import: Add updater for rust crates.

* guix/import/crate.scm (crate-package?, latest-release,
  %crate-updater): New variables.
* guix/scripts/refresh.scm (%updaters): Add crate updater.
* doc/guix.texi: Add crate updater to table.

doc/guix.texi

@@ -5396,6 +5396,8 @@ the updater for @uref{https://rubygems.org, RubyGems} packages.
 the updater for @uref{https://github.com, GitHub} packages.
 @item hackage
 the updater for @uref{https://hackage.haskell.org, Hackage} packages.
+@item crate
+the updater for @uref{https://crates.io, Crates} packages.
 @end table
 
 For instance, the following command only checks for updates of Emacs

guix/import/crate.scm

@@ -36,7 +36,8 @@
   #:use-module (srfi srfi-2)
   #:use-module (srfi srfi-26)
   #:export (crate->guix-package
-            guix-package->crate-name))
+            guix-package->crate-name
+            %crate-updater))
 
 (define (crate-fetch crate-name callback)
   "Fetch the metadata for CRATE-NAME from crates.io and call the callback."
@@ -123,3 +124,36 @@ VERSION, INPUTS, NATIVE-INPUTS, HOME-PAGE, SYNOPSIS, DESCRIPTION, and LICENSE."
 (define (crate-name->package-name name)
   (string-append "rust-" (string-join (string-split name #\_) "-")))
 
+;;;
+;;; Updater
+;;;
+
+(define (crate-package? package)
+  "Return true if PACKAGE is a Rust crate from crates.io."
+  (let ((source-url (and=> (package-source package) origin-uri))
+        (fetch-method (and=> (package-source package) origin-method)))
+    (and (eq? fetch-method download:url-fetch)
+         (match source-url
+           ((? string?)
+            (crate-url? source-url))
+           ((source-url ...)
+            (any crate-url? source-url))))))
+
+(define (latest-release package)
+  "Return an <upstream-source> for the latest release of PACKAGE."
+  (let* ((crate-name (guix-package->crate-name package))
+         (callback (lambda* (#:key version #:allow-other-keys) version))
+         (version (crate-fetch crate-name callback))
+         (url (crate-uri crate-name version)))
+    (upstream-source
+     (package (package-name package))
+     (version version)
+     (urls (list url)))))
+
+(define %crate-updater
+  (upstream-updater
+   (name 'crates)
+   (description "Updater for crates.io packages")
+   (pred crate-package?)
+   (latest latest-release)))
+

guix/scripts/refresh.scm

@@ -210,7 +210,8 @@ unavailable optional dependencies such as Guile-JSON."
                  ((guix import cpan) => %cpan-updater)
                  ((guix import pypi) => %pypi-updater)
                  ((guix import gem) => %gem-updater)
-                 ((guix import github) => %github-updater)))
+                 ((guix import github) => %github-updater)
+                 ((guix import crate) => %crate-updater)))
 
 (define (lookup-updater-by-name name)
   "Return the updater called NAME."