Print warning in tsgo on currently unsupported file types (microsoft#427)

Author: jakebailey

cmd/tsgo/main.go

@@ -229,6 +229,17 @@ func main() {
 		printDiagnostics(ts.SortAndDeduplicateDiagnostics(diagnostics), host, compilerOptions)
 	}
 
+	var unsupportedExtensions []string
+	for _, file := range program.SourceFiles() {
+		extension := tspath.TryGetExtensionFromPath(file.FileName())
+		if extension == tspath.ExtensionTsx || slices.Contains(tspath.SupportedJSExtensionsFlat, extension) {
+			unsupportedExtensions = core.AppendIfUnique(unsupportedExtensions, extension)
+		}
+	}
+	if len(unsupportedExtensions) != 0 {
+		fmt.Fprintf(os.Stderr, "Warning: The project contains unsupported file types (%s), which are currently not fully type-checked.\n", strings.Join(unsupportedExtensions, ", "))
+	}
+
 	if compilerOptions.ListFiles.IsTrue() {
 		listFiles(program)
 	}