Allow app web helpers in Backpex extensions

[Flo0807]

Summary

• import Phoenix component helpers for item actions, filters, and metrics without registering a second declarative compile hook
• allow custom fields to use their application's LiveComponent entrypoint via live_component: {MyAppWeb, :live_component}
• keep full Phoenix.Component setup in Backpex's built-in filters and value metric because they declare attr
• document application Gettext/component/verified-route usage and the upgrade impact
• add compile fixtures covering both use orders and host helpers under compiler verification

Why

PR #2055 fixed duplicate Phoenix.Component.Declarative @before_compile hooks for LiveResources. The same duplicate hook was still introduced by BackpexWeb, :item_action, :filter, and :metric when consumers also used MyAppWeb, :html.

Fields need a different path because they are real LiveComponents. The new option lets the host application's standard :live_component entrypoint perform the LiveComponent setup exactly once while Backpex adds only its field-specific aliases and helpers.

User impact

Item actions, custom filters, typed filters, and metrics may now use MyAppWeb, :html in either order to access application helpers. Extensions that declare their own attr or slot must explicitly use their application HTML entrypoint or Phoenix.Component.

Custom fields can use:

use Backpex.Field,
  config_schema: @config_schema,
  live_component: {MyAppWeb, :live_component}

Existing fields without this option keep the current Backpex LiveComponent setup.

Checks

• MIX_ENV=test mix lint — 275 tests passed (100 doctests, 175 tests), Credo clean
• mix test test/backpex/web_helpers_test.exs — passed with no compile or runtime diagnostics

[Copilot]

Pull request overview

This PR improves how Backpex extension modules (item actions, filters, metrics, and custom fields) access host-application web helpers (Gettext/components/verified routes) while avoiding duplicate Phoenix.Component.Declarative @before_compile hooks that can fail compilation under --warnings-as-errors.

Changes:

• Introduce a BackpexWeb, :heex entrypoint and update :item_action, :filter, and :metric to import Phoenix.Component (instead of use), preventing duplicate declarative hooks when combined with MyAppWeb, :html.
• Add a live_component: {MyAppWeb, :live_component} option to Backpex.Field so custom fields can reuse the host LiveComponent setup (and helpers) exactly once.
• Add compiler-verification fixtures/tests plus documentation and upgrade notes covering the new usage patterns and required attr/slot setup.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/fixtures/web_helpers/extension_modules.fixture	Compile fixture covering both use orders and host helper availability across extensions.
test/backpex/web_helpers_test.exs	Test that compiling the fixture produces no compile/runtime diagnostics.
lib/backpex/metrics/value.ex	Ensures Backpex’s built-in value metric keeps full Phoenix.Component setup for attr.
lib/backpex/filters/select.ex	Ensures built-in select filter keeps full Phoenix.Component setup for attr.
lib/backpex/filters/range.ex	Ensures built-in range filter keeps full Phoenix.Component setup for attr.
lib/backpex/filters/multi_select.ex	Ensures built-in multi-select filter keeps full Phoenix.Component setup for attr.
lib/backpex/filters/boolean.ex	Ensures built-in boolean filter keeps full Phoenix.Component setup for attr.
lib/backpex/field.ex	Adds :live_component option handling so custom fields can use host LiveComponent entrypoint.
lib/backpex_web.ex	Adds :heex + :field_helpers entrypoints and switches extension entrypoints to use :heex.
guides/upgrading/v0.19.md	Upgrade notes explaining the behavior change and required actions for attr/slot.
guides/filter/custom-filter.md	Docs for using host :html in custom/built-in filter macros and supported use orders.
guides/fields/custom-fields.md	Docs for configuring host LiveComponent entrypoint in custom fields.
guides/actions/item-actions.md	Docs for using host :html helpers in item actions (either use order).

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