11 files changed, 454 insertions, 203 deletions

diff --git a/app/models/commit.rb b/app/models/commit.rb
index 174ccbaea6c..2ef3973c160 100644
--- a/app/models/commit.rb
+++ b/app/models/commit.rb
@@ -214,6 +214,13 @@ class Commit
     @raw.short_id(7)
   end
 
+  def diff_refs
+    Gitlab::Diff::DiffRefs.new(
+      base_sha: self.parent_id || self.sha,
+      head_sha: self.sha
+    )
+  end
+
   def pipelines
     @pipeline ||= project.pipelines.where(sha: sha)
   end
diff --git a/app/models/concerns/note_on_diff.rb b/app/models/concerns/note_on_diff.rb
new file mode 100644
index 00000000000..2785fbb21c9
--- /dev/null
+++ b/app/models/concerns/note_on_diff.rb
@@ -0,0 +1,52 @@
+module NoteOnDiff
+  extend ActiveSupport::Concern
+
+  NUMBER_OF_TRUNCATED_DIFF_LINES = 16
+
+  included do
+    delegate :blob, :highlighted_diff_lines, to: :diff_file, allow_nil: true
+  end
+
+  def diff_note?
+    true
+  end
+
+  def diff_file
+    raise NotImplementedError
+  end
+
+  def diff_line
+    raise NotImplementedError
+  end
+
+  def for_line?(line)
+    raise NotImplementedError
+  end
+
+  def diff_attributes
+    raise NotImplementedError
+  end
+
+  def can_be_award_emoji?
+    false
+  end
+
+  # Returns an array of at most 16 highlighted lines above a diff note
+  def truncated_diff_lines
+    prev_lines = []
+
+    highlighted_diff_lines.each do |line|
+      if line.meta?
+        prev_lines.clear
+      else
+        prev_lines << line
+
+        break if for_line?(line)
+
+        prev_lines.shift if prev_lines.length >= NUMBER_OF_TRUNCATED_DIFF_LINES
+      end
+    end
+
+    prev_lines
+  end
+end
diff --git a/app/models/deployment.rb b/app/models/deployment.rb
index e498ca96e3c..520026c18dd 100644
--- a/app/models/deployment.rb
+++ b/app/models/deployment.rb
@@ -11,6 +11,8 @@ class Deployment < ActiveRecord::Base
 
