ExSlop

https://hexdocs.pm/ex_slop
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ExSlop is a Credo plugin that detects and catches AI-generated code slop in Elixir projects through...
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### Good Doc Example with Behavior and Examples

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.NarratorDoc.md

This example shows a 'good' function documentation comment that details behavior, constraints, and includes an example, which is preferred over simply stating the function's action.

```elixir
    # good â€” document behavior, constraints, examples
    @doc """
    Passwords must be at least 12 characters. Returns
    `{:error, :weak_password}` for common dictionary words.

    ## Examples

        iex> create_user(%{email: "a@b.c", password: "hunter2"})
        {:error, :weak_password}
    """

```

--------------------------------

### Good Documentation Example (with constraints)

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.BoilerplateDocParams.md

This example demonstrates a 'good' @doc string where the ## Parameters section documents the constraints and requirements for the parameters, rather than just their names.

```elixir
    @doc """
    Renders the index page.

    ## Parameters

    - params: Must include `"page"` (integer >= 1) and
      optionally `"per_page"` (default 20, max 100).
    """

```

--------------------------------

### Bad Documentation Example

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.BoilerplateDocParams.md

This example shows a 'bad' @doc string where the ## Parameters section merely restates the function signature, adding no value.

```elixir
    @doc """
    Renders the index page.

    ## Parameters

    - conn: The connection struct
    - params: A map of parameters
    """
    def index(conn, params)
```

--------------------------------

### Good Moduledoc Example

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.NarratorDoc.md

This example illustrates a 'good' moduledoc that provides valuable context and details beyond the module name, such as implementation details and rate-limiting behavior.

```elixir
    # good â€” explain WHY, not WHAT
    @moduledoc """
    Wraps Bcrypt and session token generation.
    Rate-limits login attempts per IP via a sliding window.
    """

```

--------------------------------

### Good Documentation Example (no parameters section)

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.BoilerplateDocParams.md

This example shows another 'good' @doc string where the ## Parameters section is omitted entirely, which is acceptable when no specific parameter constraints need to be documented.

```elixir
    @doc """
    Renders the index page, paginated.
    """

```

--------------------------------

### Bad Doc Example

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.NarratorDoc.md

This example demonstrates a 'bad' function documentation comment that simply states what the function does, a pattern flagged by the NarratorDoc check.

```elixir
    # bad
    @doc """
    This function creates a new user.
    """
    def create_user(attrs)

```

--------------------------------

### Bad Moduledoc Example

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.NarratorDoc.md

This example shows a 'bad' moduledoc that restates the module's purpose, which the NarratorDoc check aims to identify.

```elixir
    # bad
    @moduledoc """
    This module provides functionality for handling user authentication.
    """
    defmodule MyApp.Auth do

```

--------------------------------

### Identify Identity Map (Bad Example)

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.IdentityMap.md

These examples show the 'bad' pattern of using `Enum.map` as an identity map. This pattern is redundant and should be refactored.

```elixir
list |> Enum.map(fn x -> x end)
```

```elixir
Enum.map(list, fn item -> item end)
```

--------------------------------

### GenServer as a dumb key-value wrapper

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.GenserverAsKvStore.md

This code demonstrates a GenServer implementing basic get and put operations, which is flagged by the check. Use Agent or ETS for better performance and built-in functionality.

```elixir
defmodule MyCache do
  use GenServer

  def handle_call({:get, key}, _from, state) do
    {:reply, Map.get(state, key), state}
  end

  def handle_call({:put, key, value}, _from, state) do
    {:reply, :ok, Map.put(state, key, value)}
  end
end
```

--------------------------------

### ExSlop NarratorComment Check Examples

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.NarratorComment.md

Illustrates comments flagged by the NarratorComment check and provides examples of how to refactor them into more concise and informative comments, or to remove them when the code is self-explanatory.

```elixir
# bad
# Here we fetch the user from the database
user = Repo.get!(User, id)

# Now we validate the input
changeset = User.changeset(user, attrs)

# Let's create a new changeset
changeset = change(user)
```

```elixir
# good â€” no comment needed, the code is clear

# good â€” explains WHY
# Bypass validation for admin imports (they're pre-validated upstream)
Repo.insert!(changeset, skip_validations: true)
```

--------------------------------

### Remove Identity Map (Good Example)

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.IdentityMap.md

This example shows the 'good' pattern after refactoring. The identity map is simply removed, leaving the original list.

```elixir
list
```

--------------------------------

### Redundant Enum.join Separator Example

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.RedundantEnumJoinSeparator.md

