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A static code analysis tool with a focus on code consistency and teaching.
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lib/credo/check/refactor/function_arity.ex
defmodule Credo.Check.Refactor.FunctionArity do
@moduledoc """
A function can take as many parameters as needed, but even in a functional
language there can be too many parameters.
Can optionally ignore private functions.
"""
@explanation [
check: @moduledoc,
params: [
max_arity: "The maximum number of parameters which a function should take.",
ignore_defp: "Set to `true` to ignore private functions."
]
]
@default_params [max_arity: 5, ignore_defp: false]
@def_ops [:def, :defp, :defmacro]
alias Credo.Code.Parameters
use Credo.Check
def run(%SourceFile{ast: ast} = source_file, params \\ []) do
issue_meta = IssueMeta.for(source_file, params)
max_arity = params |> Params.get(:max_arity, @default_params)
ignore_defp = params |> Params.get(:ignore_defp, @default_params)
Credo.Code.traverse(ast, &traverse(&1, &2, issue_meta, max_arity, ignore_defp))
end
for op <- @def_ops do
defp traverse({unquote(op) = op, meta, arguments} = ast, issues, issue_meta, max_arity, ignore_defp) when is_list(arguments) do
arity = Parameters.count(ast)
if issue?(op, ignore_defp, arity, max_arity) do
fun_name = CodeHelper.def_name(ast)
{ast, issues ++ [issue_for(issue_meta, meta[:line], fun_name, max_arity, arity)]}
else
{ast, issues}
end
end
end
defp traverse(ast, issues, _issue_meta, _max_arity, _ignore_defp) do
{ast, issues}
end
def issue?(:defp, true, _, _), do: false
def issue?(_, _, arity, max_arity) when arity > max_arity, do: true
def issue?(_, _, _, _), do: false
def issue_for(issue_meta, line_no, trigger, max_value, actual_value) do
format_issue issue_meta,
message: "Function takes too many parameters (arity is #{actual_value}, max is #{max_value}).",
trigger: trigger,
line_no: line_no,
severity: Severity.compute(actual_value, max_value)
end
end