Runs SwiftLint on all code snippets found in a markdown file

lint_snippets_in_markdown.rb

#!/usr/bin/env ruby

require 'tmpdir'
require 'open3'

# The first parameter is supposed to be the path to the markdown file
input_file = ARGV.first
config_file = ARGV[1] || '.swiftlint.yml'
config_param = File.exist?(config_file) ? " --config #{File.realpath(config_file)}" : ''


Dir.mktmpdir('snippets') do |tmpdir|
  buffer = nil
  offsets = {}
  snippet_index = 0

  # Read the markdown file line by line, and extract each snippet into its own file
  File.foreach(input_file).each_with_index do |line, line_number|
    if line.chomp == '```' && !buffer.nil?
      # end of snippet
      path = "#{tmpdir}/snippet-#{snippet_index}.swift"
      File.write(path, buffer)
      buffer = nil
    elsif line =~ /^```(.*)$/
      # beginning of snippet
      unless $1.empty? || $1 == 'swift' # skip non-swift snippets
        puts "Snippet found on line #{line_number} but not swift (#{$1})"
        next
      end
      snippet_index += 1
      offsets[snippet_index] = line_number + 1
      buffer = ''
    elsif !buffer.nil?
      # inside snippet
      buffer += line
    end
  end

  # Run Swiftlint and dump the output
  Open3.popen3("swiftlint lint --path #{tmpdir}#{config_param}") do |stdin, stdout, stderr|
    # Print "Linting …" while processing
    while line = stderr.gets
      STDERR.puts line
    end

    puts '-----'

    # Order the lint violation messages, as Swiftlint doesn't
    # guarantee to lint files in alphabetical order
    ordered_errors = Array.new(snippet_index) { [] }
    stdout.each_line do |line|
      if line =~ %r{^#{tmpdir}/snippet-([0-9]+)\.swift:([0-9]+):(.*)$}
        new_line_number = $2.to_i + offsets[$1.to_i]
        line = "#{input_file}:#{new_line_number}:#{$3}"
      end
      ordered_errors[$1.to_i - 1] << line
    end
    STDOUT.puts ordered_errors.flatten
  end
end

Example output:

$ ./lint_snippets_in_markdown.rb README.md
Loading configuration from '/Users/[…]/[…]/.swiftlint.yml'
Linting Swift files at path /var/folders/ng/98cn3mbs14sbflfdm0dl8frmym018y/T/snippets20190115-28364-1obh28
Linting 'snippet-15.swift' (1/18)
Linting 'snippet-17.swift' (2/18)
Linting 'snippet-13.swift' (3/18)
Linting 'snippet-11.swift' (4/18)
Linting 'snippet-9.swift' (5/18)
Linting 'snippet-16.swift' (6/18)
Linting 'snippet-14.swift' (7/18)
Linting 'snippet-10.swift' (8/18)
Linting 'snippet-8.swift' (9/18)
Linting 'snippet-12.swift' (10/18)
Linting 'snippet-6.swift' (11/18)
Linting 'snippet-4.swift' (12/18)
Linting 'snippet-18.swift' (13/18)
Linting 'snippet-2.swift' (14/18)
Linting 'snippet-5.swift' (15/18)
Linting 'snippet-7.swift' (16/18)
Linting 'snippet-3.swift' (17/18)
Linting 'snippet-1.swift' (18/18)
Done linting! Found 9 violations, 0 serious in 18 files.
-----
README.md:80: warning: Trailing Whitespace Violation: Lines should not have trailing whitespace. (trailing_whitespace)
README.md:95: warning: Trailing Whitespace Violation: Lines should not have trailing whitespace. (trailing_whitespace)
README.md:98: warning: Trailing Whitespace Violation: Lines should not have trailing whitespace. (trailing_whitespace)
README.md:127: warning: Trailing Whitespace Violation: Lines should not have trailing whitespace. (trailing_whitespace)
README.md:129: warning: Trailing Whitespace Violation: Lines should not have trailing whitespace. (trailing_whitespace)
README.md:150: warning: Trailing Whitespace Violation: Lines should not have trailing whitespace. (trailing_whitespace)
README.md:190:39: warning: Colon Violation: Colons should be next to the identifier when specifying a type and next to the key in dictionary literals. (colon)
README.md:376:3: warning: Identifier Name Violation: Variable name should be between 3 and 40 characters long: 'vc' (identifier_name)
README.md:416: warning: Trailing Whitespace Violation: Lines should not have trailing whitespace. (trailing_whitespace)