import: crate: crate-name->package-name: Move to (guix build-system cargo).

* guix/import/crate.scm (crate-name->package-name): Move to...
* guix/build-system/cargo.scm (crate-name->package-name): ...here and export.

Change-Id: Ie9813179d6c40d159956cc1e2ae59a74dea0a42d

guix/build-system/cargo.scm

@@ -44,7 +44,8 @@
             %crate-base-url
             crate-url
             crate-url?
-            crate-uri))
+            crate-uri
+            crate-name->package-name))
 
 (define %crate-base-url
   (make-parameter "https://crates.io"))
@@ -58,6 +59,9 @@
 to NAME and VERSION."
   (string-append crate-url name "/" version "/download"))
 
+(define (crate-name->package-name name)
+  (downstream-package-name "rust-" name))
+
 (define (default-rust target)
   "Return the default Rust package."
   ;; Lazily resolve the binding to avoid a circular dependency.

guix/import/crate.scm

@@ -481,10 +481,6 @@ look up the development dependencs for the given crate."
     (match parts
       ((name _ ...) name))))
 
-(define (crate-name->package-name name)
-  (downstream-package-name "rust-" name))
-
-
 
 ;;;
 ;;; Updater
@@ -528,4 +524,3 @@ prefix when PARTIAL-VERSION? is #t."
    (description "Updater for crates.io packages")
    (pred crate-package?)
    (import import-release)))
-