Demonstrates the incorrect usage of `Enum.join` with an empty string separator and the correct, simplified version. This check helps refactor code to be more concise.

```elixir
Enum.join(parts, "")
```

```elixir
parts |> Enum.join("")
```

```elixir
Enum.join(parts)
```

--------------------------------

### Example of Good Practice: Documented or Private Functions

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.DocFalseOnPublicFunction.md

This code shows the preferred approach: either document public functions or make them private. This snippet serves as a contrast to the anti-pattern flagged by the check.

```elixir
defmodule MyAppWeb.UserController do
  def index(conn, _params), do: ...
  def show(conn, %{"id" => id}), do: ...
end
```

--------------------------------

### Acceptable Single Use

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.UnaliasedModuleUse.md

This example shows a function where a module is used only once. The UnaliasedModuleUse check does not flag this, as an alias is not necessary for readability when a module is referenced just one time.

```elixir
def run(source_file) do
  Credo.Code.prewalk(source_file, &walk/2, ctx)
end
```

--------------------------------

### Example of Bad Practice: Multiple @doc false

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.DocFalseOnPublicFunction.md

This code demonstrates the anti-pattern where every public function in a module is annotated with `@doc false`. This check aims to flag such occurrences.

```elixir
defmodule MyAppWeb.UserController do
  @doc false
  def index(conn, _params), do: ...

  @doc false
  def show(conn, %{"id" => id}), do: ...

  @doc false
  def create(conn, %{"user" => params}), do: ...
end
```

--------------------------------

### Obvious Comment Example

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.ObviousComment.md

Illustrates comments that are flagged as obvious and those that are not. Obvious comments restate code actions, while good comments explain the 'how' or 'why'.

```elixir
# bad
# Fetch the user
user = Repo.get(User, id)

# Create the changeset
changeset = User.changeset(user, attrs)

# Return the result
{:ok, changeset}
```

```elixir
# good â€” no comment needed, the code is clear
```

```elixir
# good â€” explains HOW or WHY (not flagged despite starting with "Fetch")
# Fetch the connection from the pool, blocking up to 5s
conn = ConnectionPool.checkout!(pool, timeout: 5_000)
```

--------------------------------

### Flagged AI Slop (Multiple Uses)

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.UnaliasedModuleUse.md

This example demonstrates code that would be flagged by the UnaliasedModuleUse check due to repeated use of `Credo.Code` within a single function. Enable this check to identify such patterns.

```elixir
def run(source_file) do
  Credo.Code.prewalk(source_file, &walk/2, ctx)
  Credo.Code.remove_metadata(pattern)
  Credo.Code.remove_metadata(body)
end
```

--------------------------------

### Refactor Redundant `with` Statement (Good)

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.WithIdentityDo.md

This example demonstrates the 'good' pattern after refactoring a redundant `with` statement. The direct expression is used instead of the `with` construct when the `do` block only returns the matched value.

```elixir
do_something()
```

--------------------------------

### Refactor Redundant `with` Statement (Bad)

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.WithIdentityDo.md

This example shows a 'bad' pattern where a `with` statement's `do` block returns the matched pattern, indicating redundancy. This check is disabled by default and can be enabled via `.credo.exs`.

```elixir
with {:ok, result} <- do_something() do
  {:ok, result}
end
```

--------------------------------

### Corrected Code with Alias

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.UnaliasedModuleUse.md

This is the corrected version of the previous example, using an `alias` to shorten repeated module references within the function. This improves readability and avoids triggering the UnaliasedModuleUse check.

```elixir
def run(source_file) do
  alias Credo.Code
  Code.prewalk(source_file, &walk/2, ctx)
  Code.remove_metadata(pattern)
  Code.remove_metadata(body)
end
```

--------------------------------

### Refactoring with Pipe Operator in Elixir

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.StepComment.md

This snippet shows the refactored version of the previous example, using the pipe operator to represent sequential steps. This is the preferred style.

```elixir
def process(data) do
  data
  |> validate()
  |> transform()
  |> save()
end
```

--------------------------------

### Use Agent for key-value storage

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.GenserverAsKvStore.md

This code shows the recommended way to implement a key-value store using Elixir's `Agent` module. It provides a more idiomatic and efficient solution.

```elixir
defmodule MyCache do
  use Agent

  def start_link(initial) do
    Agent.start_link(fn -> initial end, name: __MODULE__)
  end

  def get(key), do: Agent.get(__MODULE__, &Map.get(&1, key))
  def put(key, value), do: Agent.update(__MODULE__, &Map.put(&1, key, value))
end
```

