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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/negated_is_nil.ex
defmodule Credo.Check.Refactor.NegatedIsNil do
@moduledoc false
@checkdoc """
We should avoid negating the `is_nil` predicate function.
Here are a couple of examples:
The code here ...
def fun(%{external_id: external_id, id: id}) when not is_nil(external_id) do
...
end
... can be refactored to look like this:
def fun(%{external_id: nil, id: id}) do
...
end
def fun(%{external_id: external_id, id: id}) do
...
end
Similar to negating unless blocks, the reason for this check is not
technical, but a human one. If we can use the positive, more direct and human
friendly case, we should.
"""
@explanation [check: @checkdoc]
use Credo.Check, base_priority: :low
@doc false
def run(source_file, params \\ []) do
issue_meta = IssueMeta.for(source_file, params)
Credo.Code.prewalk(source_file, &traverse(&1, &2, issue_meta))
end
defp traverse({:when, meta, [_, {negation, _, [{:is_nil, _, _}]}]} = ast, issues, issue_meta)
when negation in [:!, :not] do
issue =
format_issue(
issue_meta,
message: "Negated is_nil in guard clause found",
trigger: "when !/not is_nil",
line_no: meta[:line]
)
{ast, [issue | issues]}
end
defp traverse(ast, issues, _), do: {ast, issues}
end