zorbash/PHOENIX_AGENTS.md

## PHOENIX_AGENTS.md

      
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              PHOENIX_AGENTS.md
            
          
    Project guidelines


Use mix precommit alias when you are done with all changes and fix any pending issues
Use the already included and available :req (Req) library for HTTP requests, avoid :httpoison, :tesla, and :httpc. Req is included by default and is the preferred HTTP client for Phoenix apps

Phoenix v1.8 guidelines


Always begin your LiveView templates with <Layouts.app flash={@flash} ...> which wraps all inner content
The MyAppWeb.Layouts module is aliased in the my_app_web.ex file, so you can use it without needing to alias it again
Anytime you run into errors with no current_scope assign:

You failed to follow the Authenticated Routes guidelines, or you failed to pass current_scope to <Layouts.app>
Always fix the current_scope error by moving your routes to the proper live_session and ensure you pass current_scope as needed


Phoenix v1.8 moved the <.flash_group> component to the Layouts module. You are forbidden from calling <.flash_group> outside of the layouts.ex module
Out of the box, core_components.ex imports an <.icon name="hero-x-mark" class="w-5 h-5"/> component for for hero icons. Always use the <.icon> component for icons, never use Heroicons modules or similar
Always use the imported <.input> component for form inputs from core_components.ex when available. <.input> is imported and using it will save steps and prevent errors
If you override the default input classes (<.input class="myclass px-2 py-1 rounded-lg">)) class with your own values, no default classes are inherited, so your
custom classes must fully style the input


Elixir guidelines


Elixir lists do not support index based access via the access syntax
Never do this (invalid):
i = 0
mylist = ["blue", "green"]
mylist[i]

Instead, always use Enum.at, pattern matching, or List for index based list access, ie:
i = 0
mylist = ["blue", "green"]
Enum.at(mylist, i)


Elixir variables are immutable, but can be rebound, so for block expressions like if, case, cond, etc
you must bind the result of the expression to a variable if you want to use it and you CANNOT rebind the result inside the expression, ie:
# INVALID: we are rebinding inside the `if` and the result never gets assigned
if connected?(socket) do
  socket = assign(socket, :val, val)
end

# VALID: we rebind the result of the `if` to a new variable
socket =
  if connected?(socket) do
    assign(socket, :val, val)
  end


Never nest multiple modules in the same file as it can cause cyclic dependencies and compilation errors


Never use map access syntax (changeset[:field]) on structs as they do not implement the Access behaviour by default. For regular structs, you must access the fields directly, such as my_struct.field or use higher level APIs that are available on the struct if they exist, Ecto.Changeset.get_field/2 for changesets


Elixir's standard library has everything necessary for date and time manipulation. Familiarize yourself with the common Time, Date, DateTime, and Calendar interfaces by accessing their documentation as necessary. Never install additional dependencies unless asked or for date/time parsing (which you can use the date_time_parser package)


Don't use String.to_atom/1 on user input (memory leak risk)


Predicate function names should not start with is_ and should end in a question mark. Names like is_thing should be reserved for guards


Elixir's builtin OTP primitives like DynamicSupervisor and Registry, require names in the child spec, such as {DynamicSupervisor, name: MyApp.MyDynamicSup}, then you can use DynamicSupervisor.start_child(MyApp.MyDynamicSup, child_spec)


Use Task.async_stream(collection, callback, options) for concurrent enumeration with back-pressure. The majority of times you will want to pass timeout: :infinity as option


Mix guidelines


Read the docs and options before using tasks (by using mix help task_name)
To debug test failures, run tests in a specific file with mix test test/my_test.exs or run all previously failed tests with mix test --failed
mix deps.clean --all is almost never needed. Avoid using it unless you have good reason

Test guidelines


Always use start_supervised!/1 to start processes in tests as it guarantees cleanup between tests
Avoid Process.sleep/1 and Process.alive?/1 in tests


Instead of sleeping to wait for a process to finish, always use Process.monitor/1 and assert on the DOWN message:
ref = Process.monitor(pid)
assert_receive {:DOWN, ^ref, :process, ^pid, :normal}


Instead of sleeping to synchronize before the next call, always use _ = :sys.get_state/1 to ensure the process has handled prior messages


Phoenix guidelines


Remember Phoenix router scope blocks include an optional alias which is prefixed for all routes within the scope. Always be mindful of this when creating routes within a scope to avoid duplicate module prefixes.


You never need to create your own alias for route definitions! The scope provides the alias, ie:
scope "/admin", AppWeb.Admin do
  pipe_through :browser

  live "/users", UserLive, :index
end

the UserLive route would point to the AppWeb.Admin.UserLive module


Phoenix.View no longer is needed or included with Phoenix, don't use it


Ecto Guidelines


Always preload Ecto associations in queries when they'll be accessed in templates, ie a message that needs to reference the message.user.email
Remember import Ecto.Query and other supporting modules when you write seeds.exs
Ecto.Schema fields always use the :string type, even for :text, columns, ie: field :name, :string
Ecto.Changeset.validate_number/2 DOES NOT SUPPORT the :allow_nil option. By default, Ecto validations only run if a change for the given field exists and the change value is not nil, so such as option is never needed
You must use Ecto.Changeset.get_field(changeset, :field) to access changeset fields
Fields which are set programatically, such as user_id, must not be listed in cast calls or similar for security purposes. Instead they must be explicitly set when creating the struct
Always invoke mix ecto.gen.migration migration_name_using_underscores when generating migration files, so the correct timestamp and conventions are applied
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