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A static code analysis tool with a focus on code consistency and teaching.
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Files
lib/credo/check/refactor/nesting.ex
defmodule Credo.Check.Refactor.Nesting do
use Credo.Check,
id: "EX4021",
param_defaults: [max_nesting: 2],
explanations: [
check: """
Code should not be nested more than once inside a function.
defmodule CredoSampleModule do
def some_function(parameter1, parameter2) do
Enum.reduce(var1, list, fn({_hash, nodes}, list) ->
filenames = nodes |> Enum.map(&(&1.filename))
Enum.reduce(list, [], fn(item, acc) ->
if item.filename do
item # <-- this is nested 3 levels deep
end
acc ++ [item]
end)
end)
end
end
At this point it might be a good idea to refactor the code to separate the
different loops and conditions.
""",
params: [
max_nesting: "The maximum number of levels code should be nested."
]
]
@def_ops [:def, :defp, :defmacro]
@nest_ops [:if, :unless, :case, :cond, :fn, :for, :with]
@doc false
@impl true
def run(%SourceFile{} = source_file, params) do
ctx = Context.build(source_file, params, __MODULE__)
result = Credo.Code.prewalk(source_file, &walk/2, ctx)
result.issues
end
for op <- @def_ops do
defp walk(
{unquote(op) = op, meta, arguments} = ast,
%{params: %{max_nesting: max_nesting}} = ctx
)
when is_list(arguments) do
arguments
|> find_depth([], meta[:line], op)
|> handle_depth(ast, ctx, max_nesting)
end
end
defp walk(ast, ctx) do
{ast, ctx}
end
defp handle_depth(nil, ast, ctx, _max_nesting) do
{ast, ctx}
end
defp handle_depth({depth, line_no, trigger}, ast, ctx, max_nesting) when depth > max_nesting do
{ast, put_issue(ctx, issue_for(ctx, line_no, trigger, max_nesting, depth))}
end
defp handle_depth(_, ast, ctx, _max_nesting) do
{ast, ctx}
end
# Searches for the depth level and returns a tuple `{depth, line_no, trigger}`
# where the greatest depth was reached.
defp find_depth(arguments, nest_list, line_no, trigger) when is_list(arguments) do
arguments
|> Credo.Code.Block.all_blocks_for!()
|> Enum.flat_map(fn block ->
block
|> List.wrap()
|> Enum.map(&find_depth(&1, nest_list, line_no, trigger))
end)
|> Enum.sort()
|> List.last()
end
for op <- @nest_ops do
defp find_depth({unquote(op) = op, meta, arguments}, nest_list, _, _)
when is_list(arguments) do
arguments
|> Enum.map(&find_depth(&1, nest_list ++ [op], meta[:line], op))
|> Enum.sort()
|> List.last()
end
end
defp find_depth({atom, _meta, arguments}, nest_list, line_no, trigger)
when (is_atom(atom) or is_tuple(atom)) and is_list(arguments) do
arguments
|> Enum.map(&find_depth(&1, nest_list, line_no, trigger))
|> Enum.sort()
|> List.last()
end
defp find_depth(_, nest_list, line_no, trigger) do
{Enum.count(nest_list), line_no, trigger}
end
defp issue_for(ctx, line_no, trigger, max_value, actual_value) do
format_issue(
ctx,
message:
"Function body is nested too deep (max depth is #{max_value}, was #{actual_value}).",
line_no: line_no,
trigger: trigger,
severity: Severity.compute(actual_value, max_value)
)
end
end