fix: include index in typesVersions because it's always matched

.changeset/thirty-dodos-play.md

@@ -0,0 +1,5 @@
+---
+'svelte-migrate': patch
+---
+
+fix: include index in typesVersions because it's always matched

documentation/docs/30-advanced/70-packaging.md

@@ -152,7 +152,7 @@ The second option is to (ab)use the `typesVersions` feature from TypeScript to w
 }
 ```
 
-`>4.0` tells TypeScript to check the inner map if the used TypeScript version is greater than 4 (which should in practice always be true). The inner map tells TypeScript that the typings for `your-library/foo` are found within `./dist/foo.d.ts`, which essentially replicates the `exports` condition. You also have `*` as a wildcard at your disposal to make many type definitions at once available without repeating yourself.
+`>4.0` tells TypeScript to check the inner map if the used TypeScript version is greater than 4 (which should in practice always be true). The inner map tells TypeScript that the typings for `your-library/foo` are found within `./dist/foo.d.ts`, which essentially replicates the `exports` condition. You also have `*` as a wildcard at your disposal to make many type definitions at once available without repeating yourself. Note that if you opt into `typesVersions` you have to declare all type imports through it, including the root import (which is defined as `"index": [..]`).
 
 You can read more about that feature [here](https://www.typescriptlang.org/docs/handbook/declaration-files/publishing.html#version-selection-with-typesversions).
 

packages/migrate/migrations/package/migrate_pkg.js

@@ -113,15 +113,16 @@ export function update_pkg_json(config, pkg, files) {
 				file.is_svelte ? `${file.dest}.d.ts` : file.dest.slice(0, -'.js'.length) + '.d.ts'
 			}`;
 
-			if (has_type && key.slice(2) /* don't add root index type */) {
+			if (has_type) {
+				const type_key = key.slice(2) || 'index';
 				if (!pkg.exports[key]) {
-					types_versions[key.slice(2)] = [out_dir_type_path];
+					types_versions[type_key] = [out_dir_type_path];
 				} else {
 					const path_without_ext = pkg.exports[key].slice(
 						0,
 						-path.extname(pkg.exports[key]).length
 					);
-					types_versions[key.slice(2)] = [
+					types_versions[type_key] = [
 						`./${out_dir}/${(pkg.exports[key].types ?? path_without_ext + '.d.ts').slice(2)}`
 					];
 				}
@@ -188,7 +189,10 @@ export function update_pkg_json(config, pkg, files) {
 
 	// https://www.typescriptlang.org/docs/handbook/declaration-files/publishing.html#version-selection-with-typesversions
 	// A hack to get around the limitation that TS doesn't support "exports" field  with moduleResolution: 'node'
-	if (Object.keys(types_versions).length > 0) {
+	if (
+		Object.keys(types_versions).length > 1 ||
+		(Object.keys(types_versions).length > 0 && !types_versions['index'])
+	) {
 		pkg.typesVersions = { '>4.0': types_versions };
 	}
 

packages/migrate/migrations/package/migrate_pkg.spec.js

@@ -95,6 +95,7 @@ test('Updates package.json', () => {
 		svelte: './package/index.js',
 		typesVersions: {
 			'>4.0': {
+				index: ['./package/index.d.ts'],
 				'foo/Bar.svelte': ['./package/foo/Bar.svelte.d.ts'],
 				baz: ['./package/baz.d.ts'],
 				bar: ['./package/bar/index.d.ts'],