Tiny script to build GNU Make dependency files for JS `import` rules or CSS `@import` rules.

asset-makedepend

#!/usr/bin/env ruby

# Generate make dependencies by parsing a tree of JS / CSS files.
#
# Usage
# -----
#
# Add this to your Makefile:
#
#   ```
#   .deps.js.mk:
#           makedepend --js ./assets/js > $@
#
#   .deps.css.mk:
#           makedepend --css ./assets/css > $@
#
#   -include .deps.js.mk .deps.css.mk
#   ```
#
# How it works
# ------------
#
#   ```
#   // foo.js
#   import Bar from './bar.js'
#   import './baz.js'
#   import _ from 'lodash'
#   <code>
#
#   // bar.js
#   import './baz.js'
#   <code>
#
#   // baz.js
#   <code, but no imports>
#   ```
#
# It will generate the following output:
#
#   ```
#   foo.js: bar.js baz.js
#           @touch $@
#
#   bar.js: baz.js
#           @touch $@
#   ```
#
# You can see `baz` is not set as a rule -- only a dependency, since it doesn't
# depend on anything itself. Finally, `lodash` doesn't resolve to a file in our
# tree (it's most likely an npm dependency), so there's no need to have a rule
# for that.

require "pathname"
require "optparse"

Format = Struct.new(:desc, :glob, :scanner, :extractor)

types = {
  js: Format.new(
    "Scan for ES2016 `import` statements",
    "**/*.js", /^\s*import/, /^.*["'](.+)["'].*$/
  ),
  css: Format.new(
    "Scan for CSS `@import` statements",
    "**/*.css", /^\s*@import/, /^.*["'](.+)["'].*$/
  )
}

type = nil
parser = OptionParser.new do |opts|
  opts.banner = "Usage: #{$0} [--js|--css] <directory>"

  types.each do |key, format|
    opts.on("--#{key}", format.desc) do |set|
      type = format if set
    end
  end
end

parser.parse!

puts Pathname.new(ARGV.fetch(0) { abort parser.banner })
  .glob(type.glob)
  .each_with_object({}) { |file, deps|
    deps[file] = file.each_line
      .grep(type.scanner)
      .map { |import| file.dirname + import.sub(type.extractor, '\1').chomp }
      .select { |import| import.file? }
  }
  .select { |_, deps| deps.any? }
  .map { |file, deps| format("%s: %s\n\t@touch $@", file, deps.join(" ")) }
  .join("\n\n")