# `Soundcheck.Check.Warning.OptionalAttrWithoutDefault`
[🔗](https://github.com/leonqadirie/soundcheck/blob/v0.1.0/lib/soundcheck/check/warning/optional_attr_without_default.ex#L1)

## Basics

> #### This check is disabled by default. {: .neutral}
>
> [Learn how to enable it](`e:credo:config_file.html#checks`) via `.credo.exs`.

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

## Explanation

Flags `@key` reads of an optional `attr` that declares no default.
Phoenix puts only declared defaults into a component's assigns, so
when a caller omits the attr, `@key` raises `KeyError`, even inside
`:if={@key}`.

Before:

    attr :icon, :string

    def badge(assigns), do: ~H"<span :if={@icon}>{@icon}</span>"

After:

    attr :icon, :string, default: nil

    def badge(assigns), do: ~H"<span :if={@icon}>{@icon}</span>"

Reading the attr as `assigns[:icon]` never raises and is not
reported. Attrs marked `required: true`, `:global` attrs, keys the
component body assigns before rendering (`assign_new/3` included),
components whose body rebinds `assigns` through another function, and
LiveView or LiveComponent `render/1` functions are skipped.

Confidence: medium. 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"]`.

### `:strict`

  Unused.

*This parameter defaults to* `false`.

## General Parameters

Like with all checks, [general params](`e:credo:check_params.html`) can be applied.

Parameters can be configured via the [`.credo.exs` config file](`e:credo:config_file.html`).

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*Consult [api-reference.md](api-reference.md) for complete listing*