Coerce Ecto.Enum search values to their dumped representation

[Actalab]

Problem

Filtering on an Ecto.Enum field via q crashes at the adapter. A field like:

field :status, Ecto.Enum, values: [down: 0, up: 1]

filtered with q[status_in][]=up (or through an association, e.g. q[category_status_in][]=published) builds WHERE status = ANY($1) but passes the raw string ["up"]. The column is an integer, so Postgrex raises:

DBConnection.EncodeError: Postgrex expected an integer in -2147483648..2147483647, got "up"

The search builder never applied the field's schema type, so enum values were sent uncast/undumped.

Fix

• Attribute now carries the resolved schema type — but only when the value needs coercion (i.e. Ecto.Enum). Plain fields keep type: nil and pass through unchanged, so there is no behavior change for string/integer/uuid/etc. columns. The field is hidden from Inspect (@derive {Inspect, optional: [:type]}) so it doesn't leak into output.
• BuildSearchQuery.coerce_values/2 casts then dumps each value through that type before the query is built ("up" → :up → 1). If a value can't be cast to the enum it falls back to the raw value.
• Where coerces per attribute before delegating to handle_expr.

Works for every Ecto.Enum (direct field or via association), including string-backed enums (dump returns the string).

Tests

• Unit coverage for coerce_values/2 (enum dump, untyped passthrough, invalid-value fallback).
• End-to-end test filtering posts by an associated enum (category_status_in) — this reproduces the reported crash and now returns the matching rows.

35 doctests, 107 tests, 0 failures.