FunctionClauseError: no function clause matching in Lightning.Projects.projects_for_user_query/1

[sentry-io]

This appears to happen whenever someone tries to do somehthing but their session token is no longer valid. They get redirected to the login page on the front-end. How should we handle these in Elixir and Sentry?

Sentry Issue: LIGHTNING-1C

FunctionClauseError: no function clause matching in Lightning.Projects.projects_for_user_query/1
  File "lib/lightning/projects.ex", line 350, in Lightning.Projects.projects_for_user_query/1
  File "lib/lightning/projects.ex", line 359, in Lightning.Projects.get_projects_for_user/1
  File "lib/lightning_web/hooks.ex", line 23, in LightningWeb.Hooks.on_mount/4
  File "lib/phoenix_live_view/lifecycle.ex", line 149, in anonymous fn/4 in Phoenix.LiveView.Lifecycle.mount/3
  File "lib/phoenix_live_view/lifecycle.ex", line 212, in Phoenix.LiveView.Lifecycle.reduce_socket/3
...
(3 additional frame(s) were not displayed)

(FunctionClauseError no function clause matching in Lightning.Projects.projects_for_user_query/1)

[stuartc]

This is an interesting one, because the router does correctly redirect users that don't have a session anymore - but it seems like the socket is still connected or at least the "request" is a LiveView request.

In InitAssigns we assume the user is logged in; because "hey that's handled upstream". And I'm not convinced that we should handle redirection there either.

However, the actual line where things break is:

def on_mount(:project_scope, %{"project_id" => project_id}, _session, socket) do
  %{current_user: current_user} = socket.assigns

  project = Lightning.Projects.get_project(project_id)

  projects = Lightning.Projects.get_projects_for_user(current_user) # <= HERE
  #...
end

I think there is quite a bit we can improve with our routing/on_mount hooks here.

But for now I think it would be ok for us to redirect inside the :project_scope hook, if there is no current_user on the socket. I'd recommend pattern matching for it in a clause above the current one.