   delegate :name, to: :environment, prefix: true
 
+  after_save :keep_around_commit
+
   def commit
     project.commit(sha)
   end
@@ -26,4 +28,8 @@ class Deployment < ActiveRecord::Base
   def last?
     self == environment.last_deployment
   end
+
+  def keep_around_commit
+    project.repository.keep_around(self.sha)
+  end
 end
diff --git a/app/models/diff_note.rb b/app/models/diff_note.rb
new file mode 100644
index 00000000000..9671955db36
--- /dev/null
+++ b/app/models/diff_note.rb
@@ -0,0 +1,127 @@
+class DiffNote < Note
+  include NoteOnDiff
+
+  serialize :original_position, Gitlab::Diff::Position
+  serialize :position, Gitlab::Diff::Position
+
+  validates :original_position, presence: true
+  validates :position, presence: true
+  validates :diff_line, presence: true
+  validates :line_code, presence: true, line_code: true
+  validates :noteable_type, inclusion: { in: ['Commit', 'MergeRequest'] }
+  validate :positions_complete
+  validate :verify_supported
+
+  before_validation :set_original_position, :update_position, on: :create
+  before_validation :set_line_code
+  after_save :keep_around_commits
+
+  class << self
+    def build_discussion_id(noteable_type, noteable_id, position)
+      [super(noteable_type, noteable_id), *position.key].join("-")
+    end
+  end
+
+  def new_diff_note?
+    true
+  end
+
+  def diff_attributes
+    { position: position.to_json }
+  end
+
+  def discussion_id
+    @discussion_id ||= self.class.build_discussion_id(noteable_type, noteable_id || commit_id, position)
+  end
+
+  def original_discussion_id
+    @original_discussion_id ||= self.class.build_discussion_id(noteable_type, noteable_id || commit_id, original_position)
+  end
+
+  def position=(new_position)
+    if new_position.is_a?(String)
+      new_position = JSON.parse(new_position) rescue nil
+    end
+
+    if new_position.is_a?(Hash)
+      new_position = new_position.with_indifferent_access
+      new_position = Gitlab::Diff::Position.new(new_position)
+    end
+
+    super(new_position)
+  end
+
+  def diff_file
+    @diff_file ||= self.original_position.diff_file(self.project.repository)
+  end
+
+  def diff_line
+    @diff_line ||= diff_file.line_for_position(self.original_position) if diff_file
+  end
+
+  def for_line?(line)
+    diff_file.position(line) == self.original_position
+  end
+
+  def active?(diff_refs = nil)
+    return false unless supported?
+    return true if for_commit?
+
+    diff_refs ||= self.noteable.diff_refs
+
+    self.position.diff_refs == diff_refs
+  end
+
+  private
+
+  def supported?
+    !self.for_merge_request? || self.noteable.support_new_diff_notes?
+  end
+
+  def set_original_position
+    self.original_position = self.position.dup
+  end
+
+  def set_line_code
+    self.line_code = self.position.line_code(self.project.repository)
+  end
+
+  def update_position
+    return unless supported?
+    return if for_commit?
+
+    return if active?
+
+    Notes::DiffPositionUpdateService.new(
+      self.project,
+      nil,
+      old_diff_refs: self.position.diff_refs,
+      new_diff_refs: self.noteable.diff_refs,
+      paths: self.position.paths
+    ).execute(self)
+  end
+
+  def verify_supported
+    return if supported?
+
+    errors.add(:noteable, "doesn't support new-style diff notes")
+  end
+
+  def positions_complete
+    return if self.original_position.complete? && self.position.complete?
+
+    errors.add(:position, "is invalid")
+  end
+
+  def keep_around_commits
+    project.repository.keep_around(self.original_position.base_sha)
+    project.repository.keep_around(self.original_position.start_sha)
+    project.repository.keep_around(self.original_position.head_sha)
+
+    if self.position != self.original_position
+      project.repository.keep_around(self.position.base_sha)
+      project.repository.keep_around(self.position.start_sha)
+      project.repository.keep_around(self.position.head_sha)
+    end
+  end
+end
diff --git a/app/models/legacy_diff_note.rb b/app/models/legacy_diff_note.rb
index 33d2a69ebaf..790dfd4d480 100644
--- a/app/models/legacy_diff_note.rb
+++ b/app/models/legacy_diff_note.rb
@@ -1,4 +1,6 @@
 class LegacyDiffNote < Note
+  include NoteOnDiff
+
   serialize :st_diff
 
   validates :line_code, presence: true, line_code: true
@@ -11,12 +13,12 @@ class LegacyDiffNote < Note
     end
   end
 
-  def diff_note?
+  def legacy_diff_note?
     true
   end
 
-  def legacy_diff_note?
-    true
+  def diff_attributes
+    { line_code: line_code }
   end
 
   def discussion_id
@@ -27,61 +29,20 @@ class LegacyDiffNote < Note
     line_code.split('_')[0] if line_code
   end
 
-  def diff_old_line
-    line_code.split('_')[1].to_i if line_code
-  end
-
-  def diff_new_line
-    line_code.split('_')[2].to_i if line_code
-  end
-
   def diff
     @diff ||= Gitlab::Git::Diff.new(st_diff) if st_diff.respond_to?(:map)
   end
 
-  def diff_file_path
-    diff.new_path.presence || diff.old_path
-  end
-
-  def diff_lines
-    @diff_lines ||= Gitlab::Diff::Parser.new.parse(diff.diff.each_line)
+  def diff_file
+    @diff_file ||= Gitlab::Diff::File.new(diff, repository: self.project.repository) if diff
   end
 
   def diff_line
-    @diff_line ||= diff_lines.find { |line| generate_line_code(line) == self.line_code }
+    @diff_line ||= diff_file.line_for_line_code(self.line_code)
   end
 
