# `Mutare.Ecto.Changeset`
[🔗](https://github.com/foxbenjaminfox/mutare_ecto/blob/v0.4.2/lib/mutare/ecto/changeset.ex#L1)

Drop a transparent step from a changeset pipeline — the changeset equivalent of removing a
guard. `cs |> validate_required([:name])` → `cs`. A surviving mutant means **no test
exercises** the behaviour that step contributes. Matched by resolving the call to
`Ecto.Changeset` (direct, aliased, or the common `import Ecto.Changeset`), so the form the
call uses doesn't matter.

Two families, dropped by the same machinery but kept apart because the thing being removed
differs:

  * **`:validation_drop`** — a validator or constraint (`validate_required`, `unique_constraint`,
    …). Each returns the changeset unchanged on the happy path, so dropping it is always
    behaviour-preserving *except* for the rule it enforces. A survivor means the rule is untested.
  * **`:hook_drop`** — a deferred Repo-time hook (`prepare_changes`, `optimistic_lock`). These
    are **not** validators: they register code/locks the Repo runs at `insert`/`update` time
    (a counter bump, a derived column, a stale-version guard). Dropping one is still
    compile-safe and changeset-shape-preserving, but the gap it surfaces is "this side effect /
    concurrency guard is never asserted", a different question — so it gets its own family.

`Mutare.Ecto.StageDrop` collapses the call to its changeset argument.

# `mutations`

```elixir
@spec mutations(Macro.t(), Mutare.Ecto.Context.t()) :: [Mutare.Ecto.Tag.t()]
```

Changeset-step drop mutations for an `Ecto.Changeset` call as tags, or `[]`.
A validator/constraint drops under `:validation_drop`; a Repo-time hook under `:hook_drop`.

# `stages`

```elixir
@spec stages() :: [atom()]
```

Every pipeline stage the plugin mutates — the droppable validators/constraints and the Repo-time
hooks. The one list `Mutare.Ecto.call_routes/0` registers `:routing` (through
`Mutare.Ecto.Changeset.Routing`), so a stage is routed exactly when it is mutated.

---

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