matplotlib.sphinxext.plot_directive generates incorrect links when using dirhtml builder #13858

When using the dirhtml builder in sphinx with the .. plot:: directive, the generated links are relative to the source file tree not the output, i.e. the source file name become a directory containing index.html, however the relative path generated is based on the location of the source file

I fixed this locally using the the following hack, however I don't think this is the appropriate solution there should be some way to make the directive use the output path not the input path, which would remove the need for a hack solution. Hence I'm posting this as a issue rather than a patch.

    if setup.app.builder.name == 'dirhtml':
        subdir = os.path.basename(os.path.splitext(rst_file)[0])
        dest_dir_link = os.path.join(relpath(setup.confdir, os.path.join(rst_dir, subdir)),
                                     source_rel_dir).replace(os.path.sep, '/')
    else:
        dest_dir_link = os.path.join(relpath(setup.confdir, rst_dir),
                                     source_rel_dir).replace(os.path.sep, '/')