Add vue/require-default-export rule (#2494)

Co-authored-by: Flo Edelmann <[email protected]>

docs/rules/index.md

@@ -268,6 +268,7 @@ For example:
 | [vue/prefer-prop-type-boolean-first](./prefer-prop-type-boolean-first.md) | enforce `Boolean` comes first in component prop types | :bulb: | :warning: |
 | [vue/prefer-separate-static-class](./prefer-separate-static-class.md) | require static class names in template to be in a separate `class` attribute | :wrench: | :hammer: |
 | [vue/prefer-true-attribute-shorthand](./prefer-true-attribute-shorthand.md) | require shorthand form attribute when `v-bind` value is `true` | :bulb: | :hammer: |
+| [vue/require-default-export](./require-default-export.md) | require components to be the default export |  | :warning: |
 | [vue/require-direct-export](./require-direct-export.md) | require the component to be directly exported |  | :hammer: |
 | [vue/require-emit-validator](./require-emit-validator.md) | require type definitions in emits | :bulb: | :hammer: |
 | [vue/require-explicit-slots](./require-explicit-slots.md) | require slots to be explicitly defined |  | :warning: |

docs/rules/one-component-per-file.md

@@ -49,6 +49,10 @@ export default {
 
 Nothing.
 
+## :couple: Related Rules
+
+- [vue/require-default-export](./require-default-export.md)
+
 ## :books: Further Reading
 
 - [Style guide - Component files](https://vuejs.org/style-guide/rules-strongly-recommended.html#component-files)

docs/rules/require-default-export.md

@@ -0,0 +1,57 @@
+---
+pageClass: rule-details
+sidebarDepth: 0
+title: vue/require-default-export
+description: require components to be the default export
+---
+
+# vue/require-default-export
+
+> require components to be the default export
+
+- :exclamation: <badge text="This rule has not been released yet." vertical="middle" type="error"> _**This rule has not been released yet.**_ </badge>
+
+## :book: Rule Details
+
+This rule reports when a Vue component does not have a default export, if the component is not defined as `<script setup>`.
+
+<eslint-code-block :rules="{'vue/require-default-export': ['error']}">
+
+```vue
+<!-- ✗ BAD -->
+<script>
+const foo = 'foo';
+</script>
+```
+
+</eslint-code-block>
+
+<eslint-code-block :rules="{'vue/require-default-export': ['error']}">
+
+```vue
+<!-- ✓ GOOD -->
+<script>
+export default {
+  data() {
+    return {
+      foo: 'foo'
+    };
+  }
+};
+</script>
+```
+
+</eslint-code-block>
+
+## :wrench: Options
+
+Nothing.
+
+## :couple: Related Rules
+
+- [vue/one-component-per-file](./one-component-per-file.md)
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/vuejs/eslint-plugin-vue/blob/master/lib/rules/require-default-export.js)
+- [Test source](https://github.com/vuejs/eslint-plugin-vue/blob/master/tests/lib/rules/require-default-export.js)

lib/index.js

@@ -209,6 +209,7 @@ const plugin = {
     'prop-name-casing': require('./rules/prop-name-casing'),
     'quote-props': require('./rules/quote-props'),
     'require-component-is': require('./rules/require-component-is'),
+    'require-default-export': require('./rules/require-default-export'),
     'require-default-prop': require('./rules/require-default-prop'),
     'require-direct-export': require('./rules/require-direct-export'),
     'require-emit-validator': require('./rules/require-emit-validator'),

