Add vue/no-unused-properties rule (from #871) (#1145)

* New: add vue/no-unused-properties rule (#631)

* Update

* Updated to trace function calls.

Co-authored-by: Michaela Robosova <[email protected]>

Author: ota-meshi

Diff for: docs/rules/README.md

@@ -295,6 +295,7 @@ For example:
 | [vue/no-template-target-blank](./no-template-target-blank.md) | disallow target="_blank" attribute without rel="noopener noreferrer" |  |
 | [vue/no-unregistered-components](./no-unregistered-components.md) | disallow using components that are not registered inside templates |  |
 | [vue/no-unsupported-features](./no-unsupported-features.md) | disallow unsupported Vue.js syntax on the specified version | :wrench: |
+| [vue/no-unused-properties](./no-unused-properties.md) | disallow unused properties |  |
 | [vue/object-curly-spacing](./object-curly-spacing.md) | enforce consistent spacing inside braces | :wrench: |
 | [vue/padding-line-between-blocks](./padding-line-between-blocks.md) | require or disallow padding lines between blocks | :wrench: |
 | [vue/prefer-template](./prefer-template.md) | require template literals instead of string concatenation | :wrench: |

Diff for: docs/rules/no-unused-properties.md

@@ -0,0 +1,164 @@
+---
+pageClass: rule-details
+sidebarDepth: 0
+title: vue/no-unused-properties
+description: disallow unused properties
+---
+# vue/no-unused-properties
+> disallow unused properties
+
+## :book: Rule Details
+
+This rule is aimed at eliminating unused properties.
+
+::: warning Note
+This rule cannot be checked for use in other components (e.g. `mixins`, Property access via `$refs`) and use in places where the scope cannot be determined.
+:::
+
+<eslint-code-block :rules="{'vue/no-unused-properties': ['error']}">
+
+```vue
+<!-- ✓ GOOD -->
+<template>
+  <div>{{ count }}</div>
+</template>
+<script>
+  export default {
+    props: ['count']
+  }
+</script>
+```
+
+</eslint-code-block>
+
+<eslint-code-block :rules="{'vue/no-unused-properties': ['error']}">
+
+```vue
+<!-- ✗ BAD (`count` property not used) -->
+<template>
+  <div>{{ cnt }}</div>
+</template>
+<script>
+  export default {
+    props: ['count']
+  }
+</script>
+```
+
+</eslint-code-block>
+
+## :wrench: Options
+
+```json
+{
+  "vue/no-unused-properties": ["error", {
+    "groups": ["props"]
+  }]
+}
+```
+
+- `"groups"` (`string[]`) Array of groups to search for properties. Default is `["props"]`. The value of the array is some of the following strings:
+  - `"props"`
+  - `"data"`
+  - `"computed"`
+  - `"methods"`
+  - `"setup"`
+
+### `"groups": ["props", "data"]`
+
+<eslint-code-block :rules="{'vue/no-unused-properties': ['error', {groups: ['props', 'data']}]}">
+
+```vue
+<!-- ✓ GOOD -->
+<script>
+  export default {
+    data() {
+      return {
+        count: null
+      }
+    },
+    created() {
+      this.count = 2
+    }
+  }
+</script>
+```
+
+</eslint-code-block>
+
+<eslint-code-block :rules="{'vue/no-unused-properties': ['error', {groups: ['props', 'data']}]}">
+
+```vue
+<!-- ✓ BAD (`count` data not used) -->
+<script>
+  export default {
+    data() {
+      return {
+        count: null
+      }
+    },
+    created() {
+      this.cnt = 2
+    }
+  }
+</script>
+```
+
+</eslint-code-block>
+
+### `"groups": ["props", "computed"]`
+
+<eslint-code-block :rules="{'vue/no-unused-properties': ['error', {groups: ['props', 'computed']}]}">
+
+```vue
+<!-- ✓ GOOD -->
+<template>
+  <p>{{ reversedMessage }}</p>
+</template>
+<script>
+  export default {
+    data() {
+      return {
+        message: 'Hello'
+      }
+    },
+    computed: {
+      reversedMessage() {
+        return this.message.split('').reverse().join('')
+      }
+    }
+  }
+</script>
+```
+
+</eslint-code-block>
+
+<eslint-code-block :rules="{'vue/no-unused-properties': ['error', {groups: ['props', 'computed']}]}">
+
+```vue
+<!-- ✓ BAD (`reversedMessage` computed property not used) -->
+<template>
+  <p>{{ message }}</p>
+</template>
+<script>
+  export default {
+    data() {
+      return {
+        message: 'Hello'
+      }
+    },
+    computed: {
+      reversedMessage() {
+        return this.message.split('').reverse().join('')
+      }
+    }
+  }
+</script>
+```
+
+</eslint-code-block>
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/vuejs/eslint-plugin-vue/blob/master/lib/rules/no-unused-properties.js)
+- [Test source](https://github.com/vuejs/eslint-plugin-vue/blob/master/tests/lib/rules/no-unused-properties.js)

Diff for: lib/index.js

@@ -84,6 +84,7 @@ module.exports = {
     'no-unregistered-components': require('./rules/no-unregistered-components'),
     'no-unsupported-features': require('./rules/no-unsupported-features'),
     'no-unused-components': require('./rules/no-unused-components'),
+    'no-unused-properties': require('./rules/no-unused-properties'),
     'no-unused-vars': require('./rules/no-unused-vars'),
     'no-use-v-if-with-v-for': require('./rules/no-use-v-if-with-v-for'),
     'no-v-html': require('./rules/no-v-html'),