From 22258923488242498ea504482dcb8fe56d88371b Mon Sep 17 00:00:00 2001
From: Peeyush Kushwaha <peeyush.p97@gmail.com>
Date: Tue, 25 Jul 2017 00:13:17 +0530
Subject: [PATCH] Use first binding for multiple var declarations (#5745)

* Use first binding for multiple var declarations
Since var declarations after initial binding have no effect, use the
first declaration. Fixes #2378

* Include hoisted function bindings

* Missing newline in expected.js

* Simplify constantViolations in new Binding on existing

* clarify comment language
---
 packages/babel-traverse/src/scope/binding.js     | 16 ++++++++--------
 .../rename/parameter-redeclaration/actual.js     | 11 +++++++++++
 .../rename/parameter-redeclaration/expected.js   | 12 ++++++++++++
 .../rename/parameter-redeclaration/options.json  |  3 +++
 .../rename/parameter-redeclaration/plugin.js     |  9 +++++++++
 5 files changed, 43 insertions(+), 8 deletions(-)
 create mode 100644 packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/actual.js
 create mode 100644 packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/expected.js
 create mode 100644 packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/options.json
 create mode 100644 packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/plugin.js

diff --git a/packages/babel-traverse/src/scope/binding.js b/packages/babel-traverse/src/scope/binding.js
index 694becff86..3c5c645dfb 100644
--- a/packages/babel-traverse/src/scope/binding.js
+++ b/packages/babel-traverse/src/scope/binding.js
@@ -13,6 +13,14 @@ import type NodePath from "../path";
 
 export default class Binding {
   constructor({ existing, identifier, scope, path, kind }) {
+    // this if condition is true only if the re-binding does not result in an error
+    // e.g. if rebinding kind is 'var' or 'hoisted', and previous was 'param'
+    if (existing) {
+      // we maintain the original binding but update constantViolations
+      existing.constantViolations = existing.constantViolations.concat(path);
+      return existing;
+    }
+
     this.identifier = identifier;
     this.scope = scope;
     this.path = path;
@@ -26,14 +34,6 @@ export default class Binding {
     this.references = 0;
 
     this.clearValue();
-
-    if (existing) {
-      this.constantViolations = [].concat(
-        existing.path,
-        existing.constantViolations,
-        this.constantViolations,
-      );
-    }
   }
 
   constantViolations: Array<NodePath>;
diff --git a/packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/actual.js b/packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/actual.js
new file mode 100644
index 0000000000..9f0435f951
--- /dev/null
+++ b/packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/actual.js
@@ -0,0 +1,11 @@
+function f(a, b) {
+  var a = "redeclared";
+  return b;
+}
+
+function g(a) {
+  function a() {
+    return "function, redeclared";
+  }
+  return a();
+}
diff --git a/packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/expected.js b/packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/expected.js
new file mode 100644
index 0000000000..64957cbe2c
--- /dev/null
+++ b/packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/expected.js
@@ -0,0 +1,12 @@
+function f(z, b) {
+  var z = "redeclared";
+  return b;
+}
+
+function g(z) {
+  function z() {
+    return "function, redeclared";
+  }
+
+  return z();
+}
diff --git a/packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/options.json b/packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/options.json
new file mode 100644
index 0000000000..14af0e5fea
--- /dev/null
+++ b/packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/options.json
@@ -0,0 +1,3 @@
+{
+  "plugins": ["./plugin"]
+}
diff --git a/packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/plugin.js b/packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/plugin.js
new file mode 100644
index 0000000000..4cc132b829
--- /dev/null
+++ b/packages/babel-traverse/test/fixtures/rename/parameter-redeclaration/plugin.js
@@ -0,0 +1,9 @@
+module.exports = function() {
+  return {
+    visitor: {
+      Function(path) {
+        path.scope.rename("a", "z");
+      }
+    }
+  };
+}