Preserve commits/diff/comments for PRs that were merged on GitHub

app/models/merge_request.rb

@@ -26,6 +26,10 @@ class MergeRequest < ActiveRecord::Base
   # when creating new merge request
   attr_accessor :can_be_created, :compare_commits, :compare
 
+  # Temporary fields to store target_sha, and base_sha to
+  # compare when importing pull requests from GitHub
+  attr_accessor :base_target_sha, :head_source_sha
+
   state_machine :state, initial: :opened do
     event :close do
       transition [:reopened, :opened] => :closed
@@ -490,10 +494,14 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def target_sha
-    @target_sha ||= target_project.repository.commit(target_branch).try(:sha)
+    return @base_target_sha if defined?(@base_target_sha)
+
+    target_project.repository.commit(target_branch).try(:sha)
   end
 
   def source_sha
+    return @head_source_sha if defined?(@head_source_sha)
+
     last_commit.try(:sha) || source_tip.try(:sha)
   end
 

app/models/merge_request_diff.rb

@@ -6,7 +6,7 @@ class MergeRequestDiff < ActiveRecord::Base
 
   belongs_to :merge_request
 
-  delegate :target_branch, :source_branch, to: :merge_request, prefix: nil
+  delegate :head_source_sha, :target_branch, :source_branch, to: :merge_request, prefix: nil
 
   state_machine :state, initial: :empty do
     state :collected
@@ -38,8 +38,8 @@ class MergeRequestDiff < ActiveRecord::Base
       @diffs_no_whitespace ||= begin
         compare = Gitlab::Git::Compare.new(
           self.repository.raw_repository,
-          self.target_branch,
-          self.source_sha,
+          self.base,
+          self.head,
         )
         compare.diffs(options)
       end
@@ -144,7 +144,7 @@ class MergeRequestDiff < ActiveRecord::Base
 
     self.st_diffs = new_diffs
 
-    self.base_commit_sha = self.repository.merge_base(self.source_sha, self.target_branch)
+    self.base_commit_sha = self.repository.merge_base(self.head, self.base)
 
     self.save
   end
@@ -160,10 +160,24 @@ class MergeRequestDiff < ActiveRecord::Base
   end
 
   def source_sha
+    return head_source_sha if head_source_sha.present?
+
     source_commit = merge_request.source_project.commit(source_branch)
     source_commit.try(:sha)
   end
 
+  def target_sha
+    merge_request.target_sha
+  end
+
+  def base
+    self.target_sha || self.target_branch
+  end
+
+  def head
+    self.source_sha
+  end
+
   def compare
     @compare ||=
       begin
@@ -172,8 +186,8 @@ class MergeRequestDiff < ActiveRecord::Base
 
         Gitlab::Git::Compare.new(
           self.repository.raw_repository,
-          self.target_branch,
-          self.source_sha
+          self.base,
+          self.head
         )
       end
   end

lib/gitlab/github_import/pull_request_formatter.rb

@@ -8,8 +8,10 @@ module Gitlab
           description: description,
           source_project: source_project,
           source_branch: source_branch,
+          head_source_sha: source_sha,
           target_project: target_project,
           target_branch: target_branch,
+          base_target_sha: target_sha,
           state: state,
           milestone: milestone,
           author_id: author_id,

spec/lib/gitlab/github_import/pull_request_formatter_spec.rb

@@ -41,8 +41,10 @@ describe Gitlab::GithubImport::PullRequestFormatter, lib: true do
           description: "*Created by: octocat*\n\nPlease pull these awesome changes",
           source_project: project,
           source_branch: 'feature',
+          head_source_sha: '2e5d3239642f9161dcbbc4b70a211a68e5e45e2b',
           target_project: project,
           target_branch: 'master',
+          base_target_sha: '8ffb3c15a5475e59ae909384297fede4badcb4c7',
           state: 'opened',
           milestone: nil,
           author_id: project.creator_id,
@@ -66,8 +68,10 @@ describe Gitlab::GithubImport::PullRequestFormatter, lib: true do
           description: "*Created by: octocat*\n\nPlease pull these awesome changes",
           source_project: project,
           source_branch: 'feature',
+          head_source_sha: '2e5d3239642f9161dcbbc4b70a211a68e5e45e2b',
           target_project: project,
           target_branch: 'master',
+          base_target_sha: '8ffb3c15a5475e59ae909384297fede4badcb4c7',
           state: 'closed',
           milestone: nil,
           author_id: project.creator_id,
@@ -91,8 +95,10 @@ describe Gitlab::GithubImport::PullRequestFormatter, lib: true do
           description: "*Created by: octocat*\n\nPlease pull these awesome changes",
           source_project: project,
           source_branch: 'feature',
+          head_source_sha: '2e5d3239642f9161dcbbc4b70a211a68e5e45e2b',
           target_project: project,
           target_branch: 'master',
+          base_target_sha: '8ffb3c15a5475e59ae909384297fede4badcb4c7',
           state: 'merged',
           milestone: nil,
           author_id: project.creator_id,

spec/models/merge_request_spec.rb

@@ -64,7 +64,13 @@ describe MergeRequest, models: true do
 
   describe '#target_sha' do
     context 'when the target branch does not exist anymore' do
-      subject { create(:merge_request).tap { |mr| mr.update_attribute(:target_branch, 'deleted') } }
+      let(:project) { create(:project) }
+
+      subject { create(:merge_request, source_project: project, target_project: project) }
+
+      before do
+        project.repository.raw_repository.delete_branch(subject.target_branch)
+      end
 
       it 'returns nil' do
         expect(subject.target_sha).to be_nil
@@ -289,7 +295,12 @@ describe MergeRequest, models: true do
     let(:fork_project) { create(:project, forked_from_project: project) }
 
     context 'when the target branch does not exist anymore' do
-      subject { create(:merge_request).tap { |mr| mr.update_attribute(:target_branch, 'deleted') } }
+      subject { create(:merge_request, source_project: project, target_project: project) }
+
+      before do
+        project.repository.raw_repository.delete_branch(subject.target_branch)
+        subject.reload
+      end
 
       it 'does not crash' do
         expect{ subject.diverged_commits_count }.not_to raise_error