Support accessing the latest processed revision for a branch

This makes is easier to get the latest data for a branch in a single request,
rather than making one request to find the latest revision, then another to
get the data.

guix-data-service/model/git-branch.scm

@@ -1,4 +1,5 @@
 (define-module (guix-data-service model git-branch)
+  #:use-module (ice-9 match)
   #:use-module (squee)
   #:use-module (srfi srfi-19)
   #:use-module (guix-data-service model utils)
@@ -6,6 +7,7 @@
             git-branches-for-commit
             git-branches-with-repository-details-for-commit
             most-recent-commits-for-branch
+            latest-processed-commit-for-branch
             all-branches-with-most-recent-commit))
 
 (define (insert-git-branch-entry conn
@@ -75,6 +77,25 @@ WHERE git_branches.commit = $1")
    query
    (list branch-name)))
 
+(define* (latest-processed-commit-for-branch conn branch-name)
+  (define query
+    (string-append
+     "SELECT git_branches.commit "
+     "FROM git_branches "
+     "INNER JOIN guix_revisions ON git_branches.commit = guix_revisions.commit "
+     "WHERE git_branches.name = $1 "
+     "ORDER BY datetime DESC "
+     "LIMIT 1"))
+
+  (match (exec-query
+          conn
+          query
+          (list branch-name))
+    (((commit-hash))
+     commit-hash)
+    ('()
+     #f)))
+
 (define (all-branches-with-most-recent-commit conn)
   (define query
     (string-append

guix-data-service/web/controller.scm

@@ -682,6 +682,44 @@
                                             'after_date)
                      #:before-date (assq-ref parsed-query-parameters
                                              'before_date)))))))
+    ((GET "branch" branch-name "latest-processed-revision")
+     (let ((commit-hash
+            (latest-processed-commit-for-branch conn branch-name)))
+       (if commit-hash
+           (render-view-revision mime-types
+                                 conn
+                                 commit-hash)
+           (render-unknown-revision mime-types
+                                    conn
+                                    commit-hash))))
+    ((GET "branch" branch-name "latest-processed-revision" "packages")
+     (let ((commit-hash
+            (latest-processed-commit-for-branch conn branch-name)))
+       (if commit-hash
+           (let ((parsed-query-parameters
+                  (guard-against-mutually-exclusive-query-parameters
+                   (parse-query-parameters
+                    request
+                    `((after_name     ,identity)
+                      (field          ,identity #:multi-value
+                                      #:default ("version" "synopsis"))
+                      (search_query   ,identity)
+                      (limit_results  ,parse-result-limit
+                                      #:no-default-when (all_results)
+                                      #:default 100)
+                      (all_results    ,parse-checkbox-value)))
+                   ;; You can't specify a search query, but then also limit the
+                   ;; results by filtering for after a particular package name
+                   '((after_name search_query)
+                     (limit_results all_results)))))
+
+             (render-revision-packages mime-types
+                                       conn
+                                       commit-hash
+                                       parsed-query-parameters))
+           (render-unknown-revision mime-types
+                                    conn
+                                    commit-hash))))
     ((GET "gnu" "store" filename)
      ;; These routes are a little special, as the extensions aren't used for
      ;; content negotiation, so just use the path from the request