From 552766955c011618f86c0f39451b9e288383c67a Mon Sep 17 00:00:00 2001
From: Vignesh Shanmugam <vignesh.shanmugam22@gmail.com>
Date: Tue, 1 May 2018 19:40:46 +0200
Subject: [PATCH] fix(merge-sibling-var): recalculate dedeclaratios when
 concatenating variables (#826)

---
 .../src/index.js                              | 16 ++++++++++---
 .../__tests__/minify-env-tests.js             | 23 +++++++++++++++++++
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/packages/babel-plugin-transform-merge-sibling-variables/src/index.js b/packages/babel-plugin-transform-merge-sibling-variables/src/index.js
index ba69d2511..968b248f1 100644
--- a/packages/babel-plugin-transform-merge-sibling-variables/src/index.js
+++ b/packages/babel-plugin-transform-merge-sibling-variables/src/index.js
@@ -57,14 +57,24 @@ module.exports = function({ types: t }) {
 
             let sibling = path.getSibling(path.key + 1);
 
+            let declarations = [];
+
             while (sibling.isVariableDeclaration({ kind: node.kind })) {
-              node.declarations = node.declarations.concat(
-                sibling.node.declarations
-              );
+              declarations = declarations.concat(sibling.node.declarations);
+
               sibling.remove();
 
               sibling = path.getSibling(path.key + 1);
             }
+
+            if (declarations.length > 0) {
+              path.replaceWith(
+                t.variableDeclaration(node.kind, [
+                  ...node.declarations,
+                  ...declarations
+                ])
+              );
+            }
           },
 
           // concat `var` declarations next to for loops with it's initialisers.
diff --git a/packages/babel-preset-minify/__tests__/minify-env-tests.js b/packages/babel-preset-minify/__tests__/minify-env-tests.js
index 8f1f5a24e..20575215e 100644
--- a/packages/babel-preset-minify/__tests__/minify-env-tests.js
+++ b/packages/babel-preset-minify/__tests__/minify-env-tests.js
@@ -158,4 +158,27 @@ describe("preset along with env", () => {
       }
     `
   );
+
+  thePlugin(
+    "should fix issue#825-merge-sibling-vars",
+    `
+    (function() {
+      const blah = 71;
+
+      var start = 1, navx = '';
+      while (start < 71) {
+          navx += 'a';
+          start += 10;
+      }
+      return 'b' + navx;
+    })();
+  `,
+    `
+    (function () {
+      for (var a = 1, b = ''; 71 > a;) b += 'a', a += 10;
+
+      return 'b' + b;
+    })();
+  `
+  );
 });