# `Mix.SCM`
[🔗](https://github.com/elixir-lang/elixir/blob/7ff272706afc522e74121493b7166719985cb099/lib/mix/lib/mix/scm.ex#L5)

This module provides helper functions and defines the
behaviour required by any source code manager (SCM) used by Mix.

# `opts`

```elixir
@type opts() :: keyword()
```

# `t`

```elixir
@type t() :: module()
```

A module implementing the `Mix.SCM` behaviour.

# `accepts_options`

```elixir
@callback accepts_options(app :: atom(), opts()) :: opts() | nil
```

This behaviour function receives a keyword list of `opts`
and should return an updated list in case the SCM consumes
the available options. For example, when a developer specifies
a dependency:

    {:foo, "0.1.0", github: "foo/bar"}

Each registered SCM will be asked if they consume this dependency,
receiving `[github: "foo/bar"]` as argument. Since this option makes
sense for the Git SCM, it will return an update list of options
while other SCMs would simply return `nil`.

# `checked_out?`

```elixir
@callback checked_out?(opts()) :: boolean()
```

This behaviour function returns a boolean if the
dependency is available.

# `checkout`

```elixir
@callback checkout(opts()) :: any()
```

This behaviour function checks out dependencies.

If the dependency is locked, a lock is received in `opts`
and the repository must be check out at the lock. Otherwise,
no lock is given and the repository can be checked out
to the latest version.

It must return the current lock.

# `equal?`

```elixir
@callback equal?(opts1 :: opts(), opts2 :: opts()) :: boolean()
```

Receives two options and must return `true` if they refer to the
same repository. The options are guaranteed to belong to the
same SCM.

# `fetchable?`

```elixir
@callback fetchable?() :: boolean()
```

Returns a boolean if the dependency can be fetched
or it is meant to be previously available in the
file system.

Local dependencies (i.e. non-fetchable ones) are automatically
recompiled every time the parent project is compiled.

# `format`

```elixir
@callback format(opts()) :: String.t()
```

Returns a string representing the SCM. This is used
when printing the dependency and not for inspection,
so the amount of information should be concise and
easy to spot.

# `format_lock`

```elixir
@callback format_lock(opts()) :: String.t() | nil
```

Returns a string representing the SCM. This is used
when printing the dependency and not for inspection,
so the amount of information should be concise and
easy to spot.

If nil is returned, it means no lock information is available.

# `lock_status`

```elixir
@callback lock_status(opts()) :: :mismatch | :outdated | :ok
```

This behaviour function checks the status of the lock. In
particular, it checks if the revision stored in the lock
is the same as the repository it is currently in.

It may return:

  * `:mismatch` - if the lock doesn't match and we need to
    simply move to the latest lock

  * `:outdated` - the repository options are outdated in the
    lock and we need to trigger a full update

  * `:ok` - everything is fine

The lock is sent via `opts[:lock]` but it may not always be
available. In such cases, if the SCM requires a lock, it must
return `:mismatch`, otherwise simply `:ok`.

Note the lock may also belong to another SCM and as such, an
structural check is required. A structural mismatch should always
return `:outdated`.

# `managers`

```elixir
@callback managers(opts()) :: [atom()]
```

Returns the usable managers for the dependency. This can be used
if the SCM has extra knowledge of the dependency, otherwise it
should return an empty list.

# `update`

```elixir
@callback update(opts()) :: any()
```

This behaviour function updates dependencies. It may be
called by `deps.get` or `deps.update`.

In the first scenario, a lock is received in `opts` and
the repository must be updated to the lock. In the second,
no lock is given and the repository can be updated freely.

It must return the current lock.

# `append`

Appends the given SCM module to the list of available SCMs.

# `available`

Returns all available SCMs. Each SCM is tried in order
until a matching one is found.

# `delete`
*since 1.16.2* 

Deletes the given SCM from the list of available SCMs.

# `prepend`

Prepends the given SCM module to the list of available SCMs.

---

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