fix(core): missing-injectable migration should not migrate providers with "useExisting" (#33286)

We should not migrate the reference from `useExisting`. This is because
developers can only use the `useExisting` value as a token. e.g.

```ts
@NgModule({
  providers: [
    {provide: AppRippleConfig, useValue: rippleOptions},
    {provide: MAT_RIPPLE_OPTIONS, useExisting: AppRippleConfig},
  ]
})
export class AppModule {}
```

In the case above, nothing should be decorated with `@Injectable`. The
`AppRippleConfig` class is just used as a token for injection.

PR Close #33286

packages/core/schematics/migrations/missing-injectable/transform.ts

@@ -169,12 +169,11 @@ export class MissingInjectableTransform {
     if (value instanceof Reference && ts.isClassDeclaration(value.node)) {
       this.migrateProviderClass(value.node, module);
     } else if (value instanceof Map) {
-      if (!value.has('provide') || value.has('useValue') || value.has('useFactory')) {
+      if (!value.has('provide') || value.has('useValue') || value.has('useFactory') ||
+          value.has('useExisting')) {
         return [];
       }
-      if (value.has('useExisting')) {
-        return this._visitProviderResolvedValue(value.get('useExisting') !, module);
-      } else if (value.has('useClass')) {
+      if (value.has('useClass')) {
         return this._visitProviderResolvedValue(value.get('useClass') !, module);
       } else {
         return this._visitProviderResolvedValue(value.get('provide') !, module);

packages/core/schematics/test/google3/missing_injectable_rule_spec.ts

@@ -151,7 +151,7 @@ describe('Google3 missing injectable tslint rule', () => {
       expect(getFile('/index.ts')).toMatch(/@Injectable\(\)\s+export class MyServiceB/);
       expect(getFile('/index.ts')).toMatch(/@Injectable\(\)\s+export class MyServiceC/);
       expect(getFile('/index.ts')).toMatch(/@Injectable\(\)\s+export class MyServiceD/);
-      expect(getFile('/index.ts')).toMatch(/@Injectable\(\)\s+export class MyServiceE/);
+      expect(getFile('/index.ts')).toMatch(/MyServiceD {}\s+export class MyServiceE/);
       expect(getFile('/index.ts')).toMatch(/MyServiceE {}\s+export class MyServiceF/);
       expect(getFile('/index.ts')).toMatch(/MyServiceF {}\s+export class MyServiceG/);
     });

packages/core/schematics/test/missing_injectable_migration_spec.ts

@@ -189,24 +189,24 @@ describe('Missing injectable migration', () => {
       expect(tree.readContent('/index.ts')).not.toContain('@Injectable');
     });
 
-    it(`should migrate object literal provider with "useExisting" in ${type}`, async() => {
+    it(`should not migrate object literal provider with "useExisting" in ${type}`, async() => {
       writeFile('/index.ts', `
         import {${type}} from '@angular/core';
       
         export class MyService {}
         export class MyToken {}
             
-        @${type}({${propName}: [{provide: MyToken, useExisting: MyService}]})
+        @${type}({${propName}: [
+          {provide: MyService: useValue: null},
+          {provide: MyToken, useExisting: MyService},
+        ]})
         export class TestClass {}
       `);
 
       await runMigration();
 
       expect(warnOutput.length).toBe(0);
-      expect(tree.readContent('/index.ts')).toMatch(/@Injectable\(\)\s+export class MyService/);
-      expect(tree.readContent('/index.ts')).toMatch(/MyService {}\s+export class MyToken/);
-      expect(tree.readContent('/index.ts'))
-          .toContain(`{ ${type}, Injectable } from '@angular/core`);
+      expect(tree.readContent('/index.ts')).not.toContain('@Injectable');
     });
 
     it(`should migrate object literal provider with "useClass" in ${type}`, async() => {
@@ -229,6 +229,41 @@ describe('Missing injectable migration', () => {
           .toContain(`{ ${type}, Injectable } from '@angular/core`);
     });
 
+    it(`should not migrate references for providers with "useExisting" in ${type}, but migrate ` +
+           `existing token if declared in other ${type}`,
+       async() => {
+         writeFile('/index.ts', `
+        import {${type}} from '@angular/core';
+      
+        export class MyService {}
+        export class MyToken {}
+            
+        @${type}({
+          ${propName}: [
+            {provide: MyToken, useExisting: MyService},
+          ],
+        })
+        export class TestClass {}
+      `);
+
+         writeFile('/other.ts', `
+        import {${type} from '@angular/core';
+        import {MyService} from './index';
+        
+        export @${type}({
+          ${propName}: [{provide: MyService}],
+        })
+        export class OtherClass {}
+      `);
+
+         await runMigration();
+
+         expect(warnOutput.length).toBe(0);
+         expect(tree.readContent('/index.ts'))
+             .toMatch(/@angular\/core';\s+@Injectable\(\)\s+export class MyService/);
+         expect(tree.readContent('/index.ts')).toMatch(/MyService {}\s+export class MyToken/);
+       });
+
     it('should not migrate provider which is already decorated with @Injectable', async() => {
       writeFile('/index.ts', `
         import {Injectable, ${type}} from '@angular/core';