Overlapping entries in mypy.ini are processed in nondeterministic order

[gvanrossum]

Suppose you have these entries in mypy.ini:

[mypy-metaserver.lib.shared_folder.*]
ignore_errors = True
[mypy-metaserver.lib.shared_folder.perms.*]
ignore_errors = False

For a submodule of package metaserver.lib.shared_folder.perms it will be nondeterministic whether that file is processed with ignore_errors = True or ignore_errors = False.

The reason is that Options.clone_for_module() in mypy/options.py loops over self.per_module_options which is a dict, and dict ordering is randomized by default in Python 3 (unless PYTHONHASHSEED is set).

[gvanrossum]

Fortunate the solution seems straightforward, we just need to use OrderedDict to hold per_module_options.

[gvanrossum]

Note that the problem only occurs in Python 3.5 or before, because in Python 3.6 the standard dict type preserves order.

Also note that this relies on ConfigParser preserving order -- which it does (it uses OrderedDict for everything by default).