Prevent copying folders inside themselves

- contains now performs a case-insensitive comparison. While this is a
   little dubious, it's required for systems like Windows, where foo and
   Foo are the same folder.
 - Impose a depth limit on copyRecursive. If there are any other cases
   where we may try to copy a folder into itself, this should prevent
   the computer entirely crashing.

src/main/java/dan200/computercraft/api/filesystem/FileOperationException.java

@@ -27,7 +27,7 @@ public FileOperationException( @Nullable String filename, @Nonnull String messag
         this.filename = filename;
     }
 
-    public FileOperationException( String message )
+    public FileOperationException( @Nonnull String message )
     {
         super( Objects.requireNonNull( message, "message cannot be null" ) );
         this.filename = null;

src/main/java/dan200/computercraft/core/filesystem/FileSystem.java

@@ -29,6 +29,14 @@
 
 public class FileSystem
 {
+    /**
+     * Maximum depth that {@link #copyRecursive(String, MountWrapper, String, MountWrapper, int)} will descend into.
+     *
+     * This is a pretty arbitrary value, though hopefully it is large enough that it'll never be normally hit. This
+     * exists to prevent it overflowing if it ever gets into an infinite loop.
+     */
+    private static final int MAX_COPY_DEPTH = 128;
+
     private static class MountWrapper
     {
         private String m_label;
@@ -611,15 +619,13 @@ public synchronized void copy( String sourcePath, String destPath ) throws FileS
         {
             throw new FileSystemException( "/" + sourcePath + ": Can't copy a directory inside itself" );
         }
-        copyRecursive( sourcePath, getMount( sourcePath ), destPath, getMount( destPath ) );
+        copyRecursive( sourcePath, getMount( sourcePath ), destPath, getMount( destPath ), 0 );
     }
 
-    private synchronized void copyRecursive( String sourcePath, MountWrapper sourceMount, String destinationPath, MountWrapper destinationMount ) throws FileSystemException
+    private synchronized void copyRecursive( String sourcePath, MountWrapper sourceMount, String destinationPath, MountWrapper destinationMount, int depth ) throws FileSystemException
     {
-        if( !sourceMount.exists( sourcePath ) )
-        {
-            return;
-        }
+        if( !sourceMount.exists( sourcePath ) ) return;
+        if( depth >= MAX_COPY_DEPTH ) throw new FileSystemException( "Too many directories to copy" );
 
         if( sourceMount.isDirectory( sourcePath ) )
         {
@@ -634,7 +640,8 @@ private synchronized void copyRecursive( String sourcePath, MountWrapper sourceM
             {
                 copyRecursive(
                     combine( sourcePath, child ), sourceMount,
-                    combine( destinationPath, child ), destinationMount
+                    combine( destinationPath, child ), destinationMount,
+                    depth + 1
                 );
             }
         }
@@ -854,8 +861,8 @@ else if( part.length() >= 255 )
 
     public static boolean contains( String pathA, String pathB )
     {
-        pathA = sanitizePath( pathA );
-        pathB = sanitizePath( pathB );
+        pathA = sanitizePath( pathA ).toLowerCase( Locale.ROOT );
+        pathB = sanitizePath( pathB ).toLowerCase( Locale.ROOT );
 
         if( pathB.equals( ".." ) )
         {

src/test/java/dan200/computercraft/core/computer/BasicEnvironment.java

@@ -116,7 +116,7 @@ public static IMount createMount( Class<?> klass, String path, String fallback )
             while( baseFile != null && !wholeFile.exists() )
             {
                 baseFile = baseFile.getParentFile();
-                wholeFile = new File( baseFile, "resources/" + fallback + "/" + path );
+                wholeFile = new File( baseFile, "src/" + fallback + "/resources/" + path );
             }
 
             if( !wholeFile.exists() ) throw new IllegalStateException( "Cannot find ROM mount at " + file );

src/test/resources/test-rom/spec/apis/fs_spec.lua

@@ -125,6 +125,21 @@ describe("The fs library", function()
         it("fails on read-only mounts", function()
             expect.error(fs.copy, "rom", "rom/startup"):eq("/rom/startup: Access denied")
         end)
+
+        it("fails to copy a folder inside itself", function()
+            fs.makeDir("some-folder")
+            expect.error(fs.copy, "some-folder", "some-folder/x"):eq("/some-folder: Can't copy a directory inside itself")
+            expect.error(fs.copy, "some-folder", "Some-Folder/x"):eq("/some-folder: Can't copy a directory inside itself")
+        end)
+
+        it("copies folders", function()
+            fs.delete("some-folder")
+            fs.delete("another-folder")
+
+            fs.makeDir("some-folder")
+            fs.copy("some-folder", "another-folder")
+            expect(fs.isDir("another-folder")):eq(true)
+        end)
     end)
 
     describe("fs.move", function()