New: no-unused-disable rule

Author: mysticatea

docs/rules/no-unused-disable.md

@@ -0,0 +1,40 @@
+# disallows unused `eslint-disable` comments (eslint-comments/no-unused-disable)
+
+Since refactoring or a bug fix of upstream, an `eslint-disable` directive-comment may become unnecessary.
+In that case, you should remove the garbage as soon as possible since the garbage may cause to overlook ESLint warnings in future.
+
+This rule warns unnecessary `eslint-disable` directive-comments.
+
+## Rule Details
+
+Examples of :-1: **incorrect** code for this rule:
+
+```js
+/*eslint eslint-comments/no-unused-disable: error */
+
+var foo = bar() //eslint-disable-line no-undef,eqeqeq
+                  "※ 'eqeqeq' rule is disabled but never reported."
+```
+
+```js
+/*eslint eslint-comments/no-unused-disable: error */
+/*globals doSomething */
+
+doSomething() //eslint-disable-line
+                "※ ESLint rules are disabled but never reported."
+```
+
+Examples of :+1: **correct** code for this rule:
+
+```js
+/*eslint eslint-comments/no-unused-disable: error */
+
+var foo = bar() //eslint-disable-line no-undef
+```
+
+```js
+/*eslint eslint-comments/no-unused-disable: error */
+/*globals doSomething */
+
+doSomething()
+```

lib/rules/no-unused-disable.js

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+/**
+ * @author Toru Nagashima
+ * @copyright 2016 Toru Nagashima. All rights reserved.
+ * See LICENSE file in root directory for full license.
+ */
+"use strict"
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const DisabledArea = require("../disabled-area")
+const utils = require("../utils")
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        docs: {
+            description: "disallows unused `eslint-disable` comments",
+            category: "Best Practices",
+            recommended: false,
+        },
+        fixable: false,
+        schema: [],
+    },
+
+    create(context) {
+        const originalReport = context.eslint.report
+        const sourceCode = context.getSourceCode()
+        const disabledArea = DisabledArea.get(sourceCode)
+
+        // Override `report` method to mark disabled-area as reported.
+        context.eslint.report = function(ruleId, _severity, node, locationArg) {
+            const location = (typeof locationArg === "string")
+                ? node.loc.start
+                : locationArg.start || locationArg
+
+            disabledArea.report(ruleId, location)
+
+            originalReport.apply(this, arguments)
+        }
+
+        /**
+         * Reports the result.
+         *
+         * @returns {void}
+         */
+        function report() {
+            for (const area of disabledArea.areas) {
+                if (area.reported) {
+                    continue
+                }
+
+                context.report({
+                    loc: utils.toRuleIdLocation(area.comment, area.ruleId),
+                    message: (area.ruleId) ?
+                        "'{{ruleId}}' rule is disabled but never reported." :
+                        "ESLint rules are disabled but never reported.",
+                    data: area,
+                })
+            }
+
+            // Restore
+            context.eslint.report = originalReport
+        }
+
+        return {
+            Program() {
+                // Ensure that this listener is the last in `Program:exit` listeners
+                // even if this rule was initialized before other rules.
+                context.eslint.on("Program:exit", report)
+            },
+        }
+    },
+}