Remove Username lookup when resolving users in MembersMapper

- This change removes usage of username when
  mapping users on Project Import due to risks of
  incorrect users being mapped to project's data
- This has a higher chance of occurrence on GitLab.com
  since username of a user on source can be already taken on
  destination

changelogs/unreleased/georgekoltsov-remove-username-lookup-from-members-mapper.yml

+---
+title: Remove username lookup when mapping users when importing projects using Project
+  Import/Export and rely on email only
+merge_request: 24464
+author:
+type: changed

doc/user/project/settings/import_export.md

@@ -26,7 +26,7 @@ Note the following:
   and are deleted every 24 hours by a specific worker.
 - Group members are exported as project members, as long as the user has
   maintainer or admin access to the group where the exported project lives. An admin
-  in the import side is required to map the users, based on email or username.
+  in the import side is required to map the users, based on email.
   Otherwise, a supplementary comment is left to mention the original author and
   the MRs, notes, or issues will be owned by the importer.
 - Project members with owner access will be imported as maintainers.

ee/spec/fixtures/lib/gitlab/import_export/designs/project.json

@@ -439,7 +439,7 @@
          "override":false,
          "user":{
             "id":2,
-            "email":"user_2@example.com",
+            "email":"user_2@gitlabexample.com",
             "username":"user_2"
          }
       }

ee/spec/lib/ee/gitlab/import_export/project_tree_restorer_spec.rb

@@ -70,8 +70,8 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
   end
 
   describe 'restoring design management data' do
-    let_it_be(:user) { create(:admin, username: 'user_1') }
-    let_it_be(:second_user) { create(:user, username: 'user_2' )}
+    let_it_be(:user) { create(:admin, email: 'user_1@gitlabexample.com') }
+    let_it_be(:second_user) { create(:user, email: 'user_2@gitlabexample.com') }
     let_it_be(:project) do
       create(:project, :builds_disabled, :issues_disabled,
              { name: 'project', path: 'project' })
@@ -91,9 +91,9 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
     describe 'restores issue associations correctly' do
       let(:issue) { project.issues.offset(index).first }
 
-      where(:index, :design_filenames, :version_shas, :events, :author_usernames) do
-        0 | %w[chirrido3.jpg jonathan_richman.jpg mariavontrap.jpeg] | %w[27702d08f5ee021ae938737f84e8fe7c38599e85 9358d1bac8ff300d3d2597adaa2572a20f7f8703 e1a4a501bcb42f291f84e5d04c8f927821542fb6] | %w[creation creation creation modification modification deletion] | %w[user_1 user_1 user_2]
-        1 | ['1 (1).jpeg', '2099743.jpg', 'a screenshot (1).jpg', 'chirrido3.jpg'] | %w[73f871b4c8c1d65c62c460635e023179fb53abc4 8587e78ab6bda3bc820a9f014c3be4a21ad4fcc8 c9b5f067f3e892122a4b12b0a25a8089192f3ac8] | %w[creation creation creation creation modification] | %w[user_1 user_2 user_2]
+      where(:index, :design_filenames, :version_shas, :events, :author_emails) do
+        0 | %w[chirrido3.jpg jonathan_richman.jpg mariavontrap.jpeg] | %w[27702d08f5ee021ae938737f84e8fe7c38599e85 9358d1bac8ff300d3d2597adaa2572a20f7f8703 e1a4a501bcb42f291f84e5d04c8f927821542fb6] | %w[creation creation creation modification modification deletion] | %w[user_1@gitlabexample.com user_1@gitlabexample.com user_2@gitlabexample.com]
+        1 | ['1 (1).jpeg', '2099743.jpg', 'a screenshot (1).jpg', 'chirrido3.jpg'] | %w[73f871b4c8c1d65c62c460635e023179fb53abc4 8587e78ab6bda3bc820a9f014c3be4a21ad4fcc8 c9b5f067f3e892122a4b12b0a25a8089192f3ac8] | %w[creation creation creation creation modification] | %w[user_1@gitlabexample.com user_2@gitlabexample.com user_2@gitlabexample.com]
       end
 
