feat: show failed dependencies in package results.

This table existed in the App Engine version and was temporarily removed,
now it's back! Unlike the "packages broken by this one", the table is
not AJAX, for various reasons. The main reason is that we already have
the list of failed dependencies, so no need for another round trip.

pages/bulktracker.go

@@ -202,7 +202,14 @@ func (p *PkgDetails) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	res, err := p.DB.GetSingleResult(ctx, resultID)
+	db, cancel, err := p.DB.BeginReadOnlyTransaction(ctx)
+	if err != nil {
+		log.Errorf(ctx, "starting r/o transaction: %v", err)
+		return
+	}
+	defer cancel()
+
+	res, err := db.GetSingleResult(ctx, resultID)
 	if err != nil {
 		if !errors.Is(err, sql.ErrNoRows) {
 			log.Errorf(ctx, "GetSingleResult: %v", err)
@@ -230,22 +237,26 @@ func (p *PkgDetails) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 	failedDeps := strings.Split(res.FailedDeps, ",")
 	fmt.Fprintf(w, "<h2>This package has %d failed dependencies</h2>", len(failedDeps))
-	// // TODO(bsiegert) Unfortunately, we save a list of package names, not a
-	// // list of corresponding datastore keys. So we need to fetch them one by
-	// // one.
-	// templates.TableBegin(w, "Location", "Package Name", "Status", "Breaks")
-	// dp := &bulk.Pkg{}
-	// for _, dep := range p.FailedDeps {
-	// 	it := datastore.NewQuery("pkg").Ancestor(buildKey).Filter("PkgName =", dep).Limit(1).Run(ctx)
-	// 	key, err := it.Next(dp)
-	// 	if err != nil {
-	// 		continue
-	// 	}
-	// 	dp.Key = key.Encode()
-	// 	templates.TablePkgs(w, dp)
-	// }
-	// io.WriteString(w, templates.TableEnd)
+	templates.TableBegin(w, "Location", "Package Name", "Status", "Breaks")
 
+	sqlBuildID := sql.NullInt64{
+		Valid: true,
+		Int64: res.BuildID,
+	}
+	rows := make([]ddao.GetSingleResultByPkgNameRow, 0, len(failedDeps))
+	for _, dep := range failedDeps {
+		row, err := db.GetSingleResultByPkgName(ctx, ddao.GetSingleResultByPkgNameParams{
+			PkgName: dep,
+			BuildID: sqlBuildID,
+		})
+		if err != nil {
+			// Swallow and ignore error.
+			continue
+		}
+		rows = append(rows, row)
+	}
+	templates.TablePkgs(w, rows)
+	templates.TableEnd(w)
 }
 
 // Dirs is a handler for a subpage showing all the package directories for a given category.