Return an error for an invalid ref_name

* Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/351520
* Sentry error: https://sentry.gitlab.net/gitlab/gitlabcom/issues/3173142/

**Problem**

Git ref cannot start with `-`. Currently we return an ArgumentError
from the Gitaly.

**Solution**

Verify the ref_name with regexp

Changelog: fixed

lib/api/commits.rb

@@ -32,7 +32,7 @@ module API
         success Entities::Commit
       end
       params do
-        optional :ref_name, type: String, desc: 'The name of a repository branch or tag, if not given the default branch is used'
+        optional :ref_name, type: String, desc: 'The name of a repository branch or tag, if not given the default branch is used', regexp: /\A#{Gitlab::PathRegex.git_reference_regex}\z|\A\z/
         optional :since, type: DateTime, desc: 'Only commits after or on this date will be returned'
         optional :until, type: DateTime, desc: 'Only commits before or on this date will be returned'
         optional :path, type: String, desc: 'The file path'

lib/gitlab/path_regex.rb

@@ -234,7 +234,7 @@ module Gitlab
       @git_reference_regex ||= single_line_regexp %r{
         (?!
            (?# doesn't begins with)
-           \/|                    (?# rule #6)
+           \/|-|                  (?# rule #6)
            (?# doesn't contain)
            .*(?:
               [\/.]\.|            (?# rule #1,3)

spec/lib/gitlab/path_regex_spec.rb

@@ -530,6 +530,18 @@ RSpec.describe Gitlab::PathRegex do
       it { is_expected.not_to match('snippets/1.wiki.git') }
     end
 
+    describe '.git_reference_regex' do
+      subject { %r{\A#{described_class.git_reference_regex}\z} }
+
+      it { is_expected.to match('main') }
+      it { is_expected.to match('v1.2.3') }
+      it { is_expected.to match('refs/heads/main') }
+      it { is_expected.to match('1-2-3') }
+      it { is_expected.to match('1-----') }
+      it { is_expected.not_to match('-main') }
+      it { is_expected.not_to match('') }
+    end
+
     describe '.full_snippets_repository_path_regex' do
       subject { described_class.full_snippets_repository_path_regex }
 

spec/requests/api/commits_spec.rb

@@ -127,6 +127,14 @@ RSpec.describe API::Commits do
         it_behaves_like 'project commits'
       end
 
+      context 'with incorrect ref_name parameter' do
+        let(:route) { "/projects/#{project_id}/repository/commits?ref_name=-main" }
+
+        it_behaves_like '400 response' do
+          let(:request) { get api(route, user) }
+        end
+      end
+
       context "path optional parameter" do
         it "returns project commits matching provided path parameter" do
           path = 'files/ruby/popen.rb'