Link issues from comments and automatically close them

Any mention of Issues, MergeRequests, or Commits via GitLab-flavored markdown
references in descriptions, titles, or attached Notes creates a back-reference
Note that links to the original referencer. Furthermore, pushing commits with
commit messages that match a (configurable) regexp to a project's default
branch will close any issues mentioned by GFM in the matched closing phrase.
If accepting a merge request would close any Issues in this way, a banner is
appended to the merge request's main panel to indicate this.

6 files changed, 152 insertions, 12 deletions

diff --git a/app/models/commit.rb b/app/models/commit.rb
index da80c2940ff..f8ca6a5fe82 100644
--- a/app/models/commit.rb
+++ b/app/models/commit.rb
@@ -2,6 +2,9 @@ class Commit
   include ActiveModel::Conversion
   include StaticModel
   extend ActiveModel::Naming
+  include Mentionable
+
+  attr_mentionable :safe_message
 
   # Safe amount of files with diffs in one commit to render
   # Used to prevent 500 error on huge commits by suppressing diff
@@ -65,6 +68,29 @@ class Commit
     end
   end
 
+  # Regular expression that identifies commit message clauses that trigger issue closing.
+  def issue_closing_regex
+    @issue_closing_regex ||= Regexp.new(Gitlab.config.gitlab.issue_closing_pattern)
+  end
+
+  # Discover issues should be closed when this commit is pushed to a project's
+  # default branch.
+  def closes_issues project
+    md = issue_closing_regex.match(safe_message)
+    if md
+      extractor = Gitlab::ReferenceExtractor.new
+      extractor.analyze(md[0])
+      extractor.issues_for(project)
+    else
+      []
+    end
+  end
+
+  # Mentionable override.
+  def gfm_reference
+    "commit #{sha[0..5]}"
+  end
+
   def method_missing(m, *args, &block)
     @raw.send(m, *args, &block)
   end
diff --git a/app/models/concerns/mentionable.rb b/app/models/concerns/mentionable.rb
index f22070f8504..27e39339ae8 100644
--- a/app/models/concerns/mentionable.rb
+++ b/app/models/concerns/mentionable.rb
@@ -1,12 +1,47 @@
 # == Mentionable concern
 #
-# Contains common functionality shared between Issues and Notes
+# Contains functionality related to objects that can mention Users, Issues, MergeRequests, or Commits by
+# GFM references.
 #
-# Used by Issue, Note
+# Used by Issue, Note, MergeRequest, and Commit.
 #
 module Mentionable
   extend ActiveSupport::Concern
 
+  module ClassMethods
+    # Indicate which attributes of the Mentionable to search for GFM references.
+    def attr_mentionable *attrs
+      mentionable_attrs.concat(attrs.map(&:to_s))
+    end
+
+    # Accessor for attributes marked mentionable.
+    def mentionable_attrs
+      @mentionable_attrs ||= []
+    end
+  end
+
+  # Generate a GFM back-reference that will construct a link back to this Mentionable when rendered. Must
+  # be overridden if this model object can be referenced directly by GFM notation.
+  def gfm_reference
+    raise NotImplementedError.new("#{self.class} does not implement #gfm_reference")
+  end
+
+  # Construct a String that contains possible GFM references.
+  def mentionable_text
+    self.class.mentionable_attrs.map { |attr| send(attr) || '' }.join
+  end
+
+  # The GFM reference to this Mentionable, which shouldn't be included in its #references.
+  def local_reference
+    self
+  end
+
+  # Determine whether or not a cross-reference Note has already been created between this Mentionable and
+  # the specified target.
+  def has_mentioned? target
+    Note.cross_reference_exists?(target, local_reference)
+  end
+
   def mentioned_users
     users = []
     return users if mentionable_text.blank?
@@ -24,14 +59,39 @@ module Mentionable
     users.uniq
   end
 
-  def mentionable_text
-    if self.class == Issue
-      description
-    elsif self.class == Note
-      note
-    else
-      nil
+  # Extract GFM references to other Mentionables from this Mentionable. Always excludes its #local_reference.
+  def references p = project, text = mentionable_text
+    return [] if text.blank?
+    ext = Gitlab::ReferenceExtractor.new
+    ext.analyze(text)
+    (ext.issues_for(p) + ext.merge_requests_for(p) + ext.commits_for(p)).uniq - [local_reference]
+  end
+
+  # Create a cross-reference Note for each GFM reference to another Mentionable found in +mentionable_text+.
+  def create_cross_references! p = project, a = author, without = []
+    refs = references(p) - without
+    refs.each do |ref|
+      Note.create_cross_reference_note(ref, local_reference, a, p)
     end
   end
 