lib/rules/require-default-export.js

@@ -0,0 +1,68 @@
+/**
+ * @author ItMaga
+ * See LICENSE file in root directory for full license.
+ */
+'use strict'
+
+const utils = require('../utils')
+
+module.exports = {
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'require components to be the default export',
+      categories: undefined,
+      url: 'https://eslint.vuejs.org/rules/require-default-export.html'
+    },
+    fixable: null,
+    schema: [],
+    messages: {
+      missing: 'Missing default export.',
+      mustBeDefaultExport: 'Component must be the default export.'
+    }
+  },
+  /** @param {RuleContext} context */
+  create(context) {
+    const sourceCode = context.getSourceCode()
+    const documentFragment = sourceCode.parserServices.getDocumentFragment?.()
+
+    const hasScript =
+      documentFragment &&
+      documentFragment.children.some(
+        (e) => utils.isVElement(e) && e.name === 'script'
+      )
+
+    if (utils.isScriptSetup(context) || !hasScript) {
+      return {}
+    }
+
+    let hasDefaultExport = false
+    let hasDefinedComponent = false
+
+    return utils.compositingVisitors(
+      utils.defineVueVisitor(context, {
+        onVueObjectExit() {
+          hasDefinedComponent = true
+        }
+      }),
+
+      {
+        'Program > ExportDefaultDeclaration'() {
+          hasDefaultExport = true
+        },
+
+        /**
+         * @param {Program} node
+         */
+        'Program:exit'(node) {
+          if (!hasDefaultExport && node.body.length > 0) {
+            context.report({
+              loc: node.tokens[node.tokens.length - 1].loc,
+              messageId: hasDefinedComponent ? 'mustBeDefaultExport' : 'missing'
+            })
+          }
+        }
+      }
+    )
+  }
+}

tests/lib/rules/require-default-export.js

@@ -0,0 +1,190 @@
+/**
+ * @author ItMaga
+ * See LICENSE file in root directory for full license.
+ */
+'use strict'
+
+const RuleTester = require('../../eslint-compat').RuleTester
+const rule = require('../../../lib/rules/require-default-export')
+
+const tester = new RuleTester({
+  languageOptions: {
+    parser: require('vue-eslint-parser'),
+    ecmaVersion: 2020,
+    sourceType: 'module'
+  }
+})
+
+tester.run('require-default-export', rule, {
+  valid: [
+    {
+      filename: 'test.vue',
+      code: `
+      <template>Without script</template>
+      `
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <script>
+        import { ref } from 'vue';
+        
+        export default {}
+      </script>
+      `
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <script setup>
+        const foo = 'foo';
+      </script>
+      `
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <script>
+      const component = {};
+
+      export default component;
+      </script>
+      `
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <script>
+      import {defineComponent} from 'vue';
+
+      export default defineComponent({});
+      </script>
+      `
+    },
+    {
+      filename: 'test.js',
+      code: `
+      const foo = 'foo';
+      export const bar = 'bar';
+      `
+    },
+    {
+      filename: 'test.js',
+      code: `
+      import {defineComponent} from 'vue';
+      defineComponent({});
+      `
+    }
+  ],
+  invalid: [
+    {
+      filename: 'test.vue',
+      code: `
+      <script>
+      const foo = 'foo';
+      </script>
+      `,
+      errors: [
+        {
+          messageId: 'missing',
+          line: 4,
+          endLine: 4,
+          column: 7,
+          endColumn: 16
+        }
+      ]
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <script>
+      export const foo = 'foo';
+      </script>
+      `,
+      errors: [
+        {
+          messageId: 'missing',
+          line: 4,
+          endLine: 4,
+          column: 7,
+          endColumn: 16
+        }
+      ]
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <script>
+      const foo = 'foo';
+
+      export { foo };
+      </script>
+      `,
+      errors: [
+        {
+          messageId: 'missing',
+          line: 6,
+          endLine: 6,
+          column: 7,
+          endColumn: 16
+        }
+      ]
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <script>
+      export const foo = 'foo';
+      export const bar = 'bar';
+      </script>
+      `,
+      errors: [
+        {
+          messageId: 'missing',
+          line: 5,
+          endLine: 5,
+          column: 7,
+          endColumn: 16
+        }
+      ]
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <script>
+      import { defineComponent } from 'vue';
+
+      export const component = defineComponent({});
+      </script>
+      `,
+      errors: [
+        {
+          messageId: 'mustBeDefaultExport',
+          line: 6,
+          endLine: 6,
+          column: 7,
+          endColumn: 16
+        }
+      ]
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <script>
+      import Vue from 'vue';
+
+      const component = Vue.component('foo', {});
+      </script>
+      `,
+      errors: [
+        {
+          messageId: 'mustBeDefaultExport',
+          line: 6,
+          endLine: 6,
+          column: 7,
+          endColumn: 16
+        }
+      ]
+    }
+  ]
+})