Make FormView generic over form type

Subclasses can now parameterize `FormView[MyForm]` to get type-safe
access to their specific form in `form_valid`, `get_success_url`, etc.
without Liskov violations. The `form_class` attribute must still be
set separately at runtime — a future typed-views arc explores DRY
options via __init_subclass__.

Updates plain-loginlink and plain-passwords to use the generic
parameterization, dropping 4 `# ty: ignore[invalid-method-override]`
suppressions and the `assert isinstance(form, LoginLinkForm)` runtime
check added in the previous ty upgrade commit.

Author: davegaeddert

plain-loginlink/plain/loginlink/views.py

@@ -4,7 +4,6 @@
 
 from plain.auth import login, logout
 from plain.auth.views import AuthView
-from plain.forms import BaseForm
 from plain.http import RedirectResponse, Response
 from plain.runtime import settings
 from plain.urls import reverse, reverse_lazy
@@ -19,7 +18,7 @@
 )
 
 
-class LoginLinkFormView(AuthView, FormView):
+class LoginLinkFormView(AuthView, FormView[LoginLinkForm]):
     form_class = LoginLinkForm
     success_url = reverse_lazy("loginlink:sent")
 
@@ -31,12 +30,11 @@ def get(self) -> Response:
 
         return super().get()
 
-    def form_valid(self, form: BaseForm) -> Response:
-        assert isinstance(form, LoginLinkForm)
+    def form_valid(self, form: LoginLinkForm) -> Response:
         form.maybe_send_link(self.request)
         return super().form_valid(form)
 
-    def get_success_url(self, form: BaseForm) -> str:
+    def get_success_url(self, form: LoginLinkForm) -> str:
         if next_url := form.cleaned_data.get("next"):
             # Keep the next URL in the query string so the sent
             # view can redirect to it if reloaded and logged in already.

plain-passwords/plain/passwords/views.py

@@ -32,7 +32,7 @@
     from plain.postgres import Model
 
 
-class PasswordForgotView(FormView):
+class PasswordForgotView(FormView[PasswordResetForm]):
     form_class = PasswordResetForm
     reset_confirm_url_name: str
 
@@ -52,14 +52,14 @@ def generate_password_reset_url(self, user: Any) -> str:
         url = reverse(self.reset_confirm_url_name) + f"?token={token}"
         return self.request.build_absolute_uri(url)
 
-    def form_valid(self, form: PasswordResetForm) -> Response:  # ty: ignore[invalid-method-override]
+    def form_valid(self, form: PasswordResetForm) -> Response:
         form.save(
             generate_reset_url=self.generate_password_reset_url,
         )
         return super().form_valid(form)
 
 
-class PasswordResetView(AuthView, FormView):
+class PasswordResetView(AuthView, FormView[PasswordSetForm]):
     form_class = PasswordSetForm
     reset_token_max_age = 60 * 60  # 1 hour
     _reset_token_session_key = "_password_reset_token"
@@ -135,15 +135,15 @@ def get_form_kwargs(self) -> dict:
         kwargs["user"] = self.get_user()
         return kwargs
 
-    def form_valid(self, form: PasswordSetForm) -> Response:  # ty: ignore[invalid-method-override]
+    def form_valid(self, form: PasswordSetForm) -> Response:
         form.save()
         del self.session[self._reset_token_session_key]
         # If you wanted, you could log in the user here so they don't have to
         # go through the log in form again.
         return super().form_valid(form)
 
 
-class PasswordChangeView(AuthView, FormView):
+class PasswordChangeView(AuthView, FormView[PasswordChangeForm]):
     # Change to PasswordSetForm if you want to set new passwords
     # without confirming the old one.
     form_class = PasswordChangeForm
@@ -153,15 +153,15 @@ def get_form_kwargs(self) -> dict:
         kwargs["user"] = self.user
         return kwargs
 
-    def form_valid(self, form: PasswordChangeForm) -> Response:  # ty: ignore[invalid-method-override]
+    def form_valid(self, form: PasswordChangeForm) -> Response:
         form.save()
         # Updating the password logs out all other sessions for the user
         # except the current one.
         update_session_auth_hash(self.request, form.user)
         return super().form_valid(form)
 
 
-class PasswordLoginView(AuthView, FormView):
+class PasswordLoginView(AuthView, FormView[PasswordLoginForm]):
     form_class = PasswordLoginForm
     success_url = "/"
 
@@ -172,7 +172,7 @@ def get(self) -> Response:
 
         return super().get()
 
-    def form_valid(self, form: PasswordLoginForm) -> Response:  # ty: ignore[invalid-method-override]
+    def form_valid(self, form: PasswordLoginForm) -> Response:
         # Log the user in and redirect
         auth_login(self.request, form.get_user())
 

plain/plain/views/forms.py

@@ -10,13 +10,18 @@
     from plain.forms import BaseForm
 
 
-class FormView(TemplateView):
-    """A view for displaying a form and rendering a template response."""
+class FormView[F: "BaseForm"](TemplateView):
+    """A view for displaying a form and rendering a template response.
 
-    form_class: type["BaseForm"] | None = None
+    Generic over the form type. Subclasses that want type-safe access to
+    their specific form should parameterize: `FormView[MyForm]`. The
+    `form_class` attribute must still be set separately at runtime.
+    """
+
+    form_class: type[F] | None = None
     success_url: Callable | str | None = None
 
-    def get_form(self) -> "BaseForm":
+    def get_form(self) -> F:
         """Return an instance of the form to be used in this view."""
         if not self.form_class:
             raise ImproperlyConfigured(
@@ -32,17 +37,17 @@ def get_form_kwargs(self) -> dict[str, Any]:
             "request": self.request,
         }
 
-    def get_success_url(self, form: "BaseForm") -> str:
+    def get_success_url(self, form: F) -> str:
         """Return the URL to redirect to after processing a valid form."""
         if not self.success_url:
             raise ImproperlyConfigured("No URL to redirect to. Provide a success_url.")
         return str(self.success_url)  # success_url may be lazy
 
-    def form_valid(self, form: "BaseForm") -> Response:
+    def form_valid(self, form: F) -> Response:
         """If the form is valid, redirect to the supplied URL."""
         return RedirectResponse(self.get_success_url(form))
 
-    def form_invalid(self, form: "BaseForm") -> Response:
+    def form_invalid(self, form: F) -> Response:
         """If the form is invalid, render the invalid form."""
         context = {
             **self.get_template_context(),