-  def diff_line_text
-    diff_line.try(:text)
-  end
-
-  def diff_line_type
-    diff_line.try(:type)
-  end
-
-  def highlighted_diff_lines
-    Gitlab::Diff::Highlight.new(diff_lines).highlight
-  end
-
-  def truncated_diff_lines
-    max_number_of_lines = 16
-    prev_match_line = nil
-    prev_lines = []
-
-    highlighted_diff_lines.each do |line|
-      if line.type == "match"
-        prev_lines.clear
-        prev_match_line = line
-      else
-        prev_lines << line
-
-        break if generate_line_code(line) == self.line_code
-
-        prev_lines.shift if prev_lines.length >= max_number_of_lines
-      end
-    end
-
-    prev_lines
+  def for_line?(line)
+    !line.meta? && diff_file.line_code(line) == self.line_code
   end
 
   # Check if this note is part of an "active" discussion
@@ -102,7 +63,7 @@ class LegacyDiffNote < Note
     if noteable_diff
       parsed_lines = Gitlab::Diff::Parser.new.parse(noteable_diff.diff.each_line)
 
-      @active = parsed_lines.any? { |line_obj| line_obj.text == diff_line_text }
+      @active = parsed_lines.any? { |line_obj| line_obj.text == diff_line.text }
     else
       @active = false
     end
@@ -110,10 +71,6 @@ class LegacyDiffNote < Note
     @active
   end
 
-  def award_emoji_supported?
-    false
-  end
-
   private
 
   def find_diff
@@ -149,10 +106,6 @@ class LegacyDiffNote < Note
     self.class.where(attributes).last.try(:diff)
   end
 
-  def generate_line_code(line)
-    Gitlab::Diff::LineCode.generate(diff_file_path, line.new_pos, line.old_pos)
-  end
-
   # Find the diff on noteable that matches our own
   def find_noteable_diff
     diffs = noteable.diffs(Commit.max_diff_options)
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 4f7e1d2f302..083e93f1ee7 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -16,7 +16,7 @@ class MergeRequest < ActiveRecord::Base
 
   serialize :merge_params, Hash
 
-  after_create :create_merge_request_diff, unless: :importing
+  after_create :create_merge_request_diff, unless: :importing?
   after_update :update_merge_request_diff
 
   delegate :commits, :diffs, :real_size, to: :merge_request_diff, prefix: nil
@@ -29,10 +29,6 @@ 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
@@ -89,12 +85,7 @@ class MergeRequest < ActiveRecord::Base
     state :cannot_be_merged
 
     around_transition do |merge_request, transition, block|
-      merge_request.record_timestamps = false
-      begin
-        block.call
-      ensure
-        merge_request.record_timestamps = true
-      end
+      Gitlab::Timeless.timeless(merge_request, &block)
     end
   end
 
@@ -169,10 +160,6 @@ class MergeRequest < ActiveRecord::Base
     reference
   end
 