--------------------------------

### Register ExSlop Plugin in .credo.exs

Source: https://hexdocs.pm/ex_slop/readme.md

Configure your `.credo.exs` file to register ExSlop as a plugin. This enables a default set of high-signal checks.

```elixir
# .credo.exs
%{ 
  configs: [
    %{ 
      name: "default",
      plugins: [{ExSlop, []}]
    }
  ]
}
```

--------------------------------

### Add ExSlop to mix.exs

Source: https://hexdocs.pm/ex_slop/readme.md

Include ExSlop as a development dependency in your `mix.exs` file. Ensure it's only loaded for development and test environments.

```elixir
def deps do
  [
    {:ex_slop, "~> 0.1", only: [:dev, :test], runtime: false}
  ]
end
```

--------------------------------

### Configure ExSlop Credo Plugin

Source: https://hexdocs.pm/ex_slop/ExSlop.md

Add ExSlop to your `.credo.exs` configuration to enable its checks. Alternatively, cherry-pick individual checks in `checks.enabled`.

```elixir
%{
  configs: [%{name: "default", plugins: [{ExSlop, []}]}]
}
```

--------------------------------

### Avoid Fragile Path Expansion in Elixir

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.PathExpandPriv.md

Use `Application.app_dir/2` for locating application resources to ensure compatibility across development, testing, and release environments. Avoid `Path.expand` with relative paths as it is fragile and breaks in releases.

```elixir
Path.expand("../../priv/prompts/system.md", __DIR__)
```

```elixir
Application.app_dir(:my_app, "priv/prompts/system.md")
```

--------------------------------

### Rescue Specific Exceptions

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.BlanketRescue.md

This is the recommended approach for handling expected errors. It allows for targeted logging and error management without swallowing unexpected exceptions.

```elixir
rescue
  e in [ArgumentError, RuntimeError] ->
    Logger.warning("Failed: #{Exception.message(e)}")
    {:error, :invalid_input}
```

--------------------------------

### Refactoring Map Creation in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces a two-step process of mapping and then converting to a map with `Map.new`.

```elixir
Enum.map(...) |> Enum.into(%{})
```

```elixir
Map.new(...)
```

--------------------------------

### Normalize Map Keys in Elixir

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.DualKeyAccess.md

Shows the correct way to handle map key access by normalizing the data once at the boundary and then using a single key type. This is the recommended pattern to avoid the DualKeyAccess warning.

```elixir
Map.get(usage, :input_tokens, 0)
```

--------------------------------

### Avoid try/rescue with safe alternatives in Elixir

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.TryRescueWithSafeAlternative.md

Use safe alternatives like `Integer.parse/1` instead of `String.to_integer/1` within a `try/rescue` block. This improves code clarity and avoids unnecessary exception handling.

```elixir
try do
  String.to_integer(value)
rescue
  _ -> nil
end
```

```elixir
case Integer.parse(value) do
  {int, ""} -> int
  _ -> nil
end
```

--------------------------------

### Use ETS for key-value storage

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.GenserverAsKvStore.md

This code demonstrates using Erlang Term Storage (ETS) for efficient key-value storage. ETS is a high-performance, in-memory data store suitable for this purpose.

```erlang
:ets.new(:cache, [:named_table, :public])
:ets.insert(:cache, {key, value})
:ets.lookup(:cache, key)
```

--------------------------------

### Avoid List.last/1

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.ListLast.md

Demonstrates inefficient use of `List.last/1` and a more efficient alternative when list construction is controlled.

```elixir
# bad
List.last(items)
```

```elixir
# better when you control construction
[last | _] = Enum.reverse(items)
```

--------------------------------

### Refactor Sort and Reverse Pattern

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.SortThenReverse.md

This snippet shows the 'good' patterns that replace the identified sort and reverse operations. It demonstrates using `Enum.sort/2` with the `:desc` option or `Enum.sort_by/3` with the `:desc` option for a more concise and efficient solution.

```elixir
Enum.sort(list, :desc)
Enum.sort_by(list, &fun/1, :desc)
```

--------------------------------

### Identify N+1 Queries in Enum.map

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.QueryInEnumMap.md

This snippet demonstrates the anti-pattern of performing database queries inside `Enum.map`, leading to N+1 queries. Use `Repo.preload/3` for efficient data fetching instead.

```elixir
users
|> Enum.map(fn user ->
  posts = Repo.all(from p in Post, where: p.user_id == ^user.id)
  %{user | posts: posts}
end)
```

```elixir
users |> Repo.preload(:posts)
```

