From 5043ec78bcded1dd6f3418cd42d029023dfbe62f Mon Sep 17 00:00:00 2001
From: Nikolay Emrikh <redishko@gmail.com>
Date: Thu, 16 Aug 2018 08:54:50 +0300
Subject: [PATCH] Fixes setter paratemer default value (#8479)

* Fixes setter paratemer default value

* Not changes doesn't mutate loose variable
---
 .../babel-plugin-transform-parameters/src/params.js    |  6 +++---
 .../test/fixtures/parameters/default-setter/exec.js    |  9 +++++++++
 .../test/fixtures/parameters/default-setter/input.js   |  5 +++++
 .../test/fixtures/parameters/default-setter/output.js  | 10 ++++++++++
 4 files changed, 27 insertions(+), 3 deletions(-)
 create mode 100644 packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-setter/exec.js
 create mode 100644 packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-setter/input.js
 create mode 100644 packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-setter/output.js

diff --git a/packages/babel-plugin-transform-parameters/src/params.js b/packages/babel-plugin-transform-parameters/src/params.js
index 391c87160e..000a8505a5 100644
--- a/packages/babel-plugin-transform-parameters/src/params.js
+++ b/packages/babel-plugin-transform-parameters/src/params.js
@@ -60,7 +60,8 @@ export default function convertFunctionParams(path, loose) {
   for (let i = 0; i < params.length; i++) {
     const param = params[i];
 
-    if (param.isAssignmentPattern() && loose) {
+    const paramIsAssignmentPattern = param.isAssignmentPattern();
+    if (paramIsAssignmentPattern && (loose || node.kind === "set")) {
       const left = param.get("left");
       const right = param.get("right");
 
@@ -87,13 +88,12 @@ export default function convertFunctionParams(path, loose) {
         );
         param.replaceWith(paramName);
       }
-    } else if (param.isAssignmentPattern()) {
+    } else if (paramIsAssignmentPattern) {
       if (firstOptionalIndex === null) firstOptionalIndex = i;
 
       const left = param.get("left");
       const right = param.get("right");
 
-      //
       if (!state.iife) {
         if (right.isIdentifier() && !isSafeBinding(scope, right.node)) {
           // the right hand side references a parameter
diff --git a/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-setter/exec.js b/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-setter/exec.js
new file mode 100644
index 0000000000..f11b28a623
--- /dev/null
+++ b/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-setter/exec.js
@@ -0,0 +1,9 @@
+const defaultValue = 1;
+const obj = {
+  set field(num = defaultValue) {
+    this.num = num;
+  }
+};
+obj.field = void 0;
+
+expect(obj.num).toBe(defaultValue);
diff --git a/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-setter/input.js b/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-setter/input.js
new file mode 100644
index 0000000000..d2fd1cdef5
--- /dev/null
+++ b/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-setter/input.js
@@ -0,0 +1,5 @@
+const obj = {
+  set field(num = 1) {
+    this.num = num;
+  }
+};
diff --git a/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-setter/output.js b/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-setter/output.js
new file mode 100644
index 0000000000..d55125d953
--- /dev/null
+++ b/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-setter/output.js
@@ -0,0 +1,10 @@
+var obj = {
+  set field(num) {
+    if (num === void 0) {
+      num = 1;
+    }
+
+    this.num = num;
+  }
+
+};