use FileSystems.newCompositeFileSystem() api to handle delegating to real FS

Author: tomasstupka

graalpython/org.graalvm.python.embedding/src/org/graalvm/python/embedding/utils/GraalPyResources.java

@@ -259,7 +259,7 @@ public static Context.Builder contextBuilder() {
     public static Context.Builder contextBuilder(VirtualFileSystem vfs) {
         return createContextBuilder().
         // allow access to the virtual and the host filesystem, as well as sockets
-                        allowIO(IOAccess.newBuilder().allowHostSocketAccess(true).fileSystem(vfs.impl).build()).
+                        allowIO(IOAccess.newBuilder().allowHostSocketAccess(true).fileSystem(vfs.delegatingFileSystem).build()).
                         // The sys.executable path, a virtual path that is used by the interpreter
                         // to discover packages
                         option("python.Executable", vfs.impl.vfsVenvPath() + (VirtualFileSystemImpl.isWindows() ? "\\Scripts\\python.exe" : "/bin/python")).

graalpython/org.graalvm.python.embedding/src/org/graalvm/python/embedding/utils/VirtualFileSystem.java

@@ -40,13 +40,16 @@
  */
 package org.graalvm.python.embedding.utils;
 
+import org.graalvm.polyglot.io.FileSystem;
+
 import java.io.IOException;
 import java.nio.file.Path;
 import java.util.function.Predicate;
 
 public final class VirtualFileSystem implements AutoCloseable {
 
     final VirtualFileSystemImpl impl;
+    final FileSystem delegatingFileSystem;
 
     public static enum HostIO {
         NONE,
@@ -178,6 +181,7 @@ private VirtualFileSystem(Predicate<Path> extractFilter,
                     boolean caseInsensitive) {
 
         this.impl = new VirtualFileSystemImpl(extractFilter, mountPoint, allowHostIO, resourceLoadingClass, caseInsensitive);
+        this.delegatingFileSystem = VirtualFileSystemImpl.createDelegatingFileSystem(impl);
     }
 
     public static Builder newBuilder() {