git-hardening/.crosslink/rules/elixir-phoenix.md

Phoenix & LiveView Rules

HEEx Template Syntax (Critical)

• Attributes use {}: <div id={@id}> — never <%= %> in attributes
• Body values use {}: {@value} — use <%= %> only for blocks (if/for/cond)
• Class lists require []: class={["base", @flag && "active"]} — bare {} is invalid
• No else if: Use cond for multiple conditions
• Comments: <%!-- comment --%>
• Literal curlies: Use phx-no-curly-interpolation on parent tag

Phoenix v1.8

• Wrap templates with <Layouts.app flash={@flash}> (already aliased)
• current_scope errors → move routes to proper live_session, pass to Layouts.app
• <.flash_group> only in layouts.ex
• Use <.icon name="hero-x-mark"> for icons, <.input> for form fields

LiveView

• Use <.link navigate={}> / push_navigate, not deprecated live_redirect
• Hooks with own DOM need phx-update="ignore"
• Avoid LiveComponents unless necessary
• No inline <script> tags — use assets/js/app.js

Streams (Always use for collections)

stream(socket, :items, items)           # append
stream(socket, :items, items, at: -1)   # prepend
stream(socket, :items, items, reset: true)  # filter/refresh

Template: <div id="items" phx-update="stream"> with :for={{id, item} <- @streams.items}

• Streams aren't enumerable — refetch + reset to filter
• Empty states: <div class="hidden only:block">Empty</div> as sibling

Forms

# LiveView: always use to_form
assign(socket, form: to_form(changeset))

<%!-- Template: always @form, never @changeset --%>
<.form for={@form} id="my-form" phx-submit="save">
  <.input field={@form[:name]} type="text" />
</.form>

• Never <.form let={f}> or <.form for={@changeset}>

Router

• Scope alias is auto-prefixed: scope "/", AppWeb do → live "/users", UserLive = AppWeb.UserLive

Ecto

• Preload associations accessed in templates
• Use Ecto.Changeset.get_field/2 to read changeset fields
• Don't cast programmatic fields (user_id) — set explicitly

Testing

• Use has_element?(view, "#my-id"), not raw HTML matching
• Debug selectors: LazyHTML.filter(LazyHTML.from_fragment(render(view)), "selector")