feat: add eslint plugin no-html-links (#8156)

Co-authored-by: Joshua Chen <sidachen2003@gmail.com>
Co-authored-by: Viktor Malmedal <viktor.malmedal@eniro.com>
Co-authored-by: sebastienlorber <lorber.sebastien@gmail.com>
Co-authored-by: Sébastien Lorber <slorber@users.noreply.github.com>

packages/docusaurus-theme-classic/src/theme/EditThisPage/index.tsx

@@ -8,22 +8,19 @@
 import React from 'react';
 import Translate from '@docusaurus/Translate';
 import {ThemeClassNames} from '@docusaurus/theme-common';
+import Link from '@docusaurus/Link';
 import IconEdit from '@theme/Icon/Edit';
 import type {Props} from '@theme/EditThisPage';
 
 export default function EditThisPage({editUrl}: Props): JSX.Element {
   return (
-    <a
-      href={editUrl}
-      target="_blank"
-      rel="noreferrer noopener"
-      className={ThemeClassNames.common.editThisPage}>
+    <Link to={editUrl} className={ThemeClassNames.common.editThisPage}>
       <IconEdit />
       <Translate
         id="theme.common.editThisPage"
         description="The link label to edit the current page">
         Edit this page
       </Translate>
-    </a>
+    </Link>
   );
 }

packages/docusaurus-theme-classic/src/theme/Heading/index.tsx

@@ -9,6 +9,7 @@ import React from 'react';
 import clsx from 'clsx';
 import {translate} from '@docusaurus/Translate';
 import {useThemeConfig} from '@docusaurus/theme-common';
+import Link from '@docusaurus/Link';
 import type {Props} from '@theme/Heading';
 
 import styles from './styles.module.css';
@@ -34,16 +35,16 @@ export default function Heading({as: As, id, ...props}: Props): JSX.Element {
       )}
       id={id}>
       {props.children}
-      <a
+      <Link
         className="hash-link"
-        href={`#${id}`}
+        to={`#${id}`}
         title={translate({
           id: 'theme.common.headingLinkTitle',
           message: 'Direct link to heading',
           description: 'Title for link to heading',
         })}>
         &#8203;
-      </a>
+      </Link>
     </As>
   );
 }

packages/docusaurus-theme-classic/src/theme/SkipToContent/index.tsx

@@ -7,7 +7,6 @@
 
 import React from 'react';
 import {SkipToContentLink} from '@docusaurus/theme-common';
-
 import styles from './styles.module.css';
 
 export default function SkipToContent(): JSX.Element {

packages/docusaurus-theme-classic/src/theme/TOCItems/Tree.tsx

@@ -6,6 +6,7 @@
  */
 
 import React from 'react';
+import Link from '@docusaurus/Link';
 import type {Props} from '@theme/TOCItems/Tree';
 
 // Recursive component rendering the toc tree
@@ -22,12 +23,10 @@ function TOCItemTree({
     <ul className={isChild ? undefined : className}>
       {toc.map((heading) => (
         <li key={heading.id}>
-          {/* eslint-disable-next-line jsx-a11y/control-has-associated-label */}
-          <a
-            href={`#${heading.id}`}
+          <Link
+            to={`#${heading.id}`}
             className={linkClassName ?? undefined}
             // Developer provided the HTML, so assume it's safe.
-            // eslint-disable-next-line react/no-danger
             dangerouslySetInnerHTML={{__html: heading.value}}
           />
           <TOCItemTree

packages/docusaurus-theme-common/src/utils/skipToContentUtils.tsx

@@ -90,6 +90,7 @@ export function SkipToContentLink(props: SkipToContentLinkProps): JSX.Element {
       ref={containerRef}
       role="region"
       aria-label={DefaultSkipToContentLabel}>
+      {/* eslint-disable-next-line @docusaurus/no-html-links */}
       <a
         {...props}
         // Note this is a fallback href in case JS is disabled

