Load commit in batches for pipelines#index

Uses `list_commits_by_oid` on the CommitService, to request the needed
commits for pipelines. These commits are needed to display the user that
created the commit and the commit title.

This includes fixes for tests failing that depended on the commit
being `nil`. However, now these are batch loaded, this doesn't happen
anymore and the commits are an instance of BatchLoader.

3 files changed, 36 insertions, 9 deletions

diff --git a/app/models/ci/pipeline.rb b/app/models/ci/pipeline.rb
index 28f154581a9..d4690da3be6 100644
--- a/app/models/ci/pipeline.rb
+++ b/app/models/ci/pipeline.rb
@@ -287,8 +287,12 @@ module Ci
       Ci::Pipeline.truncate_sha(sha)
     end
 
+    # NOTE: This is loaded lazily and will never be nil, even if the commit
+    # cannot be found.
+    #
+    # Use constructs like: `pipeline.commit.present?`
     def commit
-      @commit ||= project.commit_by(oid: sha)
+      @commit ||= Commit.lazy(project, sha)
     end
 
     def branch?
@@ -338,12 +342,9 @@ module Ci
     end
 
     def latest?
-      return false unless ref
-
-      commit = project.commit(ref)
-      return false unless commit
+      return false unless ref && commit.present?
 
-      commit.sha == sha
+      project.commit(ref) == commit
     end
 
     def retried
diff --git a/app/models/commit.rb b/app/models/commit.rb
index 13c31111134..2be07ca7d3c 100644
--- a/app/models/commit.rb
+++ b/app/models/commit.rb
@@ -86,6 +86,20 @@ class Commit
     def valid_hash?(key)
       !!(/\A#{COMMIT_SHA_PATTERN}\z/ =~ key)
     end
+
+    def lazy(project, oid)
+      BatchLoader.for({ project: project, oid: oid }).batch do |items, loader|
+        items_by_project = items.group_by { |i| i[:project] }
+
+        items_by_project.each do |project, commit_ids|
+          oids = commit_ids.map { |i| i[:oid] }
+
+          project.repository.commits_by(oids: oids).each do |commit|
+            loader.call({ project: commit.project, oid: commit.id }, commit) if commit
+          end
+        end
+      end
+    end
   end
 
   attr_accessor :raw
@@ -103,7 +117,7 @@ class Commit
   end
 
   def ==(other)
-    (self.class === other) && (raw == other.raw)
+    other.is_a?(self.class) && raw == other.raw
   end
 
   def self.reference_prefix
@@ -224,8 +238,8 @@ class Commit
     notes.includes(:author)
   end
 
-  def method_missing(m, *args, &block)
-    @raw.__send__(m, *args, &block) # rubocop:disable GitlabSecurity/PublicSend
+  def method_missing(method, *args, &block)
+    @raw.__send__(method, *args, &block) # rubocop:disable GitlabSecurity/PublicSend
   end
 
   def respond_to_missing?(method, include_private = false)
diff --git a/app/models/repository.rb b/app/models/repository.rb
index 552a354d1ce..fc7081a9f34 100644
--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -118,6 +118,18 @@ class Repository
     @commit_cache[oid] = find_commit(oid)
   end
 
+  def commits_by(oids:)
+    return [] unless oids.present?
+
+    commits = Gitlab::Git::Commit.batch_by_oid(raw_repository, oids)
+
+    if commits.present?
+      Commit.decorate(commits, @project)
+    else
+      []
+    end
+  end
+
   def commits(ref, path: nil, limit: nil, offset: nil, skip_merges: false, after: nil, before: nil)
     options = {
       repo: raw_repository,