svn-download: Reduce svn-multi-fetch builder duplication.

Rather than creating a different builder in the store for every different
download (by hash), remove the hash from the builder and pass it in via an
environment variable.  This means that when svn-multi-fetch is used by two
different package sources, the derivations will still differ but the builder
will be shared.

It used to be this way, but changed with
0e73f933b291c7e154c7e019b6de1e2f3a97e4c1.  I noticed the hash in the builder
script when wondering why the build coordinator on bayfront was substituting
svn-multi-download files over and over again.

To try and make the effects of introducing variance in to the builder script
more obvious, separate it out in to it's own procedure, so that it's clearer
when there's new data going in that could cause variance.

* guix/svn-download.scm (svn-multi-fetch): Extract out builder script, include
hash in the derivation as an environment variable and update comment to be
more directive.
(svn-multi-fetch-builder): New procedure.

Change-Id: I83c60140ae09e189ee5e5428038a9428ecb8e281

1 files changed, 83 insertions, 68 deletions

diff --git a/guix/svn-download.scm b/guix/svn-download.scm
index bdd9c39eb5..812a46c9d4 100644
--- a/guix/svn-download.scm
+++ b/guix/svn-download.scm
@@ -30,6 +30,7 @@
   #:use-module ((guix build utils) #:select (mkdir-p))
   #:use-module (ice-9 match)
   #:use-module (srfi srfi-1)
+  #:use-module (rnrs bytevectors)
   #:export (svn-reference
             svn-reference?
             svn-reference-url
@@ -179,14 +180,7 @@ HASH-ALGO (a symbol).  Use NAME as the file name, or a generic name if #f."
   (user-name  svn-multi-reference-user-name (default #f))
   (password   svn-multi-reference-password (default #f)))
 
-(define* (svn-multi-fetch ref hash-algo hash
-                          #:optional name
-                          #:key (system (%current-system)) (guile (default-guile))
-                          (svn (subversion-package)))
-  "Return a fixed-output derivation that fetches REF, a <svn-multi-reference>
-object.  The output is expected to have recursive hash HASH of type
-HASH-ALGO (a symbol).  Use NAME as the file name, or a generic name if #f."
-
+(define (svn-multi-fetch-builder svn hash-algo)
   (define guile-json
     (module-ref (resolve-interface '(gnu packages guile)) 'guile-json-4))
 
@@ -202,69 +196,83 @@ HASH-ALGO (a symbol).  Use NAME as the file name, or a generic name if #f."
           (module-ref (resolve-interface '(gnu packages base))
                       'tar)))
 
-  (define build
-    (with-imported-modules
-        (source-module-closure '((guix build svn)
-                                 (guix build download)
-                                 (guix build download-nar)
-                                 (guix build utils)
-                                 (guix swh)))
-      (with-extensions (list guile-json guile-gnutls   ;for (guix swh)
-                             guile-lzlib)
-        #~(begin
-            (use-modules (guix build svn)
-                         (guix build utils)
-                         ((guix build download)
-                          #:select (download-method-enabled?))
-                         (guix build download-nar)
-                         (guix swh)
-                         (srfi srfi-1)
-                         (ice-9 match))
+  (with-imported-modules
+      (source-module-closure '((guix build svn)
+                               (guix build download)
+                               (guix build download-nar)
+                               (guix build utils)
+                               (guix swh)))
+    (with-extensions (list guile-json guile-gnutls   ;for (guix swh)
+                           guile-lzlib)
+      #~(begin
+          (use-modules (guix build svn)
+                       (guix build utils)
+                       ((guix build download)
+                        #:select (download-method-enabled?))
+                       (guix build download-nar)
+                       (guix swh)
+                       (srfi srfi-1)
+                       (ice-9 match)
+                       (rnrs bytevectors))
 
-            ;; Add tar and gzip to $PATH so
-            ;; 'swh-download-directory-by-nar-hash' can invoke them.
-            (set-path-environment-variable "PATH" '("bin") '(#+@tar+gzip))
+          ;; Add tar and gzip to $PATH so
+          ;; 'swh-download-directory-by-nar-hash' can invoke them.
+          (set-path-environment-variable "PATH" '("bin") '(#+@tar+gzip))
 