       with_them do
@@ -101,7 +101,7 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
           expect(issue.designs.pluck(:filename)).to contain_exactly(*design_filenames)
           expect(issue.design_versions.pluck(:sha)).to contain_exactly(*version_shas)
           expect(issue.design_versions.flat_map(&:actions).map(&:event)).to contain_exactly(*events)
-          expect(issue.design_versions.map(&:author).map(&:username)).to contain_exactly(*author_usernames)
+          expect(issue.design_versions.map(&:author).map(&:email)).to contain_exactly(*author_emails)
         end
       end
     end

lib/gitlab/import_export/members_mapper.rb

@@ -82,7 +82,7 @@ module Gitlab
       end
 
       def find_user_query(member)
-        user_arel[:email].eq(member['user']['email']).or(user_arel[:username].eq(member['user']['username']))
+        user_arel[:email].eq(member['user']['email'])
       end
 
       def user_arel

spec/fixtures/lib/gitlab/import_export/complex/project.json

@@ -2398,7 +2398,7 @@
       "requested_at": null,
       "user": {
         "id": 16,
-        "email": "maritza_schoen@block.ca",
+        "email": "bernard_willms@gitlabexample.com",
         "username": "bernard_willms"
       }
     },
@@ -2418,7 +2418,7 @@
       "requested_at": null,
       "user": {
         "id": 6,
-        "email": "shaina@koelpindenesik.com",
+        "email": "saul_will@gitlabexample.com",
         "username": "saul_will"
       }
     },

spec/fixtures/lib/gitlab/import_export/group_exports/complex/group.json

@@ -348,7 +348,7 @@
       "override": false,
       "user": {
         "id": 206,
-        "email": "margaret.bergnaum@reynolds.us",
+        "email": "gwendolyn_robel@gitlabexample.com",
         "username": "gwendolyn_robel"
       }
     },
@@ -394,7 +394,7 @@
       "override": false,
       "user": {
         "id": 1624,
-        "email": "nakesha.herzog@powlowski.com",
+        "email": "adriene.mcclure@gitlabexample.com",
         "username": "adriene.mcclure"
       }
     },

spec/lib/gitlab/import_export/group_tree_restorer_spec.rb

@@ -10,9 +10,9 @@ describe Gitlab::ImportExport::GroupTreeRestorer do
   describe 'restore group tree' do
     before(:context) do
       # Using an admin for import, so we can check assignment of existing members
-      user = create(:admin, username: 'root')
-      create(:user, username: 'adriene.mcclure')
-      create(:user, username: 'gwendolyn_robel')
+      user = create(:admin, email: 'root@gitlabexample.com')
+      create(:user, email: 'adriene.mcclure@gitlabexample.com')
+      create(:user, email: 'gwendolyn_robel@gitlabexample.com')
 
       RSpec::Mocks.with_temporary_scope do
         @group = create(:group, name: 'group', path: 'group')
@@ -56,7 +56,7 @@ describe Gitlab::ImportExport::GroupTreeRestorer do
       end
 
       it 'has group members' do
-        expect(@group.members.map(&:user).map(&:username)).to contain_exactly('root', 'adriene.mcclure', 'gwendolyn_robel')
+        expect(@group.members.map(&:user).map(&:email)).to contain_exactly('root@gitlabexample.com', 'adriene.mcclure@gitlabexample.com', 'gwendolyn_robel@gitlabexample.com')
       end
     end
   end

spec/lib/gitlab/import_export/project_tree_restorer_spec.rb

@@ -13,8 +13,8 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
       # Using an admin for import, so we can check assignment of existing members
       @user = create(:admin)
       @existing_members = [
-        create(:user, username: 'bernard_willms'),
-        create(:user, username: 'saul_will')
+        create(:user, email: 'bernard_willms@gitlabexample.com'),
+        create(:user, email: 'saul_will@gitlabexample.com')
       ]
 
       RSpec::Mocks.with_temporary_scope do