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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/operation_on_same_values.ex
defmodule Credo.Check.Warning.OperationOnSameValues do
@moduledoc """
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.
"""
@explanation [check: @moduledoc]
@ops_and_constant_results [
{:==, "Comparison", true},
{:>=, "Comparison", true},
{:<=, "Comparison", true},
{:!=, "Comparison", false},
{:>, "Comparison", false},
{:<, "Comparison", false},
{:/, "Operation", 1},
{:-, "Operation", 0}
]
use Credo.Check, base_priority: :high
@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
for {op, operation_name, constant_result} <- @ops_and_constant_results do
defp traverse({unquote(op), meta, [lhs, rhs]} = ast, issues, issue_meta) do
if CodeHelper.remove_metadata(lhs) == CodeHelper.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 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