feat: add packageId

Author: velut

lib/utils/package-id.test.ts

@@ -0,0 +1,18 @@
+import { expect, test } from "vitest";
+import { packageId } from "./package-id";
+
+test("bare package, root subpath", () => {
+	expect(packageId("foo", ".")).toMatchInlineSnapshot(`"foo"`);
+});
+
+test("scoped package, root subpath", () => {
+	expect(packageId("@foo/bar", ".")).toMatchInlineSnapshot(`"@foo/bar"`);
+});
+
+test("bare package, other subpath", () => {
+	expect(packageId("foo", "my/subpath")).toMatchInlineSnapshot(`"foo/my/subpath"`);
+});
+
+test("scoped package, other subpath", () => {
+	expect(packageId("@foo/bar", "my/subpath")).toMatchInlineSnapshot(`"@foo/bar/my/subpath"`);
+});

lib/utils/package-id.ts

@@ -0,0 +1,5 @@
+export function packageId(pkg: string, subpath: string): string {
+	// Assume subpath was already normalized.
+	if (subpath === ".") return pkg;
+	return `${pkg}/${subpath}`;
+}