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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/cyclomatic_complexity.ex
defmodule Credo.Check.Refactor.CyclomaticComplexity do
@moduledoc """
Cyclomatic complexity is a software complexity metric closely correlated with
coding errors.
If a function feels like it's gotten too complex, it more often than not also
has a high CC value. So, if anything, this is useful to convince team members
and bosses of a need to refactor parts of the code based on "objective"
metrics.
"""
@explanation [
check: @moduledoc,
params: [
max_complexity: "The maximum cyclomatic complexity a function should have."
]
]
@default_params [max_complexity: 9]
@def_ops [:def, :defp, :defmacro]
# these have two outcomes: it succeds or does not
@double_condition_ops [:if, :unless, :for, :try, :and, :or, :&&, :||]
# these can have multiple outcomes as they are defined in their do blocks
@multiple_condition_ops [:case, :cond]
@op_complexity_map [
def: 1,
defp: 1,
defmacro: 1,
if: 1,
unless: 1,
for: 1,
try: 1,
and: 1,
or: 1,
&&: 1,
||: 1,
case: 1,
cond: 1,
]
alias Credo.Check.CodeHelper
alias Credo.SourceFile
use Credo.Check
def run(%SourceFile{ast: ast} = source_file, params \\ []) do
issue_meta = IssueMeta.for(source_file, params)
max_complexity = params |> Params.get(:max_complexity, @default_params)
Credo.Code.traverse(ast, &traverse(&1, &2, issue_meta, max_complexity))
end
# exception for `__using__` macros
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_complexity) when is_list(arguments) do
complexity = ast |> complexity_for |> round
if complexity > max_complexity do
fun_name = CodeHelper.def_name(ast)
{ast, issues ++ [issue_for(issue_meta, meta[:line], fun_name, max_complexity, complexity)]}
else
{ast, issues}
end
end
end
defp traverse(ast, issues, _source_file, _max_complexity) do
{ast, issues}
end
@doc """
Returns the Cyclomatic Complexity score 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.CyclomaticComplexity.complexity_for
1.0
"""
def complexity_for({_def_op, _meta, _arguments} = ast) do
Credo.Code.traverse(ast, &traverse_complexity/2, 0)
end
for op <- @def_ops do
defp traverse_complexity({unquote(op) = op, _meta, arguments} = ast, complexity) when is_list(arguments) do
{ast, complexity + @op_complexity_map[op]}
end
end
for op <- @double_condition_ops do
defp traverse_complexity({unquote(op) = op, _meta, arguments} = ast, complexity) when is_list(arguments) do
{ast, complexity + @op_complexity_map[op]}
end
end
for op <- @multiple_condition_ops do
defp traverse_complexity({unquote(op), _meta, nil} = ast, complexity) do
{ast, complexity}
end
defp traverse_complexity({unquote(op) = op, _meta, arguments} = ast, complexity) when is_list(arguments) do
block_cc =
arguments
|> CodeHelper.do_block_for!
|> do_block_complexity(op)
{ast, complexity + block_cc}
end
end
defp traverse_complexity(ast, complexity) do
{ast, complexity}
end
defp do_block_complexity(nil, _), do: 0
defp do_block_complexity(block, op) do
count = block |> List.wrap |> Enum.count
count * @op_complexity_map[op]
end
def issue_for(issue_meta, line_no, trigger, max_value, actual_value) do
format_issue issue_meta,
message: "Function is too complex (CC is #{actual_value}, max is #{max_value}).",
trigger: trigger,
line_no: line_no,
severity: Severity.compute(actual_value, max_value)
end
end