Add option to show warnings when props could be accessed via this

docs/rules/no-unused-properties.md

@@ -14,7 +14,7 @@ since: v7.0.0
 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 `$refs`) and use in places where the scope cannot be determined.
+This rule cannot check for use of properties by other components (e.g. `mixins`, property access via `$refs`) and use in places where the scope cannot be determined. Some access to properties might be implied, for example accessing data or computed via a variable such as `this[varName]`. In this case, the default is to assume all properties, methods, etc. are 'used'. See the `unreferencedOptions` for a more strict interpretation of 'use' in these cases.
 :::
 
 <eslint-code-block :rules="{'vue/no-unused-properties': ['error']}">
@@ -56,7 +56,8 @@ This rule cannot be checked for use in other components (e.g. `mixins`, Property
   "vue/no-unused-properties": ["error", {
     "groups": ["props"],
     "deepData": false,
-    "ignorePublicMembers": false
+    "ignorePublicMembers": false,
+    "unreferencedOptions": []
   }]
 }
 ```
@@ -69,6 +70,7 @@ This rule cannot be checked for use in other components (e.g. `mixins`, Property
   - `"setup"`
 - `deepData` (`boolean`) If `true`, the object of the property defined in `data` will be searched deeply. Default is `false`. Include `"data"` in `groups` to use this option.
 - `ignorePublicMembers` (`boolean`) If `true`, members marked with a [JSDoc `/** @public */` tag](https://jsdoc.app/tags-public.html) will be ignored. Default is `false`.
+- `unreferencedOptions` (`string[]`) Array of access methods that should be interpreted as leaving properties unreferenced. Currently, two such methods are available: `unknownMemberAsUnreferenced`, and `returnAsUnreferenced`. See examples below.
 
 ### `"groups": ["props", "data"]`
 
@@ -218,6 +220,71 @@ This rule cannot be checked for use in other components (e.g. `mixins`, Property
 
 </eslint-code-block>
 
+### `{ "groups": ["computed"], "unreferencedOptions": ["unknownMemberAsUnreferenced"] }`
+
+<eslint-code-block :rules="{'vue/no-unused-properties': ['error', {groups: ['computed'], unreferencedOptions: ['unknownMemberAsUnreferenced']}]}">
+
+```vue
+<template>
+
+</template>
+<script>
+  export default {
+    computed: {
+      one () {
+        return 1
+      },
+      two () {
+        return 2
+      }
+    },
+    methods: {
+      handler () {
+        /* ✓ GOOD - explicit access to computed */
+        const a = this.one
+        const i = 'two'
+        /* ✗ BAD - unknown access via a variable, two will be reported as unreferenced */
+        return this[i]
+      },
+    }
+  }
+</script>
+```
+
+</eslint-code-block>
+
+### `{ "groups": ["computed"], "unreferencedOptions": ["returnAsUnreferenced"] }`
+
+<eslint-code-block :rules="{'vue/no-unused-properties': ['error', {groups: ['computed'], unreferencedOptions: ['returnAsUnreferenced']}]}">
+
+```vue
+<template>
+
+</template>
+<script>
+  export default {
+    computed: {
+      one () {
+        return 1
+      },
+      two () {
+        return 2
+      }
+    },
+    methods: {
+      handler () {
+        /* ✓ GOOD - explicit access to computed */
+        const a = this.one
+        /* ✗ BAD - any property could be accessed by returning `this`, but two will still be reported as unreferenced */
+        return this
+      },
+    }
+  }
+</script>
+```
+
+</eslint-code-block>
+
 ## :rocket: Version
 
 This rule was introduced in eslint-plugin-vue v7.0.0

lib/rules/no-unused-properties.js

@@ -55,6 +55,9 @@ const GROUP_SETUP = 'setup'
 const GROUP_WATCHER = 'watch'
 const GROUP_EXPOSE = 'expose'
 
+const UNREFERENCED_UNKNOWN_MEMBER = 'unknownMemberAsUnreferenced'
+const UNREFERENCED_RETURN = 'returnAsUnreferenced'
+
 const PROPERTY_LABEL = {
   props: 'property',
   data: 'data',
@@ -206,7 +209,15 @@ module.exports = {
             uniqueItems: true
           },
           deepData: { type: 'boolean' },
-          ignorePublicMembers: { type: 'boolean' }
+          ignorePublicMembers: { type: 'boolean' },
+          unreferencedOptions: {
+            type: 'array',
+            items: {
+              enum: [UNREFERENCED_UNKNOWN_MEMBER, UNREFERENCED_RETURN]
+            },
+            additionalItems: false,
+            uniqueItems: true
+          }
         },
         additionalProperties: false
       }
@@ -221,8 +232,17 @@ module.exports = {
     const groups = new Set(options.groups || [GROUP_PROPERTY])
     const deepData = Boolean(options.deepData)
     const ignorePublicMembers = Boolean(options.ignorePublicMembers)
+    const unreferencedOptions = new Set(options.unreferencedOptions || [])
 
-    const propertyReferenceExtractor = definePropertyReferenceExtractor(context)
+    const propertyReferenceExtractor = definePropertyReferenceExtractor(
+      context,
+      {
+        unknownMemberAsUnreferenced: unreferencedOptions.has(
+          UNREFERENCED_UNKNOWN_MEMBER
+        ),
+        returnAsUnreferenced: unreferencedOptions.has(UNREFERENCED_RETURN)
+      }
+    )
 
     /** @type {TemplatePropertiesContainer} */
     const templatePropertiesContainer = {

lib/utils/property-references.js

@@ -92,7 +92,10 @@ module.exports = {
 /**
  * @param {RuleContext} context The rule context.
  */
-function definePropertyReferenceExtractor(context) {
+function definePropertyReferenceExtractor(
+  context,
+  { unknownMemberAsUnreferenced = false, returnAsUnreferenced = false } = {}
+) {
