From 61ebcb49c7808030b78b01e0c85039a79290cf4b Mon Sep 17 00:00:00 2001
From: "Diogo Franco (Kovensky)" <diogomfranco@gmail.com>
Date: Fri, 17 Mar 2017 10:25:37 +0900
Subject: [PATCH] Allow exporting a binding before its declaration

---
 src/compiler/checker.ts                       |  7 +++++++
 tests/baselines/reference/exportBinding.js    | 19 +++++++++++++++++++
 .../baselines/reference/exportBinding.symbols | 14 ++++++++++++++
 tests/baselines/reference/exportBinding.types | 15 +++++++++++++++
 .../conformance/es6/modules/exportBinding.ts  |  5 +++++
 5 files changed, 60 insertions(+)
 create mode 100644 tests/baselines/reference/exportBinding.js
 create mode 100644 tests/baselines/reference/exportBinding.symbols
 create mode 100644 tests/baselines/reference/exportBinding.types
 create mode 100644 tests/cases/conformance/es6/modules/exportBinding.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 00498191f287a..736b3154fbc03 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -742,6 +742,13 @@ namespace ts {
             // declaration is after usage, but it can still be legal if usage is deferred:
             // 1. inside a function
             // 2. inside an instance property initializer, a reference to a non-instance property
+            // 3. inside an export specifier
+
+            if (usage.parent.kind === SyntaxKind.ExportSpecifier) {
+                // export specifiers do not use the variable, they only make it available for use
+                return true;
+            }
+
             const container = getEnclosingBlockScopeContainer(declaration);
             const isInstanceProperty = declaration.kind === SyntaxKind.PropertyDeclaration && !(getModifierFlags(declaration) & ModifierFlags.Static);
             return isUsedInFunctionOrInstanceProperty(usage, isInstanceProperty, container);
diff --git a/tests/baselines/reference/exportBinding.js b/tests/baselines/reference/exportBinding.js
new file mode 100644
index 0000000000000..5059c5356a376
--- /dev/null
+++ b/tests/baselines/reference/exportBinding.js
@@ -0,0 +1,19 @@
+//// [exportBinding.ts]
+export { x }
+const x = 'x'
+
+export { Y as Z }
+class Y {}
+
+
+//// [exportBinding.js]
+"use strict";
+exports.__esModule = true;
+var x = 'x';
+exports.x = x;
+var Y = (function () {
+    function Y() {
+    }
+    return Y;
+}());
+exports.Z = Y;
diff --git a/tests/baselines/reference/exportBinding.symbols b/tests/baselines/reference/exportBinding.symbols
new file mode 100644
index 0000000000000..cb3b58a5776a2
--- /dev/null
+++ b/tests/baselines/reference/exportBinding.symbols
@@ -0,0 +1,14 @@
+=== tests/cases/conformance/es6/modules/exportBinding.ts ===
+export { x }
+>x : Symbol(x, Decl(exportBinding.ts, 0, 8))
+
+const x = 'x'
+>x : Symbol(x, Decl(exportBinding.ts, 1, 5))
+
+export { Y as Z }
+>Y : Symbol(Z, Decl(exportBinding.ts, 3, 8))
+>Z : Symbol(Z, Decl(exportBinding.ts, 3, 8))
+
+class Y {}
+>Y : Symbol(Y, Decl(exportBinding.ts, 3, 17))
+
diff --git a/tests/baselines/reference/exportBinding.types b/tests/baselines/reference/exportBinding.types
new file mode 100644
index 0000000000000..e2553ba1eaa58
--- /dev/null
+++ b/tests/baselines/reference/exportBinding.types
@@ -0,0 +1,15 @@
+=== tests/cases/conformance/es6/modules/exportBinding.ts ===
+export { x }
+>x : "x"
+
+const x = 'x'
+>x : "x"
+>'x' : "x"
+
+export { Y as Z }
+>Y : typeof Y
+>Z : typeof Y
+
+class Y {}
+>Y : Y
+
diff --git a/tests/cases/conformance/es6/modules/exportBinding.ts b/tests/cases/conformance/es6/modules/exportBinding.ts
new file mode 100644
index 0000000000000..1e6b0314f0bd0
--- /dev/null
+++ b/tests/cases/conformance/es6/modules/exportBinding.ts
@@ -0,0 +1,5 @@
+export { x }
+const x = 'x'
+
+export { Y as Z }
+class Y {}