packages: Introduce <content-hash> and use it in <origin>.

* guix/packages.scm (<content-hash>): New record type.
(define-content-hash-constructor, build-content-hash)
(content-hash): New macros.
(print-content-hash): New procedure.
(<origin>): Rename constructor to '%origin'.
[sha256]: Remove field.
[hash]: New field.  Adjust users.
(origin-compatibility-helper, origin): New macros.
(origin-sha256): New deprecated procedure.
(origin->derivation): Adjust accordingly.
* tests/packages.scm ("package-source-derivation, origin, sha512"): New
test.
* guix/tests.scm: Hide (gcrypt hash) 'sha256' for proper syntax
matching.
* tests/challenge.scm: Add #:prefix for (gcrypt hash) and adjust users.
* tests/derivations.scm: Likewise.
* tests/store.scm: Likewise.
* tests/graph.scm ("bag DAG, including origins"): Provide 'sha256' field
with the right length.
* gnu/packages/aspell.scm (aspell-dictionary)
(aspell-dict-ca, aspell-dict-it): Use 'hash' and 'content-hash' for
proper syntax matching.
* gnu/packages/bash.scm (bash-patch): Rename 'sha256' to 'sha256-bv'.
* gnu/packages/bootstrap.scm (bootstrap-executable): Rename 'sha256' to 'bv'.
* gnu/packages/readline.scm (readline-patch): Likewise.
* gnu/packages/virtualization.scm (qemu-patch): Rename 'sha256' to
'sha256-bv'.
* guix/import/utils.scm: Hide (gcrypt hash) 'sha256'.

tests/packages.scm

@@ -29,7 +29,7 @@
                 #:renamer (lambda (name)
                             (cond ((eq? name 'location) 'make-location)
                                   (else name))))
-  #:use-module (gcrypt hash)
+  #:use-module ((gcrypt hash) #:hide (sha256))
   #:use-module (guix derivations)
   #:use-module (guix packages)
   #:use-module (guix grafts)
@@ -51,6 +51,7 @@
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-35)
   #:use-module (srfi srfi-64)
+  #:use-module (rnrs bytevectors)
   #:use-module (rnrs io ports)
   #:use-module (ice-9 vlist)
   #:use-module (ice-9 regex)
@@ -497,6 +498,31 @@
                      (search-path %load-path "guix/base32.scm")
                    get-bytevector-all)))))
 
+(test-equal "package-source-derivation, origin, sha512"
+  "hello"
+  (let* ((bash    (search-bootstrap-binary "bash" (%current-system)))
+         (builder (add-text-to-store %store "my-fixed-builder.sh"
+                                     "echo -n hello > $out" '()))
+         (method  (lambda* (url hash-algo hash #:optional name
+                                #:rest rest)
+                    (and (eq? hash-algo 'sha512)
+                         (raw-derivation name bash (list builder)
+                                         #:sources (list builder)
+                                         #:hash hash
+                                         #:hash-algo hash-algo))))
+         (source  (origin
+                    (method method)
+                    (uri "unused://")
+                    (file-name "origin-sha512")
+                    (hash (content-hash
+                           (bytevector-hash (string->utf8 "hello")
+                                            (hash-algorithm sha512))
+                           sha512))))
+         (drv    (package-source-derivation %store source))
+         (output (derivation->output-path drv)))
+    (build-derivations %store (list drv))
+    (call-with-input-file output get-string-all)))
+
 (unless (network-reachable?) (test-skip 1))
 (test-equal "package-source-derivation, snippet"
   "OK"