Don't mutate string parameters

To avoid errors when the strings are immutable.
See https://gitlab.com/gitlab-org/gitlab/-/merge_requests/33216#note_351391995

lib/gitlab/gitaly_client/commit_service.rb

@@ -247,8 +247,8 @@ module Gitlab
         request = Gitaly::CommitsByMessageRequest.new(
           repository: @gitaly_repo,
           query: query,
-          revision: revision.to_s.force_encoding(Encoding::ASCII_8BIT),
-          path: path.to_s.force_encoding(Encoding::ASCII_8BIT),
+          revision: encode_binary(revision),
+          path: encode_binary(path),
           limit: limit.to_i,
           offset: offset.to_i
         )

spec/lib/gitlab/gitaly_client/commit_service_spec.rb

@@ -326,4 +326,59 @@ describe Gitlab::GitalyClient::CommitService do
       client.find_commits(order: 'default', author: "Billy Baggins <bilbo@shire.com>")
     end
   end
+
+  describe '#commits_by_message' do
+    shared_examples 'a CommitsByMessageRequest' do
+      let(:commits) { create_list(:gitaly_commit, 2) }
+
+      before do
+        request = Gitaly::CommitsByMessageRequest.new(
+          repository: repository_message,
+          query: query,
+          revision: (options[:revision] || '').dup.force_encoding(Encoding::ASCII_8BIT),
+          path: (options[:path] || '').dup.force_encoding(Encoding::ASCII_8BIT),
+          limit: (options[:limit] || 1000).to_i,
+          offset: (options[:offset] || 0).to_i
+        )
+
+        allow_any_instance_of(Gitaly::CommitService::Stub)
+          .to receive(:commits_by_message)
+          .with(request, kind_of(Hash))
+          .and_return([Gitaly::CommitsByMessageResponse.new(commits: commits)])
+      end
+
+      it 'sends an RPC request with the correct payload' do
+        expect(client.commits_by_message(query, options)).to match_array(wrap_commits(commits))
+      end
+    end
+
+    let(:query) { 'Add a feature' }
+    let(:options) { {} }
+
+    context 'when only the query is provided' do
+      include_examples 'a CommitsByMessageRequest'
+    end
+
+    context 'when all arguments are provided' do
+      let(:options) { { revision: 'feature-branch', path: 'foo.txt', limit: 10, offset: 20 } }
+
+      include_examples 'a CommitsByMessageRequest'
+    end
+
+    context 'when limit and offset are not integers' do
+      let(:options) { { limit: '10', offset: '60' } }
+
+      include_examples 'a CommitsByMessageRequest'
+    end
+
+    context 'when revision and path contain non-ASCII characters' do
+      let(:options) { { revision: "branch\u011F", path: "foo/\u011F.txt" } }
+
+      include_examples 'a CommitsByMessageRequest'
+    end
+
+    def wrap_commits(commits)
+      commits.map { |commit| Gitlab::Git::Commit.new(repository, commit) }
+    end
+  end
 end

spec/lib/gitlab/project_search_results_spec.rb

@@ -532,7 +532,7 @@ describe Gitlab::ProjectSearchResults do
 
       context 'when repository_ref is provided' do
         let(:message) { 'Feature added' }
-        let(:repository_ref) { +'feature' }
+        let(:repository_ref) { 'feature' }
 
         it 'searches in the specified ref' do
           commits = described_class.new(user, project, message, repository_ref).objects('commits')