packages/docusaurus-theme-search-algolia/src/theme/SearchPage/index.tsx

@@ -426,10 +426,8 @@ function SearchPageContent(): JSX.Element {
               'text--right',
               styles.searchLogoColumn,
             )}>
-            <a
-              target="_blank"
-              rel="noopener noreferrer"
-              href="https://www.algolia.com/"
+            <Link
+              to="https://www.algolia.com/"
               aria-label={translate({
                 id: 'theme.SearchPage.algoliaLabel',
                 message: 'Search by Algolia',
@@ -451,7 +449,7 @@ function SearchPageContent(): JSX.Element {
                   />
                 </g>
               </svg>
-            </a>
+            </Link>
           </div>
         </div>
 

packages/docusaurus/src/client/exports/Link.tsx

@@ -148,7 +148,7 @@ function Link(
   }
 
   return isRegularHtmlLink ? (
-    // eslint-disable-next-line jsx-a11y/anchor-has-content
+    // eslint-disable-next-line jsx-a11y/anchor-has-content, @docusaurus/no-html-links
     <a
       ref={innerRef}
       href={targetLink}

packages/eslint-plugin/src/index.ts

@@ -14,6 +14,7 @@ export = {
       plugins: ['@docusaurus'],
       rules: {
         '@docusaurus/string-literal-i18n-messages': 'error',
+        '@docusaurus/no-html-links': 'warn',
       },
     },
     all: {
@@ -21,6 +22,7 @@ export = {
       rules: {
         '@docusaurus/string-literal-i18n-messages': 'error',
         '@docusaurus/no-untranslated-text': 'warn',
+        '@docusaurus/no-html-links': 'warn',
       },
     },
   },

packages/eslint-plugin/src/rules/__tests__/no-html-links.test.ts

@@ -0,0 +1,90 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import rule from '../no-html-links';
+import {RuleTester} from './testUtils';
+
+const errorsJSX = [{messageId: 'link'}] as const;
+
+const ruleTester = new RuleTester({
+  parser: '@typescript-eslint/parser',
+  parserOptions: {
+    ecmaFeatures: {
+      jsx: true,
+    },
+  },
+});
+
+ruleTester.run('prefer-docusaurus-link', rule, {
+  valid: [
+    {
+      code: '<Link to="/test">test</Link>',
+    },
+    {
+      code: '<Link to="https://twitter.com/docusaurus">Twitter</Link>',
+    },
+    {
+      code: '<a href="https://twitter.com/docusaurus">Twitter</a>',
+      options: [{ignoreFullyResolved: true}],
+    },
+    {
+      code: '<a href={`https://twitter.com/docusaurus`}>Twitter</a>',
+      options: [{ignoreFullyResolved: true}],
+    },
+    {
+      code: '<a href="mailto:viktor@malmedal.dev">Contact</a>  ',
+      options: [{ignoreFullyResolved: true}],
+    },
+    {
+      code: '<a href="tel:123456789">Call</a>',
+      options: [{ignoreFullyResolved: true}],
+    },
+  ],
+  invalid: [
+    {
+      code: '<a href="/test">test</a>',
+      errors: errorsJSX,
+    },
+    {
+      code: '<a href="https://twitter.com/docusaurus" target="_blank">test</a>',
+      errors: errorsJSX,
+    },
+    {
+      code: '<a href="https://twitter.com/docusaurus" target="_blank" rel="noopener noreferrer">test</a>',
+      errors: errorsJSX,
+    },
+    {
+      code: '<a href="mailto:viktor@malmedal.dev">Contact</a>  ',
+      errors: errorsJSX,
+    },
+    {
+      code: '<a href="tel:123456789">Call</a>',
+      errors: errorsJSX,
+    },
+    {
+      code: '<a href={``}>Twitter</a>',
+      errors: errorsJSX,
+    },
+    {
+      code: '<a href={`https://www.twitter.com/docusaurus`}>Twitter</a>',
+      errors: errorsJSX,
+    },
+    {
+      code: '<a href="www.twitter.com/docusaurus">Twitter</a>',
+      options: [{ignoreFullyResolved: true}],
+      errors: errorsJSX,
+    },
+    {
+      // TODO we might want to make this test pass
+      // Can template literals be statically pre-evaluated? (Babel can do it)
+      // eslint-disable-next-line no-template-curly-in-string
+      code: '<a href={`https://twitter.com/${"docu" + "saurus"} ${"rex"}`}>Twitter</a>',
+      options: [{ignoreFullyResolved: true}],
+      errors: errorsJSX,
+    },
+  ],
+});

