guix: Separate the package name and version with "@", not "-".

* guix/packages.scm (package-full-name): By default, use "@" to separate
  the package name and package version.  Add an optional delimiter
  argument so that there is still a way to explicitly use a different
  delimiter.
* gnu/packages/commencement.scm (gcc-boot0) <unpack-gmp&co>: Adjust
  accordingly.
* tests/graph.scm: Adjust accordingly.
* tests/profiles.scm: Adjust accordingly.
* NEWS: Mention the change.

Fixes: <https://bugs.gnu.org/31088>.
Reported by Pierre Neidhardt <ambrevar@gmail.com>.

NEWS

@@ -10,6 +10,11 @@ Copyright © 2013, 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
 
 Please send Guix bug reports to bug-guix@gnu.org.
 
+* Changes in 0.15.0 (since 0.14.0)
+** Programming interfaces
+
+*** package-full-name (guix packages) now uses "@" as its delimiter.
+    (<https://bugs.gnu.org/31088>)
 * Changes in 0.14.0 (since 0.13.0)
 
 ** Package management

gnu/packages/commencement.scm

@@ -282,7 +282,7 @@
                             ;; Drop trailing letters, as gmp-6.0.0a unpacks
                             ;; into gmp-6.0.0.
                             `(symlink ,(string-trim-right
-                                        (package-full-name lib)
+                                        (package-full-name lib "-")
                                         char-set:letter)
                                       ,(package-name lib)))
                           (list gmp-6.0 mpfr mpc))))

guix/packages.scm

@@ -388,10 +388,11 @@ object."
 (define-condition-type &package-cross-build-system-error &package-error
   package-cross-build-system-error?)
 
-
-(define (package-full-name package)
-  "Return the full name of PACKAGE--i.e., `NAME-VERSION'."
-  (string-append (package-name package) "-" (package-version package)))
+(define* (package-full-name package #:optional (delimiter "@"))
+  "Return the full name of PACKAGE--i.e., `NAME@VERSION'.  By specifying
+DELIMITER (a string), you can customize what will appear between the name and
+the version.  By default, DELIMITER is \"@\"."
+  (string-append (package-name package) delimiter (package-version package)))
 
 (define (%standard-patch-inputs)
   (let* ((canonical (module-ref (resolve-interface '(gnu packages base))
@@ -935,6 +936,10 @@ and return it."
               (($ <package> name version source build-system
                             args inputs propagated-inputs native-inputs
                             self-native-input? outputs)
+               ;; Even though we prefer to use "@" to separate the package
+               ;; name from the package version in various user-facing parts
+               ;; of Guix, checkStoreName (in nix/libstore/store-api.cc)
+               ;; prohibits the use of "@", so use "-" instead.
                (or (make-bag build-system (string-append name "-" version)
                              #:system system
                              #:target target

tests/graph.scm

@@ -134,7 +134,7 @@ edges."
                      (map (lambda (destination)
                             (list "p-0.drv"
                                   (string-append
-                                   (package-full-name destination)
+                                   (package-full-name destination "-")
                                    ".drv")))
                           implicit)))))))
 

tests/profiles.scm

@@ -242,8 +242,8 @@
                                         #:hooks '()
                                         #:locales? #t
                                         #:target target)))
-    (define (find-input name)
-      (let ((name (string-append name ".drv")))
+    (define (find-input package)
+      (let ((name (string-append (package-full-name package "-") ".drv")))
         (any (lambda (input)
                (let ((input (derivation-input-path input)))
                  (and (string-suffix? name input) input)))
@@ -252,12 +252,11 @@
     ;; The inputs for grep and sed should be cross-build derivations, but that
     ;; for the glibc-utf8-locales should be a native build.
     (return (and (string=? (derivation-system drv) (%current-system))
-                 (string=? (find-input (package-full-name packages:grep))
+                 (string=? (find-input packages:grep)
                            (derivation-file-name grep))
-                 (string=? (find-input (package-full-name packages:sed))
+                 (string=? (find-input packages:sed)
                            (derivation-file-name sed))
-                 (string=? (find-input
-                            (package-full-name packages:glibc-utf8-locales))
+                 (string=? (find-input packages:glibc-utf8-locales)
                            (derivation-file-name locales))))))
 
 (test-assert "package->manifest-entry defaults to \"out\""