Fix SystemStackError when Peek bar is active with Rugged callssh-fix-infite-loop-peek-bar

Peek attempts to serialize results with `to_json`, which calls
`ActiveSupport::JSON`. If an object is passed to `to_json` that contains
instance variables, `ActiveSupport` will attempt to recursively traverse
all variables.

The problem is that we can get into an infinite loop if the instance
references to an instance that references to something else that points
back to the same instance.

To avoid this mess, we just call `to_s` on the object. It appears only
`Gitlab::Git::Repository` and `::Repository` are the culprits here.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/65404

2 files changed, 13 insertions, 5 deletions

diff --git a/lib/peek/views/rugged.rb b/lib/peek/views/rugged.rb
index 6b9d3e7b1a3..18b3f422852 100644
--- a/lib/peek/views/rugged.rb
+++ b/lib/peek/views/rugged.rb
@@ -29,8 +29,12 @@ module Peek
 
       def format_args(args)
         args.map do |arg|
-          # Needed to avoid infinite as_json calls
-          if arg.is_a?(Gitlab::Git::Repository)
+          # ActiveSupport::JSON recursively calls as_json on all
+          # instance variables, and if that instance variable points to
+          # something that refers back to the same instance, we can wind
+          # up in an infinite loop. Currently this only seems to happen with
+          # Gitlab::Git::Repository and ::Repository.
+          if arg.instance_variables.present?
             arg.to_s
           else
             arg
diff --git a/spec/lib/peek/views/rugged_spec.rb b/spec/lib/peek/views/rugged_spec.rb
index 8bf996fc6bc..d07d6b51a1f 100644
--- a/spec/lib/peek/views/rugged_spec.rb
+++ b/spec/lib/peek/views/rugged_spec.rb
@@ -24,7 +24,7 @@ describe Peek::Views::Rugged, :request_store do
                                                      args: [project.repository.raw, 'HEAD'],
                                                      duration: 0.123)
     ::Gitlab::RuggedInstrumentation.add_call_details(feature: :rugged_test2,
-                                                     args: [project.repository.raw, 'refs/heads/master'],
+                                                     args: [project.repository, 'refs/heads/master'],
                                                      duration: 0.456)
 
     results = subject.results
@@ -32,7 +32,11 @@ describe Peek::Views::Rugged, :request_store do
     expect(results[:duration]).to eq('1234.00ms')
     expect(results[:details].count).to eq(2)
 
-    expect(results[:details][0][:args]).to eq([project.repository.raw.to_s, "refs/heads/master"])
-    expect(results[:details][1][:args]).to eq([project.repository.raw.to_s, "HEAD"])
+    expected = [
+      [project.repository.raw.to_s, "HEAD"],
+      [project.repository.to_s, "refs/heads/master"]
+    ]
+
+    expect(results[:details].map { |data| data[:args] }).to match_array(expected)
   end
 end