Add github commit compare URL to job request detail page

jobserver/views/job_requests.py

@@ -235,6 +235,13 @@ def get(self, request, *args, **kwargs):
 
         is_missing_updates = incomplete and over_30_minutes_ago
 
+        previous = JobRequest.objects.previous(job_request)
+        compare_url = (
+            job_request.workspace.repo.get_compare_url(previous.sha, job_request.sha)
+            if previous
+            else None
+        )
+
         context = {
             "honeycomb_can_view_links": honeycomb_can_view_links,
             "honeycomb_links": {},
@@ -243,6 +250,7 @@ def get(self, request, *args, **kwargs):
             "job_request": job_request,
             "jobs": jobs,
             "project_yaml": self.get_project_yaml(job_request),
+            "compare_url": compare_url,
             "user_can_cancel_jobs": can_cancel_jobs,
             "view": self,
         }

templates/job_request/detail.html

@@ -298,6 +298,14 @@ <h1 class="text-3xl tracking-tight break-words font-bold text-slate-900 sm:text-
         </dl>
       {% /card %}
 
+      {% if compare_url %}
+        {% #card title="Previous Job Request" %}
+          {% #description_item title="Compare code" stacked=True %}
+            {% link href=compare_url text="View on GitHub" %}
+          {% /description_item %}
+        {% /card %}
+      {% endif %}
+
       {% if honeycomb_can_view_links %}
         {% #card title="Monitoring" subtitle="Honeycomb login required" %}
           {% #list_group small=True %}

tests/unit/jobserver/views/test_job_requests.py

@@ -922,7 +922,7 @@ def test_jobrequestdetail_with_permission(
     request = rf.get("/")
     request.user = user
 
-    with django_assert_num_queries(8):
+    with django_assert_num_queries(9):
         response = JobRequestDetail.as_view()(
             request,
             project_slug=job_request.workspace.project.slug,