lint: source: Validate URLs of Git references.

Until now the 'source' checker would look at URL for 'url-fetch' origins
but not for 'git-fetch' origins.

* guix/lint.scm (check-source): Add case for 'git-reference?'.
* tests/lint.scm ("source, git-reference: 301 -> 200"): New test.

guix/lint.scm

@@ -793,8 +793,9 @@ descriptions maintained upstream."
             (loop rest (cons warning warnings))))))))
 
   (let ((origin (package-source package)))
-    (if (and (origin? origin)
-             (eqv? (origin-method origin) url-fetch))
+    (if (origin? origin)
+        (cond
+         ((eq? (origin-method origin) url-fetch)
           (let* ((uris     (append-map (cut maybe-expand-mirrors <> %mirrors)
                                        (map string->uri (origin-uris origin))))
                  (warnings (warnings-for-uris uris)))
@@ -812,8 +813,12 @@ descriptions maintained upstream."
                                (G_ "all the source URIs are unreachable:")
                                #:field 'source)
                  warnings)
-              '()))
                 '())))
+         ((git-reference? (origin-uri origin))
+          (warnings-for-uris
+           (list (string->uri (git-reference-url (origin-uri origin))))))
+         (else
+          '())))))
 
 (define (check-source-file-name package)
   "Emit a warning if PACKAGE's origin has no meaningful file name."

tests/lint.scm

@@ -697,6 +697,26 @@
                 (and (? lint-warning?) second-warning))
                (lint-warning-message second-warning)))))))))
 
+(test-skip (if (http-server-can-listen?) 0 1))
+(test-equal "source, git-reference: 301 -> 200"
+  "permanent redirect from http://localhost:10000/foo/bar to http://localhost:9999/foo/bar"
+  (with-http-server `((200 ,%long-string))
+    (let* ((initial-url (%local-url))
+           (redirect    (build-response #:code 301
+                                        #:headers
+                                        `((location
+                                           . ,(string->uri initial-url))))))
+      (parameterize ((%http-server-port (+ 1 (%http-server-port))))
+        (with-http-server `((,redirect ""))
+          (let ((pkg (dummy-package
+                      "x"
+                      (source (origin
+                                (method git-fetch)
+                                (uri (git-reference (url (%local-url))
+                                                    (commit "v1.0.0")))
+                                (sha256 %null-sha256))))))
+            (single-lint-warning-message (check-source pkg))))))))
+
 (test-skip (if (http-server-can-listen?) 0 1))
 (test-equal "source: 301 -> 404"
   "URI http://localhost:10000/foo/bar not reachable: 404 (\"Such is life\")"