Don't show revert button if commit/MR has already been reverted.

app/models/commit.rb

@@ -219,14 +219,20 @@ class Commit
     "revert-#{short_id}"
   end
 
+  def revert_description
+    if merged_merge_request
+      "This reverts merge request #{merged_merge_request.to_reference}"
+    else
+      "This reverts commit #{sha}"
+    end
+  end
+
   def revert_message
-    description = if merged_merge_request
-                    "This reverts merge request #{merged_merge_request.to_reference}"
-                  else
-                    "This reverts commit #{sha}"
-                  end
+    "Revert \"#{title}\"" + "\n\n#{revert_description}"
+  end
 
-    "Revert \"#{title}\"" + "\n\n#{description}"
+  def reverts_commit?(commit)
+    description.include?(commit.revert_description)
   end
 
   def merge_commit?
@@ -239,6 +245,14 @@ class Commit
     @merged_merge_request = merge_commit? && MergeRequest.find_by(merge_commit_sha: id)
   end
 
+  def has_been_reverted?(current_user = nil, noteable = self)
+    Gitlab::ReferenceExtractor.lazily do
+      [self, *noteable.notes].flat_map do |note|
+        note.all_references(current_user).commits
+      end
+    end.any? { |commit_ref| commit_ref.reverts_commit?(self) }
+  end
+
   private
 
   def repo_changes

app/models/merge_request.rb

@@ -533,4 +533,14 @@ class MergeRequest < ActiveRecord::Base
 
     [diff_base_commit, last_commit]
   end
+
+  def merge_commit
+    @merge_commit ||= project.commit(merge_commit_sha) if merge_commit_sha
+  end
+
+  def has_been_reverted?(current_user = nil)
+    if merge_commit
+      merge_commit.has_been_reverted?(current_user, self)
+    end
+  end
 end

app/views/projects/commit/_commit_box.html.haml

@@ -16,7 +16,8 @@
     = link_to namespace_project_tree_path(@project.namespace, @project, @commit), class: "btn btn-grouped" do
       = icon('files-o')
       Browse Files
-    = revert_commit_link(namespace_project_commit_path(@project.namespace, @project, @commit.id))
+    - unless @commit.has_been_reverted?(current_user)
+      = revert_commit_link(namespace_project_commit_path(@project.namespace, @project, @commit.id))
   %div
 
 %p

app/views/projects/merge_requests/_show.html.haml

@@ -85,8 +85,8 @@
         = spinner
 
 = render 'shared/issuable/sidebar', issuable: @merge_request
-- if @merge_request.merge_commit_sha
-  = render "projects/commit/revert", commit_id: @merge_request.merge_commit_sha, title: @merge_request.title
+- if @merge_request.merge_commit && !@merge_request.has_been_reverted?(current_user)
+  = render "projects/commit/revert", commit_id: @merge_request.merge_commit.id, title: @merge_request.title
 
 :javascript
   var merge_request;

app/views/projects/merge_requests/widget/_merged.html.haml

@@ -6,7 +6,7 @@
       - if @merge_request.merge_event
         by #{link_to_member(@project, @merge_request.merge_event.author, avatar: true)}
         #{time_ago_with_tooltip(@merge_request.merge_event.created_at)}
-      - if @merge_request.merge_commit_sha.present?
+      - unless @merge_request.has_been_reverted?(current_user)
         = revert_commit_link(namespace_project_merge_request_path(@project.namespace, @project, @merge_request), btn_class: 'sm')
     %div
       - if !@merge_request.source_branch_exists? || (params[:delete_source] == 'true')