From d3c2334646eae9287d5be9e457d041e445efb512 Mon Sep 17 00:00:00 2001
From: David Waller <info@krawaller.se>
Date: Sat, 14 Sep 2019 03:03:56 +0200
Subject: [PATCH] Update: flag nested block with declaration as error (#12193)

---
 lib/rules/no-lone-blocks.js       |  7 +++++-
 tests/lib/rules/no-lone-blocks.js | 36 ++++++++++++++++++++++++++++++-
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/lib/rules/no-lone-blocks.js b/lib/rules/no-lone-blocks.js
index 6b51795863b..4365b047861 100644
--- a/lib/rules/no-lone-blocks.js
+++ b/lib/rules/no-lone-blocks.js
@@ -79,7 +79,7 @@ module.exports = {
             }
         };
 
-        // ES6: report blocks without block-level bindings
+        // ES6: report blocks without block-level bindings, or that's only child of another block
         if (context.parserOptions.ecmaVersion >= 6) {
             ruleDef = {
                 BlockStatement(node) {
@@ -91,6 +91,11 @@ module.exports = {
                     if (loneBlocks.length > 0 && loneBlocks[loneBlocks.length - 1] === node) {
                         loneBlocks.pop();
                         report(node);
+                    } else if (
+                        node.parent.type === "BlockStatement" &&
+                        node.parent.body.length === 1
+                    ) {
+                        report(node);
                     }
                 }
             };
diff --git a/tests/lib/rules/no-lone-blocks.js b/tests/lib/rules/no-lone-blocks.js
index 3640a10127f..139e24c9d04 100644
--- a/tests/lib/rules/no-lone-blocks.js
+++ b/tests/lib/rules/no-lone-blocks.js
@@ -56,7 +56,8 @@ ruleTester.run("no-lone-blocks", rule, {
               baz;
             }
           }
-        `
+        `,
+        { code: "function foo() { { const x = 4 } const x = 3 }", parserOptions: { ecmaVersion: 6 } }
     ],
     invalid: [
         { code: "{}", errors: [{ message: "Block is redundant.", type: "BlockStatement" }] },
@@ -118,6 +119,39 @@ ruleTester.run("no-lone-blocks", rule, {
               }
             `,
             errors: [{ message: "Block is redundant.", type: "BlockStatement", line: 4 }]
+        },
+        {
+            code: `
+              function foo () {
+                {
+                  const x = 4;
+                }
+              }
+            `,
+            parserOptions: { ecmaVersion: 6 },
+            errors: [
+                {
+                    message: "Nested block is redundant.",
+                    type: "BlockStatement",
+                    line: 3
+                }
+            ]
+        },
+        {
+            code: `
+              function foo () {
+                {
+                  var x = 4;
+                }
+              }
+            `,
+            errors: [
+                {
+                    message: "Nested block is redundant.",
+                    type: "BlockStatement",
+                    line: 3
+                }
+            ]
         }
     ]
 });