Fixed #36878 -- Unified data type for *_together options in ModelState.

Ever since the beginning of Django's migration framework, there's been a
bit of an inconsistency on how index_together and unique_together values
have been stored on the ModelState[^1].

It's only really obvious, when looking at the current code for
`from_model()`[^2] and the `rename_field()` state alteration code[^3].

The problem in the autodetector's detection of the `*_together` options
as raised in the ticket, reinforces the inconsistency[^4]: the old value
is being normalized to a set of tuples, whereas the new value is taken
as-is.

Why this hasn't been caught before, is likely to the fact, that we
never really look at a `to_state` that comes from migration operations
in the autodetector. Instead, in both usages in Django[^5], [^6] the
`to_state` is a `ProjectState.from_apps()`. And that state is
consistently using sets of tuples and not lists of lists.

[^1]: https://github.com/django/django/commit/67dcea711e92025d0e8676b869b7ef15dbc6db73#diff-5dd147e9e978e645313dd99eab3a7bab1f1cb0a53e256843adb68aeed71e61dcR85-R87
[^2]: https://github.com/django/django/blob/b1ffa9a9d78b0c2c5ad6ed5a1d84e380d5cfd010/django/db/migrations/state.py#L842
[^3]: https://github.com/django/django/blob/b1ffa9a9d78b0c2c5ad6ed5a1d84e380d5cfd010/django/db/migrations/state.py#L340-L345
[^4]: https://github.com/django/django/blob/b1ffa9a9d78b0c2c5ad6ed5a1d84e380d5cfd010/django/db/migrations/autodetector.py#L1757-L1771
[^5]: https://github.com/django/django/blob/2351c1b12cc9cf82d642f769c774bc3ea0cc4006/django/core/management/commands/makemigrations.py#L215-L219
[^6]: https://github.com/django/django/blob/2351c1b12cc9cf82d642f769c774bc3ea0cc4006/django/core/management/commands/migrate.py#L329-L332

1 files changed, 7 insertions, 6 deletions

diff --git a/django/db/migrations/state.py b/django/db/migrations/state.py
index 802aeb0b5e..9e9cc58fae 100644
--- a/django/db/migrations/state.py
+++ b/django/db/migrations/state.py
@@ -192,9 +192,10 @@ class ProjectState:
     def remove_model_options(self, app_label, model_name, option_name, value_to_remove):
         model_state = self.models[app_label, model_name]
         if objs := model_state.options.get(option_name):
-            model_state.options[option_name] = [
-                obj for obj in objs if tuple(obj) != tuple(value_to_remove)
-            ]
+            new_value = [obj for obj in objs if tuple(obj) != tuple(value_to_remove)]
+            if option_name in {"index_together", "unique_together"}:
+                new_value = set(normalize_together(new_value))
+            model_state.options[option_name] = new_value
         self.reload_model(app_label, model_name, delay=True)
 
     def alter_model_managers(self, app_label, model_name, managers):
@@ -339,10 +340,10 @@ class ProjectState:
         options = model_state.options
         for option in ("index_together", "unique_together"):
             if option in options:
-                options[option] = [
-                    [new_name if n == old_name else n for n in together]
+                options[option] = {
+                    tuple(new_name if n == old_name else n for n in together)
                     for together in options[option]
-                ]
+                }
         # Fix to_fields to refer to the new field.
         delay = True
         references = get_references(self, model_key, (old_name, found))