Soundcheck.Check.Warning.UndeclaredComponentAttr (soundcheck v0.1.0)

Basics

This check has a base priority of normal and works with any version of Elixir.

Explanation

Flags @assign reads in a function component that declares its interface with attr/slot but declares no attr or slot of that name.

Phoenix only puts declared attrs (and their defaults) into a component's assigns, and warns at call sites that pass undeclared ones. An undeclared @key therefore raises KeyError on every render that does not happen to receive it.

Before:

attr :title, :string, required: true

def card(assigns) do
  ~H"<h2>{@title}</h2><p>{@subtitle}</p>"
end

After:

attr :title, :string, required: true
attr :subtitle, :string, default: nil

def card(assigns) do
  ~H"<h2>{@title}</h2><p>{@subtitle}</p>"
end

The check skips a component when:

• it declares no attr or slot at all (its interface is undeclared by design);
• it is a LiveView or LiveComponent render/1, whose assigns come from the socket rather than from attrs;
• its body assigns keys from a non-literal source, such as assign(assigns, some_map), Map.merge/2, or assigns = normalize(assigns), because the set of keys is then unknown;
• its module calls it directly as a function, which bypasses attr validation.

Keys assigned in the component body before rendering (assign(assigns, :key, value), assign_new/3, update/3) count as declared.

Confidence: high. Tier: syntactic (works without compiling).

Check-Specific Parameters

Use the following parameters to configure this check:

:excluded_paths

Paths to skip (atoms, binaries as path segments, or regexes).

This parameter defaults to [~r/\/test\//, "test"].

:implicit_assigns

Assign keys never reported (Phoenix-provided or global by convention).

This parameter defaults to [:inner_block, :rest, :__changed__, :__given__].

:strict

Report unverifiable findings too.

This parameter defaults to false.

General Parameters

Like with all checks, general params can be applied.

Parameters can be configured via the .credo.exs config file.