-  def last_commit
-    merge_request_diff ? merge_request_diff.last_commit : compare_commits.last
-  end
-
   def first_commit
     merge_request_diff ? merge_request_diff.first_commit : compare_commits.first
   end
@@ -182,15 +169,86 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def diff_base_commit
-    if merge_request_diff
+    if persisted?
       merge_request_diff.base_commit
-    elsif source_sha
-      self.target_project.merge_base_commit(self.source_sha, self.target_branch)
+    elsif diff_start_commit && diff_head_commit
+      self.target_project.merge_base_commit(diff_start_sha, diff_head_sha)
+    end
+  end
+
+  # MRs created before 8.4 don't store a MergeRequestDiff#base_commit_sha,
+  # but we need to get a commit for the "View file @ ..." link by deleted files,
+  # so we find the likely one if we can't get the actual one.
+  # This will not be the actual base commit if the target branch was merged into
+  # the source branch after the merge request was created, but it is good enough
+  # for the specific purpose of linking to a commit.
+  # It is not good enough for use in `Gitlab::Git::DiffRefs`, which needs the
+  # true base commit, so we can't simply have `#diff_base_commit` fall back on
+  # this method.
+  def likely_diff_base_commit
+    first_commit.parent || first_commit
+  end
+
+  def diff_start_commit
+    if persisted?
+      merge_request_diff.start_commit
+    else
+      target_branch_head
+    end
+  end
+
+  def diff_head_commit
+    if persisted?
+      merge_request_diff.head_commit
+    else
+      source_branch_head
     end
   end
 
-  def last_commit_short_sha
-    last_commit.short_id
+  def diff_start_sha
+    diff_start_commit.try(:sha)
+  end
+
+  def diff_base_sha
+    diff_base_commit.try(:sha)
+  end
+
+  def diff_head_sha
+    diff_head_commit.try(:sha)
+  end
+
+  # When importing a pull request from GitHub, the old and new branches may no
+  # longer actually exist by those names, but we need to recreate the merge
+  # request diff with the right source and target shas.
+  # We use these attributes to force these to the intended values.
+  attr_writer :target_branch_sha, :source_branch_sha
+
+  def source_branch_head
+    source_branch_ref = @source_branch_sha || source_branch
+    source_project.repository.commit(source_branch) if source_branch_ref
+  end
+
+  def target_branch_head
+    target_branch_ref = @target_branch_sha || target_branch
+    target_project.repository.commit(target_branch) if target_branch_ref
+  end
+
+  def target_branch_sha
+    target_branch_head.try(:sha)
+  end
+
+  def source_branch_sha
+    source_branch_head.try(:sha)
+  end
+
+  def diff_refs
+    return unless diff_start_commit || diff_base_commit
+
+    Gitlab::Diff::DiffRefs.new(
+      base_sha:  diff_base_sha,
+      start_sha: diff_start_sha,
+      head_sha:  diff_head_sha
+    )
   end
 
   def validate_branches
@@ -227,21 +285,30 @@ class MergeRequest < ActiveRecord::Base
 
   def update_merge_request_diff
     if source_branch_changed? || target_branch_changed?
-      reload_code
+      reload_diff
     end
   end
 
-  def reload_code
-    if merge_request_diff && open?
-      merge_request_diff.reload_content
-    end
+  def reload_diff
+    return unless merge_request_diff && open?
+
+    old_diff_refs = self.diff_refs
+
+    merge_request_diff.reload_content
+
+    new_diff_refs = self.diff_refs
+
+    update_diff_notes_positions(
+      old_diff_refs: old_diff_refs,
+      new_diff_refs: new_diff_refs
+    )
   end
 
   def check_if_can_be_merged
     return unless unchecked?
 
     can_be_merged =
-      !broken? && project.repository.can_be_merged?(source_sha, target_branch)
+      !broken? && project.repository.can_be_merged?(diff_head_sha, target_branch)
 
     if can_be_merged
       mark_as_mergeable
@@ -293,7 +360,7 @@ class MergeRequest < ActiveRecord::Base
     !source_project.protected_branch?(source_branch) &&
       !source_project.root_ref?(source_branch) &&
       Ability.abilities.allowed?(current_user, :push_code, source_project) &&
-      last_commit == source_project.commit(source_branch)
+      diff_head_commit == source_branch_head
   end
 
   def should_remove_source_branch?
@@ -331,8 +398,8 @@ class MergeRequest < ActiveRecord::Base
       work_in_progress: work_in_progress?
     }
 
-    if last_commit
-      attrs.merge!(last_commit: last_commit.hook_attrs)
+    if diff_head_commit
+      attrs.merge!(last_commit: diff_head_commit.hook_attrs)
     end
 
     attributes.merge!(attrs)
@@ -510,22 +577,6 @@ class MergeRequest < ActiveRecord::Base
     end
   end
 
