Merge pull request #6789 from Microsoft/transpileJs

suppress validation of output paths in transpile scenarios

src/compiler/program.ts

@@ -1717,7 +1717,7 @@ namespace ts {
             }
 
             // If the emit is enabled make sure that every output file is unique and not overwriting any of the input files
-            if (!options.noEmit) {
+            if (!options.noEmit && !options.suppressOutputPathCheck) {
                 const emitHost = getEmitHost();
                 const emitFilesSeen = createFileMap<boolean>(!host.useCaseSensitiveFileNames() ? key => key.toLocaleLowerCase() : undefined);
                 forEachExpectedEmitFile(emitHost, (emitFileNames, sourceFiles, isBundledEmit) => {

src/compiler/types.ts

@@ -2426,6 +2426,8 @@ namespace ts {
 
         // Skip checking lib.d.ts to help speed up tests.
         /* @internal */ skipDefaultLibCheck?: boolean;
+        // Do not perform validation of output file name in transpile scenarios
+        /* @internal */ suppressOutputPathCheck?: boolean;
 
         [option: string]: string | number | boolean | TsConfigOnlyOptions;
     }

src/services/services.ts

@@ -1876,6 +1876,9 @@ namespace ts {
 
         options.isolatedModules = true;
 
+        // transpileModule does not write anything to disk so there is no need to verify that there are no conflicts between input and output paths. 
+        options.suppressOutputPathCheck = true;
+
         // Filename can be non-ts file.
         options.allowNonTsExtensions = true;