-            (or (every
-                 (lambda (location)
-                   ;; The directory must exist if we are to fetch only a
-                   ;; single file.
-                   (unless (string-suffix? "/" location)
-                     (mkdir-p (string-append #$output "/" (dirname location))))
-                   (and (download-method-enabled? 'upstream)
-                        (svn-fetch (string-append (getenv "svn url") "/" location)
-                                   (string->number (getenv "svn revision"))
-                                   (if (string-suffix? "/" location)
-                                       (string-append #$output "/" location)
-                                       (string-append #$output "/" (dirname location)))
-                                   #:svn-command #+(file-append svn "/bin/svn")
-                                   #:recursive? (match (getenv "svn recursive?")
-                                                  ("yes" #t)
-                                                  (_ #f))
-                                   #:user-name (getenv "svn user name")
-                                   #:password (getenv "svn password"))))
-                 (call-with-input-string (getenv "svn locations")
-                   read))
-                (begin
-                  (when (file-exists? #$output)
-                    (delete-file-recursively #$output))
-                  (or (and (download-method-enabled? 'nar)
-                           (download-nar #$output))
-                      (and (download-method-enabled? 'swh)
-                           ;; SWH keeps HASH as an ExtID for the combination
-                           ;; of files/directories, which allows us to
-                           ;; retrieve the entire combination at once:
-                           ;; <https://gitlab.softwareheritage.org/swh/infra/sysadm-environment/-/issues/5263>.
-                           (parameterize ((%verify-swh-certificate? #f))
-                             (swh-download-directory-by-nar-hash
-                              #$hash '#$hash-algo #$output))))))))))
+          (or (every
+               (lambda (location)
+                 ;; The directory must exist if we are to fetch only a
+                 ;; single file.
+                 (unless (string-suffix? "/" location)
+                   (mkdir-p (string-append #$output "/" (dirname location))))
+                 (and (download-method-enabled? 'upstream)
+                      (svn-fetch (string-append (getenv "svn url") "/" location)
+                                 (string->number (getenv "svn revision"))
+                                 (if (string-suffix? "/" location)
+                                     (string-append #$output "/" location)
+                                     (string-append #$output "/" (dirname location)))
+                                 #:svn-command #+(file-append svn "/bin/svn")
+                                 #:recursive? (match (getenv "svn recursive?")
+                                                ("yes" #t)
+                                                (_ #f))
+                                 #:user-name (getenv "svn user name")
+                                 #:password (getenv "svn password"))))
+               (call-with-input-string (getenv "svn locations")
+                 read))
+              (begin
+                (when (file-exists? #$output)
+                  (delete-file-recursively #$output))
+                (or (and (download-method-enabled? 'nar)
+                         (download-nar #$output))
+                    (and (download-method-enabled? 'swh)
+                         ;; SWH keeps HASH as an ExtID for the combination
+                         ;; of files/directories, which allows us to
+                         ;; retrieve the entire combination at once:
+                         ;; <https://gitlab.softwareheritage.org/swh/infra/sysadm-environment/-/issues/5263>.
+                         (parameterize ((%verify-swh-certificate? #f))
+                           (swh-download-directory-by-nar-hash
+                            (u8-list->bytevector
+                             (map string->number
+                                  (string-split (getenv "hash") #\,)))
+                            '#$hash-algo
+                            #$output))))))))))
 
+(define* (svn-multi-fetch ref hash-algo hash
+                          #:optional name
+                          #:key (system (%current-system)) (guile (default-guile))
+                          (svn (subversion-package)))
+  "Return a fixed-output derivation that fetches REF, a <svn-multi-reference>
+object.  The output is expected to have recursive hash HASH of type
+HASH-ALGO (a symbol).  Use NAME as the file name, or a generic name if #f."
   (mlet %store-monad ((guile (package->derivation guile system)))
-    (gexp->derivation (or name "svn-checkout") build
-
-                      ;; Use environment variables and a fixed script name so
-                      ;; there's only one script in store for all the
-                      ;; downloads.
+    (gexp->derivation (or name "svn-checkout")
+                      ;; Avoid the builder differing for every single use as
+                      ;; having less builder is more efficient for computing
+                      ;; derivations.
+                      ;;
+                      ;; Don't pass package specific data in to the following
+                      ;; procedure, use #:env-vars below instead.
+                      (svn-multi-fetch-builder svn hash-algo)
                       #:script-name "svn-multi-download"
                       #:env-vars
                       `(("svn url" . ,(svn-multi-reference-url ref))
@@ -286,7 +294,14 @@ HASH-ALGO (a symbol).  Use NAME as the file name, or a generic name if #f."
                         ,@(match (getenv "GUIX_DOWNLOAD_METHODS")
                             (#f '())
                             (value
-                             `(("GUIX_DOWNLOAD_METHODS" . ,value)))))
+                             `(("GUIX_DOWNLOAD_METHODS" . ,value))))
+                        ;; To avoid pulling in (guix base32) in the builder
+                        ;; script, use bytevector->u8-list from (rnrs
+                        ;; bytevectors)
+                        ("hash" . ,(string-join
+                                    (map number->string
+                                         (bytevector->u8-list hash))
+                                    ",")))
 
                       #:leaked-env-vars '("http_proxy" "https_proxy"
                                           "LC_ALL" "LC_MESSAGES" "LANG"