From 4293229709dde105692347241513766e953664dd Mon Sep 17 00:00:00 2001
From: Milos Djermanovic <milos.djermanovic@gmail.com>
Date: Fri, 14 Feb 2020 16:52:28 +0100
Subject: [PATCH] Breaking: use-isnan enforceForSwitchCase default `true`
 (fixes #12810) (#12913)

---
 docs/rules/use-isnan.md      | 36 ++++++++++++++++++++++++++++++------
 lib/rules/use-isnan.js       |  4 ++--
 tests/lib/rules/use-isnan.js | 28 ++++++++++++++++++----------
 3 files changed, 50 insertions(+), 18 deletions(-)

diff --git a/docs/rules/use-isnan.md b/docs/rules/use-isnan.md
index 0d75251e440..ae9fefe36af 100644
--- a/docs/rules/use-isnan.md
+++ b/docs/rules/use-isnan.md
@@ -45,17 +45,15 @@ if (!isNaN(foo)) {
 
 This rule has an object option, with two options:
 
-* `"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)`.
-* `"enforceForIndexOf"` when set to `true` disallows the use of `indexOf` and `lastIndexOf` methods with `NaN`. Default is `false`, meaning that this rule by default does not warn about `indexOf(NaN)` or `lastIndexOf(NaN)` method calls.
+* `"enforceForSwitchCase": true` (default) additionally disallows `case NaN` and `switch(NaN)` in `switch` statements.
+* `"enforceForIndexOf": true` additionally disallows the use of `indexOf` and `lastIndexOf` methods with `NaN`. Default is `false`, meaning that this rule by default does not warn about `indexOf(NaN)` or `lastIndexOf(NaN)` method calls.
 
 ### 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`:
+Examples of **incorrect** code for this rule with `"enforceForSwitchCase"` option set to `true` (default):
 
 ```js
 /*eslint use-isnan: ["error", {"enforceForSwitchCase": true}]*/
@@ -81,7 +79,7 @@ switch (NaN) {
 }
 ```
 
-Examples of **correct** code for this rule with `"enforceForSwitchCase"` option set to `true`:
+Examples of **correct** code for this rule with `"enforceForSwitchCase"` option set to `true` (default):
 
 ```js
 /*eslint use-isnan: ["error", {"enforceForSwitchCase": true}]*/
@@ -104,6 +102,32 @@ if (Number.isNaN(a)) {
 } // ...
 ```
 
+Examples of **correct** code for this rule with `"enforceForSwitchCase"` option set to `false`:
+
+```js
+/*eslint use-isnan: ["error", {"enforceForSwitchCase": false}]*/
+
+switch (foo) {
+    case NaN:
+        bar();
+        break;
+    case 1:
+        baz();
+        break;
+    // ...
+}
+
+switch (NaN) {
+    case a:
+        bar();
+        break;
+    case b:
+        baz();
+        break;
+    // ...
+}
+```
+
 ### enforceForIndexOf
 
 The following methods internally use the `===` comparison to match the given value with an array element:
diff --git a/lib/rules/use-isnan.js b/lib/rules/use-isnan.js
index cd9ccdbaf89..7b466be75f2 100644
--- a/lib/rules/use-isnan.js
+++ b/lib/rules/use-isnan.js
@@ -45,7 +45,7 @@ module.exports = {
                 properties: {
                     enforceForSwitchCase: {
                         type: "boolean",
-                        default: false
+                        default: true
                     },
                     enforceForIndexOf: {
                         type: "boolean",
@@ -66,7 +66,7 @@ module.exports = {
 
     create(context) {
 
-        const enforceForSwitchCase = context.options[0] && context.options[0].enforceForSwitchCase;
+        const enforceForSwitchCase = !context.options[0] || context.options[0].enforceForSwitchCase;
         const enforceForIndexOf = context.options[0] && context.options[0].enforceForIndexOf;
 
         /**
diff --git a/tests/lib/rules/use-isnan.js b/tests/lib/rules/use-isnan.js
index e494fc014ad..aa1b1746fcd 100644
--- a/tests/lib/rules/use-isnan.js
+++ b/tests/lib/rules/use-isnan.js
@@ -41,16 +41,6 @@ ruleTester.run("use-isnan", rule, {
         // enforceForSwitchCase
         //------------------------------------------------------------------------------
 
-        "switch(NaN) { case foo: break; }",
-        "switch(foo) { case NaN: break; }",
-        {
-            code: "switch(NaN) { case foo: break; }",
-            options: [{}]
-        },
-        {
-            code: "switch(foo) { case NaN: break; }",
-            options: [{}]
-        },
         {
             code: "switch(NaN) { case foo: break; }",
             options: [{ enforceForSwitchCase: false }]
@@ -282,6 +272,24 @@ ruleTester.run("use-isnan", rule, {
         // enforceForSwitchCase
         //------------------------------------------------------------------------------
 
+        {
+            code: "switch(NaN) { case foo: break; }",
+            errors: [{ messageId: "switchNaN", type: "SwitchStatement", column: 1 }]
+        },
+        {
+            code: "switch(foo) { case NaN: break; }",
+            errors: [{ messageId: "caseNaN", type: "SwitchCase", column: 15 }]
+        },
+        {
+            code: "switch(NaN) { case foo: break; }",
+            options: [{}],
+            errors: [{ messageId: "switchNaN", type: "SwitchStatement", column: 1 }]
+        },
+        {
+            code: "switch(foo) { case NaN: break; }",
+            options: [{}],
+            errors: [{ messageId: "caseNaN", type: "SwitchCase", column: 15 }]
+        },
         {
             code: "switch(NaN) {}",
             options: [{ enforceForSwitchCase: true }],