-  def target_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
-
-  def source_tip
-    source_branch && source_project.repository.commit(source_branch)
-  end
-
   def fetch_ref
     target_project.repository.fetch_ref(
       source_project.repository.path_to_repo,
@@ -558,10 +609,10 @@ class MergeRequest < ActiveRecord::Base
   def diverged_commits_count
     cache = Rails.cache.read(:"merge_request_#{id}_diverged_commits")
 
-    if cache.blank? || cache[:source_sha] != source_sha || cache[:target_sha] != target_sha
+    if cache.blank? || cache[:source_sha] != source_branch_sha || cache[:target_sha] != target_branch_sha
       cache = {
-        source_sha: source_sha,
-        target_sha: target_sha,
+        source_sha: source_branch_sha,
+        target_sha: target_branch_sha,
         diverged_commits_count: compute_diverged_commits_count
       }
       Rails.cache.write(:"merge_request_#{id}_diverged_commits", cache)
@@ -571,9 +622,9 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def compute_diverged_commits_count
-    return 0 unless source_sha && target_sha
+    return 0 unless source_branch_sha && target_branch_sha
 
-    Gitlab::Git::Commit.between(target_project.repository.raw_repository, source_sha, target_sha).size
+    Gitlab::Git::Commit.between(target_project.repository.raw_repository, source_branch_sha, target_branch_sha).size
   end
   private :compute_diverged_commits_count
 
@@ -582,13 +633,7 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def pipeline
-    @pipeline ||= source_project.pipeline(last_commit.id, source_branch) if last_commit && source_project
-  end
-
-  def diff_refs
-    return nil unless diff_base_commit
-
-    [diff_base_commit, last_commit]
+    @pipeline ||= source_project.pipeline(diff_head_sha, source_branch) if diff_head_sha && source_project
   end
 
   def merge_commit
@@ -603,6 +648,36 @@ class MergeRequest < ActiveRecord::Base
     merge_commit
   end
 
+  def support_new_diff_notes?
+    diff_refs && diff_refs.complete?
+  end
+
+  def update_diff_notes_positions(old_diff_refs:, new_diff_refs:)
+    return unless support_new_diff_notes?
+    return if new_diff_refs == old_diff_refs
+
+    active_diff_notes = self.notes.diff_notes.select do |note|
+      note.new_diff_note? && note.active?(old_diff_refs)
+    end
+
+    return if active_diff_notes.empty?
+
+    paths = active_diff_notes.flat_map { |n| n.diff_file.paths }.uniq
+
+    service = Notes::DiffPositionUpdateService.new(
+      self.project,
+      nil,
+      old_diff_refs: old_diff_refs,
+      new_diff_refs: new_diff_refs,
+      paths: paths
+    )
+
+    active_diff_notes.each do |note|
+      service.execute(note)
+      Gitlab::Timeless.timeless(note, &:save)
+    end
+  end
+
   def keep_around_commit
     project.repository.keep_around(self.merge_commit_sha)
   end
diff --git a/app/models/merge_request_diff.rb b/app/models/merge_request_diff.rb
index 0fcde6fc8f1..ba235750aeb 100644
--- a/app/models/merge_request_diff.rb
+++ b/app/models/merge_request_diff.rb
@@ -7,7 +7,7 @@ class MergeRequestDiff < ActiveRecord::Base
 
   belongs_to :merge_request
 
-  delegate :head_source_sha, :target_branch, :source_branch, to: :merge_request, prefix: nil
+  delegate :source_branch_sha, :target_branch_sha, :target_branch, :source_branch, to: :merge_request, prefix: nil
 
   state_machine :state, initial: :empty do
     state :collected
@@ -24,7 +24,7 @@ class MergeRequestDiff < ActiveRecord::Base
   serialize :st_diffs
 
   after_create :reload_content, unless: :importing?
-  after_save :keep_around_commit
+  after_save :keep_around_commits, unless: :importing?
 
