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const { promises: fsPromises } = require('fs');
const path = require('path');
/** @type {Map<string, string | undefined>} */
let packageJsonTypeMap = new Map();
/**
* Infers the current active module system from loader context and options.
* @this {import('webpack').loader.LoaderContext}
* @param {import('webpack').ModuleFilenameHelpers} ModuleFilenameHelpers Webpack's module filename helpers.
* @param {import('../types').NormalizedLoaderOptions} options The normalized loader options.
* @return {Promise<'esm' | 'cjs'>} The inferred module system.
*/
async function getModuleSystem(ModuleFilenameHelpers, options) {
// Check loader options -
// if `esModule` is set we don't have to do extra guess work.
switch (typeof options.esModule) {
case 'boolean': {
return options.esModule ? 'esm' : 'cjs';
}
case 'object': {
if (
options.esModule.include &&
ModuleFilenameHelpers.matchPart(this.resourcePath, options.esModule.include)
) {
return 'esm';
}
if (
options.esModule.exclude &&
ModuleFilenameHelpers.matchPart(this.resourcePath, options.esModule.exclude)
) {
return 'cjs';
}
break;
}
default: // Do nothing
}
// Check current resource's extension
if (/\.mjs$/.test(this.resourcePath)) return 'esm';
if (/\.cjs$/.test(this.resourcePath)) return 'cjs';
if (typeof this.addMissingDependency !== 'function') {
// This is Webpack 4 which does not support `import.meta`.
// We assume `.js` files are CommonJS because the output cannot be ESM anyway.
return 'cjs';
}
// We will assume CommonJS if we cannot determine otherwise
let packageJsonType = '';
// We begin our search for relevant `package.json` files,
// at the directory of the resource being loaded.
// These paths should already be resolved,
// but we resolve them again to ensure we are dealing with an aboslute path.
const resourceContext = path.dirname(this.resourcePath);
let searchPath = resourceContext;
let previousSearchPath = '';
// We start our search just above the root context of the webpack compilation
const stopPath = path.dirname(this.rootContext);
// If the module context is a resolved symlink outside the `rootContext` path,
// then we will never find the `stopPath` - so we also halt when we hit the root.
// Note that there is a potential that the wrong `package.json` is found in some pathalogical cases,
// such as a folder that is conceptually a package + does not have an ancestor `package.json`,
// but there exists a `package.json` higher up.
// This might happen if you have a folder of utility JS files that you symlink but did not organize as a package.
// We consider this an unsupported edge case for now.
while (searchPath !== stopPath && searchPath !== previousSearchPath) {
// If we have already determined the `package.json` type for this path we can stop searching.
// We do however still need to cache the found value,
// from the `resourcePath` folder up to the matching `searchPath`,
// to avoid retracing these steps when processing sibling resources.
if (packageJsonTypeMap.has(searchPath)) {
packageJsonType = packageJsonTypeMap.get(searchPath);
let currentPath = resourceContext;
while (currentPath !== searchPath) {
// We set the found type at least level from `resourcePath` folder up to the matching `searchPath`
packageJsonTypeMap.set(currentPath, packageJsonType);
currentPath = path.dirname(currentPath);
}
break;
}
let packageJsonPath = path.join(searchPath, 'package.json');
try {
const packageSource = await fsPromises.readFile(packageJsonPath, 'utf-8');
try {
const packageObject = JSON.parse(packageSource);
// Any package.json is sufficient as long as it can be parsed.
// If it does not explicitly have a `type: "module"` it will be assumed to be CommonJS.
packageJsonType = typeof packageObject.type === 'string' ? packageObject.type : '';
packageJsonTypeMap.set(searchPath, packageJsonType);
// We set the type in the cache for all paths from the `resourcePath` folder,
// up to the matching `searchPath` to avoid retracing these steps when processing sibling resources.
let currentPath = resourceContext;
while (currentPath !== searchPath) {
packageJsonTypeMap.set(currentPath, packageJsonType);
currentPath = path.dirname(currentPath);
}
} catch (e) {
// `package.json` exists but could not be parsed.
// We track it as a dependency so we can reload if this file changes.
}
this.addDependency(packageJsonPath);
break;
} catch (e) {
// `package.json` does not exist.
// We track it as a missing dependency so we can reload if this file is added.
this.addMissingDependency(packageJsonPath);
}
// Try again at the next level up
previousSearchPath = searchPath;
searchPath = path.dirname(searchPath);
}
// Check `package.json` for the `type` field -
// fallback to use `cjs` for anything ambiguous.
return packageJsonType === 'module' ? 'esm' : 'cjs';
}
module.exports = getModuleSystem;
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