feat(core): Set default Component changeDetection strategy to OnPush

The default change detection strategy is now OnPush.

BREAKING CHANGE: Component with undefined `changeDetection` property are now `OnPush` by default. Specify `changeDetection: ChangeDetectionStrategy.Eager` to keep the previous behavior.

packages/compiler-cli/linker/src/file_linker/partial_linkers/partial_component_linker_1.ts

@@ -36,10 +36,10 @@ import {AstObject, AstValue} from '../../ast/ast_value';
 import {FatalLinkerError} from '../../fatal_linker_error';
 import {GetSourceFileFn} from '../get_source_file';
 
+import {AbsoluteFsPath} from '../../../../src/ngtsc/file_system/src/types';
 import {toR3DirectiveMeta} from './partial_directive_linker_1';
 import {LinkedDefinition, PartialLinker} from './partial_linker';
 import {extractForwardRef, PLACEHOLDER_VERSION} from './util';
-import {AbsoluteFsPath} from '../../../../src/ngtsc/file_system/src/types';
 
 function makeDirectiveMetadata<TExpression>(
   directiveExpr: AstObject<R3DeclareDirectiveDependencyMetadata, TExpression>,
@@ -68,9 +68,10 @@ function makeDirectiveMetadata<TExpression>(
 /**
  * A `PartialLinker` that is designed to process `ɵɵngDeclareComponent()` call expressions.
  */
-export class PartialComponentLinkerVersion1<TStatement, TExpression>
-  implements PartialLinker<TExpression>
-{
+export class PartialComponentLinkerVersion1<
+  TStatement,
+  TExpression,
+> implements PartialLinker<TExpression> {
   constructor(
     private readonly getSourceFile: GetSourceFileFn,
     private sourceUrl: AbsoluteFsPath,
@@ -103,6 +104,7 @@ export class PartialComponentLinkerVersion1<TStatement, TExpression>
     const enableBlockSyntax = major >= 17 || version === PLACEHOLDER_VERSION;
     const enableLetSyntax =
       major > 18 || (major === 18 && minor >= 1) || version === PLACEHOLDER_VERSION;
+    const hasOnPushByDefault = major >= 22 || version === PLACEHOLDER_VERSION;
 
     const template = parseTemplate(templateInfo.code, templateInfo.sourceUrl, {
       escapedString: templateInfo.isEscaped,
@@ -242,7 +244,9 @@ export class PartialComponentLinkerVersion1<TStatement, TExpression>
         : ViewEncapsulation.Emulated,
       changeDetection: metaObj.has('changeDetection')
         ? parseChangeDetectionStrategy(metaObj.getValue('changeDetection'))
-        : ChangeDetectionStrategy.Default,
+        : hasOnPushByDefault
+          ? ChangeDetectionStrategy.OnPush
+          : ChangeDetectionStrategy.Eager,
       animations: metaObj.has('animations') ? metaObj.getOpaque('animations') : null,
       relativeContextFilePath: this.sourceUrl,
       relativeTemplatePath: null,

packages/compiler-cli/test/ngtsc/ngtsc_spec.ts

@@ -5987,7 +5987,7 @@ runInEachFileSystem((os: string) => {
       expect(messageText).toContain("Value is of type 'string'.");
     });
 
-    it('should handle `changeDetection` field', () => {
+    it('should handle `changeDetection` field with the "default" value: OnPush', () => {
       env.write(
         `test.ts`,
         `
@@ -6003,7 +6003,27 @@ runInEachFileSystem((os: string) => {
 
       env.driveMain();
       const jsContents = env.getContents('test.js');
-      expect(jsContents).toContain('changeDetection: 0');
+      // because this default value is implicit
+      expect(jsContents).not.toContain('changeDetection: 0');
+    });
+
+    it('should handle `changeDetection` field', () => {
+      env.write(
+        `test.ts`,
+        `
+      import {Component, ChangeDetectionStrategy} from '@angular/core';
+      @Component({
+        selector: 'comp-a',
+        template: '...',
+        changeDetection: ChangeDetectionStrategy.Eager
+      })
+      class CompA {}
+    `,
+      );
+
+      env.driveMain();
+      const jsContents = env.getContents('test.js');
+      expect(jsContents).toContain('changeDetection: 1');
     });
 
     it('should throw if `changeDetection` contains invalid value', () => {