From 98424f80af0354e19881b7df6c4e8d67bd54a2fb Mon Sep 17 00:00:00 2001
From: Henry Zhu <hi@henryzoo.com>
Date: Thu, 11 Jun 2015 21:46:25 -0400
Subject: [PATCH] template-literals: remove unnecessary strings, only add "" to
 beginning if second node isn't a string - fixes #1732

---
 .../transformers/es6/template-literals.js     | 19 ++++++++++++++++---
 .../expression-first/actual.js                |  8 ++++++++
 .../expression-first/expected.js              | 10 ++++++++++
 3 files changed, 34 insertions(+), 3 deletions(-)
 create mode 100644 test/core/fixtures/transformation/es6.template-literals/expression-first/actual.js
 create mode 100644 test/core/fixtures/transformation/es6.template-literals/expression-first/expected.js

diff --git a/src/babel/transformation/transformers/es6/template-literals.js b/src/babel/transformation/transformers/es6/template-literals.js
index 9c65385f43..5c770f7216 100644
--- a/src/babel/transformation/transformers/es6/template-literals.js
+++ b/src/babel/transformation/transformers/es6/template-literals.js
@@ -45,6 +45,10 @@ export function TaggedTemplateExpression(node, parent, scope, file) {
   return t.callExpression(node.tag, args);
 }
 
+function isString(node) {
+  return t.isLiteral(node) && typeof node.value === "string";
+}
+
 export function TemplateLiteral(node, parent, scope, file) {
   var nodes = [];
 
@@ -56,9 +60,18 @@ export function TemplateLiteral(node, parent, scope, file) {
   }
 
   if (nodes.length > 1) {
-    // remove redundant '' at the end of the expression
-    var last = nodes[nodes.length - 1];
-    if (t.isLiteral(last, { value: "" })) nodes.pop();
+    // filter out empty string literals
+    nodes = nodes.filter(n => !t.isLiteral(n, { value: "" }));
+
+    if (nodes.length === 1 && isString(nodes[0])) {
+      return nodes[0];
+    }
+
+    // since `+` is left-to-right associative
+    // ensure the first node is a string if first/second isn't
+    if (!isString(nodes[0]) && !isString(nodes[1])) {
+      nodes.unshift(t.literal(""));
+    }
 
     var root = buildBinaryExpression(nodes.shift(), nodes.shift());
 
diff --git a/test/core/fixtures/transformation/es6.template-literals/expression-first/actual.js b/test/core/fixtures/transformation/es6.template-literals/expression-first/actual.js
new file mode 100644
index 0000000000..ee6e49ef50
--- /dev/null
+++ b/test/core/fixtures/transformation/es6.template-literals/expression-first/actual.js
@@ -0,0 +1,8 @@
+const foo = 5;
+const bar = 10;
+const baz = 15;
+
+const example = `${"a"}`;
+const example2 = `${1}`;
+const example3 = 1 + `${foo}${bar}${baz}`;
+const example4 = 1 + `${foo}bar${baz}`;
diff --git a/test/core/fixtures/transformation/es6.template-literals/expression-first/expected.js b/test/core/fixtures/transformation/es6.template-literals/expression-first/expected.js
new file mode 100644
index 0000000000..5185926b93
--- /dev/null
+++ b/test/core/fixtures/transformation/es6.template-literals/expression-first/expected.js
@@ -0,0 +1,10 @@
+"use strict";
+
+var foo = 5;
+var bar = 10;
+var baz = 15;
+
+var example = "a";
+var example2 = "" + 1;
+var example3 = 1 + ("" + foo + bar + baz);
+var example4 = 1 + (foo + "bar" + baz);