From 035c7ca90504dd31a8a0f65659c366ba0e3e8cc7 Mon Sep 17 00:00:00 2001
From: Andrew Branch <andrewbranch@users.noreply.github.com>
Date: Thu, 10 Dec 2020 10:17:28 -0800
Subject: [PATCH] Elide export assignment when it does not resolve to a value
 (#41904)

* Only mark aliases that resolve to values referenced

* Update other affected baselines

* Remove redundant check
---
 src/compiler/checker.ts                           | 13 ++++++++-----
 .../reference/exportDefaultImportedType.js        | 15 +++++++++++++++
 ...ything-setup-correctly-and-reports-no-error.js |  1 -
 .../demo/updates-with-circular-reference.js       |  1 -
 tests/cases/compiler/exportDefaultImportedType.ts | 10 ++++++++++
 5 files changed, 33 insertions(+), 7 deletions(-)
 create mode 100644 tests/baselines/reference/exportDefaultImportedType.js
 create mode 100644 tests/cases/compiler/exportDefaultImportedType.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 9f85b552378..08030f8452e 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -22868,11 +22868,14 @@ namespace ts {
 
         function markAliasReferenced(symbol: Symbol, location: Node) {
             if (isNonLocalAlias(symbol, /*excludes*/ SymbolFlags.Value) && !isInTypeQuery(location) && !getTypeOnlyAliasDeclaration(symbol)) {
-                if (compilerOptions.preserveConstEnums && isExportOrExportExpression(location) || !isConstEnumOrConstEnumOnlyModule(resolveAlias(symbol))) {
-                    markAliasSymbolAsReferenced(symbol);
-                }
-                else {
-                    markConstEnumAliasAsReferenced(symbol);
+                const target = resolveAlias(symbol);
+                if (target.flags & SymbolFlags.Value) {
+                    if (compilerOptions.preserveConstEnums && isExportOrExportExpression(location) || !isConstEnumOrConstEnumOnlyModule(target)) {
+                        markAliasSymbolAsReferenced(symbol);
+                    }
+                    else {
+                        markConstEnumAliasAsReferenced(symbol);
+                    }
                 }
             }
         }
diff --git a/tests/baselines/reference/exportDefaultImportedType.js b/tests/baselines/reference/exportDefaultImportedType.js
new file mode 100644
index 00000000000..e2531cd9d84
--- /dev/null
+++ b/tests/baselines/reference/exportDefaultImportedType.js
@@ -0,0 +1,15 @@
+//// [tests/cases/compiler/exportDefaultImportedType.ts] ////
+
+//// [exported.ts]
+type Foo = number;
+export { Foo };
+
+//// [main.ts]
+import { Foo } from "./exported";
+export default Foo;
+
+
+//// [exported.js]
+export {};
+//// [main.js]
+export {};
diff --git a/tests/baselines/reference/tsbuild/demo/initial-build/in-master-branch-with-everything-setup-correctly-and-reports-no-error.js b/tests/baselines/reference/tsbuild/demo/initial-build/in-master-branch-with-everything-setup-correctly-and-reports-no-error.js
index 54546e00acb..d761f8eff2b 100644
--- a/tests/baselines/reference/tsbuild/demo/initial-build/in-master-branch-with-everything-setup-correctly-and-reports-no-error.js
+++ b/tests/baselines/reference/tsbuild/demo/initial-build/in-master-branch-with-everything-setup-correctly-and-reports-no-error.js
@@ -215,7 +215,6 @@ export { createDog, Dog };
 "use strict";
 Object.defineProperty(exports, "__esModule", { value: true });
 exports.createDog = void 0;
-var animal_1 = require("./animal");
 var dog_1 = require("./dog");
 Object.defineProperty(exports, "createDog", { enumerable: true, get: function () { return dog_1.createDog; } });
 
diff --git a/tests/baselines/reference/tsbuild/watchMode/demo/updates-with-circular-reference.js b/tests/baselines/reference/tsbuild/watchMode/demo/updates-with-circular-reference.js
index b3d953ce202..e17c8d56528 100644
--- a/tests/baselines/reference/tsbuild/watchMode/demo/updates-with-circular-reference.js
+++ b/tests/baselines/reference/tsbuild/watchMode/demo/updates-with-circular-reference.js
@@ -387,7 +387,6 @@ export default interface Animal {
 "use strict";
 Object.defineProperty(exports, "__esModule", { value: true });
 exports.createDog = void 0;
-var animal_1 = require("./animal");
 var dog_1 = require("./dog");
 Object.defineProperty(exports, "createDog", { enumerable: true, get: function () { return dog_1.createDog; } });
 
diff --git a/tests/cases/compiler/exportDefaultImportedType.ts b/tests/cases/compiler/exportDefaultImportedType.ts
new file mode 100644
index 00000000000..93f874b26c4
--- /dev/null
+++ b/tests/cases/compiler/exportDefaultImportedType.ts
@@ -0,0 +1,10 @@
+// @module: es2015
+// @noTypesAndSymbols: true
+
+// @Filename: /exported.ts
+type Foo = number;
+export { Foo };
+
+// @Filename: /main.ts
+import { Foo } from "./exported";
+export default Foo;