Credence.Pattern.PreferHeredocForMultiLineDoc (credence v0.8.0)

Detects @doc, @moduledoc, and @typedoc strings that contain escaped newlines (\n) and should use heredoc syntax instead.

LLMs generate documentation as single-line strings with \n escapes because that's how Python docstrings work. In Elixir, multi-line documentation should use the heredoc (""") syntax for readability.

Bad

@doc "Finds the second largest number in a list.\nThe list must have at least two distinct values.\n"

Good

@doc """
Finds the second largest number in a list.
The list must have at least two distinct values.
"""

Auto-fix

Converts single-line @doc/@moduledoc/@typedoc strings containing \n escapes into heredoc format. The fixer preserves indentation and strips unnecessary trailing \n (since heredocs naturally end with a newline). Strings containing \"\"\" are left unchanged.

Scope

Only \n-escaped strings (the form LLMs emit) are converted, via a per-node patch over just the doc attribute. A doc string that already spans multiple source lines (a real-newline regular string) is left untouched: its multi-line range trips a Sourceror.patch_string edge that swallows the following newline, and the only safe alternative — rendering the whole file — would reformat unrelated, not-yet-formatted code.