Fixed false negatives when v-for and v-slot mixed or use destruct…

…uring for `vue/no-unused-var` rule. (#1164)

lib/rules/no-unused-vars.js

@@ -6,6 +6,58 @@
 
 const utils = require('../utils')
 
+/**
+ * @typedef {import('vue-eslint-parser').AST.Node} Node
+ * @typedef {import('vue-eslint-parser').AST.VElement} VElement
+ * @typedef {import('vue-eslint-parser').AST.Variable} Variable
+ */
+/**
+ * @typedef {Variable['kind']} VariableKind
+ */
+
+// ------------------------------------------------------------------------------
+// Helpers
+// ------------------------------------------------------------------------------
+
+/**
+ * Groups variables by directive kind.
+ * @param {VElement} node The element node
+ * @returns { { [kind in VariableKind]?: Variable[] } } The variables of grouped by directive kind.
+ */
+function groupingVariables(node) {
+  /** @type { { [kind in VariableKind]?: Variable[] } } */
+  const result = {}
+  for (const variable of node.variables) {
+    const vars = result[variable.kind] || (result[variable.kind] = [])
+    vars.push(variable)
+  }
+  return result
+}
+
+/**
+ * Checks if the given variable was defined by destructuring.
+ * @param {Variable} variable the given variable to check
+ * @returns {boolean} `true` if the given variable was defined by destructuring.
+ */
+function isDestructuringVar(variable) {
+  const node = variable.id
+  /** @type {Node} */
+  let parent = node.parent
+  while (parent) {
+    if (
+      parent.type === 'VForExpression' ||
+      parent.type === 'VSlotScopeExpression'
+    ) {
+      return false
+    }
+    if (parent.type === 'Property' || parent.type === 'ArrayPattern') {
+      return true
+    }
+    parent = parent.parent
+  }
+  return false
+}
+
 // ------------------------------------------------------------------------------
 // Rule Definition
 // ------------------------------------------------------------------------------
@@ -41,38 +93,52 @@ module.exports = {
       ignoreRegEx = new RegExp(ignorePattern, 'u')
     }
     return utils.defineTemplateBodyVisitor(context, {
+      /**
+       * @param {VElement} node
+       */
       VElement(node) {
-        const variables = node.variables
-        for (let i = variables.length - 1; i >= 0; i--) {
-          const variable = variables[i]
+        const vars = groupingVariables(node)
+        for (const variables of Object.values(vars)) {
+          let hasAfterUsed = false
 
-          if (variable.references.length) {
-            break
-          }
+          for (let i = variables.length - 1; i >= 0; i--) {
+            const variable = variables[i]
 
-          if (ignoreRegEx != null && ignoreRegEx.test(variable.id.name)) {
-            continue
-          }
-          context.report({
-            node: variable.id,
-            loc: variable.id.loc,
-            message: `'{{name}}' is defined but never used.`,
-            data: variable.id,
-            suggest:
-              ignorePattern === '^_'
-                ? [
-                    {
-                      desc: `Replace the ${variable.id.name} with _${variable.id.name}`,
-                      fix(fixer) {
-                        return fixer.replaceText(
-                          variable.id,
-                          `_${variable.id.name}`
-                        )
+            if (variable.references.length) {
+              hasAfterUsed = true
+              continue
+            }
+
+            if (ignoreRegEx != null && ignoreRegEx.test(variable.id.name)) {
+              continue
+            }
+
+            if (hasAfterUsed && !isDestructuringVar(variable)) {
+              // If a variable after the variable is used, it will be skipped.
+              continue
+            }
+
+            context.report({
+              node: variable.id,
+              loc: variable.id.loc,
+              message: `'{{name}}' is defined but never used.`,
+              data: variable.id,
+              suggest:
+                ignorePattern === '^_'
+                  ? [
+                      {
+                        desc: `Replace the ${variable.id.name} with _${variable.id.name}`,
+                        fix(fixer) {
+                          return fixer.replaceText(
+                            variable.id,
+                            `_${variable.id.name}`
+                          )
+                        }
                       }
-                    }
-                  ]
-                : []
-          })
+                    ]
+                  : []
+            })
+          }
         }
       }
     })

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

@@ -162,6 +162,58 @@ tester.run('no-unused-vars', rule, {
       code: '<template><div v-for="(a, _i) in foo" ></div></template>',
       options: [{ ignorePattern: '^_' }],
       errors: ["'a' is defined but never used."]
+    },
+    {
+      code:
+        '<template><my-component v-slot="a" >{{d}}</my-component></template>',
+      errors: ["'a' is defined but never used."]
+    },
+    {
+      code:
+        '<template><my-component v-for="i in foo" v-slot="a" >{{a}}</my-component></template>',
+      errors: ["'i' is defined but never used."]
+    },
+    {
+      code:
+        '<template><my-component v-for="i in foo" v-slot="a" >{{i}}</my-component></template>',
+      errors: ["'a' is defined but never used."]
+    },
+    {
+      code:
+        '<template><div v-for="({a, b}, [c, d], e, f) in foo" >{{f}}</div></template>',
+      errors: [
+        "'a' is defined but never used.",
+        "'b' is defined but never used.",
+        "'c' is defined but never used.",
+        "'d' is defined but never used."
+      ]
+    },
+    {
+      code:
+        '<template><div v-for="({a, b}, c, [d], e, f) in foo" >{{f}}</div></template>',
+      errors: [
+        "'a' is defined but never used.",
+        "'b' is defined but never used.",
+        "'d' is defined but never used."
+      ]
+    },
+    {
+      code:
+        '<template><my-component v-slot="{a, b, c, d}" >{{d}}</my-component></template>',
+      errors: [
+        "'a' is defined but never used.",
+        "'b' is defined but never used.",
+        "'c' is defined but never used."
+      ]
+    },
+    {
+      code:
+        '<template><div v-for="({a, b: bar}, c = 1, [d], e, f) in foo" >{{f}}</div></template>',
+      errors: [
+        "'a' is defined but never used.",
+        "'bar' is defined but never used.",
+        "'d' is defined but never used."
+      ]
     }
   ]
 })