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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/abc_size.ex
defmodule Credo.Check.Refactor.ABCSize do
@moduledoc """
The ABC size describes a metric based on assignments, branches and conditions.
A high ABC size is a hint that a function might be doing "more" than it
should.
As always: Take any metric with a grain of salt. Since this one was originally
introduced for C, C++ and Java, we still have to see whether or not this can
be a useful metric in a declarative language like Elixir.
"""
@explanation [
check: @moduledoc,
params: [
max_size: "The maximum ABC size a function should have.",
]
]
@default_params [
max_size: 30
]
@def_ops [:def, :defp, :defmacro]
@branch_ops [:.]
@condition_ops [:if, :unless, :for, :try, :case, :cond, :and, :or, :&&, :||]
alias Credo.SourceFile
alias Credo.Check.CodeHelper
use Credo.Check
def run(%SourceFile{ast: ast} = source_file, params \\ []) do
issue_meta = IssueMeta.for(source_file, params)
max_abc_size = params |> Params.get(:max_size, @default_params)
Credo.Code.traverse(ast, &traverse(&1, &2, issue_meta, max_abc_size))
end
defp traverse({:defmacro, _, [{:__using__, _, _}, _]} = ast, issues, _, _) do
{ast, issues}
end
for op <- @def_ops do
defp traverse({unquote(op), meta, arguments} = ast, issues, issue_meta, max_abc_size) when is_list(arguments) do
abc_size = abc_size_for(ast) |> round
if abc_size > max_abc_size do
fun_name = CodeHelper.def_name(ast)
{ast, [issue_for(issue_meta, meta[:line], fun_name, max_abc_size, abc_size) | issues]}
else
{ast, issues}
end
end
end
defp traverse(ast, issues, _issue_meta, _max_abc_size) do
{ast, issues}
end
@doc """
Returns the ABC size for the block inside the given AST, which is expected
to represent a function or macro definition.
iex> {:def, [line: 1],
...> [
...> {:first_fun, [line: 1], nil},
...> [do: {:=, [line: 2], [{:x, [line: 2], nil}, 1]}]
...> ]
...> } |> Credo.Check.Refactor.ABCSize.abc_size
1.0
"""
def abc_size_for({_def_op, _meta, arguments}) when is_list(arguments) do
arguments
|> CodeHelper.do_block_for!
|> abc_size_for(arguments)
end
def abc_size_for(nil, _arguments), do: 0
@doc false
def abc_size_for(ast, arguments) do
initial_acc = [a: 0, b: 0, c: 0, var_names: get_parameters(arguments)]
[a: a, b: b, c: c, var_names: _] = Credo.Code.traverse(ast, &traverse_abc/2,
initial_acc)
#IO.inspect [a: a, b: b, c: c]
#IO.inspect ast
:math.sqrt(a*a+b*b+c*c)
end
def get_parameters(arguments) do
case arguments |> Enum.at(0) do
{_name, _meta, nil} -> []
{_name, _meta, parameters} -> Enum.map(parameters, &var_name/1)
end
end
for op <- @def_ops do
defp traverse_abc({unquote(op), _, arguments} = ast, abc) when is_list(arguments) do
{ast, abc}
end
end
# A - assignments
defp traverse_abc({:=, _meta, [lhs | rhs]}, [a: a, b: b, c: c, var_names: var_names]) do
name = var_name(lhs)
if name, do: var_names = Enum.into var_names, [name]
{rhs, [a: a + 1, b: b, c: c, var_names: var_names]}
end
# B - branch
defp traverse_abc({:->, _meta, arguments} = ast, [a: a, b: b, c: c, var_names: var_names]) do
var_names = Enum.into var_names, fn_parameters(arguments)
{ast, [a: a, b: b + 1, c: c, var_names: var_names]}
end
for op <- @branch_ops do
defp traverse_abc({unquote(op), _meta, arguments} = ast, [a: a, b: b, c: c, var_names: var_names]) when is_list(arguments) do
{ast, [a: a, b: b + 1, c: c, var_names: var_names]}
end
end
defp traverse_abc({fun_or_var_name, _meta, nil} = ast, [a: a, b: b, c: c, var_names: var_names]) do
is_variable = Enum.member?(var_names, fun_or_var_name)
if is_variable do
{ast, [a: a, b: b, c: c, var_names: var_names]}
else
{ast, [a: a, b: b + 1, c: c, var_names: var_names]}
end
end
# C - conditions
for op <- @condition_ops do
defp traverse_abc({unquote(op), _meta, arguments} = ast, [a: a, b: b, c: c, var_names: var_names]) when is_list(arguments) do
{ast, [a: a, b: b, c: c + 1, var_names: var_names]}
end
end
defp traverse_abc(ast, abc) do
{ast, abc}
end
defp var_name({name, _, nil}) when is_atom(name), do: name
defp var_name(_), do: nil
def fn_parameters([params, tuple]) when is_list(params) and is_tuple(tuple) do
fn_parameters(params)
end
def fn_parameters([[{:when, _, params}], _]) when is_list(params) do
fn_parameters(params)
end
def fn_parameters(params) when is_list(params) do
params
|> Enum.map(&var_name/1)
|> Enum.reject(&is_nil/1)
end
def issue_for(issue_meta, line_no, trigger, max_value, actual_value) do
format_issue issue_meta,
message: "Function is too complex (ABC size is #{actual_value}, max is #{max_value}).",
trigger: trigger,
line_no: line_no,
severity: Severity.compute(actual_value, max_value)
end
end