# `OXC.Lint.Rule`
[🔗](https://github.com/elixir-volt/oxc_ex/blob/v0.19.0/lib/oxc/lint/rule.ex#L1)

Behaviour for custom lint rules in Elixir.

Rules receive the parsed ESTree AST (from `OXC.parse/2`) and return
findings located by AST node `start` and `end` offsets. Use `OXC.walk/2`, `OXC.collect/2`, or `OXC.postwalk/3`
for traversal.

## Example

    defmodule MyApp.NoConsoleLog do
      @behaviour OXC.Lint.Rule

      @impl true
      def meta do
        %{
          name: "my-app/no-console-log",
          description: "Disallow console.log in production code",
          category: :restriction,
          fixable: false
        }
      end

      @impl true
      def run(ast, _context) do
        OXC.collect(ast, fn
          %{
            type: :call_expression,
            callee: %{
              type: :member_expression,
              object: %{type: :identifier, name: "console"},
              property: %{type: :identifier, name: "log"}
            },
            start: start,
            end: stop
          } ->
            {:keep, %{start: start, end: stop, message: "Unexpected console.log"}}

          _ ->
            :skip
        end)
      end
    end

# `context`

```elixir
@type context() :: %{source: String.t(), filename: String.t(), settings: map()}
```

# `diagnostic`

```elixir
@type diagnostic() :: %{
  :start => non_neg_integer(),
  :end => non_neg_integer(),
  :message => String.t(),
  optional(:help) => String.t() | nil,
  optional(:labels) => [
    %{
      :start => non_neg_integer(),
      :end => non_neg_integer(),
      optional(:message) => String.t()
    }
  ]
}
```

A finding reported by a rule, located by the byte `start` and `end` offsets of an AST node.

`OXC.Lint.run/3` turns findings into `t:OXC.Diagnostic.t/0` maps.

# `meta`

```elixir
@type meta() :: %{
  name: String.t(),
  description: String.t(),
  category:
    :correctness
    | :suspicious
    | :pedantic
    | :perf
    | :style
    | :restriction
    | :nursery,
  fixable: boolean()
}
```

# `meta`

```elixir
@callback meta() :: meta()
```

# `run`

```elixir
@callback run(ast :: map(), context :: context()) :: [diagnostic()]
```

---

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