Add a basic page for derivation source files

Just so that the links work.

guix-data-service/web/controller.scm

@@ -147,12 +147,18 @@
 (define (render-store-item conn filename)
   (let ((derivation (select-derivation-by-output-filename conn filename)))
     (match derivation
+      (()
+       (match (select-derivation-source-file-by-store-path conn filename)
          (()
           (render-html
            #:sxml (general-not-found
                    "Store item not found"
                    "No derivation found producing this output")
            #:code 404))
+         ((id)
+          (render-html
+           #:sxml (view-derivation-source-file filename)
+           #:extra-headers http-headers-for-unchanging-content))))
       (derivations
        (render-html
         #:sxml (view-store-item filename

guix-data-service/web/view/html.scm

@@ -47,6 +47,7 @@
             view-derivation
             view-formatted-derivation
             view-store-item
+            view-derivation-source-file
             error-page))
 
 (define* (header)
@@ -516,6 +517,19 @@
              derivations
              derivations-using-store-item-list)))))
 
+(define (view-derivation-source-file filename)
+  (layout
+   #:body
+   `(,(header)
+     (div
+      (@ (class "container"))
+      (div
+       (@ (class "row"))
+       (div
+        (@ (class "col-sm-12"))
+        ,(display-store-item-title filename)
+        "Derivation source file."))))))
+
 (define (view-derivation derivation derivation-inputs derivation-outputs
                          builds)
   (layout