Add some docs

README.org

@@ -28,3 +28,44 @@ your ~~/.config/guix/channels.scm~, and call ~guix pull~.
    %default-channels)
 #+end_src
 
+** Usage
+
+*** For stable Rusts
+#+begin_src shell
+  guix search rust-bin
+#+end_src
+
+*** For latest nightly/beta
+#+begin_src
+  guix build -e '((@@ (rustup build toolchain) rustup) "stable")'
+  guix build -e '((@@ (rustup build toolchain) rustup) "beta")'
+  guix build -e '((@@ (rustup build toolchain) rustup) "nightly")'
+#+end_src
+
+*** With =guix shell= =manifest.scm=
+
+#+begin_src scheme
+  (use-modules (rustup build toolchain))
+
+  ;; (packages->manifest (list (rustup "nightly-2024-05-18")))
+
+  (packages->manifest (list (rustup)))
+#+end_src
+
+*** Rustup toolchain file
+=rustup-toolchain=
+=rustup-toolchain.toml=
+
+Procedure =rustup= will search for these two file in parent folders like
+=guix shell= search for =mainfest.scm= file. You can manully specify the
+location of the toolchain file with =(rustup "path/to/rust-toolchain")=
+
+*** =rustup= arguments
+#+begin_src scheme
+    (define* (rustup #:optional (channel-or-toolchain-file #f)
+		   #:key
+		   (components (list ))
+		   (targets (list ))
+		   (profile 'default))
+      ...)
+#+end_src

guix/rustup/build/manifest.scm

@@ -509,7 +509,9 @@
 (define* (compact-manifest str #:optional manifest)
   (define c (channel->from-str str))
   (define channel (channel->name c))
-  (define date (channel->date c))
+  (define date (or (channel->date c) (recursive-assoc-ref
+			 manifest
+			 `("date"))))
   (define* (compact-manifest data)
     (define toolchain-version
       (car (string-split

guix/rustup/build/toolchain.scm

@@ -139,9 +139,11 @@
                    aliased-str))
   (define _channel-name (channel->name channel))
   (define _channel-date (channel->date channel))
-  (define _var (module-variable
-                (resolve-module `(rustup dist ,(string->symbol _channel-date)))
-                (string->symbol (channel-str-normalize _channel-name))))
+  (define _var (if _channel-date
+                   (module-variable
+                    (resolve-module `(rustup dist ,(string->symbol _channel-date)))
+                    (string->symbol (channel-str-normalize _channel-name)))
+                   #f))
   (define _data (cond (_var
                        (variable-ref _var))
                       (else