packages/eslint-plugin/src/rules/index.ts

@@ -5,10 +5,12 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import noHtmlLinks from './no-html-links';
 import noUntranslatedText from './no-untranslated-text';
 import stringLiteralI18nMessages from './string-literal-i18n-messages';
 
 export default {
   'no-untranslated-text': noUntranslatedText,
   'string-literal-i18n-messages': stringLiteralI18nMessages,
+  'no-html-links': noHtmlLinks,
 };

packages/eslint-plugin/src/rules/no-html-links.ts

@@ -0,0 +1,103 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {createRule} from '../util';
+import type {TSESTree} from '@typescript-eslint/types/dist/ts-estree';
+
+const docsUrl = 'https://docusaurus.io/docs/docusaurus-core#link';
+
+type Options = [
+  {
+    ignoreFullyResolved: boolean;
+  },
+];
+
+type MessageIds = 'link';
+
+function isFullyResolvedUrl(urlString: string): boolean {
+  try {
+    // href gets coerced to a string when it gets rendered anyway
+    const url = new URL(String(urlString));
+    if (url.protocol) {
+      return true;
+    }
+  } catch (e) {}
+  return false;
+}
+
+export default createRule<Options, MessageIds>({
+  name: 'no-html-links',
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'enforce using Docusaurus Link component instead of <a> tag',
+      recommended: false,
+    },
+    schema: [
+      {
+        type: 'object',
+        properties: {
+          ignoreFullyResolved: {
+            type: 'boolean',
+          },
+        },
+        additionalProperties: false,
+      },
+    ],
+    messages: {
+      link: `Do not use an \`<a>\` element to navigate. Use the \`<Link />\` component from \`@docusaurus/Link\` instead. See: ${docsUrl}`,
+    },
+  },
+  defaultOptions: [
+    {
+      ignoreFullyResolved: false,
+    },
+  ],
+
+  create(context, [options]) {
+    const {ignoreFullyResolved} = options;
+
+    return {
+      JSXOpeningElement(node) {
+        if ((node.name as TSESTree.JSXIdentifier).name !== 'a') {
+          return;
+        }
+
+        if (ignoreFullyResolved) {
+          const hrefAttr = node.attributes.find(
+            (attr): attr is TSESTree.JSXAttribute =>
+              attr.type === 'JSXAttribute' && attr.name.name === 'href',
+          );
+
+          if (hrefAttr?.value?.type === 'Literal') {
+            if (isFullyResolvedUrl(String(hrefAttr.value.value))) {
+              return;
+            }
+          }
+          if (hrefAttr?.value?.type === 'JSXExpressionContainer') {
+            const container: TSESTree.JSXExpressionContainer = hrefAttr.value;
+            const {expression} = container;
+            if (expression.type === 'TemplateLiteral') {
+              // Simple static string template literals
+              if (
+                expression.expressions.length === 0 &&
+                expression.quasis.length === 1 &&
+                expression.quasis[0]?.type === 'TemplateElement' &&
+                isFullyResolvedUrl(String(expression.quasis[0].value.raw))
+              ) {
+                return;
+              }
+              // TODO add more complex TemplateLiteral cases here
+            }
+          }
+        }
+
+        context.report({node, messageId: 'link'});
+      },
+    };
+  },
+});