optimize __createBinding

When the binding is itself one that was created by `__createBinding`,
re-use its descriptor, which avoids piling multiple levels of getters in
the case of multiple levels of exports.

In addition, reuse a descriptor if the bindings is marked as
non-writable and non-configurable, which makes a getter not
necessary.  (This can be done manually if needed, even though tsc
doesn't do it now.)

Also related to microsoft#46744 and to microsoft/tslib#165.

Author: elibarzilay

src/compiler/factory/emitHelpers.ts

@@ -783,7 +783,11 @@ namespace ts {
         text: `
             var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
                 if (k2 === undefined) k2 = k;
-                Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
+                var desc = Object.getOwnPropertyDescriptor(m, k);
+                if (!desc || ("get" in desc ? !m.__esModule : desc.writable || desc.configurable)) {
+                  desc = { enumerable: true, get: function() { return m[k]; } };
+                }
+                Object.defineProperty(o, k2, desc);
             }) : (function(o, m, k, k2) {
                 if (k2 === undefined) k2 = k;
                 o[k2] = m[k];

tests/baselines/reference/ambientShorthand_reExport.js

@@ -20,7 +20,11 @@ x($);
 "use strict";
 var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
-    Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
+    var desc = Object.getOwnPropertyDescriptor(m, k);
+    if (!desc || ("get" in desc ? !m.__esModule : desc.writable || desc.configurable)) {
+      desc = { enumerable: true, get: function() { return m[k]; } };
+    }
+    Object.defineProperty(o, k2, desc);
 }) : (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
     o[k2] = m[k];
@@ -33,7 +37,11 @@ __createBinding(exports, jquery_1, "x");
 "use strict";
 var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
-    Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
+    var desc = Object.getOwnPropertyDescriptor(m, k);
+    if (!desc || ("get" in desc ? !m.__esModule : desc.writable || desc.configurable)) {
+      desc = { enumerable: true, get: function() { return m[k]; } };
+    }
+    Object.defineProperty(o, k2, desc);
 }) : (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
     o[k2] = m[k];

tests/baselines/reference/constEnumPreserveEmitReexport.js

@@ -30,7 +30,11 @@ exports["default"] = ConstEnum_1.MyConstEnum;
 "use strict";
 var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
-    Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
+    var desc = Object.getOwnPropertyDescriptor(m, k);
+    if (!desc || ("get" in desc ? !m.__esModule : desc.writable || desc.configurable)) {
+      desc = { enumerable: true, get: function() { return m[k]; } };
+    }
+    Object.defineProperty(o, k2, desc);
 }) : (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
     o[k2] = m[k];

tests/baselines/reference/declarationEmitAliasExportStar.js

@@ -16,7 +16,11 @@ exports.__esModule = true;
 "use strict";
 var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
-    Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
+    var desc = Object.getOwnPropertyDescriptor(m, k);
+    if (!desc || ("get" in desc ? !m.__esModule : desc.writable || desc.configurable)) {
+      desc = { enumerable: true, get: function() { return m[k]; } };
+    }
+    Object.defineProperty(o, k2, desc);
 }) : (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
     o[k2] = m[k];

tests/baselines/reference/declarationEmitExportAssignedNamespaceNoTripleSlashTypesReference.js

@@ -59,7 +59,11 @@ exports.obj = {
 "use strict";
 var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
-    Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
+    var desc = Object.getOwnPropertyDescriptor(m, k);
+    if (!desc || ("get" in desc ? !m.__esModule : desc.writable || desc.configurable)) {
+      desc = { enumerable: true, get: function() { return m[k]; } };
+    }
+    Object.defineProperty(o, k2, desc);
 }) : (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
     o[k2] = m[k];

tests/baselines/reference/declarationEmitReexportedSymlinkReference.js

@@ -53,7 +53,11 @@ exports.ADMIN = pkg2_1.MetadataAccessor.create('1');
 "use strict";
 var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
-    Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
+    var desc = Object.getOwnPropertyDescriptor(m, k);
+    if (!desc || ("get" in desc ? !m.__esModule : desc.writable || desc.configurable)) {
+      desc = { enumerable: true, get: function() { return m[k]; } };
+    }
+    Object.defineProperty(o, k2, desc);
 }) : (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
     o[k2] = m[k];

tests/baselines/reference/declarationEmitReexportedSymlinkReference2.js

@@ -56,7 +56,11 @@ exports.ADMIN = pkg2_1.MetadataAccessor.create('1');
 "use strict";
 var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
-    Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
+    var desc = Object.getOwnPropertyDescriptor(m, k);
+    if (!desc || ("get" in desc ? !m.__esModule : desc.writable || desc.configurable)) {
+      desc = { enumerable: true, get: function() { return m[k]; } };
+    }
+    Object.defineProperty(o, k2, desc);
 }) : (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
     o[k2] = m[k];

tests/baselines/reference/declarationEmitReexportedSymlinkReference3.js

@@ -53,7 +53,11 @@ exports.ADMIN = pkg2_1.MetadataAccessor.create('1');
 "use strict";
 var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
-    Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
+    var desc = Object.getOwnPropertyDescriptor(m, k);
+    if (!desc || ("get" in desc ? !m.__esModule : desc.writable || desc.configurable)) {
+      desc = { enumerable: true, get: function() { return m[k]; } };
+    }
+    Object.defineProperty(o, k2, desc);
 }) : (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
     o[k2] = m[k];

tests/baselines/reference/doubleUnderscoreExportStarConflict.js

@@ -27,7 +27,11 @@ exports.__foo = __foo;
 "use strict";
 var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
-    Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
+    var desc = Object.getOwnPropertyDescriptor(m, k);
+    if (!desc || ("get" in desc ? !m.__esModule : desc.writable || desc.configurable)) {
+      desc = { enumerable: true, get: function() { return m[k]; } };
+    }
+    Object.defineProperty(o, k2, desc);
 }) : (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
     o[k2] = m[k];

tests/baselines/reference/es6ExportAllInEs5.js

@@ -34,7 +34,11 @@ exports.x = 10;
 "use strict";
 var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
-    Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
+    var desc = Object.getOwnPropertyDescriptor(m, k);
+    if (!desc || ("get" in desc ? !m.__esModule : desc.writable || desc.configurable)) {
+      desc = { enumerable: true, get: function() { return m[k]; } };
+    }
+    Object.defineProperty(o, k2, desc);
 }) : (function(o, m, k, k2) {
     if (k2 === undefined) k2 = k;
     o[k2] = m[k];