fix(mf)!: Honour the skip list for sharedMappings

`Array.prototype.filter` returns a new array. The result was discarded, so the
call was a no-op and sharedMappings reached mappings.register() unfiltered.
Assign it back.

BREAKING CHANGE: a package that is both listed in `sharedMappings` and on the
skip list is no longer mapped or shared. Affected names are the ones assembled
into `skip`: tslib, zone.js, @angular-architects/module-federation,
@angular-architects/module-federation-runtime, the three @softarc/* entries,
@angular/router/upgrade, @angular/common/upgrade, and anything in the caller's
own `skip` option. In practice these are not things people put in
sharedMappings, which exists for monorepo libraries resolved through tsconfig
`paths`, but a config relying on the old behaviour will silently stop sharing
that package.

The skip list is still only consulted for an explicit `sharedMappings` array.
Omitting it maps every non-wildcard tsconfig path, skip-listed or not; the new
spec pins that asymmetry rather than changing it.

Author: Aukevanoost

libs/mf/src/utils/__fixtures__/tsconfig.paths.json

@@ -0,0 +1,11 @@
+{
+  "compilerOptions": {
+    "paths": {
+      "@angular-architects/module-federation": ["mf-runtime/src/index.ts"],
+      "tslib": ["tslib/src/index.ts"],
+      "@angular/router/upgrade": ["router-upgrade/src/index.ts"],
+      "my-lib": ["my-lib/src/index.ts"],
+      "opt-out-lib": ["opt-out-lib/src/index.ts"]
+    }
+  }
+}

libs/mf/src/utils/with-mf-plugin.spec.ts

@@ -0,0 +1,95 @@
+import { join } from 'path';
+
+// findRootTsConfigJson() walks up from cwd() to the real workspace tsconfig.
+// Point it at a fixture instead so the mappings under test are fixed.
+jest.mock('./share-utils', () => ({
+  ...jest.requireActual('./share-utils'),
+  findRootTsConfigJson: jest.fn(),
+}));
+
+import { findRootTsConfigJson } from './share-utils';
+import { withModuleFederationPlugin } from './with-mf-plugin';
+
+const FIXTURE_TSCONFIG = join(__dirname, '__fixtures__/tsconfig.paths.json');
+
+beforeEach(() => {
+  (findRootTsConfigJson as jest.Mock).mockReturnValue(FIXTURE_TSCONFIG);
+});
+
+// `shared: {}` keeps shareAll() — which reads the real root package.json — out
+// of these tests. The sharedMappings descriptors are merged into it either way.
+function build(config: Record<string, unknown>) {
+  // withModuleFederationPlugin mutates the config it is handed, merging the
+  // mapping descriptors into `shared` before passing it to the webpack plugin.
+  const mfConfig: Record<string, unknown> = { shared: {}, ...config };
+  const result = withModuleFederationPlugin(mfConfig);
+
+  return {
+    aliases: Object.keys(result.resolve.alias),
+    shared: Object.keys(mfConfig['shared']),
+  };
+}
+
+describe('withModuleFederationPlugin sharedMappings', () => {
+  it('maps a library that is not skip-listed', () => {
+    const { aliases, shared } = build({ sharedMappings: ['my-lib'] });
+
+    expect(aliases).toEqual(['my-lib']);
+    expect(shared).toEqual(['my-lib']);
+  });
+
+  it('drops entries on DEFAULT_SKIP_LIST', () => {
+    const { aliases, shared } = build({
+      sharedMappings: [
+        '@angular-architects/module-federation',
+        'tslib',
+        'my-lib',
+      ],
+    });
+
+    expect(aliases).toEqual(['my-lib']);
+    expect(shared).toEqual(['my-lib']);
+  });
+
+  it('drops entries on DEFAULT_SECONDARIES_SKIP_LIST', () => {
+    const { aliases, shared } = build({
+      sharedMappings: ['@angular/router/upgrade', 'my-lib'],
+    });
+
+    expect(aliases).toEqual(['my-lib']);
+    expect(shared).toEqual(['my-lib']);
+  });
+
+  it('drops entries named in the caller-supplied skip option', () => {
+    const { aliases, shared } = build({
+      sharedMappings: ['opt-out-lib', 'my-lib'],
+      skip: ['opt-out-lib'],
+    });
+
+    expect(aliases).toEqual(['my-lib']);
+    expect(shared).toEqual(['my-lib']);
+  });
+
+  it('maps nothing when every entry is skipped', () => {
+    // An empty array must not be mistaken for "no sharedMappings given", which
+    // is what turns on the map-every-tsconfig-path behaviour below.
+    const { aliases, shared } = build({ sharedMappings: ['tslib'] });
+
+    expect(aliases).toEqual([]);
+    expect(shared).toEqual([]);
+  });
+
+  it('maps every tsconfig path when sharedMappings is omitted', () => {
+    // Pre-existing asymmetry: the skip list is only consulted for an explicit
+    // sharedMappings array, so this path still maps skip-listed keys.
+    const { aliases } = build({});
+
+    expect(aliases).toEqual([
+      '@angular-architects/module-federation',
+      'tslib',
+      '@angular/router/upgrade',
+      'my-lib',
+      'opt-out-lib',
+    ]);
+  });
+});

libs/mf/src/utils/with-mf-plugin.ts

@@ -10,7 +10,7 @@ import { ModifyEntryPlugin } from './modify-entry-plugin';
 import ModuleFederationPlugin = require('webpack/lib/container/ModuleFederationPlugin');
 
 export function withModuleFederationPlugin(config: unknown) {
-  const sharedMappings = config['sharedMappings'];
+  let sharedMappings = config['sharedMappings'];
   delete config['sharedMappings'];
 
   const skip = [
@@ -22,7 +22,7 @@ export function withModuleFederationPlugin(config: unknown) {
   delete config['skip'];
 
   if (sharedMappings) {
-    sharedMappings.filter((m) => !skip.includes(m));
+    sharedMappings = sharedMappings.filter((m) => !skip.includes(m));
   }
 
   const mappings = new SharedMappings();