Give a better name for the boolean variable; emit __esmodule for export import

Author: Kanchalai Tanglertsampan

src/compiler/transformers/module/module.ts

@@ -45,7 +45,7 @@ namespace ts {
         let currentSourceFile: SourceFile; // The current file.
         let currentModuleInfo: ExternalModuleInfo; // The ExternalModuleInfo for the current file.
         let noSubstitution: boolean[]; // Set of nodes for which substitution rules should be ignored.
-        let shouldAppendUnderscoreUnderscoreEsModule: boolean;  // A boolean indicating whether "__esModule" should be emitted
+        let shouldAppendEsModuleMarker: boolean;  // A boolean indicating whether "__esModule" should be emitted
 
         return transformSourceFile;
 
@@ -63,7 +63,7 @@ namespace ts {
 
             currentSourceFile = node;
             currentModuleInfo = collectExternalModuleInfo(node, resolver, compilerOptions);
-            shouldAppendUnderscoreUnderscoreEsModule = false;
+            shouldAppendEsModuleMarker = false;
             moduleInfoMap[getOriginalNodeId(node)] = currentModuleInfo;
 
             // Perform the transformation.
@@ -90,7 +90,7 @@ namespace ts {
             addRange(statements, endLexicalEnvironment());
             addExportEqualsIfNeeded(statements, /*emitAsReturn*/ false);
 
-            if (shouldAppendUnderscoreUnderscoreEsModule) {
+            if (shouldAppendEsModuleMarker) {
                 append(statements, createUnderscoreUnderscoreESModule());
             }
 
@@ -383,7 +383,7 @@ namespace ts {
             // Append the 'export =' statement if provided.
             addExportEqualsIfNeeded(statements, /*emitAsReturn*/ true);
 
-            if (shouldAppendUnderscoreUnderscoreEsModule) {
+            if (shouldAppendEsModuleMarker) {
                 append(statements, createUnderscoreUnderscoreESModule());
             }
 
@@ -666,7 +666,7 @@ namespace ts {
             }
 
             const generatedName = getGeneratedNameForNode(node);
-            shouldAppendUnderscoreUnderscoreEsModule = true;
+            shouldAppendEsModuleMarker = true;
 
             if (node.exportClause) {
                 const statements: Statement[] = [];
@@ -833,9 +833,10 @@ namespace ts {
             let expressions: Expression[];
 
             const parseTreeNode = getParseTreeNode(node);
-            if (!shouldAppendUnderscoreUnderscoreEsModule) {
+            if (parseTreeNode && !shouldAppendEsModuleMarker) {
                 // class declaration get down-level transformed to be variable statement
-                shouldAppendUnderscoreUnderscoreEsModule = (parseTreeNode.kind === SyntaxKind.VariableStatement || parseTreeNode.kind === SyntaxKind.ClassDeclaration) && hasModifier(parseTreeNode, ModifierFlags.Export);
+                shouldAppendEsModuleMarker = (parseTreeNode.kind === SyntaxKind.VariableStatement || parseTreeNode.kind === SyntaxKind.ClassDeclaration || parseTreeNode.kind === SyntaxKind.ImportEqualsDeclaration)
+                    && hasModifier(parseTreeNode, ModifierFlags.Export);
             }
 
             if (hasModifier(node, ModifierFlags.Export)) {
@@ -1125,7 +1126,7 @@ namespace ts {
          * @param allowComments Whether to allow comments on the export.
          */
         function appendExportStatement(statements: Statement[] | undefined, exportName: Identifier, expression: Expression, location?: TextRange, allowComments?: boolean): Statement[] | undefined {
-            shouldAppendUnderscoreUnderscoreEsModule = true;
+            shouldAppendEsModuleMarker = true;
             statements = append(statements, createExportStatement(exportName, expression, location, allowComments));
             return statements;
         }