fix(runtime-core): guard targetShared.get before calling in loadShare

.changeset/fix-shared-get-guard.md

@@ -0,0 +1,18 @@
+---
+'@module-federation/runtime-core': patch
+'@module-federation/metro-core': patch
+---
+
+fix: guard `targetShared.get` before calling in `loadShare`
+
+When the host's share scope contains a dependency that a remote does not
+declare, the share scope entry has no `get()` factory. `loadShare` called
+`targetShared.get!()` without checking, crashing with
+`targetShared.get is not a function`. Added a typeof guard before both
+call sites in `SharedHandler.loadShare`, returning `false` (the documented
+miss sentinel) so callers can fall back correctly.
+
+Also guard the `factory()` call in `metro-core`'s `remote-module-registry`
+to handle the `false` return from `loadShare` without crashing.
+
+Fixes #2497

packages/metro-core/src/runtime/remote-module-registry.js

@@ -55,6 +55,9 @@ export async function loadSharedToRegistryAsync(id) {
     registry[id] = {};
     loading[id] = (async () => {
       const factory = await loadShare(id);
+      if (!factory) {
+        return;
+      }
       const sharedModule = factory();
       cloneModule(sharedModule, registry[id]);
     })();
@@ -67,7 +70,9 @@ export function loadSharedToRegistrySync(id) {
     return;
   }
   loading[id] = loadShareSync(id);
-  registry[id] = loading[id]();
+  if (loading[id]) {
+    registry[id] = loading[id]();
+  }
 }
 
 export function getModuleFromRegistry(id) {

packages/runtime-core/src/shared/index.ts

@@ -189,7 +189,10 @@ export class SharedHandler {
         return factory;
       } else {
         const asyncLoadProcess = async () => {
-          const factory = await targetShared.get!();
+          if (typeof targetShared.get !== 'function') {
+            return false as unknown as () => T;
+          }
+          const factory = await targetShared.get();
           addUseIn(targetShared, host.options.name);
           targetShared.loaded = true;
           targetShared.lib = factory;
@@ -217,7 +220,10 @@ export class SharedHandler {
       const targetShared = directShare(shareOptionsRes, _useTreeShaking);
 
       const asyncLoadProcess = async () => {
-        const factory = await targetShared.get!();
+        if (typeof targetShared.get !== 'function') {
+          return false as unknown as () => T;
+        }
+        const factory = await targetShared.get();
         targetShared.lib = factory;
         targetShared.loaded = true;
         addUseIn(targetShared, host.options.name);

packages/runtime/__tests__/shares.spec.ts

@@ -948,4 +948,50 @@ describe('load share while shared has multiple versions', () => {
     assert(sharedRes, "sharedRes can't be null");
     expect(sharedRes.version).toEqual('16.0.0');
   });
+
+  // Regression test for https://github.com/module-federation/core/issues/2497
+  // When the host's share scope contains a dep the remote doesn't declare,
+  // the scope entry has no get() factory. loadShare must not crash.
+  it('loadShare does not crash when share scope entry has no get factory', async () => {
+    const host = init({
+      name: '@federation/host-extra-dep',
+      remotes: [],
+      shared: {
+        react: {
+          version: '18.0.0',
+          scope: ['default'],
+          get: () =>
+            Promise.resolve(() => ({
+              default: 'react',
+              version: '18.0.0',
+              from: '@federation/host-extra-dep',
+            })),
+          shareConfig: {
+            singleton: true,
+            requiredVersion: '^18.0.0',
+          },
+        },
+      },
+    });
+
+    // Inject a share scope entry without a get() factory, simulating what
+    // happens when the host registers a shared dep the remote doesn't declare.
+    const scope = host.shareScopeMap['default'] || {};
+    host.shareScopeMap['default'] = scope;
+    scope['moment'] = {
+      '2.30.0': {
+        version: '2.30.0',
+        from: 'remote-without-moment',
+        scope: ['default'],
+        shareConfig: {
+          singleton: false,
+          requiredVersion: '^2.30.0',
+        },
+      } as any,
+    };
+
+    // Should return false (miss sentinel) instead of crashing
+    const result = await host.loadShare<any>('moment');
+    expect(result).toBe(false);
+  });
 });