+  # If the mentionable_text field is about to change, locate any *added* references and create cross references for
+  # them. Invoke from an observer's #before_save implementation.
+  def notice_added_references p = project, a = author
+    ch = changed_attributes
+    original, mentionable_changed = "", false
+    self.class.mentionable_attrs.each do |attr|
+      if ch[attr]
+        original << ch[attr]
+        mentionable_changed = true
+      end
+    end
+
+    # Only proceed if the saved changes actually include a chance to an attr_mentionable field.
+    return unless mentionable_changed
+
+    preexisting = references(p, original)
+    create_cross_references!(p, a, preexisting)
+  end
+
 end
diff --git a/app/models/issue.rb b/app/models/issue.rb
index 03c1c166137..ffe9681fc83 100644
--- a/app/models/issue.rb
+++ b/app/models/issue.rb
@@ -32,6 +32,7 @@ class Issue < ActiveRecord::Base
   attr_accessible :title, :assignee_id, :position, :description,
                   :milestone_id, :label_list, :author_id_of_changes,
                   :state_event
+  attr_mentionable :title, :description
 
   acts_as_taggable_on :labels
 
@@ -56,4 +57,10 @@ class Issue < ActiveRecord::Base
 
   # Both open and reopened issues should be listed as opened
   scope :opened, -> { with_state(:opened, :reopened) }
+
+  # Mentionable overrides.
+
+  def gfm_reference
+    "issue ##{iid}"
+  end
 end
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 0bb4b231f62..514fc79f7c5 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -31,7 +31,7 @@ class MergeRequest < ActiveRecord::Base
   belongs_to :source_project, foreign_key: :source_project_id, class_name: "Project"
 
   attr_accessible :title, :assignee_id, :source_project_id, :source_branch, :target_project_id, :target_branch, :milestone_id, :author_id_of_changes, :state_event
-
+  attr_mentionable :title
 
   attr_accessor :should_remove_source_branch
 
@@ -255,6 +255,20 @@ class MergeRequest < ActiveRecord::Base
     target_project
   end
 
+  # Return the set of issues that will be closed if this merge request is accepted.
+  def closes_issues
+    if target_branch == project.default_branch
+      unmerged_commits.map { |c| c.closes_issues(project) }.flatten.uniq.sort_by(&:id)
+    else
+      []
+    end
+  end
+
+  # Mentionable override.
+  def gfm_reference
+    "merge request !#{iid}"
+  end
+
   private
 
   def dump_commits(commits)
diff --git a/app/models/note.rb b/app/models/note.rb
index 7598978ad4d..e819a5516b5 100644
--- a/app/models/note.rb
+++ b/app/models/note.rb
@@ -24,6 +24,7 @@ class Note < ActiveRecord::Base
 
   attr_accessible :note, :noteable, :noteable_id, :noteable_type, :project_id,
                   :attachment, :line_code, :commit_id
+  attr_mentionable :note
 
   belongs_to :project
   belongs_to :noteable, polymorphic: true
@@ -54,15 +55,36 @@ class Note < ActiveRecord::Base
   serialize :st_diff
   before_create :set_diff, if: ->(n) { n.line_code.present? }
 
-  def self.create_status_change_note(noteable, project, author, status)
+  def self.create_status_change_note(noteable, project, author, status, source)
+    body = "_Status changed to #{status}#{' by ' + source.gfm_reference if source}_"
+
+    create({
+      noteable: noteable,
+      project: project,
+      author: author,
+      note: body,
+      system: true
+    }, without_protection: true)
+  end
+
+  # +noteable+ was referenced from +mentioner+, by including GFM in either +mentioner+'s description or an associated Note.
+  # Create a system Note associated with +noteable+ with a GFM back-reference to +mentioner+.
+  def self.create_cross_reference_note(noteable, mentioner, author, project)
     create({
       noteable: noteable,
+      commit_id: (noteable.sha if noteable.respond_to? :sha),
       project: project,
       author: author,
-      note: "_Status changed to #{status}_"
+      note: "_mentioned in #{mentioner.gfm_reference}_",
+      system: true
     }, without_protection: true)
   end
 
+  # Determine whether or not a cross-reference note already exists.
+  def self.cross_reference_exists?(noteable, mentioner)
+    where(noteable_id: noteable.id, system: true, note: "_mentioned in #{mentioner.gfm_reference}_").any?
+  end
+
   def commit_author
     @commit_author ||=
       project.users.find_by_email(noteable.author_email) ||
@@ -191,6 +213,16 @@ class Note < ActiveRecord::Base
     for_issue? || (for_merge_request? && !for_diff_line?)
   end
 
+  # Mentionable override.
+  def gfm_reference
+    noteable.gfm_reference
+  end
+
+  # Mentionable override.
+  def local_reference
+    noteable
+  end
+
   def noteable_type_name
     if noteable_type.present?
       noteable_type.downcase
diff --git a/app/models/repository.rb b/app/models/repository.rb
index 3d649519d8f..aeec48ee5cc 100644
--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -18,6 +18,7 @@ class Repository
   end
 
   def commit(id = nil)
+    return nil unless raw_repository
     commit = Gitlab::Git::Commit.find(raw_repository, id)
     commit = Commit.new(commit) if commit
     commit