defmodule Credo.Check.Refactor.ABCSize do
use Credo.Check,
id: "EX4001",
tags: [:controversial],
param_defaults: [
max_size: 30,
excluded_functions: []
],
explanations: [
check: """
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.
""",
params: [
max_size: "The maximum ABC size a function should have.",
excluded_functions: "All functions listed will be ignored."
]
]
@ecto_functions ["where", "from", "select", "join"]
@def_ops [:def, :defp, :defmacro]
@branch_ops [:.]
@condition_ops [:if, :unless, :for, :try, :case, :cond, :and, :or, :&&, :||]
@non_calls [:==, :fn, :__aliases__, :__block__, :if, :or, :|>, :%{}]
@doc false
@impl true
def run(%SourceFile{} = source_file, params) do
ignore_ecto? = imports_ecto_query?(source_file)
issue_meta = IssueMeta.for(source_file, params)
max_abc_size = Params.get(params, :max_size, __MODULE__)
excluded_functions = Params.get(params, :excluded_functions, __MODULE__)
excluded_functions =
if ignore_ecto? do
@ecto_functions ++ excluded_functions
else
excluded_functions
end
Credo.Code.prewalk(
source_file,
&traverse(&1, &2, issue_meta, max_abc_size, excluded_functions)
)
end
defp imports_ecto_query?(source_file),
do: Credo.Code.prewalk(source_file, &traverse_for_ecto/2, false)
defp traverse_for_ecto(_, true), do: {nil, true}
defp traverse_for_ecto({:import, _, [{:__aliases__, _, [:Ecto, :Query]} | _]}, false),
do: {nil, true}
defp traverse_for_ecto(ast, false), do: {ast, false}
defp traverse(
{:defmacro, _, [{:__using__, _, _}, _]} = ast,
issues,
_issue_meta,
_max_abc_size,
_excluded_functions
) do
{ast, issues}
end
for op <- @def_ops do
defp traverse(
{unquote(op), meta, arguments} = ast,
issues,
issue_meta,
max_abc_size,
excluded_functions
)
when is_list(arguments) do
abc_size =
ast
|> abc_size_for(excluded_functions)
|> round
if abc_size > max_abc_size do
fun_name = Credo.Code.Module.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, _excluded_functions) 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}, excluded_functions) when is_list(arguments) do
arguments
|> Credo.Code.Block.do_block_for!()
|> abc_size_for(arguments, excluded_functions)
end
@doc false
def abc_size_for(nil, _arguments, _excluded_functions), do: 0
def abc_size_for(ast, arguments, excluded_functions) do
initial_acc = [a: 0, b: 0, c: 0, var_names: get_parameters(arguments)]
[a: a, b: b, c: c, var_names: _] =
Credo.Code.prewalk(ast, &traverse_abc(&1, &2, excluded_functions), initial_acc)
:math.sqrt(a * a + b * b + c * c)
end
defp get_parameters(arguments) do
case Enum.at(arguments, 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, _excluded_functions)
when is_list(arguments) do
{ast, abc}
end
end
# Ignore string interpolation
defp traverse_abc({:<<>>, _, _}, acc, _excluded_functions) do
{nil, acc}
end
# A - assignments
defp traverse_abc(
{:=, _meta, [lhs | rhs]},
[a: a, b: b, c: c, var_names: var_names],
_excluded_functions
) do
var_names =
case var_name(lhs) do
nil ->
var_names
false ->
var_names
name ->
var_names ++ [name]
end
{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],
_excluded_functions
) do
var_names = 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, [{_, _, nil}, _] = arguments} = ast,
[a: a, b: b, c: c, var_names: var_names],
_excluded_functions
)
when is_list(arguments) do
{ast, [a: a, b: b, c: c, var_names: var_names]}
end
defp traverse_abc(
{unquote(op), _meta, arguments} = ast,
[a: a, b: b, c: c, var_names: var_names],
_excluded_functions
)
when is_list(arguments) do
{ast, [a: a, b: b + 1, c: c, var_names: var_names]}
end
end
defp traverse_abc(
{fun_name, _meta, arguments} = ast,
[a: a, b: b, c: c, var_names: var_names],
excluded_functions
)
when is_atom(fun_name) and fun_name not in @non_calls and is_list(arguments) do
if Enum.member?(excluded_functions, to_string(fun_name)) do
{nil, [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
defp traverse_abc(
{fun_or_var_name, _meta, nil} = ast,
[a: a, b: b, c: c, var_names: var_names],
_excluded_functions
) 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],
_excluded_functions
)
when is_list(arguments) do
{ast, [a: a, b: b, c: c + 1, var_names: var_names]}
end
end
defp traverse_abc(ast, abc, _excluded_functions) do
{ast, abc}
end
defp var_name({name, _, nil}) when is_atom(name), do: name
defp var_name(_), do: nil
defp fn_parameters([params, tuple]) when is_list(params) and is_tuple(tuple) do
fn_parameters(params)
end
defp fn_parameters([[{:when, _, params}], _]) when is_list(params) do
fn_parameters(params)
end
defp fn_parameters(params) when is_list(params) do
params
|> Enum.map(&var_name/1)
|> Enum.reject(&is_nil/1)
end
defp 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
