Batchload blobs for diff generation

After installing a new gem, batch-loader, a construct can be used to
queue data to be fetched in bulk. The gem was also introduced in both
gitlab-org/gitlab-ce!14680 and gitlab-org/gitlab-ce!14846, but those mrs
are not merged yet.

For the generation of diffs, both the old blob and the new blob need to
be loaded. This for every file in the diff, too. Now we collect all
these so we do 1 fetch. Three `.allow_n_plus_1_calls` have been removed,
which I expect to be valid, but this needs to be confirmed by a full CI
run.

Possibly closes:
- https://gitlab.com/gitlab-org/gitlab-ce/issues/37445
- https://gitlab.com/gitlab-org/gitlab-ce/issues/37599
- https://gitlab.com/gitlab-org/gitlab-ce/issues/37431

5 files changed, 26 insertions, 14 deletions

diff --git a/app/controllers/projects/commit_controller.rb b/app/controllers/projects/commit_controller.rb
index 494d412b532..6ff96a3f295 100644
--- a/app/controllers/projects/commit_controller.rb
+++ b/app/controllers/projects/commit_controller.rb
@@ -22,12 +22,7 @@ class Projects::CommitController < Projects::ApplicationController
     apply_diff_view_cookie!
 
     respond_to do |format|
-      format.html do
-        # n+1: https://gitlab.com/gitlab-org/gitlab-ce/issues/37599
-        Gitlab::GitalyClient.allow_n_plus_1_calls do
-          render
-        end
-      end
+      format.html  { render }
       format.diff  { render text: @commit.to_diff }
       format.patch { render text: @commit.to_patch }
     end
@@ -112,7 +107,7 @@ class Projects::CommitController < Projects::ApplicationController
   end
 
   def commit
-    @noteable = @commit ||= @project.commit(params[:id])
+    @noteable = @commit ||= @project.commit_by(oid: params[:id])
   end
 
   def define_commit_vars
diff --git a/app/controllers/projects/merge_requests/diffs_controller.rb b/app/controllers/projects/merge_requests/diffs_controller.rb
index 7d16e77ef66..d60a24d3f1d 100644
--- a/app/controllers/projects/merge_requests/diffs_controller.rb
+++ b/app/controllers/projects/merge_requests/diffs_controller.rb
@@ -10,10 +10,7 @@ class Projects::MergeRequests::DiffsController < Projects::MergeRequests::Applic
   def show
     @environment = @merge_request.environments_for(current_user).last
 
-    # n+1: https://gitlab.com/gitlab-org/gitlab-ce/issues/37431
-    Gitlab::GitalyClient.allow_n_plus_1_calls do
-      render json: { html: view_to_html_string("projects/merge_requests/diffs/_diffs") }
-    end
+    render json: { html: view_to_html_string("projects/merge_requests/diffs/_diffs") }
   end
 
   def diff_for_path
diff --git a/app/models/blob.rb b/app/models/blob.rb
index ad0bc2e2ead..29e762724e3 100644
--- a/app/models/blob.rb
+++ b/app/models/blob.rb
@@ -76,12 +76,24 @@ class Blob < SimpleDelegator
     new(blob, project)
   end
 
+  def self.lazy(project, commit_id, path)
+    BatchLoader.for(commit_id: commit_id, path: path).batch do |items, loader|
+      project.repository.blobs_at(items.map(&:values)).each do |blob|
+        loader.call({ commit_id: blob.commit_id, path: blob.path }, blob) if blob
+      end
+    end
+  end
+
   def initialize(blob, project = nil)
     @project = project
 
     super(blob)
   end
 
+  def inspect
+    "#<#{self.class.name} oid:#{id[0..8]} commit:#{commit_id[0..8]} path:#{path}>"
+  end
+
   # Returns the data of the blob.
   #
   # If the blob is a text based blob the content is converted to UTF-8 and any
@@ -95,7 +107,10 @@ class Blob < SimpleDelegator
   end
 
   def load_all_data!
-    super(project.repository) if project
+    # Endpoint needed: gitlab-org/gitaly#756
+    Gitlab::GitalyClient.allow_n_plus_1_calls do
+      super(project.repository) if project
+    end
   end
 
   def no_highlighting?
diff --git a/app/models/commit.rb b/app/models/commit.rb
index a31ebe9cc87..8401d99a08f 100644
--- a/app/models/commit.rb
+++ b/app/models/commit.rb
@@ -84,7 +84,7 @@ class Commit
   end
 
   def id
-    @raw.id
+    raw.id
   end
 
   def ==(other)
@@ -361,7 +361,7 @@ class Commit
     @deltas ||= raw.deltas
   end
 
-  def diffs(diff_options = nil)
+  def diffs(diff_options = {})
     Gitlab::Diff::FileCollection::Commit.new(self, diff_options: diff_options)
   end
 
diff --git a/app/models/repository.rb b/app/models/repository.rb
index 8a6a8377de9..26d1bc12232 100644
--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -478,6 +478,11 @@ class Repository
     nil
   end
 
+  # items is an Array like: [[oid, path], [oid1, path1]]
+  def blobs_at(items)
+    raw_repository.batch_blobs(items).map { |blob| Blob.decorate(blob, project) }
+  end
+
   def root_ref
     if raw_repository
       raw_repository.root_ref