Merge branch 'fix/error-when-invalid-branch-for-new-pipeline-used' into 'master'

Fix error when using invalid branch name when creating a new pipeline

## What does this MR do?

This MR fixes `500` error when creating a new pipeline though user interface ("Run pipeline")

## Are there points in the code the reviewer needs to double check?

Is this a good approach to catch those exceptions on `Repository` level?

## Does this MR meet the acceptance criteria?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- Tests
  - [x] Added for this feature/bug

## What are the relevant issue numbers?

Closes #23982

See merge request !7324

4 files changed, 62 insertions, 7 deletions

diff --git a/app/controllers/projects/pipelines_controller.rb b/app/controllers/projects/pipelines_controller.rb
index 371cc3787fb..533af80aee0 100644
--- a/app/controllers/projects/pipelines_controller.rb
+++ b/app/controllers/projects/pipelines_controller.rb
@@ -18,7 +18,9 @@ class Projects::PipelinesController < Projects::ApplicationController
   end
 
   def create
-    @pipeline = Ci::CreatePipelineService.new(project, current_user, create_params).execute(ignore_skip_ci: true, save_on_errors: false)
+    @pipeline = Ci::CreatePipelineService
+      .new(project, current_user, create_params)
+      .execute(ignore_skip_ci: true, save_on_errors: false)
     unless @pipeline.persisted?
       render 'new'
       return
diff --git a/app/models/repository.rb b/app/models/repository.rb
index 7d06ce1e85b..fe991904601 100644
--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -84,15 +84,17 @@ class Repository
 
   def commit(ref = 'HEAD')
     return nil unless exists?
+
     commit =
       if ref.is_a?(Gitlab::Git::Commit)
         ref
       else
         Gitlab::Git::Commit.find(raw_repository, ref)
       end
+
     commit = ::Commit.new(commit, @project) if commit
     commit
-  rescue Rugged::OdbError
+  rescue Rugged::OdbError, Rugged::TreeError
     nil
   end
 
@@ -232,6 +234,8 @@ class Repository
 
   def ref_exists?(ref)
     rugged.references.exist?(ref)
+  rescue Rugged::ReferenceError
+    false
   end
 
   def update_ref!(name, newrev, oldrev)
@@ -270,11 +274,7 @@ class Repository
   end
 
   def kept_around?(sha)
-    begin
-      ref_exists?(keep_around_ref_name(sha))
-    rescue Rugged::ReferenceError
-      false
-    end
+    ref_exists?(keep_around_ref_name(sha))
   end
 
   def tag_names
diff --git a/changelogs/unreleased/fix-error-when-invalid-branch-for-new-pipeline-used.yml b/changelogs/unreleased/fix-error-when-invalid-branch-for-new-pipeline-used.yml
new file mode 100644
index 00000000000..ad6aa214f0f
--- /dev/null
+++ b/changelogs/unreleased/fix-error-when-invalid-branch-for-new-pipeline-used.yml
@@ -0,0 +1,4 @@
+---
+title: Fix error when using invalid branch name when creating a new pipeline
+merge_request: 7324
+author: 
diff --git a/spec/models/repository_spec.rb b/spec/models/repository_spec.rb
index 12989d4db53..fe26b4ac18c 100644
--- a/spec/models/repository_spec.rb
+++ b/spec/models/repository_spec.rb
@@ -113,6 +113,26 @@ describe Repository, models: true do
     end
   end
 
+  describe '#ref_exists?' do
+    context 'when ref exists' do
+      it 'returns true' do
+        expect(repository.ref_exists?('refs/heads/master')).to be true
+      end
+    end
+
+    context 'when ref does not exist' do
+      it 'returns false' do
+        expect(repository.ref_exists?('refs/heads/non-existent')).to be false
+      end
+    end
+
+    context 'when ref format is incorrect' do
+      it 'returns false' do
+        expect(repository.ref_exists?('refs/heads/invalid:master')).to be false
+      end
+    end
+  end
+
   describe '#last_commit_for_path' do
     subject { repository.last_commit_for_path(sample_commit.id, '.gitignore').id }
 
@@ -197,6 +217,35 @@ describe Repository, models: true do
     end
   end
 
+  describe '#commit' do
+    context 'when ref exists' do
+      it 'returns commit object' do
+        expect(repository.commit('master'))
+          .to be_an_instance_of Commit
+      end
+    end
+
+    context 'when ref does not exist' do
+      it 'returns nil' do
+        expect(repository.commit('non-existent-ref')).to be_nil
+      end
+    end
+
+    context 'when ref is not valid' do
+      context 'when preceding tree element exists' do
+        it 'returns nil' do
+          expect(repository.commit('master:ref')).to be_nil
+        end
+      end
+
+      context 'when preceding tree element does not exist' do
+        it 'returns nil' do
+          expect(repository.commit('non-existent:ref')).to be_nil
+        end
+      end
+    end
+  end
+
   describe "#commit_dir" do
     it "commits a change that creates a new directory" do
       expect do