From 960754931236d3b03ac89b868d6424d6e1d21b3a Mon Sep 17 00:00:00 2001
From: Mac Siri <krairit.siri@gmail.com>
Date: Wed, 8 Jul 2020 05:55:53 -0400
Subject: [PATCH] Use custom UglifierCompressor to enable source-maps (#9188)

---
 config/environments/production.rb             |  2 +-
 ...ts_uglifier_with_source_maps_compressor.rb | 49 +++++++++++++++++++
 2 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 config/initializers/sprockets_uglifier_with_source_maps_compressor.rb

diff --git a/config/environments/production.rb b/config/environments/production.rb
index 5927cb6e7..70541a747 100644
--- a/config/environments/production.rb
+++ b/config/environments/production.rb
@@ -31,7 +31,7 @@ Rails.application.configure do
   }
 
   # Compress JavaScripts and CSS.
-  config.assets.js_compressor = Uglifier.new(harmony: true)
+  config.assets.js_compressor = :uglify_with_source_maps
   # config.assets.css_compressor = :sass
 
   # Do not fallback to assets pipeline if a precompiled asset is missed.
diff --git a/config/initializers/sprockets_uglifier_with_source_maps_compressor.rb b/config/initializers/sprockets_uglifier_with_source_maps_compressor.rb
new file mode 100644
index 000000000..0659168a8
--- /dev/null
+++ b/config/initializers/sprockets_uglifier_with_source_maps_compressor.rb
@@ -0,0 +1,49 @@
+require "sprockets/digest_utils"
+require "sprockets/uglifier_compressor"
+
+module Sprockets
+  class UglifierWithSourceMapsCompressor < Sprockets::UglifierCompressor
+    def call(input)
+      data = input.fetch(:data) # Non-Uglified contents of the JS file
+      name = input.fetch(:name) # name of the to-be-compressed JS file.
+
+      @uglifier ||= Autoload::Uglifier.new(@options.merge({ harmony: true }))
+      compressed_data, sourcemap_json = @uglifier.compile_with_map(input[:data])
+
+      # Update source map according to the version 3 spec: https://sourcemaps.info/spec.html
+      sourcemap                   = JSON.parse(sourcemap_json)
+      sourcemap["sources"]        = [name + ".js"]
+      sourcemap["sourceRoot"]     = ::Rails.application.config.assets.prefix
+      sourcemap["sourcesContent"] = [data]
+      sourcemap_json              = sourcemap.to_json
+
+      sourcemap_filename = File.join(
+        ::Rails.application.config.assets.prefix,
+        "#{name}-#{digest(sourcemap_json)}.js.map",
+      )
+      sourcemap_path = File.join(::Rails.public_path, sourcemap_filename)
+      sourcemap_url  = filename_to_url(sourcemap_filename)
+
+      FileUtils.mkdir_p File.dirname(sourcemap_path)
+      File.open(sourcemap_path, "w") { |f| f.write sourcemap_json }
+
+      # Add the source map URL to the compressed JS file.
+      compressed_data.concat "\n//# sourceMappingURL=#{sourcemap_url}\n"
+    end
+
+    def filename_to_url(filename)
+      url_root = ::Rails.application.config.assets.source_maps_domain
+      File.join url_root.to_s, filename
+    end
+
+    def digest(io)
+      Sprockets::DigestUtils.pack_hexdigest Sprockets::DigestUtils.digest(io)
+    end
+  end
+end
+
+Sprockets.register_compressor(
+  "application/javascript",
+  :uglify_with_source_maps,
+  Sprockets::UglifierWithSourceMapsCompressor,
+)