--------------------------------

### Cherry-pick ExSlop Checks

Source: https://hexdocs.pm/ex_slop/readme.md

Manually select specific ExSlop checks by appending them to the `extra` list in your `.credo.exs` configuration. This allows for fine-grained control over which patterns are flagged.

```elixir
# .credo.exs
{ExSlop.Check.Warning.BlanketRescue, []},
{ExSlop.Check.Warning.RescueWithoutReraise, []},
{ExSlop.Check.Warning.RepoAllThenFilter, []},
{ExSlop.Check.Warning.QueryInEnumMap, []},
{ExSlop.Check.Warning.GenserverAsKvStore, []},
{ExSlop.Check.Warning.PathExpandPriv, []},
{ExSlop.Check.Warning.DualKeyAccess, []},

{ExSlop.Check.Refactor.FilterNil, []},
{ExSlop.Check.Refactor.RejectNil, []},
{ExSlop.Check.Refactor.ReduceAsMap, []},
{ExSlop.Check.Refactor.MapIntoLiteral, []},
{ExSlop.Check.Refactor.IdentityPassthrough, []},
{ExSlop.Check.Refactor.IdentityMap, []},
{ExSlop.Check.Refactor.CaseTrueFalse, []},
{ExSlop.Check.Refactor.TryRescueWithSafeAlternative, []},
{ExSlop.Check.Refactor.WithIdentityElse, []},
{ExSlop.Check.Refactor.WithIdentityDo, []},
{ExSlop.Check.Refactor.SortThenReverse, []},
{ExSlop.Check.Refactor.StringConcatInReduce, []},
{ExSlop.Check.Refactor.ReduceMapPut, []},
{ExSlop.Check.Refactor.RedundantBooleanIf, []},
{ExSlop.Check.Refactor.FlatMapFilter, []},
{ExSlop.Check.Refactor.RedundantEnumJoinSeparator, []},
{ExSlop.Check.Refactor.UseMapJoin, []},
{ExSlop.Check.Refactor.PreferEnumSlice, []},
{ExSlop.Check.Refactor.GraphemesLength, []},
{ExSlop.Check.Refactor.ManualStringReverse, []},
{ExSlop.Check.Refactor.SortThenAt, []},
{ExSlop.Check.Refactor.SortForTopK, []},
{ExSlop.Check.Refactor.ListFold, []},
{ExSlop.Check.Refactor.ListLast, []},
{ExSlop.Check.Refactor.LengthInGuard, []},
{ExSlop.Check.Refactor.ExplicitSumReduce, []},
{ExSlop.Check.Readability.NarratorDoc, []},
{ExSlop.Check.Readability.DocFalseOnPublicFunction, []},
{ExSlop.Check.Readability.BoilerplateDocParams, []},
{ExSlop.Check.Readability.ObviousComment, [additional_keywords: []]},
{ExSlop.Check.Readability.StepComment, []},
{ExSlop.Check.Readability.NarratorComment, []},
{ExSlop.Check.Readability.UnaliasedModuleUse, []}
```

--------------------------------

### Inefficient Sorting vs. Optimized Alternatives

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.SortForTopK.md

Avoid sorting an entire collection when only the minimum or maximum element is required. Use `Enum.min/1` or `Enum.max/1` for better performance.

```elixir
list |> Enum.sort() |> Enum.take(1)
list |> Enum.sort() |> hd()
```

```elixir
Enum.min(list)
Enum.max(list)
```

--------------------------------

### Identity Passthrough with With and Else

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.IdentityPassthrough.md

This pattern demonstrates an identity passthrough using a `with` statement combined with an `else` clause. The `with` block returns `{:ok, result}` if `do_something()` succeeds, and the `else` clause handles the error case by returning `{:error, reason}`, effectively just passing the result through.

```elixir
with {:ok, result} <- do_something() do
  {:ok, result}
else
  {:error, reason} -> {:error, reason}
end
```

```elixir
do_something()
```

--------------------------------

### String Reversal (Good)

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.ManualStringReverse.md

This is the recommended way to reverse a string in Elixir using the built-in `String.reverse/1` function.

```elixir
String.reverse(string)
```

--------------------------------

### Avoid `length/1` in Guards

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.LengthInGuard.md

Use pattern matching instead of `length/1` in guards for better performance when checking for empty lists. This check is disabled by default and can be enabled in your `.credo.exs` configuration.

```elixir
def empty?(list) when length(list) == 0, do: true
```

```elixir
def empty?([]), do: true
```

--------------------------------

### Return Error Information from Rescue Blocks

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.RescueWithoutReraise.md

Use this pattern to log an error and return specific error information, such as a tuple. This is useful when the error should be handled gracefully by the caller without halting execution.

```elixir
rescue
  e in RuntimeError ->
    {:error, Exception.message(e)}
```

