Use CI source project for path to exposed job artifacts

When routing paths to exposed job artifacts, we were always using the
destination project. However, in a cross-project MR, the job exposing
the artifacts is run in the source project, not in the destination
project. Change the arguments to project_job_path() to always use the
job's project for constructing the URL path.

!23738 tried a more expansive fix but this wasn't doable thanks to
project_job_path() also being a hidden Rails-generated helper function
which did take both project and job as an argument.

Fixes: #37341

app/services/ci/find_exposed_artifacts_service.rb

@@ -35,7 +35,7 @@ module Ci
       {
         text: job.artifacts_expose_as,
         url: path_for_entries(metadata_entries, job),
-        job_path: project_job_path(project, job),
+        job_path: project_job_path(job.project, job),
         job_name: job.name
       }
     end
@@ -59,9 +59,9 @@ module Ci
       return if entries.empty?
 
       if single_artifact?(entries)
-        file_project_job_artifacts_path(project, job, entries.first.path)
+        file_project_job_artifacts_path(job.project, job, entries.first.path)
       else
-        browse_project_job_artifacts_path(project, job)
+        browse_project_job_artifacts_path(job.project, job)
       end
     end
 

spec/services/ci/find_exposed_artifacts_service_spec.rb

@@ -172,5 +172,47 @@ describe Ci::FindExposedArtifactsService do
         ])
       end
     end
+
+    context 'cross-project MR' do
+      let!(:foreign_project) { create(:project) }
+      let!(:pipeline) { create(:ci_pipeline, project: foreign_project) }
+
+      let!(:job_show) do
+        create_job_with_artifacts({
+          artifacts: {
+            expose_as: 'file artifact',
+            paths: ['ci_artifacts.txt']
+          }
+        })
+      end
+
+      let!(:job_browse) do
+        create_job_with_artifacts({
+          artifacts: {
+            expose_as: 'directory artifact',
+            paths: ['tests_encoding/']
+          }
+        })
+      end
+
+      subject { described_class.new(project, user).for_pipeline(pipeline, limit: 2) }
+
+      it 'returns the correct path for cross-project MRs' do
+        expect(subject).to eq([
+          {
+            text: 'file artifact',
+            url: file_project_job_artifacts_path(foreign_project, job_show, 'ci_artifacts.txt'),
+            job_name: job_show.name,
+            job_path: project_job_path(foreign_project, job_show)
+          },
+          {
+            text: 'directory artifact',
+            url: browse_project_job_artifacts_path(foreign_project, job_browse),
+            job_name: job_browse.name,
+            job_path: project_job_path(foreign_project, job_browse)
+          }
+        ])
+      end
+    end
   end
 end