⭐️New: Add vue/valid-v-bind-sync rule

README.md

@@ -238,6 +238,7 @@ Enforce all the rules in this category, as well as all higher priority rules, wi
 | :wrench: | [vue/script-indent](./docs/rules/script-indent.md) | enforce consistent indentation in `<script>` |
 | :wrench: | [vue/singleline-html-element-content-newline](./docs/rules/singleline-html-element-content-newline.md) | require a line break before and after the contents of a singleline element |
 |  | [vue/use-v-on-exact](./docs/rules/use-v-on-exact.md) | enforce usage of `exact` modifier on `v-on` |
+|  | [vue/valid-v-bind-sync](./docs/rules/valid-v-bind-sync.md) | enforce valid `.sync` modifier on `v-bind` directives |
 
 ### Deprecated
 

docs/rules/valid-v-bind-sync.md

@@ -0,0 +1,50 @@
+# enforce valid `.sync` modifier on `v-bind` directives (vue/valid-v-bind-sync)
+
+This rule checks whether every `.sync` modifier on `v-bind` directives is valid.
+
+## :book: Rule Details
+
+This rule reports `.sync` modifier on `v-bind` directives in the following cases:
+
+- The `.sync` modifier does not have the attribute value which is valid as LHS. E.g. `<MyComponent v-bind:aaa.sync="foo() + bar()" />`
+- The `.sync` modifier is on non Vue-components. E.g. `<input v-bind:aaa.sync="foo"></div>`
+- The `.sync` modifier's reference is iteration variables. E.g. `<div v-for="x in list"><MyComponent v-bind:aaa.sync="x" /></div>`
+
+This rule does not check syntax errors in directives because it's checked by [no-parsing-error] rule.
+
+:-1: Examples of **incorrect** code for this rule:
+
+```vue
+<MyComponent v-bind:aaa.sync="foo + bar" />
+<MyComponent :aaa.sync="foo + bar" />
+
+<input v-bind:aaa.sync="foo">
+<input :aaa.sync="foo">
+
+<div v-for="todo in todos">
+  <MyComponent v-bind:aaa.sync="todo" />
+  <MyComponent :aaa.sync="todo" />
+</div>
+```
+
+:+1: Examples of **correct** code for this rule:
+
+```vue
+<MyComponent v-bind:aaa.sync="foo"/>
+<MyComponent :aaa.sync="foo"/>
+
+<div v-for="todo in todos">
+  <MyComponent v-bind:aaa.sync="todo.name"/>
+  <MyComponent :aaa.sync="todo.name"/>
+</div>
+```
+
+## :wrench: Options
+
+Nothing.
+
+## :couple: Related rules
+
+- [no-parsing-error]
+
+[no-parsing-error]: no-parsing-error.md

lib/index.js

@@ -56,6 +56,7 @@ module.exports = {
     'v-bind-style': require('./rules/v-bind-style'),
     'v-on-style': require('./rules/v-on-style'),
     'valid-template-root': require('./rules/valid-template-root'),
+    'valid-v-bind-sync': require('./rules/valid-v-bind-sync'),
     'valid-v-bind': require('./rules/valid-v-bind'),
     'valid-v-cloak': require('./rules/valid-v-cloak'),
     'valid-v-else-if': require('./rules/valid-v-else-if'),

lib/rules/valid-v-bind-sync.js

@@ -0,0 +1,136 @@
+/**
+ * @fileoverview enforce valid `.sync` modifier on `v-bind` directives
+ * @author Yosuke Ota
+ */
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+const utils = require('../utils')
+
+// ------------------------------------------------------------------------------
+// Helpers
+// ------------------------------------------------------------------------------
+
+/**
+ * Check whether the given node is valid or not.
+ * @param {ASTNode} node The element node to check.
+ * @returns {boolean} `true` if the node is valid.
+ */
+function isValidElement (node) {
+  if (
+    (!utils.isHtmlElementNode(node) && !utils.isSvgElementNode(node)) ||
+    utils.isHtmlWellKnownElementName(node.rawName) ||
+    utils.isSvgWellKnownElementName(node.rawName)
+  ) {
+    // non Vue-component
+    return false
+  }
+  return true
+}
+
+/**
+ * Check whether the given node can be LHS.
+ * @param {ASTNode} node The node to check.
+ * @returns {boolean} `true` if the node can be LHS.
+ */
+function isLhs (node) {
+  return Boolean(node) && (
+    node.type === 'Identifier' ||
+    node.type === 'MemberExpression'
+  )
+}
+
+/**
+ * Get the variable by names.
+ * @param {string} name The variable name to find.
+ * @param {ASTNode} leafNode The node to look up.
+ * @returns {Variable|null} The found variable or null.
+ */
+function getVariable (name, leafNode) {
+  let node = leafNode
+
+  while (node) {
+    const variables = node.variables
+    const variable = variables && variables.find(v => v.id.name === name)
+
+    if (variable) {
+      return variable
+    }
+
+    node = node.parent
+  }
+
+  return null
+}
+
+// ------------------------------------------------------------------------------
+// Rule Definition
+// ------------------------------------------------------------------------------
+
+module.exports = {
+  meta: {
+    docs: {
+      description: 'enforce valid `.sync` modifier on `v-bind` directives',
+      category: undefined,
+      url: 'https://github.com/vuejs/eslint-plugin-vue/blob/v5.0.0-beta.4/docs/rules/valid-v-bind-sync.md'
+    },
+    fixable: null,
+    schema: [],
+    messages: {
+      unexpectedInvalidElement: "'.sync' modifiers aren't supported on <{{name}}> non Vue-components.",
+      unexpectedNonLhsExpression: "'.sync' modifiers require the attribute value which is valid as LHS.",
+      unexpectedUpdateIterationVariable: "'.sync' modifiers cannot update the iteration variable '{{varName}}' itself."
+    }
+  },
+
+  create (context) {
+    return utils.defineTemplateBodyVisitor(context, {
+      "VAttribute[directive=true][key.name='bind']" (node) {
+        if (node.key.modifiers.indexOf('sync') < 0) {
+          return
+        }
+        const element = node.parent.parent
+        const name = element.name
+
+        if (!isValidElement(element)) {
+          context.report({
+            node,
+            loc: node.loc,
+            messageId: 'unexpectedInvalidElement',
+            data: { name }
+          })
+        }
+
+        if (node.value) {
+          if (!isLhs(node.value.expression)) {
+            context.report({
+              node,
+              loc: node.loc,
+              messageId: 'unexpectedNonLhsExpression'
+            })
+          }
+
+          for (const reference of node.value.references) {
+            const id = reference.id
+            if (id.parent.type !== 'VExpressionContainer') {
+              continue
+            }
+
+            const variable = getVariable(id.name, element)
+            if (variable) {
+              context.report({
+                node,
+                loc: node.loc,
+                messageId: 'unexpectedUpdateIterationVariable',
+                data: { varName: id.name }
+              })
+            }
+          }
+        }
+      }
+    })
+  }
+}