--------------------------------

### Refactor Enum.drop/Enum.take to Enum.slice

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.PreferEnumSlice.md

Use Enum.slice/3 when you need to drop a certain number of elements and then take a specific number of elements from a list. This is more readable than chaining Enum.drop/2 and Enum.take/2.

```elixir
items |> Enum.drop(offset) |> Enum.take(limit)
```

```elixir
Enum.slice(items, offset, limit)
```

--------------------------------

### Avoid Blanket Rescues Returning Nil

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.BlanketRescue.md

This pattern swallows all exceptions by returning nil. Use specific exception handling or let the BEAM handle unexpected errors.

```elixir
try do
  do_something()
rescue
  _ -> nil
end
```

--------------------------------

### Avoid Loading All Records Then Filtering

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.RepoAllThenFilter.md

This code demonstrates an inefficient pattern where all records are loaded into memory before filtering. Use Ecto query conditions to filter at the database level instead.

```elixir
Repo.all(User) |> Enum.filter(& &1.active)
```

```elixir
User |> where(active: true) |> Repo.all()
```

--------------------------------

### Avoid Dual Key Access in Elixir

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.DualKeyAccess.md

Demonstrates the incorrect way to access map keys using both atoms and strings, which can lead to an unknown data shape. This pattern is flagged by the DualKeyAccess check.

```elixir
Map.get(usage, :input_tokens) || Map.get(usage, "input_tokens") || 0
get_in(data, [:path]) || get_in(data, ["path"])
payload[:kind] || payload["kind"]
```

--------------------------------

### Inefficient String Length Calculation (Elixir)

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.GraphemesLength.md

Avoid building an intermediate list of graphemes just to count them. Use `String.length/1` for a more efficient approach.

```elixir
string |> String.graphemes() |> length()
```

```elixir
length(String.graphemes(string))
```

```elixir
String.length(string)
```

--------------------------------

### Refactoring Exception Handling in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces `try/rescue` blocks for safe integer parsing with the more direct `Integer.parse/1`.

```elixir
try do String.to_integer(x) rescue _ -> nil end
```

```elixir
Integer.parse(x)
```

--------------------------------

### Manual String Reversal (Bad)

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.ManualStringReverse.md

This pattern manually reverses a string using graphemes, Enum.reverse, and Enum.join. Prefer `String.reverse/1` for simplicity and performance.

```elixir
string |> String.graphemes() |> Enum.reverse() |> Enum.join()
```

--------------------------------

### Recommended Credo Checks for AI Slop

Source: https://hexdocs.pm/ex_slop/readme.md

Lists recommended Credo built-in checks to identify common patterns in AI-generated code, such as inefficient list operations and redundant boolean logic.

```elixir
# Catches length(list) == 0 (traverses entire list) â†’ use list == [] or Enum.empty?/1
{Credo.Check.Warning.ExpensiveEmptyEnumCheck, []},
```

```elixir
# Catches acc ++ [item] (O(nÂ²) append) â†’ use [item | acc] then Enum.reverse
{Credo.Check.Refactor.AppendSingleItem, []},
```

```elixir
# Catches !!var (double negation) â€” LLMs use this to "cast to boolean"
{Credo.Check.Refactor.DoubleBooleanNegation, []},
```

```elixir
# Catches case x do true -> a; false -> b end â†’ if/else
{Credo.Check.Refactor.CondStatements, []},
```

```elixir
# Catches Enum.map |> Enum.map â†’ single Enum.map
{Credo.Check.Refactor.MapMap, []},
```

```elixir
# Catches Enum.filter |> Enum.filter â†’ single Enum.filter
{Credo.Check.Refactor.FilterFilter, []},
```

```elixir
# Catches Enum.reject |> Enum.reject â†’ single Enum.reject
{Credo.Check.Refactor.RejectReject, []},
```

```elixir
# Catches Enum.count(enum) > 0 â†’ Enum.any?/1
{Credo.Check.Refactor.FilterCount, []},
```

```elixir
# Catches negated conditions in unless â†’ rewrite with positive condition
{Credo.Check.Refactor.NegatedConditionsInUnless, []},
```

```elixir
# Catches unless x do .. else .. end â†’ if/else (clearer)
{Credo.Check.Refactor.UnlessWithElse, []}
```

--------------------------------

### Identity Passthrough with Case

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.IdentityPassthrough.md

This pattern shows an identity passthrough using a `case` statement. It matches `{:ok, value}` and `{:error, reason}` only to return them directly, which is redundant.

```elixir
case result do
  {:ok, value} -> {:ok, value}
  {:error, reason} -> {:error, reason}
end
```

```elixir
result
```

