Messed plugin config list order

[dhanak]

Hi!

TL;DR

I think that merge_dicts implementation in _utils.py is wrong:

def merge_dicts(dict_a, dict_b):
    """Recursively merge dictionary b into dictionary a.

    If override_nones is True, then
    """

    def _merge_dicts_(a, b):
        for key in set(a.keys()).union(b.keys()):
            if key in a and key in b:
                if isinstance(a[key], dict) and isinstance(b[key], dict):
                    yield (key, dict(_merge_dicts_(a[key], b[key])))
                elif isinstance(a[key], list) and isinstance(b[key], list):
                    yield (key, list(set(a[key] + b[key]))) # <--- this line here is wrong
                elif b[key] is not None:
                    yield (key, b[key])
                else:
                    yield (key, a[key])
            elif key in a:
                yield (key, a[key])
            elif b[key] is not None:
                yield (key, b[key])

    return dict(_merge_dicts_(dict_a, dict_b))

By converting the list to a set, it not only gets rid of the duplicates, but also messes up the list order unpredictably. Replacing set() with OrderedDict.fromkeys() seems to fix the issue described in detail below.

---

I'm using pylsp v1.13.1 with pylsp_mypy v0.7.0. (The whole LSP is run by Emacs v30.1 via eglot, but this probably doesn't matter.) And I noticed the following strange behavior, which I can't really put my finger on yet.

When pylsp invokes pylsp_mypy, it uses the following configuration:

[stderr]  2025-10-08 12:21:46,942 CEST - INFO - pylsp.config.config - Updated settings to {'plugins': {'jedi': {'environment': '/home/david/pyproj/.venv'}, 'ruff': {'executable': '/home/david/pyproj/.venv/bin/ruff'}, 'pylsp_mypy': {'overrides': ['--python-executable', '/home/david/pyproj/.venv/bin/python', True]}, 'flake8': {'executable': None}, 'pylint': {'executable': None}}}

Note the overrides list. The next log line after this, however, is this:

[stderr]  2025-10-08 12:21:47,475 CEST - INFO - pylsp_mypy.plugin - lint settings = {'overrides': [True, '/home/david/pyproj/.venv/bin/python', '--python-executable']} document.path = /home/david/pyproj/src/pyproj/__init__.py is_saved = False

Note how the overrides list is in reverse order. And right enough, mypy refuses to run:

error: argument --python-executable: expected one **argument**

I also noticed that it's not always reverse, the order seems to be pretty random. Sometimes it's ok and works, other times, it's messed up.