   def reload_content
     reload_commits
@@ -39,9 +39,9 @@ class MergeRequestDiff < ActiveRecord::Base
     if options[:ignore_whitespace_change]
       @diffs_no_whitespace ||= begin
         compare = Gitlab::Git::Compare.new(
-          self.repository.raw_repository,
-          self.base,
-          self.head,
+          repository.raw_repository,
+          self.start_commit_sha || self.target_branch_sha,
+          self.head_commit_sha || self.source_branch_sha,
         )
         compare.diffs(options)
       end
@@ -63,37 +63,39 @@ class MergeRequestDiff < ActiveRecord::Base
   end
 
   def base_commit
-    return nil unless self.base_commit_sha
+    return unless self.base_commit_sha
 
-    merge_request.target_project.commit(self.base_commit_sha)
+    project.commit(self.base_commit_sha)
   end
 
-  def last_commit_short_sha
-    @last_commit_short_sha ||= last_commit.short_id
-  end
+  def start_commit
+    return unless self.start_commit_sha
 
-  def dump_commits(commits)
-    commits.map(&:to_hash)
+    project.commit(self.start_commit_sha)
   end
 
-  def load_commits(array)
-    array.map { |hash| Commit.new(Gitlab::Git::Commit.new(hash), merge_request.source_project) }
-  end
+  def head_commit
+    return last_commit unless self.head_commit_sha
 
-  def dump_diffs(diffs)
-    if diffs.respond_to?(:map)
-      diffs.map(&:to_hash)
-    end
+    project.commit(self.head_commit_sha)
   end
 
-  def load_diffs(raw, options)
-    if raw.respond_to?(:each)
-      Gitlab::Git::DiffCollection.new(raw, options)
-    else
-      Gitlab::Git::DiffCollection.new([])
-    end
+  def compare
+    @compare ||=
+      begin
+        # Update ref for merge request
+        merge_request.fetch_ref
+
+        Gitlab::Git::Compare.new(
+          repository.raw_repository,
+          self.target_branch_sha,
+          self.source_branch_sha
+        )
+      end
   end
 
+  private
+
   # Collect array of Git::Commit objects
   # between target and source branches
   def unmerged_commits
@@ -106,6 +108,14 @@ class MergeRequestDiff < ActiveRecord::Base
     commits
   end
 
+  def dump_commits(commits)
+    commits.map(&:to_hash)
+  end
+
+  def load_commits(array)
+    array.map { |hash| Commit.new(Gitlab::Git::Commit.new(hash), merge_request.source_project) }
+  end
+
   # Reload all commits related to current merge request from repo
   # and save it as array of hashes in st_commits db field
   def reload_commits
@@ -120,6 +130,26 @@ class MergeRequestDiff < ActiveRecord::Base
     update_columns_serialized(new_attributes)
   end
 
+  # Collect array of Git::Diff objects
+  # between target and source branches
+  def unmerged_diffs
+    compare.diffs(Commit.max_diff_options)
+  end
+
+  def dump_diffs(diffs)
+    if diffs.respond_to?(:map)
+      diffs.map(&:to_hash)
+    end
+  end
+
+  def load_diffs(raw, options)
+    if raw.respond_to?(:each)
+      Gitlab::Git::DiffCollection.new(raw, options)
+    else
+      Gitlab::Git::DiffCollection.new([])
+    end
+  end
+
   # Reload diffs between branches related to current merge request from repo
   # and save it as array of hashes in st_diffs db field
   def reload_diffs
@@ -147,59 +177,33 @@ class MergeRequestDiff < ActiveRecord::Base
 
     new_attributes[:st_diffs] = new_diffs
 
-    base_commit_sha = self.repository.merge_base(self.head, self.base)
-    new_attributes[:base_commit_sha] = base_commit_sha
-
-    self.repository.keep_around(base_commit_sha)
+    new_attributes[:start_commit_sha] = self.target_branch_sha
+    new_attributes[:head_commit_sha] = self.source_branch_sha
+    new_attributes[:base_commit_sha] = branch_base_sha
 
     update_columns_serialized(new_attributes)
-  end
 
-  # Collect array of Git::Diff objects
-  # between target and source branches
-  def unmerged_diffs
-    compare.diffs(Commit.max_diff_options)
+    keep_around_commits
   end
 
