Export anonymous functions in 2 steps, declare as variable and then assign to exports. (microsoft#39820)

* Preserve the variable name when exporting an arrow or anonymous function
 This allows the browser or node to properly name the (arrow) function

* Updated tests to reflect previous change

* Remove duplicated comment

* Transforms variable.initializer using moduleExpressionElementVisitor

* PR feedback: rbuckton
 - Use isArrowFunction and isFunctionExpression

* PR feedback: rbuckton
- Consider ClassExpresion, they can also be named based on the
  variable.

Author: josejulio

src/compiler/transformers/module/module.ts

@@ -1195,6 +1195,7 @@ namespace ts {
 
             if (hasSyntacticModifier(node, ModifierFlags.Export)) {
                 let modifiers: NodeArray<Modifier> | undefined;
+                let removeCommentsOnExpressions = false;
 
                 // If we're exporting these variables, then these just become assignments to 'exports.x'.
                 for (const variable of node.declarationList.declarations) {
@@ -1206,7 +1207,31 @@ namespace ts {
                         variables = append(variables, variable);
                     }
                     else if (variable.initializer) {
-                        expressions = append(expressions, transformInitializedVariable(variable as InitializedVariableDeclaration));
+                        if (!isBindingPattern(variable.name) && (isArrowFunction(variable.initializer) || isFunctionExpression(variable.initializer) || isClassExpression(variable.initializer))) {
+                            const expression = factory.createAssignment(
+                                setTextRange(
+                                    factory.createPropertyAccessExpression(
+                                        factory.createIdentifier("exports"),
+                                        variable.name
+                                    ),
+                                    /*location*/ variable.name
+                                ),
+                                factory.createIdentifier(getTextOfIdentifierOrLiteral(variable.name))
+                            );
+                            const updatedVariable = factory.createVariableDeclaration(
+                                variable.name,
+                                variable.exclamationToken,
+                                variable.type,
+                                visitNode(variable.initializer, moduleExpressionElementVisitor)
+                            );
+
+                            variables = append(variables, updatedVariable);
+                            expressions = append(expressions, expression);
+                            removeCommentsOnExpressions = true;
+                        }
+                        else {
+                            expressions = append(expressions, transformInitializedVariable(variable as InitializedVariableDeclaration));
+                        }
                     }
                 }
 
@@ -1215,7 +1240,11 @@ namespace ts {
                 }
 
                 if (expressions) {
-                    statements = append(statements, setOriginalNode(setTextRange(factory.createExpressionStatement(factory.inlineExpressions(expressions)), node), node));
+                    const statement = setOriginalNode(setTextRange(factory.createExpressionStatement(factory.inlineExpressions(expressions)), node), node);
+                    if (removeCommentsOnExpressions) {
+                        removeAllComments(statement);
+                    }
+                    statements = append(statements, statement);
                 }
             }
             else {

tests/baselines/reference/aliasUsedAsNameValue.js

@@ -36,7 +36,8 @@ exports.a = void 0;
 ///<reference path='aliasUsedAsNameValue_1.ts' />
 var mod = require("./aliasUsedAsNameValue_0");
 var b = require("./aliasUsedAsNameValue_1");
-exports.a = function () {
+var a = function () {
     //var x = mod.id; // TODO needed hack that mod is loaded
     b.b(mod);
 };
+exports.a = a;

tests/baselines/reference/declarationEmitAliasExportStar.js

@@ -30,7 +30,8 @@ __exportStar(require("./thingB"), exports);
 "use strict";
 exports.__esModule = true;
 exports.thing2 = void 0;
-exports.thing2 = function (param) { return null; };
+var thing2 = function (param) { return null; };
+exports.thing2 = thing2;
 
 
 //// [thingB.d.ts]

tests/baselines/reference/declarationEmitBundleWithAmbientReferences.js

@@ -29,9 +29,10 @@ define("conditional_directive_field", ["require", "exports"], function (require,
     "use strict";
     exports.__esModule = true;
     exports.build = void 0;
-    exports.build = function () {
+    var build = function () {
         return null;
     };
+    exports.build = build;
 });
 
 

tests/baselines/reference/declarationEmitComputedNameCausesImportToBePainted.js

@@ -28,10 +28,11 @@ var context_1 = require("./context");
 exports.context = (_a = {},
     _a[context_1.Key] = 'bar',
     _a);
-exports.withContext = function (_a) {
+var withContext = function (_a) {
     var _b = context_1.Key, value = _a[_b];
     return value;
 };
+exports.withContext = withContext;
 
 
 //// [context.d.ts]

tests/baselines/reference/declarationEmitExpandoWithGenericConstraint.js

@@ -18,8 +18,10 @@ Point.zero = (): Point => Point(0, 0);
 "use strict";
 exports.__esModule = true;
 exports.Rect = exports.Point = void 0;
-exports.Point = function (x, y) { return ({ x: x, y: y }); };
-exports.Rect = function (a, b) { return ({ a: a, b: b }); };
+var Point = function (x, y) { return ({ x: x, y: y }); };
+exports.Point = Point;
+var Rect = function (a, b) { return ({ a: a, b: b }); };
+exports.Rect = Rect;
 exports.Point.zero = function () { return exports.Point(0, 0); };
 
 

tests/baselines/reference/declarationEmitExportAliasVisibiilityMarking.js

@@ -25,7 +25,8 @@ exports["default"] = (function (suit, rank) { return ({ suit: suit, rank: rank }
 "use strict";
 exports.__esModule = true;
 exports.lazyCard = void 0;
-exports.lazyCard = function () { return Promise.resolve().then(function () { return require('./Card'); }).then(function (a) { return a["default"]; }); };
+var lazyCard = function () { return Promise.resolve().then(function () { return require('./Card'); }).then(function (a) { return a["default"]; }); };
+exports.lazyCard = lazyCard;
 
 
 //// [Types.d.ts]

tests/baselines/reference/declarationEmitOptionalMethod.js

@@ -11,7 +11,8 @@ export const Foo = (opts: {
 "use strict";
 exports.__esModule = true;
 exports.Foo = void 0;
-exports.Foo = function (opts) { return ({}); };
+var Foo = function (opts) { return ({}); };
+exports.Foo = Foo;
 
 
 //// [declarationEmitOptionalMethod.d.ts]

tests/baselines/reference/declarationEmitRetainsJsdocyComments.js

@@ -52,7 +52,7 @@ exports.someMethod = exports.Foo = exports.foo = void 0;
  * comment1
  * @param p
  */
-exports.foo = function (p) {
+var foo = function (p) {
     return {
         /**
          * comment2
@@ -66,6 +66,7 @@ exports.foo = function (p) {
         bar2: function (s) { }
     };
 };
+exports.foo = foo;
 var Foo = /** @class */ (function () {
     function Foo() {
     }

tests/baselines/reference/declarationEmitTypeAliasWithTypeParameters1.js

@@ -7,7 +7,8 @@ export const y = (x: Foo<string>) => 1
 "use strict";
 exports.__esModule = true;
 exports.y = void 0;
-exports.y = function (x) { return 1; };
+var y = function (x) { return 1; };
+exports.y = y;
 
 
 //// [declarationEmitTypeAliasWithTypeParameters1.d.ts]