Update Go documentation (1.17.2)

assets/stylesheets/pages/_go.scss

@@ -3,7 +3,7 @@
 
   #short-nav, table.dir { margin-left: -1rem; }
 
-  a.source {
+  a.source, span[title^="Added in Go"] {
     float: right;
     font-size: .9em;
   }

lib/docs/filters/go/attribution.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+module Docs
+  class Go
+    class AttributionFilter < Docs::AttributionFilter
+      def attribution_link
+        url = current_url.to_s.sub! 'localhost:6060', 'golang.org'
+        %(<a href="#{url}" class="_attribution-link">#{url}</a>)
+      end
+    end
+  end
+end

lib/docs/scrapers/go.rb

@@ -1,14 +1,23 @@
 module Docs
   class Go < UrlScraper
     self.type = 'go'
-    self.release = '1.16'
+    self.release = '1.17.2'
     self.base_url = 'https://golang.org/pkg/'
     self.links = {
       home: 'https://golang.org/',
       code: 'https://go.googlesource.com/go'
     }
 
+    # Run godoc locally, since https://golang.org/pkg/ redirects to https://pkg.go.dev/std with rate limiting / scraping protection.
+
+    # curl -LO https://golang.org/dl/go1.17.2.windows-amd64.zip
+    # go install golang.org/x/tools/cmd/godoc@latest
+    # go/bin/godoc -zip=go1.17.2.windows-amd64.zip -goroot=/go
+    self.base_url = 'http://localhost:6060/pkg/'
+
+    html_filters.push 'clean_local_urls'
     html_filters.push 'go/clean_html', 'go/entries'
+    text_filters.replace 'attribution', 'go/attribution'
 
     options[:trailing_slash] = true
     options[:container] = '#page .container'
@@ -16,7 +25,7 @@ module Docs
     options[:skip_patterns] = [/\/\//]
 
     options[:fix_urls] = ->(url) do
-      url.sub 'https://golang.org/pkg//', 'https://golang.org/pkg/'
+      url.sub '/pkg//', '/pkg/'
     end
 
     options[:attribution] = <<-HTML