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A static code analysis tool with a focus on code consistency and teaching.
Current section
Files
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Current section
Files
lib/credo/check/readability/with_single_clause.ex
defmodule Credo.Check.Readability.WithSingleClause do
use Credo.Check,
id: "EX3033",
explanations: [
check: ~S"""
`with` statements are useful when you need to chain a sequence
of pattern matches, stopping at the first one that fails.
If the `with` has a single pattern matching clause and no `else`
branch, it means that if the clause doesn't match than the whole
`with` will return the value of that clause.
However, if that `with` has also an `else` clause, then you're using `with` exactly
like a `case` and a `case` should be used instead.
Take this code:
with {:ok, user} <- User.create(make_ref()) do
user
else
{:error, :db_down} ->
raise "DB is down!"
{:error, reason} ->
raise "error: #{inspect(reason)}"
end
It can be rewritten with a clearer use of `case`:
case User.create(make_ref()) do
{:ok, user} ->
user
{:error, :db_down} ->
raise "DB is down!"
{:error, reason} ->
raise "error: #{inspect(reason)}"
end
Like all `Readability` issues, this one is not a technical concern.
But you can improve the odds of others reading and liking your code by making
it easier to follow.
"""
]
alias Credo.Code.Block
@doc false
@impl true
def run(%SourceFile{} = source_file, params) do
ctx = Context.build(source_file, params, __MODULE__)
result = Credo.Code.prewalk(source_file, &walk/2, ctx)
result.issues
end
defp walk({:with, meta, [_, _ | _] = clauses_and_body} = ast, ctx) do
if Block.do_block?(ast) && Block.else_block?(ast) do
{clauses, [_body]} = Enum.split(clauses_and_body, -1)
contains_unquote_splicing? = Enum.any?(clauses, &match?({:unquote_splicing, _, _}, &1))
pattern_clauses_count = Enum.count(clauses, &match?({:<-, _, _}, &1))
if contains_unquote_splicing? == false && pattern_clauses_count <= 1 do
{ast, put_issue(ctx, issue_for(meta, ctx))}
else
{ast, ctx}
end
else
{ast, ctx}
end
end
defp walk(ast, ctx) do
{ast, ctx}
end
defp issue_for(meta, ctx) do
format_issue(ctx,
message:
"`with` contains only one <- clause and an `else` branch, consider using `case` instead",
trigger: "with",
line_no: meta[:line]
)
end
end