fix(focus): don't crash the pnpm linker when the root isn't focused

packages/zpm/src/linker/package_map.rs

@@ -254,10 +254,15 @@ impl<'a> PnpmPackageMapBuilder<'a> {
     }
 
     pub fn build(&self) -> Result<PackageMap, Error> {
-        let top_level_package_map_node
+        // A focused install that doesn't include the root workspace has no
+        // top-level dependencies to share with the loose map
+        let empty_dependencies
+            = BTreeMap::new();
+
+        let top_level_dependencies
             = self.package_map_nodes_by_locator
                 .get(&self.top_level_locator)
-                .ok_or_else(|| package_map_error("expected the top-level package to have been registered"))?;
+                .map_or(&empty_dependencies, |node| &node.dependencies);
 
         let package_ids_by_locator: BTreeMap<Locator, String>
             = self.package_map_nodes_by_locator
@@ -292,7 +297,7 @@ impl<'a> PnpmPackageMapBuilder<'a> {
                 NodePackageMapType::Standard => package_map_node.dependencies.clone(),
                 NodePackageMapType::Loose => {
                     let mut dependencies
-                        = top_level_package_map_node.dependencies.clone();
+                        = top_level_dependencies.clone();
 
                     dependencies.extend(package_map_node.dependencies.clone());
                     dependencies

tests/acceptance-tests/pkg-tests-specs/sources/commands/workspaces/focus.test.js

@@ -279,6 +279,31 @@ describe(`Commands`, () => {
         },
       ),
     );
+
+    test(
+      `should focus a workspace that doesn't depend on the root with the pnpm linker`,
+      makeTemporaryEnv(
+        {
+          private: true,
+          workspaces: [`packages/*`],
+        },
+        {
+          nodeLinker: `pnpm`,
+        },
+        async ({path, run}) => {
+          await setupProject(path);
+
+          await run(`workspaces`, `focus`, `foo`, {
+            cwd: ppath.join(path, `packages/foo`),
+          });
+
+          await expect(xfs.readJsonPromise(ppath.join(path, `packages/foo/node_modules/no-deps/package.json`))).resolves.toMatchObject({
+            name: `no-deps`,
+            version: `1.0.0`,
+          });
+        },
+      ),
+    );
   });
 });