feat(rule): only th element can have scope (#743)

Author: mohammedzamakhan

src/index.ts

@@ -35,6 +35,7 @@ export { Rule as TemplateAccessibilityValidAriaRule } from './templateAccessibil
 export { Rule as TemplatesAccessibilityAnchorContentRule } from './templateAccessibilityAnchorContentRule';
 export { Rule as TemplateClickEventsHaveKeyEventsRule } from './templateClickEventsHaveKeyEventsRule';
 export { Rule as TemplateAccessibilityAltTextRule } from './templateAccessibilityAltTextRule';
+export { Rule as TemplateAccessibilityTableScopeRule } from './templateAccessibilityTableScopeRule';
 export { Rule as TemplatesNoNegatedAsync } from './templatesNoNegatedAsyncRule';
 export { Rule as TemplateNoAutofocusRule } from './templateNoAutofocusRule';
 export { Rule as TrackByFunctionRule } from './trackByFunctionRule';

src/templateAccessibilityTableScopeRule.ts

@@ -0,0 +1,55 @@
+import { ElementAst } from '@angular/compiler';
+import { IRuleMetadata, RuleFailure, Rules, Utils } from 'tslint/lib';
+import { SourceFile } from 'typescript';
+import { NgWalker } from './angular/ngWalker';
+import { BasicTemplateAstVisitor } from './angular';
+
+class TemplateAccessibilityTableScopeVisitor extends BasicTemplateAstVisitor {
+  visitElement(ast: ElementAst, context: any) {
+    this.validateElement(ast);
+    super.visitElement(ast, context);
+  }
+
+  validateElement(element: ElementAst) {
+    if (element.name === 'th') {
+      return;
+    }
+
+    const hasScopeInput = element.inputs.some(input => input.name === 'scope');
+    const hasScopeAttr = element.attrs.some(attr => attr.name === 'scope');
+    if (hasScopeInput || hasScopeAttr) {
+      const {
+        sourceSpan: {
+          end: { offset: endOffset },
+          start: { offset: startOffset }
+        }
+      } = element;
+      this.addFailureFromStartToEnd(startOffset, endOffset, Rule.FAILURE_MESSAGE);
+    }
+  }
+}
+
+export class Rule extends Rules.AbstractRule {
+  static readonly metadata: IRuleMetadata = {
+    description: 'Ensures that scope is not used on any element except th',
+    options: null,
+    optionsDescription: 'Not configurable.',
+    rationale: Utils.dedent`
+    The scope attribute makes table navigation much easier for screen reader users, provided that it is used correctly.
+    If used incorrectly, it can make table navigation much harder and less efficient. (aXe)
+    `,
+    ruleName: 'template-accessibility-table-scope',
+    type: 'functionality',
+    typescriptOnly: true
+  };
+
+  static readonly FAILURE_MESSAGE = 'Scope attribute can only be on <th> element';
+
+  apply(sourceFile: SourceFile): RuleFailure[] {
+    return this.applyWithWalker(
+      new NgWalker(sourceFile, this.getOptions(), {
+        templateVisitorCtrl: TemplateAccessibilityTableScopeVisitor
+      })
+    );
+  }
+}

test/templateAccessibilityTableScopeRule.spec.ts

@@ -0,0 +1,60 @@
+import { Rule } from '../src/templateAccessibilityTableScopeRule';
+import { assertAnnotated, assertSuccess } from './testHelper';
+
+const {
+  FAILURE_MESSAGE,
+  metadata: { ruleName }
+} = Rule;
+
+describe(ruleName, () => {
+  describe('failure', () => {
+    it('should fail when element other than th has scope', () => {
+      const source = `
+        @Component({
+          template: \`
+            <div scope></div>
+            ~~~~~~~~~~~
+          \`
+        })
+        class Bar {}
+      `;
+      assertAnnotated({
+        message: FAILURE_MESSAGE,
+        ruleName,
+        source
+      });
+    });
+
+    it('should fail when element other than th has scope input', () => {
+      const source = `
+        @Component({
+          template: \`
+            <div [attr.scope]="scope"></div>
+            ~~~~~~~~~~~~~~~~~~~~~~~~~~
+          \`
+        })
+        class Bar {}
+      `;
+      assertAnnotated({
+        message: FAILURE_MESSAGE,
+        ruleName,
+        source
+      });
+    });
+  });
+
+  describe('success', () => {
+    it('should work when th has scope', () => {
+      const source = `
+        @Component({
+          template: \`
+            <th scope="col"></th>
+            <th [attr.scope]="col"></th>
+          \`
+        })
+        class Bar {}
+      `;
+      assertSuccess(ruleName, source);
+    });
+  });
+});