When JavacFileManager.DirectoryContainer.list encounters an InvalidPathException, it rethrows this as an IOException where the message includes the directory concatenated with the toString of the InvalidPathException:

{code}
throw new IOException("error accessing directory " + directory + e);
{code}

The directory and the exception toString has no separation, resulting in compilation errors like the following:

{code}
error accessing directory Z:\invalid-pathjava.nio.file.InvalidPathException: Illegal char <:> at index 4: file:txt
{code}

The solution is to inject a separator between the directory and the exception toString