Fix compileOnSave with external module

Author: Yui T

src/compiler/emitter.ts

@@ -3228,21 +3228,27 @@ module ts {
         }
 
         if (targetSourceFile === undefined) {
+            // No targetSourceFile is specified (i.e. calling emitter from batch compiler)
             forEach(program.getSourceFiles(), sourceFile => {
                 if (shouldEmitToOwnFile(sourceFile, compilerOptions)) {
                     var jsFilePath = getOwnEmitOutputFilePath(sourceFile, ".js");
                     emitFile(jsFilePath, sourceFile);
                 }
             });
-        }
-        else {
-            // Emit only one file specified in targetFilename. This is mainly used in compilerOnSave feature
-            var jsFilePath = getOwnEmitOutputFilePath(targetSourceFile, ".js");
-            emitFile(jsFilePath, targetSourceFile);
-        }
 
-        if (compilerOptions.out) {
-            emitFile(compilerOptions.out);
+            if (compilerOptions.out) {
+                emitFile(compilerOptions.out);
+            }
+        } else {
+            // targetSourceFile is specified (i.e. calling emitter from language service)
+            if (shouldEmitToOwnFile(targetSourceFile, compilerOptions)) {
+                // If shouldEmitToOwnFile is true or targetSouceFile is an external module file, then emit targetSourceFile in its own output file
+                var jsFilePath = getOwnEmitOutputFilePath(targetSourceFile, ".js");
+                emitFile(jsFilePath, targetSourceFile);
+            } else {
+                // If shouldEmitToOwnFile is false, then emit all, non-external-module file, into one single output file
+                emitFile(compilerOptions.out);
+            }
         }
 
         // Sort and make the unique list of diagnostics

src/services/services.ts

@@ -3881,7 +3881,8 @@ module ts {
             filename = TypeScript.switchToForwardSlashes(filename);
             var compilerOptions = program.getCompilerOptions();
             var targetSourceFile = program.getSourceFile(filename);  // Current selected file to be output
-            var emitToSingleFile = ts.shouldEmitToOwnFile(targetSourceFile, compilerOptions);
+            // If --out flag is not specified, shouldEmitToOwnFile is true. Otherwise shouldEmitToOwnFile is false.
+            var shouldEmitToOwnFile = ts.shouldEmitToOwnFile(targetSourceFile, compilerOptions);
             var emitDeclaration = compilerOptions.declaration;
             var emitOutput: EmitOutput = {
                 outputFiles: [],
@@ -3902,7 +3903,7 @@ module ts {
             var syntacticDiagnostics: Diagnostic[] = [];
             var containSyntacticErrors = false;
 
-            if (emitToSingleFile) {
+            if (shouldEmitToOwnFile) {
                 // Check only the file we want to emit
                 containSyntacticErrors = containErrors(program.getDiagnostics(targetSourceFile));
             } else {
@@ -3929,7 +3930,7 @@ module ts {
             // Perform semantic and force a type check before emit to ensure that all symbols are updated
             // EmitFiles will report if there is an error from TypeChecker and Emitter
             // Depend whether we will have to emit into a single file or not either emit only selected file in the project, emit all files into a single file
-            var emitFilesResult = emitToSingleFile ? getFullTypeCheckChecker().emitFiles(targetSourceFile) : getFullTypeCheckChecker().emitFiles();
+            var emitFilesResult = getFullTypeCheckChecker().emitFiles(targetSourceFile);;
             emitOutput.emitOutputStatus = emitFilesResult.emitResultStatus;
 
             // Reset writer back to undefined to make sure that we produce an error message if CompilerHost.writeFile method is called when we are not in getEmitOutput