--------------------------------

### Refactor Enum.map |> Enum.into to Map.new

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.MapIntoLiteral.md

Use this refactoring when you are mapping a list of key-value tuples into a map. `Map.new/2` is generally clearer than the `Enum.map` followed by `Enum.into` pattern.

```elixir
list
|> Enum.map(fn {k, v} -> {k, transform(v)} end)
|> Enum.into(%{})
```

```elixir
Map.new(list, fn {k, v} -> {k, transform(v)} end)
```

--------------------------------

### Avoid Silent Failures in Rescue Blocks

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.RescueWithoutReraise.md

Use this pattern to log an error and then re-raise it, ensuring callers are aware of the failure. This is the recommended approach when an error should halt execution or be handled further up the call stack.

```elixir
rescue
  e ->
    Logger.error("Failed: #{inspect(e)}")
    reraise e, __STACKTRACE__
```

--------------------------------

### Refactoring Manual String Reverse to String.reverse in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces manual string reversal using graphemes and join with `String.reverse/1`.

```elixir
String.graphemes(s) |> Enum.reverse() |> Enum.join()
```

```elixir
String.reverse(s)
```

--------------------------------

### Refactor Enum.reduce to Enum.map

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.ReduceAsMap.md

Avoid using `Enum.reduce` to build a reversed list or with O(n^2) list concatenation. Use `Enum.map/2` instead for a more efficient and idiomatic solution.

```elixir
Enum.reduce(items, [], fn item, acc ->
  [transform(item) | acc]
end)
```

```elixir
Enum.reduce(items, [], fn item, acc ->
  acc ++ [transform(item)]
end)
```

```elixir
Enum.map(items, &transform/1)
```

--------------------------------

### Inefficient String Concatenation in Enum.reduce/3

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.StringConcatInReduce.md

Avoid using the <> operator within Enum.reduce/3 to build strings, as this results in O(n^2) complexity. Use Enum.join/1 or Enum.map_join/2 for better performance.

```elixir
Enum.reduce(list, "", fn item, acc -> acc <> item end)
```

```elixir
Enum.reduce(list, "", fn item, acc -> acc <> to_string(item) end)
```

--------------------------------

### Using Pattern Matching for Empty Lists in Guards in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces `length(xs) == 0` in function guards with pattern matching on `[]` for efficiency.

```elixir
def f(xs) when length(xs) == 0
```

```elixir
pattern match on `[]` / `[_ | _]`
```

--------------------------------

### Refactoring Sort for Top K Elements in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces sorting a list and taking the top K elements with specialized top-k selection algorithms.

```elixir
Enum.sort() |> Enum.take(1)
```

```elixir
Enum.min/1, Enum.max/1, or top-k selection
```

--------------------------------

### Efficient String Concatenation Alternatives

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.StringConcatInReduce.md

Use Enum.join/1 for concatenating a list of strings or Enum.map_join/2 when elements need transformation before joining. These methods offer better performance than string concatenation within Enum.reduce/3.

```elixir
Enum.join(list)
```

```elixir
Enum.map_join(list, &to_string/1)
```

--------------------------------

### Refactoring Map and Join to Map.join in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces `Enum.map(...) |> Enum.join(...)` with the more efficient `Enum.map_join(...)`.

```elixir
Enum.map(...) |> Enum.join(...)
```

```elixir
Enum.map_join(...)
```

--------------------------------

### Refactoring Map Updates in Reduce to Map.new in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces `Enum.reduce` with `Map.put` to build maps with `Map.new/2`.

```elixir
Enum.reduce(%{}, fn x, acc -> Map.put(acc, k, v) end)
```

```elixir
Map.new/2
```

--------------------------------

### Refactor verbose reduce to build a map

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.ReduceMapPut.md

Avoid using `Enum.reduce` with `Map.put` to build a map. This pattern is verbose and can be replaced with more idiomatic Elixir constructs.

```elixir
Enum.reduce(batch, %{}, fn event, acc ->
  Map.put(acc, event.id, event)
end)
```

```elixir
Map.new(batch, fn event -> {event.id, event} end)
```

```elixir
for event <- batch, into: %{}, do: {event.id, event}
```

--------------------------------

### Refactoring Sort for First Element to Min/Max in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces sorting a list and taking the first element with `Enum.min/1` or `Enum.max/1`.

```elixir
Enum.sort() |> Enum.at(0)
```

```elixir
Enum.min/1, Enum.max/1, or selection logic
```

--------------------------------

### Detecting Step Comments in Elixir

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Readability.StepComment.md

This snippet demonstrates a function with step-like comments that indicate it's doing too much. This pattern is flagged by the `StepComment` check.

```elixir
def process(data) do
  # Step 1: Validate the input
  validated = validate(data)
  # Step 2: Transform the data
  transformed = transform(validated)
  # Step 3: Save to database
  save(transformed)
end
```

