fix new MR form erroneously selects tag as source when branch of same name exists #23237

app/controllers/projects/merge_requests_controller.rb

@@ -402,7 +402,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
 
     if params[:ref].present?
       @ref = params[:ref]
-      @commit = @repository.commit(@ref)
+      @commit = @repository.commit("refs/heads/#{@ref}")
     end
 
     render layout: false
@@ -413,7 +413,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
 
     if params[:ref].present?
       @ref = params[:ref]
-      @commit = @target_project.commit(@ref)
+      @commit = @target_project.commit("refs/heads/#{@ref}")
     end
 
     render layout: false

changelogs/unreleased/fix-issue-23237.yml

+---
+title: "Fixes an issue in the new merge request form, where a tag would be selected instead of a branch when they have the same names"
+merge_request: 9535
+author: Weiqing Chu

spec/features/merge_requests/create_new_mr_spec.rb

@@ -12,6 +12,33 @@ feature 'Create New Merge Request', feature: true, js: true do
     login_as user
   end
 
+  it 'selects the source branch sha when a tag with the same name exists' do
+    visit namespace_project_merge_requests_path(project.namespace, project)
+
+    click_link 'New Merge Request'
+    expect(page).to have_content('Source branch')
+    expect(page).to have_content('Target branch')
+
+    first('.js-source-branch').click
+    first('.dropdown-source-branch .dropdown-content a', text: 'v1.1.0').click
+
+    expect(page).to have_content "b83d6e3"
+  end
+
+  it 'selects the target branch sha when a tag with the same name exists' do
+    visit namespace_project_merge_requests_path(project.namespace, project)
+    
+    click_link 'New Merge Request'
+
+    expect(page).to have_content('Source branch')
+    expect(page).to have_content('Target branch')
+
+    first('.js-target-branch').click
+    first('.dropdown-target-branch .dropdown-content a', text: 'v1.1.0').click
+
+    expect(page).to have_content "b83d6e3"
+  end
+
   it 'generates a diff for an orphaned branch' do
     visit namespace_project_merge_requests_path(project.namespace, project)
 

spec/features/projects/compare_spec.rb

@@ -53,6 +53,7 @@ describe "Compare", js: true do
     dropdown = find(".js-compare-#{dropdown_type}-dropdown")
     dropdown.find(".compare-dropdown-toggle").click
     dropdown.fill_in("Filter by Git revision", with: selection)
-    find_link(selection, visible: true).click
+    wait_for_ajax
+    dropdown.find_all("a[data-ref=\"#{selection}\"]", visible: true).last.click
   end
 end

spec/support/test_env.rb

@@ -37,7 +37,8 @@ module TestEnv
     'conflict-too-large'                 => '39fa04f',
     'deleted-image-test'                 => '6c17798',
     'wip'                                => 'b9238ee',
-    'csv'                                => '3dd0896'
+    'csv'                                => '3dd0896',
+    'v1.1.0'                             => 'b83d6e3'
   }.freeze
   
   # gitlab-test-fork is a fork of gitlab-fork, but we don't necessarily