feat: support pkg.imports in playground (#1311)

* feat: support pkg.imports in playground

* tidy up

Author: Rich-Harris

packages/repl/src/lib/workers/bundler/index.ts

@@ -27,7 +27,8 @@ import {
 	parse_npm_url,
 	resolve_local,
 	resolve_subpath,
-	resolve_version
+	resolve_version,
+	type Package
 } from '../npm';
 import type { BundleResult } from '$lib/public';
 
@@ -180,6 +181,14 @@ async function get_bundle(
 			// importing from a URL
 			if (/^[a-z]+:/.test(importee)) return importee;
 
+			/** The npm package we're importing from, if any */
+			let current: null | Package;
+
+			if (importer.startsWith(NPM)) {
+				const { name, version } = parse_npm_url(importer);
+				current = await fetch_package(name, name === 'svelte' ? svelte_version : version);
+			}
+
 			// importing a relative file
 			if (importee[0] === '.') {
 				if (importer.startsWith(VIRTUAL)) {
@@ -199,18 +208,22 @@ async function get_bundle(
 					);
 				}
 
-				if (importer.startsWith(NPM)) {
-					const { name, version } = parse_npm_url(importer);
-
-					const pkg = await fetch_package(name, name === 'svelte' ? svelte_version : version);
+				if (current) {
+					const { name, version } = current.meta;
 					const path = new URL(importee, importer).href.replace(`${NPM}/${name}@${version}/`, '');
 
-					return normalize_path(pkg, path);
+					return normalize_path(current, path);
 				}
 
 				return new URL(importee, importer).href;
 			}
 
+			// importing a file from the same package via pkg.imports
+			if (importee[0] === '#' && current) {
+				const subpath = resolve_subpath(current, importee);
+				return normalize_path(current, subpath.slice(2));
+			}
+
 			// importing an external package -> `npm://$/<name>@<version>/<path>`
 			const match = /^((?:@[^/]+\/)?[^/@]+)(?:@([^/]+))?(\/.+)?$/.exec(importee);
 			if (!match) throw new Error(`Invalid import "${importee}"`);
@@ -223,11 +236,9 @@ async function get_bundle(
 
 			let default_version = 'latest';
 
-			if (importer.startsWith(NPM)) {
+			if (current) {
 				// use the version specified in importer's package.json, not `latest`
-				const { name, version } = parse_npm_url(importer);
-
-				const { meta } = await fetch_package(name, name === 'svelte' ? svelte_version : version);
+				const { meta } = current;
 
 				if (meta.name === pkg_name) {
 					default_version = meta.version;

packages/repl/src/lib/workers/npm.ts

@@ -2,7 +2,7 @@ import * as resolve from 'resolve.exports';
 import { parseTar, type FileDescription } from 'tarparser';
 import { NPM } from './constants';
 
-interface Package {
+export interface Package {
 	meta: any; // package.json contents
 	contents: Record<string, FileDescription>;
 }
@@ -126,6 +126,21 @@ export function resolve_subpath(pkg: Package, subpath: string): string {
 		return `./${pkg.meta.svelte.replace('./', '')}`;
 	}
 
+	if (subpath[0] === '#') {
+		try {
+			const resolved = resolve.imports(pkg.meta, subpath, {
+				browser: true,
+				conditions: ['svelte', 'module', 'browser', 'development']
+			});
+
+			return resolved?.[0] as string;
+		} catch {
+			throw new Error(
+				`No matched import path was found for "${subpath}" in "${pkg.meta.name}/package.json"`
+			);
+		}
+	}
+
 	// modern
 	if (pkg.meta.exports) {
 		try {