--------------------------------

### Avoid Logging and Returning Generic Atoms in Rescue Blocks

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.RescueWithoutReraise.md

This pattern is flagged by the check because it logs an error but then returns a generic atom, which can hide the actual failure from the caller. Avoid this approach in favor of re-raising or returning specific error information.

```elixir
rescue
  e ->
    Logger.error("Failed: #{inspect(e)}")
    :error
```

--------------------------------

### Refactoring Case Statements to If/Else in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces `case` statements with boolean conditions to a more concise `if/else` structure.

```elixir
case flag do true -> a; false -> b end
```

```elixir
if flag, do: a, else: b
```

--------------------------------

### Inefficient List Sorting Pattern

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.SortThenAt.md

Avoid sorting an entire list when only an element at a specific index is needed. Use `Enum.min` or `Enum.max` for finding minimum or maximum values.

```elixir
# bad
list |> Enum.sort() |> Enum.at(0)
Enum.at(Enum.sort(list), 0)
```

```elixir
# good â€” for min/max cases
Enum.min(list)
Enum.max(list)
```

--------------------------------

### Refactor Nil Rejection in Elixir

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.RejectNil.md

Use `Enum.reject(&is_nil/1)` instead of `Enum.reject(fn x -> x == nil end)` for more concise and idiomatic Elixir code. This check is disabled by default and can be enabled in your `.credo.exs` configuration file.

```elixir
list |> Enum.reject(fn x -> x == nil end)
```

```elixir
list |> Enum.reject(fn x -> x === nil end)
```

```elixir
list |> Enum.reject(fn x -> is_nil(x) end)
```

```elixir
list |> Enum.reject(&is_nil/1)
```

--------------------------------

### Refactor Nil Filtering in Elixir

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.FilterNil.md

This snippet demonstrates the incorrect and correct ways to filter out nil values from a list in Elixir. Use `Enum.reject(&is_nil/1)` for a more idiomatic and efficient approach.

```elixir
list |> Enum.filter(fn x -> x != nil end)
```

```elixir
list |> Enum.filter(fn x -> x !== nil end)
```

```elixir
list |> Enum.filter(fn x -> !is_nil(x) end)
```

```elixir
list |> Enum.reject(&is_nil/1)
```

--------------------------------

### Preferring Enum.slice over Drop and Take in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces `Enum.drop(n) |> Enum.take(k)` with the more direct `Enum.slice/3`.

```elixir
Enum.drop(n) |> Enum.take(k)
```

```elixir
Enum.slice(enum, n, k)
```

--------------------------------

### Prefer Enum.reduce/3 over List.foldl/3

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.ListFold.md

Use Enum.reduce/3 for folding lists in Elixir. This check is disabled by default and can be enabled in your .credo.exs configuration file.

```elixir
List.foldl(items, 0, fn item, acc -> item + acc end)
```

```elixir
Enum.reduce(items, 0, fn item, acc -> item + acc end)
```

--------------------------------

### Simplifying Identity Passthrough in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Removes redundant `case` statements that simply return the input value.

```elixir
case r do {:ok, v} -> {:ok, v}; {:error, e} -> {:error, e} end
```

```elixir
r
```

--------------------------------

### Refactor Enum.map/2 |> Enum.join/1 to Enum.map_join/3

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.UseMapJoin.md

Use Enum.map_join/3 to avoid creating an intermediate list when mapping and joining items. This check is disabled by default.

```elixir
items |> Enum.map(&to_string/1) |> Enum.join(",")
```

```elixir
Enum.map_join(items, ",", &to_string/1)
```

--------------------------------

### Refactor Enum.reduce/3 to Enum.sum/1

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.ExplicitSumReduce.md

Use Enum.sum/1 when Enum.reduce/3 is only used for summing values. This improves code clarity. This check is disabled by default.

```elixir
Enum.reduce(nums, 0, fn num, acc -> num + acc end)
```

```elixir
Enum.sum(nums)
```

--------------------------------

### Identify Sort and Reverse Pattern

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.SortThenReverse.md

This snippet shows the 'bad' patterns that the SortThenReverse check identifies. It highlights the use of `Enum.sort/1` followed by `Enum.reverse/1`, or `Enum.sort_by/2` followed by `Enum.reverse/1`, which can be refactored.

```elixir
list |> Enum.sort() |> Enum.reverse()
Enum.reverse(Enum.sort(list))
list |> Enum.sort_by(&fun/1) |> Enum.reverse()
```

