8282444: Module finder incorrectly assumes default file system path-separator character

src/java.base/share/classes/jdk/internal/module/ModulePath.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2022, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -663,11 +663,12 @@ private ModuleReference readJar(Path file) throws IOException {
     // -- exploded directories --
 
     private Set<String> explodedPackages(Path dir) {
+        String separator = dir.getFileSystem().getSeparator();
         try {
             return Files.find(dir, Integer.MAX_VALUE,
                     ((path, attrs) -> attrs.isRegularFile() && !isHidden(path)))
                     .map(path -> dir.relativize(path))
-                    .map(this::toPackageName)
+                    .map(path -> toPackageName(path, separator))
                     .flatMap(Optional::stream)
                     .collect(Collectors.toSet());
         } catch (IOException x) {
@@ -738,7 +739,7 @@ private Optional<String> toPackageName(String name) {
      * @throws InvalidModuleDescriptorException if the name is a class file in
      *         the top-level directory (and it's not module-info.class)
      */
-    private Optional<String> toPackageName(Path file) {
+    private Optional<String> toPackageName(Path file, String separator) {
         assert file.getRoot() == null;
 
         Path parent = file.getParent();
@@ -752,7 +753,7 @@ private Optional<String> toPackageName(Path file) {
             return Optional.empty();
         }
 
-        String pn = parent.toString().replace(File.separatorChar, '.');
+        String pn = parent.toString().replace(separator, ".");
         if (Checks.isPackageName(pn)) {
             return Optional.of(pn);
         } else {

test/jdk/java/lang/module/customfs/ModulesInCustomFileSystem.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 2022, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -23,6 +23,7 @@
 
 /**
  * @test
+ * @bug 8178380 8282444
  * @modules jdk.zipfs
  * @library /test/lib
  * @build ModulesInCustomFileSystem m1/* m2/*

test/jdk/java/lang/module/customfs/m1/p/Main.java

@@ -25,6 +25,6 @@
 
 public class Main {
     public static void main(String[] args) {
-        q.Hello.hello();
+        q.r.Hello.hello();
     }
 }

test/jdk/java/lang/module/customfs/m2/module-info.java

@@ -22,5 +22,5 @@
  */
 
 module m2 {
-    exports q;
+    exports q.r;
 }

test/jdk/java/lang/module/customfs/m2/q/Hello.java → test/jdk/java/lang/module/customfs/m2/q/r/Hello.java

@@ -21,7 +21,7 @@
  * questions.
  */
 
-package q;
+package q.r;
 
 public class Hello {
     public static void hello() {