDir, resolve, this.fs);
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// `resolve` adds all sub-paths to the dependency graph. However, we already
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// cached the mapping and we assume them to not change. So, we can safely
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// clear the dependencies here to avoid unnecessary watchers which turned out
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// to be very expensive.
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this.clearDependencies();
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if (!mapping) {
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// This file isn't a barrel and we can't apply any optimizations. Let's re-export everything.
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// Since this loader accepts `names` and the request is keyed with `names`, we can't simply
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// return the original source here. That will create these imports with different names as
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// different modules instances.
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this.callback(null, `export * from ${JSON.stringify(this.resourcePath)}`);
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return;
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}
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// It needs to keep the prefix for comments and directives like "use client".
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const prefix = mapping.prefix;
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const exportList = mapping.exportList;
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const exportMap = new Map();
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for (const [name, filePath, orig] of exportList){
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exportMap.set(name, [
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filePath,
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orig
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]);
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}
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let output = prefix;
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let missedNames = [];
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for (const name of names){
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// If the name matches
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if (exportMap.has(name)) {
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const decl = exportMap.get(name);
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if (decl[1] === "*") {
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output += `\nexport * as ${name} from ${JSON.stringify(decl[0])}`;
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} else if (decl[1] === "default") {
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output += `\nexport { default as ${name} } from ${JSON.stringify(decl[0])}`;
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} else if (decl[1] === name) {
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output += `\nexport { ${name} } from ${JSON.stringify(decl[0])}`;
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} else {
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output += `\nexport { ${decl[1]} as ${name} } from ${JSON.stringify(decl[0])}`;
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}
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} else {
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missedNames.push(name);
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}
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}
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// These are from wildcard exports.
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if (missedNames.length > 0) {
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for (const req of mapping.wildcardExports){
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output += `\nexport * from ${JSON.stringify(req.replace("__PLACEHOLDER__", missedNames.join(",") + "&wildcard"))}`;
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}
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}
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this.callback(null, output);
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};
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const _default = NextBarrelLoader;
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//# sourceMappingURL=next-barrel-loader.js.map
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