--------------------------------

### Using Enum.sum over Explicit Reduce in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces explicit `Enum.reduce` for summing numbers with the more concise `Enum.sum/1`.

```elixir
Enum.reduce(nums, 0, fn n, acc -> n + acc end)
```

```elixir
Enum.sum(nums)
```

--------------------------------

### Refactor Case True/False to If/Else

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.CaseTrueFalse.md

Use this check to refactor `case` statements that only match on `true` and `false`. This improves code readability by using `if`/`else` for boolean conditions.

```elixir
case some_condition() do
  true -> :yes
  false -> :no
end
```

```elixir
if some_condition(), do: :yes, else: :no
```

--------------------------------

### Simplifying Redundant Boolean If Statements in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces `if cond, do: true, else: false` with the condition itself.

```elixir
if cond, do: true, else: false
```

```elixir
use the condition directly
```

--------------------------------

### Simplifying Identity With Statements in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Removes redundant `with` statements that simply return the result of a function call.

```elixir
with {:ok, v} <- f() do {:ok, v} end
```

```elixir
f()
```

--------------------------------

### Refactoring String Concatenation in Reduce to Join in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces string concatenation within `Enum.reduce` with `Enum.join/1` or IO data for better performance.

```elixir
Enum.reduce("", fn x, acc -> acc <> x end)
```

```elixir
Enum.join/1 or IO data
```

--------------------------------

### Avoiding List.last after Traversal in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Suggests avoiding the need for `List.last/1` by restructuring logic to not require the last element after traversal.

```elixir
List.last(list)
```

```elixir
avoid needing the last element after traversal
```

--------------------------------

### Simplifying Redundant Enum.join Separator in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Removes the empty string separator from `Enum.join` when it's not needed.

```elixir
Enum.join(parts, "")
```

```elixir
Enum.join(parts)
```

--------------------------------

### Refactor FlatMap to Filter

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.FlatMapFilter.md

Avoid using `Enum.flat_map` with conditional logic that returns singleton or empty lists, as this is less efficient than `Enum.filter`. This refactoring applies when the `flat_map` operation's sole purpose is to filter elements based on a condition.

```elixir
Enum.flat_map(items, fn item ->
  if item.active, do: [item], else: []
end)
```

```elixir
Enum.filter(items, & &1.active)
```

--------------------------------

### Avoid Generic Error Tuples in Rescues

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Warning.BlanketRescue.md

Returning a generic error tuple like `{:error, "Something went wrong"}` loses valuable exception context. Prefer specific error types or detailed messages.

```elixir
rescue
  _e -> {:error, "Something went wrong"}
```

--------------------------------

### Refactor Redundant 'with' Identity Else

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.WithIdentityElse.md

Use this refactoring when an 'else' block in a 'with' statement returns the exact value it matched, making the 'else' block unnecessary. This check is disabled by default and can be enabled in your .credo.exs configuration file.

```elixir
    # bad â€” identity else
    with {:ok, result} <- do_something() do
      {:ok, result}
    else
      {:error, reason} -> {:error, reason}
    end
```

```elixir
    # good
    do_something()
```

--------------------------------

### Refactoring Grapheme Length to String Length in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces `String.graphemes(s) |> length()` with the more efficient `String.length(s)`.

```elixir
String.graphemes(s) |> length()
```

```elixir
String.length(s)
```

--------------------------------

### Refactoring Sort and Reverse in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Replaces `Enum.sort() |> Enum.reverse()` with the more efficient `Enum.sort(:desc)`.

```elixir
Enum.sort() |> Enum.reverse()
```

```elixir
Enum.sort(:desc)
```

--------------------------------

### Simplifying With Statements in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Removes the `else` clause from `with` statements when it's not needed.

```elixir
with {:ok, v} <- f() do v else {:error, r} -> {:error, r} end
```

```elixir
drop the `else`
```

--------------------------------

### Refactor Redundant Boolean If Expressions

Source: https://hexdocs.pm/ex_slop/ExSlop.Check.Refactor.RedundantBooleanIf.md

This check identifies and suggests refactoring for redundant boolean conditional expressions. It flags cases where a boolean condition is wrapped in an `if/true/false` structure, recommending the direct use of the expression instead.

```elixir
is_active = if status == :active, do: true, else: false
if !is_nil(x) and !is_nil(y), do: true, else: false
```

```elixir
is_active = status == :active
!is_nil(x) and !is_nil(y)
```

--------------------------------

### Removing Redundant Identity Map in Elixir

Source: https://hexdocs.pm/ex_slop/readme.md

Eliminates `Enum.map` calls where the function simply returns the input.

```elixir
Enum.map(fn x -> x end)
```

```elixir
remove the call
```
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