Add VERBOSE to importmap:verify, fix verify error

lib/tasks/helpers/importmap_helper.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "importmap/packager"
+require "diff/lcs"
 
 module ImportmapHelper
   VerifyError = Class.new(StandardError)
@@ -9,45 +10,51 @@ class Packager < Importmap::Packager
     self.endpoint = URI("https://api.jspm.io/generate")
 
     # Copied from https://github.com/rails/importmap-rails/pull/237
-    def verify(package, url)
+    def verify(package, url, verbose: false)
       ensure_vendor_directory_exists
 
       return unless vendored_package_path(package).file?
-      verify_vendored_package(package, url)
+      verify_vendored_package(package, url, verbose:)
     end
 
-    def verify_vendored_package(package, url)
+    def verify_vendored_package(package, url, verbose: false)
       vendored_body = vendored_package_path(package).read.strip
-      remote_body = load_package_file(package, url).strip
+      remote_body = load_package_file(url).strip
 
       return true if vendored_body == remote_body
 
-      raise ImportmapHelper::VerifyError, "Vendored #{package}#{extract_package_version_from(url)} does not match remote #{url}"
+      verbose_error = "\n\nDiff:\n#{verbose_diff(vendored_body, remote_body)}" if verbose
+      raise ImportmapHelper::VerifyError, "Vendored #{package}#{extract_package_version_from(url)} does not match remote #{url}#{verbose_error}"
     end
 
-    def load_package_file(package, url)
+    def load_package_file(url)
       response = Net::HTTP.get_response(URI(url))
 
       if response.code == "200"
-        format_vendored_package(package, url, response.body)
+        remove_sourcemap_comment_from(response.body).force_encoding("UTF-8")
       else
         handle_failure_response(response)
       end
     end
 
-    def format_vendored_package(package, url, source)
-      formatted = +""
-      if Gem::Version.new(Importmap::VERSION) > Gem::Version.new("2.0.1")
-        formatted.concat "// #{package}#{extract_package_version_from(url)} downloaded from #{url}\n\n"
-      end
-      formatted.concat remove_sourcemap_comment_from(source).force_encoding("UTF-8")
-      formatted
-    end
-
     def save_vendored_package(package, _url, source)
       File.write(vendored_package_path(package), source)
     end
 
+    def verbose_diff(vendored_body, remote_body)
+      diff = Diff::LCS.sdiff(vendored_body.split("\n"), remote_body.split("\n"))
+      diff.map do |diff|
+        case diff.action
+        when "!"
+          "- #{diff.old_element}"
+        when "+"
+          "+ #{diff.new_element}"
+        when "="
+          "  #{diff.old_element}"
+        end
+      end.join("\n")
+    end
+
     public :vendored_package_path
   end
 end

lib/tasks/importmap.rake

@@ -23,7 +23,7 @@ namespace :importmap do
     if (imports = packager.import(*packages, env: "production", from: "jspm.io"))
       imports.each do |package, url|
         puts %(Verifying "#{package}" download from #{url})
-        packager.verify(package, url)
+        packager.verify(package, url, verbose: ENV["VERBOSE"])
         path = packager.vendored_package_path(package)
         puts %(Verified  "#{package}" at #{path})
         all_files.delete path