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defmodule <%= @check_name %> do
@moduledoc """
Checks all lines for a given Regex.
This is fun!
@explanation [
check: @moduledoc,
params: [
regex: "All lines matching this Regex will yield an issue.",
@default_params [
regex: ~r/Creeeedo/, # our check will find this line.
# you can configure the basics of your check via the `use Credo.Check` call
use Credo.Check, base_priority: :high, category: :custom, exit_status: 0
@doc false
@impl true
def run(%SourceFile{} = source_file, params) do
lines = SourceFile.lines(source_file)
# IssueMeta helps us pass down both the source_file and params of a check
# run to the lower levels where issues are created, formatted and returned
issue_meta = IssueMeta.for(source_file, params)
# we use the `params` parameter and the `Params` module to extract a
# configuration parameter from `.credo.exs` while also providing a
# default value
line_regex = params |> Params.get(:regex, __MODULE__)
# Finally, we can run our custom made analysis.
# In this example, we look for lines in source code matching our regex:
Enum.reduce(lines, [], &process_line(&1, &2, line_regex, issue_meta))
defp process_line({line_no, line}, issues, line_regex, issue_meta) do
case, line) do
nil -> issues
matches ->
trigger = matches |> List.last
new_issue = issue_for(issue_meta, line_no, trigger)
[new_issue] ++ issues
defp issue_for(issue_meta, line_no, trigger) do
# format_issue/2 is a function provided by Credo.Check to help us format the
# found issue
format_issue issue_meta,
message: "OMG! This line matches our Regexp in @default_params!",
line_no: line_no,
trigger: trigger