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credo
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A static code analysis tool with a focus on code consistency and teaching.
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lib/credo/check/warning/unused_enum_operation.ex
defmodule Credo.Check.Warning.UnusedEnumOperation do
@moduledoc """
With the exception of `Enum.each/2`, the result of a call to the
Enum module's functions has to be used.
While this is correct ...
def prepend_my_username(my_username, usernames) do
valid_usernames = Enum.reject(usernames, &is_nil/1)
[my_username] ++ valid_usernames
end
... we forgot to save the downcased username in this example:
# This is bad because it does not modify the usernames variable!
def prepend_my_username(my_username, usernames) do
Enum.reject(usernames, &is_nil/1)
[my_username] ++ valid_usernames
end
Since Elixir variables are immutable, Enum operations never work on the
variable you pass in, but return a new variable which has to be used somehow
(the exception being `Enum.each/2` which iterates a list and returns `:ok`).
"""
@explanation [check: @moduledoc]
@funs_with_return_value ~w(all any at chunk chunk chunk_by concat concat count count dedup dedup_by drop drop_while empty fetch fetch filter filter_map find find_index find_value flat_map flat_map_reduce group_by intersperse into into join map map_join map_reduce max max_by member min min_by min_max min_max_by partition random reduce reduce reduce_while reject reverse reverse reverse_slice scan scan shuffle slice slice sort sort sort_by split split_while sum take take_every take_random take_while to_list uniq uniq_by unzip with_index zip)a
alias Credo.Check.Warning.UnusedFunctionReturnHelper
use Credo.Check, base_priority: :high
@doc false
def run(%SourceFile{} = source_file, params \\ []) do
issue_meta = IssueMeta.for(source_file, params)
all_unused_calls =
UnusedFunctionReturnHelper.find_unused_calls(source_file, params,
[:Enum], @funs_with_return_value)
all_unused_calls
|> Enum.reduce([], fn(invalid_call, issues) ->
{_, meta, _} = invalid_call
trigger =
invalid_call
|> Macro.to_string
|> String.split("(")
|> List.first
issues ++ [issue_for(meta[:line], trigger, issue_meta)]
end)
end
defp issue_for(line_no, trigger, issue_meta) do
format_issue issue_meta,
message: "There should be no unused return values for #{trigger}().",
trigger: trigger,
line_no: line_no
end
end