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operation_on_same_values.ex
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operation_on_same_values.ex
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defmodule Credo.Check.Warning.OperationOnSameValues do
use Credo.Check,
base_priority: :high,
explanations: [
check: """
Operations on the same values always yield the same result and therefore make
little sense in production code.
Examples:
x == x # always returns true
x <= x # always returns true
x >= x # always returns true
x != x # always returns false
x > x # always returns false
y / y # always returns 1
y - y # always returns 0
In practice they are likely the result of a debugging session or were made by
mistake.
"""
]
@def_ops [:def, :defp, :defmacro]
@ops ~w(== >= <= != > < / -)a
@ops_and_constant_results [
{:==, "Comparison", true},
{:>=, "Comparison", true},
{:<=, "Comparison", true},
{:!=, "Comparison", false},
{:>, "Comparison", false},
{:<, "Comparison", false},
{:/, "Operation", 1},
{:-, "Operation", 0}
]
@doc false
@impl true
def run(%SourceFile{} = source_file, params) do
issue_meta = IssueMeta.for(source_file, params)
Credo.Code.prewalk(source_file, &traverse(&1, &2, issue_meta))
end
# TODO: consider for experimental check front-loader (ast)
for op <- @def_ops do
# exclude def arguments for operators
defp traverse(
{unquote(op), _meta, [{op, _, _} | rest]},
issues,
_issue_meta
)
when op in @ops do
{rest, issues}
end
end
for {op, operation_name, constant_result} <- @ops_and_constant_results do
defp traverse({unquote(op), meta, [lhs, rhs]} = ast, issues, issue_meta) do
if variable_or_mod_attribute?(lhs) &&
Credo.Code.remove_metadata(lhs) == Credo.Code.remove_metadata(rhs) do
new_issue =
issue_for(
issue_meta,
meta[:line],
unquote(op),
unquote(operation_name),
unquote(constant_result)
)
{ast, issues ++ [new_issue]}
else
{ast, issues}
end
end
end
defp variable_or_mod_attribute?({atom, _meta, nil}) when is_atom(atom), do: true
defp variable_or_mod_attribute?({:@, _meta, list}) when is_list(list), do: true
defp variable_or_mod_attribute?(_), do: false
# exclude @spec definitions
defp traverse({:@, _meta, [{:spec, _, _} | _]}, issues, _issue_meta) do
{nil, issues}
end
defp traverse(ast, issues, _issue_meta) do
{ast, issues}
end
defp issue_for(issue_meta, line_no, trigger, operation, constant_result) do
format_issue(
issue_meta,
message: "#{operation} will always return #{constant_result}.",
trigger: trigger,
line_no: line_no
)
end
end