   /** @type {Map<Expression, IPropertyReferences>} */
   const cacheForExpression = new Map()
   /** @type {Map<Pattern, IPropertyReferences>} */
@@ -314,9 +317,15 @@ function definePropertyReferenceExtractor(context) {
           if (parent.object === node) {
             // `arg.foo`
             const name = utils.getStaticPropertyName(parent)
-            return name
-              ? new PropertyReferencesForMember(parent, name, withInTemplate)
-              : ANY
+            if (name) {
+              return new PropertyReferencesForMember(
+                parent,
+                name,
+                withInTemplate
+              )
+            } else {
+              return unknownMemberAsUnreferenced ? NEVER : ANY
+            }
           }
           return NEVER
         }
@@ -331,12 +340,18 @@ function definePropertyReferenceExtractor(context) {
           return extractFromExpression(parent, withInTemplate)
         }
         case 'ArrowFunctionExpression':
-        case 'ReturnStatement':
         case 'VExpressionContainer':
         case 'Property':
         case 'ArrayExpression': {
           return maybeExternalUsed(parent) ? ANY : NEVER
         }
+        case 'ReturnStatement': {
+          if (returnAsUnreferenced) {
+            return NEVER
+          } else {
+            return maybeExternalUsed(parent) ? ANY : NEVER
+          }
+        }
       }
       return NEVER
     }

tests/lib/rules/no-unused-properties.js

@@ -21,6 +21,33 @@ const allOptions = [
 ]
 const deepDataOptions = [{ groups: ['data'], deepData: true }]
 
+const unreferencedOptions = {
+  // Report errors when accessing via unknown property, e.g. this[varName]
+  unknownMemberAsUnreferenced: [
+    {
+      groups: ['computed'],
+      unreferencedOptions: ['unknownMemberAsUnreferenced']
+    }
+  ],
+  // Report errors when returning this
+  returnAsUnreferenced: [
+    {
+      groups: ['computed'],
+      unreferencedOptions: ['returnAsUnreferenced']
+    }
+  ],
+  // Report all
+  all: [
+    {
+      groups: ['computed'],
+      unreferencedOptions: [
+        'unknownMemberAsUnreferenced',
+        'returnAsUnreferenced'
+      ]
+    }
+  ]
+}
+
 tester.run('no-unused-properties', rule, {
   valid: [
     // a property used in a script expression
@@ -1699,7 +1726,6 @@ tester.run('no-unused-properties', rule, {
       </script>`
     }
   ],
-
   invalid: [
     // unused property
     {
@@ -2803,6 +2829,138 @@ tester.run('no-unused-properties', rule, {
           line: 10
         }
       ]
+    },
+
+    // unreferencedOptions: unknownMemberAsUnreferenced
+    {
+      filename: 'test.vue',
+      code: `
+      <script>
+        export default {
+          computed: {
+            one () {
+              return 1
+            },
+            two () {
+              return 2
+            }
+          },
+          methods: {
+            handler () {
+              const a = this.one
+              const i = 'two'
+              return this[i]
+            },
+          }
+        }
+      </script>`,
+      options: unreferencedOptions.unknownMemberAsUnreferenced,
+      errors: [
+        {
+          message: "'two' of computed property found, but never used.",
+          line: 8
+        }
+      ]
+    },
+    // unreferencedOptions: returnAsUnreferenced
+    {
+      filename: 'test.vue',
+      code: `
+      <script>
+        export default {
+          computed: {
+            one () {
+              return 1
+            },
+            two () {
+              return 2
+            }
+          },
+          methods: {
+            handler () {
+              const a = this.one
+              return this
+            },
+          }
+        }
+      </script>`,
+      options: unreferencedOptions.returnAsUnreferenced,
+      errors: [
+        {
+          message: "'two' of computed property found, but never used.",
+          line: 8
+        }
+      ]
+    },
+    // unreferencedOptions: returnAsUnreferenced via variable with deepData
+    {
+      filename: 'test.vue',
+      code: `
+      <script>
+        export default {
+          data () {
+            return {
+              foo: {
+                bar: 1
+              },
+              baz: 2
+            }
+          },
+          methods: {
+            handler () {
+              const vm = this
+              console.log(vm.baz)
+              return vm.foo
+            },
+          }
+        }
+      </script>
+      `,
+      options: [
+        {
+          groups: ['data'],
+          unreferencedOptions: ['returnAsUnreferenced'],
+          deepData: true
+        }
+      ],
+      errors: [
+        {
+          message: "'foo.bar' of data found, but never used.",
+          line: 7
+        }
+      ]
+    },
+    // unreferencedOptions: all
+    {
+      filename: 'test.vue',
+      code: `
+      <script>
+        export default {
+          computed: {
+            one () {
+              return 1
+            },
+            two () {
+              return 2
+            }
+          },
+          methods: {
+            handler () {
+              const a = this.one
+              const i = 'two'
+              const b = this[i]
+              return this
+            },
+          }
+        }
+      </script>`,
+      options: unreferencedOptions.all,
+      errors: [
+        {
+          message: "'two' of computed property found, but never used.",
+          line: 8
+        }
+      ]
     }
   ]
 })