-  def repository
-    merge_request.target_project.repository
+  def project
+    merge_request.target_project
   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)
+  def repository
+    project.repository
   end
 
-  def target_sha
-    merge_request.target_sha
-  end
+  def branch_base_commit
+    return unless self.source_branch_sha && self.target_branch_sha
 
-  def base
-    self.target_sha || self.target_branch
+    project.merge_base_commit(self.source_branch_sha, self.target_branch_sha)
   end
 
-  def head
-    self.source_sha
+  def branch_base_sha
+    branch_base_commit.try(:sha)
   end
 
-  def compare
-    @compare ||=
-      begin
-        # Update ref for merge request
-        merge_request.fetch_ref
-
-        Gitlab::Git::Compare.new(
-          self.repository.raw_repository,
-          self.base,
-          self.head
-        )
-      end
-  end
-
-  private
-
   #
   # #save or #update_attributes providing changes on serialized attributes do a lot of
   # serialization and deserialization calls resulting in bad performance.
@@ -223,7 +227,9 @@ class MergeRequestDiff < ActiveRecord::Base
     reload
   end
 
-  def keep_around_commit
-    self.repository.keep_around(self.base_commit_sha)
+  def keep_around_commits
+    repository.keep_around(target_branch_sha)
+    repository.keep_around(source_branch_sha)
+    repository.keep_around(branch_base_sha)
   end
 end
diff --git a/app/models/note.rb b/app/models/note.rb
index 81b5c47b738..ffffd0c0838 100644
--- a/app/models/note.rb
+++ b/app/models/note.rb
@@ -56,7 +56,7 @@ class Note < ActiveRecord::Base
   scope :inc_author, ->{ includes(:author) }
   scope :inc_author_project_award_emoji, ->{ includes(:project, :author, :award_emoji) }
 
-  scope :legacy_diff_notes, ->{ where(type: 'LegacyDiffNote') }
+  scope :diff_notes, ->{ where(type: ['LegacyDiffNote', 'DiffNote']) }
   scope :non_diff_notes, ->{ where(type: ['Note', nil]) }
 
   scope :with_associations, -> do
@@ -82,7 +82,7 @@ class Note < ActiveRecord::Base
     end
 
     def grouped_diff_notes
-      legacy_diff_notes.select(&:active?).sort_by(&:created_at).group_by(&:line_code)
+      diff_notes.select(&:active?).sort_by(&:created_at).group_by(&:line_code)
     end
 
     # Searches for notes matching the given query.
@@ -115,6 +115,10 @@ class Note < ActiveRecord::Base
     false
   end
 
+  def new_diff_note?
+    false
+  end
+
   def active?
     true
   end
@@ -193,7 +197,7 @@ class Note < ActiveRecord::Base
   end
 
   def award_emoji?
-    award_emoji_supported? && contains_emoji_only?
+    can_be_award_emoji? && contains_emoji_only?
   end
 
   def emoji_awardable?
@@ -204,7 +208,7 @@ class Note < ActiveRecord::Base
     self.line_code = nil if self.line_code.blank?
   end
 
