Strip reference prefixes on branch creation

changelogs/unreleased/26470-branch-names-with-reference-prefixes-results-in-buggy-branches.yml

+---
+title: Strip reference prefixes on branch creation
+merge_request: 8498
+author: Matthieu Tardy

lib/gitlab/git_ref_validator.rb

@@ -5,6 +5,9 @@ module Gitlab
     #
     # Returns true for a valid reference name, false otherwise
     def validate(ref_name)
+      return false if ref_name.start_with?('refs/heads/')
+      return false if ref_name.start_with?('refs/remotes/')
+
       Gitlab::Utils.system_silent(
         %W(#{Gitlab.config.git.bin_path} check-ref-format refs/#{ref_name}))
     end

spec/lib/git_ref_validator_spec.rb

@@ -5,6 +5,7 @@ describe Gitlab::GitRefValidator, lib: true do
   it { expect(Gitlab::GitRefValidator.validate('implement_@all')).to be_truthy }
   it { expect(Gitlab::GitRefValidator.validate('my_new_feature')).to be_truthy }
   it { expect(Gitlab::GitRefValidator.validate('#1')).to be_truthy }
+  it { expect(Gitlab::GitRefValidator.validate('feature/refs/heads/foo')).to be_truthy }
   it { expect(Gitlab::GitRefValidator.validate('feature/~new/')).to be_falsey }
   it { expect(Gitlab::GitRefValidator.validate('feature/^new/')).to be_falsey }
   it { expect(Gitlab::GitRefValidator.validate('feature/:new/')).to be_falsey }
@@ -17,4 +18,8 @@ describe Gitlab::GitRefValidator, lib: true do
   it { expect(Gitlab::GitRefValidator.validate('feature\new')).to be_falsey }
   it { expect(Gitlab::GitRefValidator.validate('feature//new')).to be_falsey }
   it { expect(Gitlab::GitRefValidator.validate('feature new')).to be_falsey }
+  it { expect(Gitlab::GitRefValidator.validate('refs/heads/')).to be_falsey }
+  it { expect(Gitlab::GitRefValidator.validate('refs/remotes/')).to be_falsey }
+  it { expect(Gitlab::GitRefValidator.validate('refs/heads/feature')).to be_falsey }
+  it { expect(Gitlab::GitRefValidator.validate('refs/remotes/origin')).to be_falsey }
 end