fix(core): handle if alias in control flow migration (#52181)

This adds the support of `if ` conditions with `as` clause when migrating to the control flow syntax.
It now adds the required semicolon before the `as` when migrating the template.

Before: `@if (user$ | async as user) {`
After: `@if (user$ | async; as user) {`

PR Close #52181

packages/core/schematics/ng-generate/control-flow-migration/util.ts

@@ -252,7 +252,9 @@ function migrateNgIf(
 
 function buildIfBlock(
     etm: ElementToMigrate, tmpl: string, offset: number): {tmpl: string, offset: number} {
-  const condition = etm.attr.value;
+  // includes the mandatory semicolon before as
+  const condition = etm.attr.value.replace(' as ', '; as ');
+
   const startBlock = `@if (${condition}) {`;
 
   const ifBlock = startBlock + getMainBlock(etm, tmpl, offset) + `}`;
@@ -266,7 +268,8 @@ function buildIfBlock(
 function buildIfElseBlock(
     etm: ElementToMigrate, ngTemplates: Map<string, Template>, tmpl: string, elseString: string,
     offset: number): {tmpl: string, offset: number} {
-  const condition = etm.getCondition(elseString);
+  // includes the mandatory semicolon before as
+  const condition = etm.getCondition(elseString).replace(' as ', '; as ');
 
   const elseTmpl = ngTemplates.get(`#${etm.getTemplateName(elseString)}`)!;
   const startBlock = `@if (${condition}) {`;
@@ -291,7 +294,7 @@ function buildIfElseBlock(
 function buildIfThenElseBlock(
     etm: ElementToMigrate, ngTemplates: Map<string, Template>, tmpl: string, thenString: string,
     elseString: string, offset: number): {tmpl: string, offset: number} {
-  const condition = etm.getCondition(thenString);
+  const condition = etm.getCondition(thenString).replace(' as ', '; as ');
 
   const startBlock = `@if (${condition}) {`;
   const elseBlock = `} @else {`;

packages/core/schematics/test/control_flow_migration_spec.ts

@@ -363,6 +363,90 @@ describe('control flow migration', () => {
         `<ng-container *ngTemplateOutlet="blockUsedElsewhere"></ng-container>`,
       ].join('\n'));
     });
+
+    it('should migrate if with alias', async () => {
+      writeFile('/comp.ts', `
+        import {Component} from '@angular/core';
+        import {NgIf} from '@angular/common';
+
+        @Component({
+          templateUrl: './comp.html'
+        })
+        class Comp {
+          user$ = of({ name: 'Jane' }})
+        }
+      `);
+
+      writeFile(
+          '/comp.html', [`<div *ngIf="user$ | async as user">{{ user.name }}</div>`].join('\n'));
+
+      await runMigration();
+      const content = tree.readContent('/comp.html');
+
+      expect(content).toBe(
+          [`@if (user$ | async; as user) {<div>{{ user.name }}</div>}`].join('\n'));
+    });
+
+    it('should migrate if/else with alias', async () => {
+      writeFile('/comp.ts', `
+        import {Component} from '@angular/core';
+        import {NgIf} from '@angular/common';
+
+        @Component({
+          templateUrl: './comp.html'
+        })
+        class Comp {
+          user$ = of({ name: 'Jane' }})
+        }
+      `);
+
+      writeFile('/comp.html', [
+        `<div>`,
+        `<div *ngIf="user$ | async as user; else noUserBlock">{{ user.name }}</div>`,
+        `<ng-template #noUserBlock>No user</ng-template>`,
+        `</div>`,
+      ].join('\n'));
+
+      await runMigration();
+      const content = tree.readContent('/comp.html');
+
+      expect(content).toBe([
+        `<div>`,
+        `@if (user$ | async; as user) {<div>{{ user.name }}</div>} @else {No user}`,
+        `</div>`,
+      ].join('\n'));
+    });
+
+    it('should migrate if/then/else with alias', async () => {
+      writeFile('/comp.ts', `
+        import {Component} from '@angular/core';
+        import {NgIf} from '@angular/common';
+
+        @Component({
+          templateUrl: './comp.html'
+        })
+        class Comp {
+          user$ = of({ name: 'Jane' }})
+        }
+      `);
+
+      writeFile('/comp.html', [
+        `<div>`,
+        `<ng-container *ngIf="user$ | async as user; then userBlock; else noUserBlock">Ignored</ng-container>`,
+        `<ng-template #userBlock>User</ng-template>`,
+        `<ng-template #noUserBlock>No user</ng-template>`,
+        `</div>`,
+      ].join('\n'));
+
+      await runMigration();
+      const content = tree.readContent('/comp.html');
+
+      expect(content).toBe([
+        `<div>`,
+        `@if (user$ | async; as user) {User} @else {No user}`,
+        `</div>`,
+      ].join('\n'));
+    });
   });
 
   describe('ngFor', () => {