FEATURE: split out max diff to 2 settings

We trust staff + tl2 and up to perform edits in grace period.
Allow them significantly more edit room in grace period prior to storing
a revision.

editing_grace_period_max_diff_high_trust applies to users with tl2 and up.

So

tl0 / 1 : we store an extra revision if more than 100 chars change
tl2 and up : we store an extra revision if more than 400 chars change

We may tweak these numbers as we go.

config/locales/server.en.yml

@@ -1023,7 +1023,8 @@ en:
     download_remote_images_max_days_old: "Don't download remote images for posts that are more than n days old."
     disabled_image_download_domains: "Remote images will never be downloaded from these domains. Pipe-delimited list."
     editing_grace_period: "For (n) seconds after posting, editing will not create a new version in the post history."
-    editing_grace_period_max_diff: "Maximum number of character changes allowed in editing grace period, if more changed store another post revision"
+    editing_grace_period_max_diff: "Maximum number of character changes allowed in editing grace period, if more changed store another post revision (trust level 0 and 1)"
+    editing_grace_period_max_diff_high_trust: "Maximum number of character changes allowed in editing grace period, if more changed store another post revision (trust level 2 and up)"
     staff_edit_locks_post: "Posts will be locked from editing if they are edited by staff members"
     post_edit_time_limit: "The author can edit or delete their post for (n) minutes after posting. Set to 0 for forever."
     edit_history_visible_to_public: "Allow everyone to see previous versions of an edited post. When disabled, only staff members can view."

config/site_settings.yml

@@ -535,6 +535,7 @@ posting:
     validator: "EnablePrivateEmailMessagesValidator"
   editing_grace_period: 300
   editing_grace_period_max_diff: 100
+  editing_grace_period_max_diff_high_trust: 400
   staff_edit_locks_post: false
   post_edit_time_limit:
     default: 86400

lib/post_revisor.rb

@@ -278,8 +278,14 @@ class PostRevisor
     return false if (@revised_at - @last_version_at) > SiteSetting.editing_grace_period.to_i
 
     if new_raw = @fields[:raw]
-      if (original_raw.length - new_raw.length).abs > SiteSetting.editing_grace_period_max_diff.to_i ||
+
-        diff_size(original_raw, new_raw) > SiteSetting.editing_grace_period_max_diff.to_i
+      max_diff = SiteSetting.editing_grace_period_max_diff.to_i
+      if @editor.staff? || (@editor.trust_level > 1)
+        max_diff = SiteSetting.editing_grace_period_max_diff_high_trust.to_i
+      end
+
+      if (original_raw.length - new_raw.length).abs > max_diff ||
+        diff_size(original_raw, new_raw) > max_diff
         return false
       end
     end

spec/components/post_revisor_spec.rb

@@ -130,6 +130,18 @@ describe PostRevisor do
 
         expect(post.revisions.first.modifications["raw"][0]).to eq("hello world")
         expect(post.revisions.first.modifications["cooked"][0]).to eq("<p>hello world</p>")
+
+        SiteSetting.editing_grace_period_max_diff_high_trust = 100
+
+        post.user.update_columns(trust_level: 2)
+
+        revisor = PostRevisor.new(post)
+        revisor.revise!(post.user, { raw: 'hello world12345678901 123456789012' }, revised_at: post.updated_at + 1.second)
+
+        post.reload
+        expect(post.version).to eq(2)
+        expect(post.revisions.count).to eq(1)
+
       end
 
       it "doesn't create a new version" do