Update: Add enforceForSwitchCase option to use-isnan (#12106)

docs/rules/use-isnan.md

@@ -40,3 +40,66 @@ if (!isNaN(foo)) {
     // ...
 }
 ```
+
+## Options
+
+This rule has an object option, with one option:
+
+* `"enforceForSwitchCase"` when set to `true` disallows `case NaN` and `switch(NaN)` in `switch` statements. Default is `false`, meaning
+that this rule by default does not warn about `case NaN` or `switch(NaN)`.
+
+### enforceForSwitchCase
+
+The `switch` statement internally uses the `===` comparison to match the expression's value to a case clause.
+Therefore, it can never match `case NaN`. Also, `switch(NaN)` can never match a case clause.
+
+Set `"enforceForSwitchCase"` to `true` if you want this rule to report `case NaN` and `switch(NaN)` in `switch` statements.
+
+Examples of **incorrect** code for this rule with `"enforceForSwitchCase"` option set to `true`:
+
+```js
+/*eslint use-isnan: ["error", {"enforceForSwitchCase": true}]*/
+
+switch (foo) {
+    case NaN:
+        bar();
+        break;
+    case 1:
+        baz();
+        break;
+    // ...
+}
+
+switch (NaN) {
+    case a:
+        bar();
+        break;
+    case b:
+        baz();
+        break;
+    // ...
+}
+```
+
+Examples of **correct** code for this rule with `"enforceForSwitchCase"` option set to `true`:
+
+```js
+/*eslint use-isnan: ["error", {"enforceForSwitchCase": true}]*/
+
+if (Number.isNaN(foo)) {
+    bar();
+} else {
+    switch (foo) {
+        case 1:
+            baz();
+            break;
+        // ...
+    }
+}
+
+if (Number.isNaN(a)) {
+    bar();
+} else if (Number.isNaN(b)) {
+    baz();
+} // ...
+```

lib/rules/use-isnan.js

@@ -5,6 +5,19 @@
 
 "use strict";
 
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+/**
+ * Determines if the given node is a NaN `Identifier` node.
+ * @param {ASTNode|null} node The node to check.
+ * @returns {boolean} `true` if the node is 'NaN' identifier.
+ */
+function isNaNIdentifier(node) {
+    return Boolean(node) && node.type === "Identifier" && node.name === "NaN";
+}
+
 //------------------------------------------------------------------------------
 // Rule Definition
 //------------------------------------------------------------------------------
@@ -20,21 +33,69 @@ module.exports = {
             url: "https://eslint.org/docs/rules/use-isnan"
         },
 
-        schema: [],
+        schema: [
+            {
+                type: "object",
+                properties: {
+                    enforceForSwitchCase: {
+                        type: "boolean",
+                        default: false
+                    }
+                },
+                additionalProperties: false
+            }
+        ],
+
         messages: {
-            useIsNaN: "Use the isNaN function to compare with NaN."
+            comparisonWithNaN: "Use the isNaN function to compare with NaN.",
+            switchNaN: "'switch(NaN)' can never match a case clause. Use Number.isNaN instead of the switch.",
+            caseNaN: "'case NaN' can never match. Use Number.isNaN before the switch."
         }
     },
 
     create(context) {
 
-        return {
-            BinaryExpression(node) {
-                if (/^(?:[<>]|[!=]=)=?$/u.test(node.operator) && (node.left.name === "NaN" || node.right.name === "NaN")) {
-                    context.report({ node, messageId: "useIsNaN" });
+        const enforceForSwitchCase = context.options[0] && context.options[0].enforceForSwitchCase;
+
+        /**
+         * Checks the given `BinaryExpression` node.
+         * @param {ASTNode} node The node to check.
+         * @returns {void}
+         */
+        function checkBinaryExpression(node) {
+            if (
+                /^(?:[<>]|[!=]=)=?$/u.test(node.operator) &&
+                (isNaNIdentifier(node.left) || isNaNIdentifier(node.right))
+            ) {
+                context.report({ node, messageId: "comparisonWithNaN" });
+            }
+        }
+
+        /**
+         * Checks the discriminant and all case clauses of the given `SwitchStatement` node.
+         * @param {ASTNode} node The node to check.
+         * @returns {void}
+         */
+        function checkSwitchStatement(node) {
+            if (isNaNIdentifier(node.discriminant)) {
+                context.report({ node, messageId: "switchNaN" });
+            }
+
+            for (const switchCase of node.cases) {
+                if (isNaNIdentifier(switchCase.test)) {
+                    context.report({ node: switchCase, messageId: "caseNaN" });
                 }
             }
+        }
+
+        const listeners = {
+            BinaryExpression: checkBinaryExpression
         };
 
+        if (enforceForSwitchCase) {
+            listeners.SwitchStatement = checkSwitchStatement;
+        }
+
+        return listeners;
     }
 };