gnu: avr: Delay all cross compilation packages.

Partially addresses <https://issues.guix.gnu.org/65716>.

* gnu/packages/avr.scm: Add commentary comment.
(avr-binutils): Turn into this...
(make-avr-binutils): ... procedure.
(avr-gcc): Likewise, into...
(make-avr-gcc): ... this.  Adjust native-inputs accordingly.
(avr-toolchain): Likewise, into...
(make-avr-toolchain): ... this.
* gnu/packages/avr-xyz.scm (simavr) [propagated-inputs]: replace avr-toolchain
with a call to the 'make-avr-toolchain' procedure.

Series-changes: 2
- Use mlambda for procedures
- Fix ((make-avr-toolchain)) typo

gnu/packages/avr-xyz.scm

@@ -71,7 +71,7 @@
                            (string-append "PREFIX=" #$output)
                            (string-append "DESTDIR=" #$output))))
     (propagated-inputs
-     (list avr-toolchain))
+     (list (make-avr-toolchain)))
     (native-inputs
      (list autoconf
            which

gnu/packages/avr.scm

@@ -25,6 +25,7 @@
 (define-module (gnu packages avr)
   #:use-module ((guix licenses) #:prefix license:)
   #:use-module (guix gexp)
+  #:use-module (guix memoization)
   #:use-module (guix utils)
   #:use-module (guix download)
   #:use-module (guix git-download)
@@ -37,15 +38,29 @@
   #:use-module (gnu packages flashing-tools)
   #:use-module (gnu packages gcc)
   #:use-module (gnu packages llvm)
-  #:use-module (gnu packages vim))
+  #:use-module (gnu packages vim)
+  #:export (make-avr-toolchain))
 
-(define-public avr-binutils
+;;; Commentary:
+;;;
+;;; This module defines a procedure that can be used to create a complete
+;;; avr-toolchain package.  The procedure must not be used at the top level,
+;;; to avoid cyclic module dependencies caused by the (gnu packages
+;;; cross-base) module referring to top level bindings from (gnu packages
+;;; gcc).
+;;;
+;;; It also contains packages for working with or targeting the AVR system.
+;;;
+
+(define make-avr-binutils
+  (mlambda ()
     (package
       (inherit (cross-binutils "avr"))
-    (name "avr-binutils")))
+      (name "avr-binutils"))))
 
-(define avr-gcc
+(define make-avr-gcc
-  (let ((xgcc (cross-gcc "avr" #:xbinutils avr-binutils)))
+  (mlambda ()
+    (let ((xgcc (cross-gcc "avr" #:xbinutils (make-avr-binutils))))
       (package
         (inherit xgcc)
         (name "avr-gcc")
@@ -56,8 +71,9 @@
                 (add-after 'set-paths 'augment-CPLUS_INCLUDE_PATH
                   (lambda* (#:key inputs #:allow-other-keys)
                     (let ((gcc (assoc-ref inputs  "gcc")))
-                    ;; Remove the default compiler from CPLUS_INCLUDE_PATH to
+                      ;; Remove the default compiler from CPLUS_INCLUDE_PATH
-                    ;; prevent header conflict with the GCC from native-inputs.
+                      ;; to prevent header conflict with the GCC from
+                      ;; native-inputs.
                       (setenv "CPLUS_INCLUDE_PATH"
                               (string-join
                                (delete (string-append gcc "/include/c++")
@@ -65,15 +81,16 @@
                                                      #\:))
                                ":"))
                       (format #t
-                            "environment variable `CPLUS_INCLUDE_PATH' changed to ~a~%"
+                              "environment variable `CPLUS_INCLUDE_PATH' \
+changed to ~a~%"
                               (getenv "CPLUS_INCLUDE_PATH")))))
                 ;; Without a working multilib build, the resulting GCC lacks
                 ;; support for nearly every AVR chip.
                 (add-after 'unpack 'fix-genmultilib
                   (lambda _
-                  ;; patch-shebang doesn't work here because there are actually
+                    ;; patch-shebang doesn't work here because there are
-                  ;; several scripts inside this script, each with a #!/bin/sh
+                    ;; actually several scripts inside this script, each with
-                  ;; that needs patching.
+                    ;; a #!/bin/sh that needs patching.
                     (substitute* "gcc/genmultilib"
                       (("#!/bin/sh") (string-append "#!" (which "sh"))))))))
            ((#:configure-flags flags)
@@ -96,9 +113,10 @@
                 (files '("avr/lib")))))
         (native-inputs
          `(("gcc" ,gcc)
-         ,@(package-native-inputs xgcc))))))
+           ,@(package-native-inputs xgcc)))))))
 
-(define avr-libc
+(define make-avr-libc
+  (mlambda ()
     (package
       (name "avr-libc")
       (version "2.0.0")
@@ -113,19 +131,24 @@
       (arguments
        '(#:out-of-source? #t
          #:configure-flags '("--host=avr")))
-    (native-inputs `(("avr-binutils" ,avr-binutils)
+      (native-inputs `(("avr-binutils" ,(make-avr-binutils))
-                     ("avr-gcc" ,avr-gcc)))
+                       ("avr-gcc" ,(make-avr-gcc))))
       (home-page "https://www.nongnu.org/avr-libc/")
       (synopsis "The AVR C Library")
       (description
-     "AVR Libc is a project whose goal is to provide a high quality C library
+       "AVR Libc is a project whose goal is to provide a high quality C
-for use with GCC on Atmel AVR microcontrollers.")
+library for use with GCC on Atmel AVR microcontrollers.")
       (license
-     (license:non-copyleft "http://www.nongnu.org/avr-libc/LICENSE.txt"))))
+       (license:non-copyleft "http://www.nongnu.org/avr-libc/LICENSE.txt")))))
 
-(define-public avr-toolchain
+(define make-avr-toolchain
-  ;; avr-libc checks the compiler version and passes "--enable-device-lib" for avr-gcc > 5.1.0.
+  (mlambda ()
-  ;; It wouldn't install the library for atmega32u4 etc if we didn't use the corret avr-gcc.
+    (let ((avr-binutils (make-avr-binutils))
+          (avr-libc (make-avr-libc))
+          (avr-gcc (make-avr-gcc)))
+      ;; avr-libc checks the compiler version and passes "--enable-device-lib"
+      ;; for avr-gcc > 5.1.0.  It wouldn't install the library for atmega32u4
+      ;; etc if we didn't use the corret avr-gcc.
       (package
         (name "avr-toolchain")
         (version (package-version avr-gcc))
@@ -143,7 +166,7 @@ microcontroller development.  This includes the GCC AVR cross compiler and
 avrdude for firmware flashing.  The supported programming languages are C and
 C++.")
         (home-page (package-home-page avr-libc))
-    (license (package-license avr-gcc))))
+        (license (package-license avr-gcc))))))
 
 (define-public microscheme
   (package