From b146b51b6f5d39a56274dcac6f92295366274ca9 Mon Sep 17 00:00:00 2001
From: Sean Gray <sgray@DigitalPrimates.net>
Date: Mon, 23 Sep 2019 18:03:55 -0500
Subject: [PATCH] Fix: no-constant-condition doesn't introspect arrays (fixes
 #12225)

---
 lib/rules/no-constant-condition.js       | 16 ++++++++++++++-
 tests/lib/rules/no-constant-condition.js | 26 ++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/lib/rules/no-constant-condition.js b/lib/rules/no-constant-condition.js
index d6d04174298c..06c35f6aab45 100644
--- a/lib/rules/no-constant-condition.js
+++ b/lib/rules/no-constant-condition.js
@@ -90,14 +90,28 @@ module.exports = {
          * @private
          */
         function isConstant(node, inBooleanPosition) {
+
+            /*
+             * Bug in espree (#425) causes [,] to return children of null
+             * so we need to check for existance until that is fixed
+             */
+            if (!node) {
+                return true;
+            }
             switch (node.type) {
                 case "Literal":
                 case "ArrowFunctionExpression":
                 case "FunctionExpression":
                 case "ObjectExpression":
-                case "ArrayExpression":
                     return true;
 
+                case "ArrayExpression": {
+                    if (inBooleanPosition) {
+                        return true;
+                    }
+                    return node.elements.every(element => isConstant(element, false));
+                }
+
                 case "UnaryExpression":
                     if (node.operator === "void") {
                         return true;
diff --git a/tests/lib/rules/no-constant-condition.js b/tests/lib/rules/no-constant-condition.js
index a5ede35cc8ea..cfc2134eb4b2 100644
--- a/tests/lib/rules/no-constant-condition.js
+++ b/tests/lib/rules/no-constant-condition.js
@@ -73,6 +73,14 @@ ruleTester.run("no-constant-condition", rule, {
         "if ((key || 'k') in obj) {}",
         "if ((foo || {}) instanceof obj) {}",
 
+        // #12225
+        "if ('' + [y] === '' + [ty]) {}",
+        "if ('a' === '' + [ty]) {}",
+        "if ('' + [y, m, d] === 'a') {}",
+        "if ('' + [y, 'm'] === '' + [ty, 'tm']) {}",
+        "if ('' + [y, 'm'] === '' + ['ty']) {}",
+        "if ([,] in\n\n($2))\n ;\nelse\n ;",
+
         // { checkLoops: false }
         { code: "while(true);", options: [{ checkLoops: false }] },
         { code: "for(;true;);", options: [{ checkLoops: false }] },
@@ -183,6 +191,24 @@ ruleTester.run("no-constant-condition", rule, {
         {
             code: "function* foo() { for (let foo = 1 + 2 + 3 + (yield); true; baz) {}}",
             errors: [{ messageId: "unexpected", type: "Literal" }]
+        },
+
+        // #12225
+        {
+            code: "if([a]) {}",
+            errors: [{ messageId: "unexpected", type: "ArrayExpression" }]
+        },
+        {
+            code: "if([]) {}",
+            errors: [{ messageId: "unexpected", type: "ArrayExpression" }]
+        },
+        {
+            code: "if(''+['a']) {}",
+            errors: [{ messageId: "unexpected", type: "BinaryExpression" }]
+        },
+        {
+            code: "if(''+[]) {}",
+            errors: [{ messageId: "unexpected", type: "BinaryExpression" }]
         }
     ]
 });