-  def award_emoji_supported?
+  def can_be_award_emoji?
     noteable.is_a?(Awardable)
   end
 
diff --git a/app/models/project_services/jira_service.rb b/app/models/project_services/jira_service.rb
index 27bf08bf7d9..97bcbacf2b9 100644
--- a/app/models/project_services/jira_service.rb
+++ b/app/models/project_services/jira_service.rb
@@ -144,7 +144,7 @@ class JiraService < IssueTrackerService
     commit_id = if entity.is_a?(Commit)
                   entity.id
                 elsif entity.is_a?(MergeRequest)
-                  entity.last_commit.id
+                  entity.diff_head_sha
                 end
     commit_url = build_entity_url(:commit, commit_id)
 
diff --git a/app/models/repository.rb b/app/models/repository.rb
index d232d422195..ba66bc47c29 100644
--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -653,16 +653,6 @@ class Repository
     end
   end
 
-  def blob_for_diff(commit, diff)
-    blob_at(commit.id, diff.file_path)
-  end
-
-  def prev_blob_for_diff(commit, diff)
-    if commit.parent_id
-      blob_at(commit.parent_id, diff.old_path)
-    end
-  end
-
   def refs_contains_sha(ref_type, sha)
     args = %W(#{Gitlab.config.git.bin_path} #{ref_type} --contains #{sha})
     names = Gitlab::Popen.popen(args, path_to_repo).first
diff --git a/app/models/sent_notification.rb b/app/models/sent_notification.rb
index a2df899d012..016172c6d7e 100644
--- a/app/models/sent_notification.rb
+++ b/app/models/sent_notification.rb
@@ -1,4 +1,6 @@
 class SentNotification < ActiveRecord::Base
+  serialize :position, Gitlab::Diff::Position
+
   belongs_to :project
   belongs_to :noteable, polymorphic: true
   belongs_to :recipient, class_name: "User"
@@ -7,7 +9,7 @@ class SentNotification < ActiveRecord::Base
   validates :reply_key, uniqueness: true
   validates :noteable_id, presence: true, unless: :for_commit?
   validates :commit_id, presence: true, if: :for_commit?
-  validates :line_code, line_code: true, allow_blank: true
+  validate :note_valid
 
   after_save :keep_around_commit
 
@@ -20,7 +22,7 @@ class SentNotification < ActiveRecord::Base
       find_by(reply_key: reply_key)
     end
 
-    def record(noteable, recipient_id, reply_key, params = {})
+    def record(noteable, recipient_id, reply_key, attrs = {})
       return unless reply_key
 
       noteable_id = nil
@@ -31,7 +33,7 @@ class SentNotification < ActiveRecord::Base
         noteable_id = noteable.id
       end
 
-      params.reverse_merge!(
+      attrs.reverse_merge!(
         project:        noteable.project,
         noteable_type:  noteable.class.name,
         noteable_id:    noteable_id,
@@ -40,13 +42,17 @@ class SentNotification < ActiveRecord::Base
         reply_key:      reply_key
       )
 
-      create(params)
+      create(attrs)
     end
 
-    def record_note(note, recipient_id, reply_key, params = {})
-      params[:line_code] = note.line_code
+    def record_note(note, recipient_id, reply_key, attrs = {})
+      if note.diff_note?
+        attrs[:note_type] = note.type
+
+        attrs.merge!(note.diff_attributes)
+      end
 
-      record(note.noteable, recipient_id, reply_key, params)
+      record(note.noteable, recipient_id, reply_key, attrs)
     end
   end
 
@@ -70,8 +76,33 @@ class SentNotification < ActiveRecord::Base
     self.reply_key
   end
 
+  def note_attributes
+    {
+      project:        self.project,
+      author:         self.recipient,
+      type:           self.note_type,
+      noteable_type:  self.noteable_type,
+      noteable_id:    self.noteable_id,
+      commit_id:      self.commit_id,
+      line_code:      self.line_code,
+      position:       self.position.to_json
+    }
+  end
+
+  def create_note(note)
+    Notes::CreateService.new(
+      self.project,
+      self.recipient,
+      self.note_attributes.merge(note: note)
+    ).execute
+  end
+
   private
 
+  def note_valid
+    Note.new(note_attributes.merge(note: "Test")).valid?
+  end
+
   def keep_around_commit
     project.repository.keep_around(self.commit_id)
   end