# `Sigra.Install.Feature`
[🔗](https://github.com/sztheory/sigra/blob/v1.20.0/lib/sigra/install/feature.ex#L1)

Behaviour that every `mix sigra.install` feature module implements.

A feature is a self-contained unit of installer work: a set of EEx
templates to render, a set of code injections to apply, a set of
migrations to emit, and a set of post-install instruction lines.

The generic walker in `Mix.Tasks.Sigra.Install` iterates a
canonical feature list (initially `[Sigra.Install.Features.Core]`)
and calls each callback in turn. Adding a feature is purely
additive: drop a new module implementing this behaviour into the
list.

Features MUST NOT reference each other (see Pitfall X-1 boundary
discipline): `Features.Core` never mentions `Features.Organizations`
and vice versa. This isolation is what makes
`mix sigra.install --no-organizations` produce a compiling app even
with no Organizations code present.

# `enabled?`

```elixir
@callback enabled?(opts :: keyword()) :: boolean()
```

Returns true when this feature should run against the given opts.

In `Sigra.Install.Features.Core` this always returns true per
Phase 11 Success Criterion #4.

# `files`

```elixir
@callback files(binding :: keyword()) :: [
  {:eex, source :: String.t(), target :: String.t()}
]
```

Returns the list of non-migration EEx template file tuples to
render. Each tuple is `{:eex, source, target}` where `source` is a
path under `priv/templates/sigra.install/<feature>/` and `target`
is the project-relative destination path.

# `injections`

```elixir
@callback injections(binding :: keyword()) :: [Sigra.Install.Injection.t()]
```

Returns a list of `%Sigra.Install.Injection{}` records describing
code injections into existing files (router, config, runtime.exs,
etc.). The walker applies each via `Sigra.Install.Injector.apply/2`.

# `migrations`

```elixir
@callback migrations(binding :: keyword()) :: [
  {slot_key :: atom(), template :: String.t(), target_basename :: String.t()}
]
```

Returns the migrations this feature needs, in intended execution
order. Each entry is `{slot_key, template_path, target_basename}`.
The central `Sigra.Install.MigrationTimestamps` allocator assigns
strictly-monotonic timestamps (GEN-07).

In `Sigra.Install.Features.Core` this returns slots `:primary`,
`:api_token`, `:audit_events`.

# `post_instructions`

```elixir
@callback post_instructions(binding :: keyword(), report :: Sigra.Install.Report.t()) :: [
  iodata()
]
```

Returns iodata lines to append to the final post-install summary.
Receives the fully-populated `Sigra.Install.Report` so features can
tailor instructions based on what was generated vs skipped.

---

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