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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/match_in_condition.ex
defmodule Credo.Check.Refactor.MatchInCondition do
@moduledoc """
Pattern matching should only ever be used for simple assignments
inside `if` and `unless` clauses.
While this fine:
# okay, simple wildcard assignment:
if contents = File.read!("foo.txt") do
do_something
end
the following should be avoided, since it mixes a pattern match with a
condition and do/else blocks.
# considered too "complex":
if {:ok, contents} = File.read("foo.txt") do
do_something
end
# also considered "complex":
if allowed? && ( contents = File.read!("foo.txt") ) do
do_something
end
If you want to match for something and execute another block otherwise,
consider using a `case` statement:
case File.read("foo.txt") do
{:ok, contents} -> do_something
_ -> do_something_else
end
"""
@explanation [check: @moduledoc]
@condition_ops [:if, :unless]
use Credo.Check
def run(%SourceFile{ast: ast} = source_file, params \\ []) do
issue_meta = IssueMeta.for(source_file, params)
Credo.Code.traverse(ast, &traverse(&1, &2, issue_meta))
end
for op <- @condition_ops do
defp traverse({unquote(op), _meta, _arguments} = ast, issues, issue_meta) do
new_issues =
Credo.Code.traverse(ast, &traverse_condition(&1, &2, ast, issue_meta))
{ast, issues ++ new_issues}
end
end
defp traverse(ast, issues, _source_file) do
{ast, issues}
end
defp traverse_condition({:=, meta, arguments} = ast, issues, {op, _, op_arguments}, issue_meta) do
case arguments do
[{atom, _, nil}, _right] when is_atom(atom) ->
# this means that the current ast is part of the `if/unless`
if op_arguments |> Enum.member?(ast) do
{ast, issues}
else
new_issue = issue_for(op, meta[:line], "=", issue_meta)
{ast, issues ++ [new_issue]}
end
_ ->
new_issue = issue_for(op, meta[:line], "=", issue_meta)
{ast, issues ++ [new_issue]}
end
end
defp traverse_condition(ast, issues, _op_ast, _issue_meta) do
{ast, issues}
end
defp issue_for(op, line_no, trigger, issue_meta) do
format_issue issue_meta,
message: "There should be no matches in `#{op}` conditions.",
trigger: trigger,
line_no: line_no
end
end