Add coverage formatter for GH action

.github/workflows/main.yml

@@ -107,6 +107,7 @@ jobs:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           minimum_suite_coverage: 100
           minimum_file_coverage: 100
+          coverage_json_path: coverage/simplecov-check-action.json
 
   rubocop:
     runs-on: ubuntu-latest

spec/simple_cov_check_action_formatter.rb

@@ -0,0 +1,78 @@
+# frozen_string_literal: true
+
+require "simplecov"
+require "json"
+
+class SimpleCovCheckActionFormatter
+  SourceFile = Data.define(:source_file) do
+    def covered_strength = source_file.covered_strength
+
+    def to_json(*)
+      {
+        filename: source_file.filename,
+        covered_percent: source_file.covered_percent,
+        coverage: source_file.coverage_data,
+        covered_strength: covered_strength.nan? ? 0.0 : covered_strength,
+        covered_lines: source_file.covered_lines.count,
+        lines_of_code: source_file.lines_of_code
+      }.to_json
+    end
+  end
+
+  Result = Data.define(:result) do
+    def included?(source_file) = result.filenames.include?(source_file.filename)
+
+    def files
+      result.files.filter_map do |source_file|
+        next unless result.filenames.include? source_file.filename
+
+        SourceFile.new(source_file)
+      end
+    end
+
+    def to_json(*) # rubocop:disable Metrics/AbcSize
+      {
+        timestamp: result.created_at.to_i,
+        command_name: result.command_name,
+        files: files,
+        metrics: {
+          covered_percent: result.covered_percent,
+          covered_strength: result.covered_strength.nan? ? 0.0 : result.covered_strength,
+          covered_lines: result.covered_lines,
+          total_lines: result.total_lines
+        }
+      }.to_json
+    end
+  end
+
+  FormatterWithOptions = Data.define(:formatter) do
+    def new = formatter
+  end
+
+  class << self
+    def with_options(...)
+      FormatterWithOptions.new(new(...))
+    end
+  end
+
+  def initialize(output_filename: "coverage.json", output_directory: SimpleCov.coverage_path)
+    @output_filename = output_filename
+    @output_directory = output_directory
+  end
+
+  attr_reader :output_filename, :output_directory
+
+  def output_filepath = File.join(output_directory, output_filename)
+
+  def format(result_data)
+    result = Result.new(result_data)
+    json = result.to_json
+    File.write(output_filepath, json)
+    puts output_message(result_data)
+    json
+  end
+
+  def output_message(result)
+    "Coverage report generated for #{result.command_name} to #{output_filepath}. #{result.covered_lines} / #{result.total_lines} LOC (#{result.covered_percent.round(2)}%) covered." # rubocop:disable Layout/LineLength
+  end
+end

spec/spec_helper.rb

@@ -3,9 +3,13 @@
 if ENV["COVERAGE"]
   require "simplecov"
   require "simplecov_json_formatter"
+  require_relative "simple_cov_check_action_formatter"
   SimpleCov.formatters = SimpleCov::Formatter::MultiFormatter.new([
     SimpleCov::Formatter::HTMLFormatter,
-    SimpleCov::Formatter::JSONFormatter
+    SimpleCov::Formatter::JSONFormatter,
+    SimpleCovCheckActionFormatter.with_options(
+      output_filename: "simplecov-check-action.json"
+    )
   ])
   SimpleCov.start do
     add_filter "/spec/"