From a23ccde36de2b76ea7aa218458fd17a03d4f4a92 Mon Sep 17 00:00:00 2001
From: Matt Lewis <mattlewis92@users.noreply.github.com>
Date: Wed, 6 Feb 2019 04:44:55 +0700
Subject: [PATCH] feat(component-change-detection): add change detection
 strategy rule (#737)

Closes #135
---
 src/componentChangeDetectionRule.ts       | 79 +++++++++++++++++++++++
 src/index.ts                              |  1 +
 test/componentChangeDetectionRule.spec.ts | 47 ++++++++++++++
 3 files changed, 127 insertions(+)
 create mode 100644 src/componentChangeDetectionRule.ts
 create mode 100644 test/componentChangeDetectionRule.spec.ts

diff --git a/src/componentChangeDetectionRule.ts b/src/componentChangeDetectionRule.ts
new file mode 100644
index 000000000..ad5316cf5
--- /dev/null
+++ b/src/componentChangeDetectionRule.ts
@@ -0,0 +1,79 @@
+import { Utils } from 'tslint/lib';
+import * as Lint from 'tslint';
+import * as ts from 'typescript';
+import { getDecoratorArgument, getDecoratorName } from './util/utils';
+import { sprintf } from 'sprintf-js';
+import { NgWalker } from './angular';
+
+export class Rule extends Lint.Rules.AbstractRule {
+  public static metadata: Lint.IRuleMetadata = {
+    ruleName: 'component-change-detection',
+    type: 'functionality',
+    description: 'Enforce the preferred component change detection type as ChangeDetectionStrategy.OnPush.',
+    descriptionDetails: Utils.dedent`
+      See more at https://angular.io/api/core/ChangeDetectionStrategy
+    `,
+    options: null,
+    optionsDescription: 'Not configurable.',
+    rationale: Utils.dedent`
+      By using OnPush for change detection, Angular will only run a change detection cycle when that 
+      components inputs or outputs change
+    `,
+    typescriptOnly: true
+  };
+
+  static CHANGE_DETECTION_INVALID_FAILURE =
+    'The changeDetection value of the component "%s" should be set to ChangeDetectionStrategy.OnPush';
+
+  apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+    return this.applyWithWalker(new ComponentChangeDetectionValidatorWalker(sourceFile, this));
+  }
+}
+
+export class ComponentChangeDetectionValidatorWalker extends NgWalker {
+  constructor(sourceFile: ts.SourceFile, private rule: Rule) {
+    super(sourceFile, rule.getOptions());
+  }
+
+  visitClassDeclaration(node: ts.ClassDeclaration) {
+    ts.createNodeArray(node.decorators).forEach(this.validateDecorator.bind(this, node.name!.text));
+    super.visitClassDeclaration(node);
+  }
+
+  private validateDecorator(className: string, decorator: ts.Decorator) {
+    const argument = getDecoratorArgument(decorator)!;
+    const name = getDecoratorName(decorator);
+
+    // Run only for Components
+    if (name === 'Component') {
+      this.validateComponentChangeDetection(className, decorator, argument);
+    }
+  }
+
+  private validateComponentChangeDetection(className: string, decorator: ts.Decorator, arg: ts.Node) {
+    if (!ts.isObjectLiteralExpression(arg)) {
+      return;
+    }
+
+    const changeDetectionAssignment = arg.properties
+      .filter(prop => ts.isPropertyAssignment(prop) && this.validateProperty(prop))
+      .map(prop => (ts.isPropertyAssignment(prop) ? prop.initializer : undefined))
+      .filter(Boolean)[0] as ts.PropertyAccessExpression;
+
+    if (!changeDetectionAssignment) {
+      this.addFailureAtNode(decorator, sprintf(Rule.CHANGE_DETECTION_INVALID_FAILURE, className));
+    } else {
+      if (!this.validateChangeDetectionType(changeDetectionAssignment!.name.escapedText as string)) {
+        this.addFailureAtNode(changeDetectionAssignment, sprintf(Rule.CHANGE_DETECTION_INVALID_FAILURE, className));
+      }
+    }
+  }
+
+  private validateProperty(p: ts.PropertyAssignment): boolean {
+    return ts.isIdentifier(p.name) && p.name.text === 'changeDetection';
+  }
+
+  private validateChangeDetectionType(changeDetectionValue: string): boolean {
+    return changeDetectionValue === 'OnPush';
+  }
+}
diff --git a/src/index.ts b/src/index.ts
index d9dd0f6cd..c3e49e849 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -39,6 +39,7 @@ export { Rule as UsePipeDecoratorRule } from './usePipeDecoratorRule';
 export { Rule as UsePipeTransformInterfaceRule } from './usePipeTransformInterfaceRule';
 export { Rule as UseViewEncapsulationRule } from './useViewEncapsulationRule';
 export { Rule as RelativePathExternalResourcesRule } from './relativeUrlPrefixRule';
+export { Rule as ComponentChangeDetectionRule } from './componentChangeDetectionRule';
 
 export * from './angular';
 
diff --git a/test/componentChangeDetectionRule.spec.ts b/test/componentChangeDetectionRule.spec.ts
new file mode 100644
index 000000000..862592453
--- /dev/null
+++ b/test/componentChangeDetectionRule.spec.ts
@@ -0,0 +1,47 @@
+import { assertSuccess, assertAnnotated } from './testHelper';
+
+describe('component-change-detection', () => {
+  describe('invalid component change detection', () => {
+    it('should fail when component used without preferred change detection type', () => {
+      let source = `
+        @Component({
+          changeDetection: ChangeDetectionStrategy.Default
+                           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+        })
+        class Test {}
+      `;
+      assertAnnotated({
+        ruleName: 'component-change-detection',
+        message: 'The changeDetection value of the component "Test" should be set to ChangeDetectionStrategy.OnPush',
+        source
+      });
+    });
+
+    it('should fail when component change detection is not set', () => {
+      let source = `
+      @Component({
+      ~~~~~~~~~~~~
+        selector: 'foo'
+      })
+      ~~
+      class Test {}`;
+      assertAnnotated({
+        ruleName: 'component-change-detection',
+        message: 'The changeDetection value of the component "Test" should be set to ChangeDetectionStrategy.OnPush',
+        source
+      });
+    });
+  });
+
+  describe('valid component selector', () => {
+    it('should succeed when a valid change detection strategy is set on @Component', () => {
+      let source = `
+        @Component({
+          changeDetection: ChangeDetectionStrategy.OnPush
+        })
+        class Test {}
+      `;
+      assertSuccess('component-change-detection', source);
+    });
+  });
+});