download: Honor ‘GUIX_DOWNLOAD_METHODS’ environment variable.

This replaces ‘GUIX_DOWNLOAD_FALLBACK_TEST’ and allows you to test
various download methods, like so:

  GUIX_DOWNLOAD_METHODS=nar guix build guile-gcrypt -S --check
  GUIX_DOWNLOAD_METHODS=disarchive guix build hello -S --check

* guix/build/download.scm (%download-methods): New variable.
(download-method-enabled?): New procedure.
(url-fetch): Define ‘initial-uris’; honor ‘download-method-enabled?’.
Call ‘disarchive-fetch/any’ only when the 'disarchive method is enabled.
* guix/build/git.scm (git-fetch-with-fallback): Honor
‘download-method-enabled?’.
* guix/download.scm (%download-methods): New variable.
(%download-fallback-test): Remove.
(built-in-download): Add #:download-methods parameter and honor it.
(url-fetch*): Pass #:content-addressed-mirrors and #:disarchive-mirrors
unconditionally.
* guix/git-download.scm (git-fetch/in-band*): Pass “git url”
unconditionally.
(git-fetch/built-in): Likewise.  Pass “download-methods”.
* guix/bzr-download.scm (bzr-fetch)[build]: Honor ‘download-method-enabled?’.
Pass ‘GUIX_DOWNLOAD_METHODS’ to #:env-vars.
* guix/cvs-download.scm (cvs-fetch)[build]: Honor ‘download-method-enabled?’.
Pass ‘GUIX_DOWNLOAD_METHODS’ to #:env-vars.
* guix/hg-download.scm (hg-fetch): Honor ‘download-method-enabled?’.
Pass #:env-vars to ‘gexp->derivation’.
* guix/scripts/perform-download.scm (perform-download): Honor
“download-methods” from DRV.  Parameterize ‘%download-methods’ before
calling ‘url-fetch’.
(perform-git-download): Likewise.
* guix/svn-download.scm (svn-fetch): Honor ‘download-method-enabled?’.
Pass ‘GUIX_DOWNLOAD_METHODS’ to #:env-vars.
(svn-multi-fetch): Likewise.

Change-Id: Ia3402e17f0303dfa964bdc761265efe8a1dd69ab

1 files changed, 10 insertions, 5 deletions

diff --git a/guix/build/git.scm b/guix/build/git.scm
index a135026fae..62877394bb 100644
--- a/guix/build/git.scm
+++ b/guix/build/git.scm
@@ -19,6 +19,8 @@
 
 (define-module (guix build git)
   #:use-module (guix build utils)
+  #:use-module ((guix build download)
+                #:select (download-method-enabled?))
   #:autoload   (guix build download-nar) (download-nar)
   #:autoload   (guix swh) (%verify-swh-certificate?
                            swh-download
@@ -102,17 +104,20 @@ for ITEM, and if that also fails, download from the Software Heritage archive.
 When HASH and HASH-ALGORITHM are provided, they are interpreted as the nar
 hash of the directory of interested and are used as its content address at
 SWH."
-  (or (git-fetch url commit directory
-                 #:lfs? lfs?
-                 #:recursive? recursive?
-                 #:git-command git-command)
-      (download-nar item directory)
+  (or (and (download-method-enabled? 'upstream)
+           (git-fetch url commit directory
+                      #:lfs? lfs?
+                      #:recursive? recursive?
+                      #:git-command git-command))
+      (and (download-method-enabled? 'nar)
+           (download-nar item directory))
 
       ;; As a last resort, attempt to download from Software Heritage.
       ;; Disable X.509 certificate verification to avoid depending
       ;; on nss-certs--we're authenticating the checkout anyway.
       ;; XXX: Currently recursive checkouts are not supported.
       (and (not recursive?)
+           (download-method-enabled? 'swh)
            (parameterize ((%verify-swh-certificate? #f))
              (format (current-error-port)
                      "Trying to download from Software Heritage...~%")