Make squash/rebase failed messages better

We could be more descriptive in these messages, so let's bring them
closer to our style standards and give more information.

Changelog: changed

app/services/merge_requests/rebase_service.rb

@@ -2,7 +2,7 @@
 
 module MergeRequests
   class RebaseService < MergeRequests::BaseService
-    REBASE_ERROR = 'Rebase failed. Please rebase locally'
+    REBASE_ERROR = 'Rebase failed: Rebase locally, resolve all conflicts, then push the branch.'
 
     attr_reader :merge_request, :rebase_error
 
@@ -35,7 +35,7 @@ module MergeRequests
     def set_rebase_error(exception)
       @rebase_error =
         if exception.is_a?(Gitlab::Git::PreReceiveError)
-          "Something went wrong during the rebase pre-receive hook: #{exception.message}."
+          "The rebase pre-receive hook failed: #{exception.message}."
         else
           REBASE_ERROR
         end

app/services/merge_requests/squash_service.rb

@@ -9,9 +9,9 @@ module MergeRequests
         return success(squash_sha: merge_request.diff_head_sha)
       end
 
-      return error(s_('MergeRequests|This project does not allow squashing commits when merge requests are accepted.')) if squash_forbidden?
+      return error(s_("MergeRequests|Squashing not allowed: This project doesn't allow you to squash commits when merging.")) if squash_forbidden?
 
-      squash! || error(s_('MergeRequests|Failed to squash. Should be done manually.'))
+      squash! || error(s_('MergeRequests|Squashing failed: Squash the commits locally, resolve any conflicts, then push the branch.'))
     end
 
     private

locale/gitlab.pot

@@ -22680,13 +22680,13 @@ msgstr ""
 msgid "MergeRequests|Create issue to resolve thread"
 msgstr ""
 
-msgid "MergeRequests|Failed to squash. Should be done manually."
+msgid "MergeRequests|Saving the comment failed"
 msgstr ""
 
-msgid "MergeRequests|Saving the comment failed"
+msgid "MergeRequests|Squashing failed: Squash the commits locally, resolve any conflicts, then push the branch."
 msgstr ""
 
-msgid "MergeRequests|This project does not allow squashing commits when merge requests are accepted."
+msgid "MergeRequests|Squashing not allowed: This project doesn't allow you to squash commits when merging."
 msgstr ""
 
 msgid "MergeRequests|Thread stays resolved"

spec/services/merge_requests/merge_service_spec.rb

@@ -388,7 +388,7 @@ RSpec.describe MergeRequests::MergeService do
         end
 
         it 'logs and saves error if there is an error when squashing' do
-          error_message = 'Failed to squash. Should be done manually'
+          error_message = 'Squashing failed: Squash the commits locally, resolve any conflicts, then push the branch.'
 
           allow_any_instance_of(MergeRequests::SquashService).to receive(:squash!).and_return(nil)
           merge_request.update!(squash: true)

spec/services/merge_requests/rebase_service_spec.rb

@@ -82,7 +82,7 @@ RSpec.describe MergeRequests::RebaseService do
 
     context 'with a pre-receive failure' do
       let(:pre_receive_error) { "Commit message does not follow the pattern 'ACME'" }
-      let(:merge_error) { "Something went wrong during the rebase pre-receive hook: #{pre_receive_error}." }
+      let(:merge_error) { "The rebase pre-receive hook failed: #{pre_receive_error}." }
 
       before do
         allow(repository).to receive(:gitaly_operation_client).and_raise(Gitlab::Git::PreReceiveError, "GitLab: #{pre_receive_error}")

spec/services/merge_requests/squash_service_spec.rb

@@ -168,7 +168,7 @@ RSpec.describe MergeRequests::SquashService do
       it 'raises a squash error' do
         expect(service.execute).to match(
           status: :error,
-          message: a_string_including('does not allow squashing commits when merge requests are accepted'))
+          message: a_string_including('allow you to squash commits when merging'))
       end
     end
 
@@ -205,7 +205,7 @@ RSpec.describe MergeRequests::SquashService do
         end
 
         it 'returns an error' do
-          expect(service.execute).to match(status: :error, message: a_string_including('squash'))
+          expect(service.execute).to match(status: :error, message: a_string_including('Squash'))
         end
       end
     end
@@ -232,7 +232,7 @@ RSpec.describe MergeRequests::SquashService do
       end
 
       it 'returns an error' do
-        expect(service.execute).to match(status: :error, message: a_string_including('squash'))
+        expect(service.execute).to match(status: :error, message: a_string_including('Squash'))
       end
 
       it 'cleans up the temporary directory' do