feat: export condition flag (#5)

README.md

@@ -150,8 +150,8 @@ The target specifies the environments the output should support. Depending on ho
 
 By default, the target is set to the version of Node.js used. It can be overwritten with the `--target` flag:
 
-```
-pkgroll --target es2020 --target node14.18.0
+```sh
+pkgroll --target=es2020 --target=node14.18.0
 ```
 
 It will also automatically detect and include the `target` specified in `tsconfig.json#compilerOptions`.
@@ -160,18 +160,28 @@ It will also automatically detect and include the `target` specified in `tsconfi
 #### Strip `node:` protocol
 Node.js builtin modules can be prefixed with the [`node:` protocol](https://nodejs.org/api/esm.html#node-imports) for explicitness:
 
-```
-import fs from 'node:fs/promises';
+```js
+import fs from 'node:fs/promises'
 ```
 
 This is a new feature and may not work in older versions of Node.js. While you can opt out of using it, your dependencies may still be using it (example package using `node:`: [path-exists](https://github.com/sindresorhus/path-exists/blob/7c95f5c1f5f811c7f4dac78ab5b9e258491f03af/index.js#L1)).
 
 Pass in a Node.js target that that doesn't support it to strip the `node:` protocol from imports:
 
+```sh
+pkgroll --target=node12.19
 ```
-pkgroll --target node12.19
+
+### Export condition
+
+Similarly to the target, the export condition specifies which fields to read from when evaluating [export](https://nodejs.org/api/packages.html#exports) and [import](https://nodejs.org/api/packages.html#imports) maps.
+
+For example, to simulate import resolutions in Node.js, pass in `node` as the export condition:
+```sh
+pkgroll --export-condition=node
 ```
 
+
 ### ESM ⇄ CJS interoperability
 
 Node.js ESM offers [interoperability with CommonJS](https://nodejs.org/api/esm.html#interoperability-with-commonjs) via [static analysis](https://github.com/nodejs/cjs-module-lexer). However, not all bundlers compile ESM to CJS syntax in a way that is statically analyzable.

package.json

@@ -66,7 +66,7 @@
 		"rollup": "^2.70.2"
 	},
 	"devDependencies": {
-		"@pvtnbr/eslint-config": "^0.20.0",
+		"@pvtnbr/eslint-config": "^0.20.1",
 		"@types/node": "^17.0.30",
 		"@types/rimraf": "^3.0.2",
 		"cleye": "^1.2.0",

src/cli.ts

@@ -50,6 +50,10 @@ const argv = cli({
 			}],
 			description: 'Compile-time environment variables (eg. --env.NODE_ENV=production)',
 		},
+		exportCondition: {
+			type: [String],
+			description: 'Export conditions for resolving dependency export and import maps (eg. --export-condition=node)',
+		},
 	},
 
 	help: {

src/utils/get-rollup-configs.ts

@@ -16,6 +16,7 @@ import { resolveTypescriptMjsCts } from './rollup-plugins/resolve-typescript-mjs
 type Options = {
 	minify: boolean;
 	target: string[];
+	exportCondition: string[];
 	env: {
 		key: string;
 		value: string;
@@ -70,6 +71,7 @@ const getConfig = {
 				}),
 				nodeResolve({
 					extensions: ['.mjs', '.js', '.ts', '.jsx', '.tsx', '.json'],
+					exportConditions: options.exportCondition,
 				}),
 				...(
 					Object.keys(env).length > 0
@@ -167,7 +169,12 @@ export async function getRollupConfigs(
 
 		let config = configs.app;
 		if (!config) {
-			config = getConfig.app(flags, aliases, env, executablePaths);
+			config = getConfig.app(
+				flags,
+				aliases,
+				env,
+				executablePaths,
+			);
 			config.external = external;
 			configs.app = config;
 		}

tests/fixture-package/src/dependency-imports-map.js

@@ -0,0 +1,3 @@
+import value from 'dependency-imports-map';
+
+console.log(value);

tests/specs/builds/dependencies.ts

@@ -60,5 +60,41 @@ export default testSuite(({ describe }, nodePath: string) => {
 
 			await fixture.cleanup();
 		});
+
+		test('imports map - default', async () => {
+			const fixture = await createFixture('./tests/fixture-package');
+
+			await fixture.writeJson('package.json', {
+				main: './dist/dependency-imports-map.js',
+			});
+
+			const pkgrollProcess = await pkgroll([], { cwd: fixture.path, nodePath });
+
+			expect(pkgrollProcess.exitCode).toBe(0);
+			expect(pkgrollProcess.stderr).toBe('');
+
+			const content = await fixture.readFile('dist/dependency-imports-map.js', 'utf8');
+			expect(content).toMatch('default');
+
+			await fixture.cleanup();
+		});
+
+		test('imports map - node', async () => {
+			const fixture = await createFixture('./tests/fixture-package');
+
+			await fixture.writeJson('package.json', {
+				main: './dist/dependency-imports-map.js',
+			});
+
+			const pkgrollProcess = await pkgroll(['--export-condition=node'], { cwd: fixture.path, nodePath });
+
+			expect(pkgrollProcess.exitCode).toBe(0);
+			expect(pkgrollProcess.stderr).toBe('');
+
+			const content = await fixture.readFile('dist/dependency-imports-map.js', 'utf8');
+			expect(content).toMatch('node');
+
+			await fixture.cleanup();
+		});
 	});
 });