system: Prefer packages from %FINAL-INPUTS.

* gnu/packages/base.scm (canonical-package): New procedure.
* gnu/system.scm (%base-packages): Pass BASH, COREUTILS, FINDUTILS,
  GREP, and SED through 'canonical-package'.

gnu/packages/base.scm

@@ -42,6 +42,7 @@
   #:use-module (guix utils)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
+  #:use-module (ice-9 vlist)
   #:use-module (ice-9 match))
 
 ;;; Commentary:
@@ -1204,6 +1205,40 @@ store.")
       ("gcc" ,gcc-final)
       ("libc" ,glibc-final))))
 
+(define-public canonical-package
+  (let ((name->package (fold (lambda (input result)
+                               (match input
+                                 ((_ package)
+                                  (vhash-cons (package-full-name package)
+                                              package result))))
+                             vlist-null
+                             `(("guile" ,guile-final)
+                               ,@%final-inputs))))
+    (lambda (package)
+      "Return the 'canonical' variant of PACKAGE---i.e., if PACKAGE is one of
+the implicit inputs of 'gnu-build-system', return that one, otherwise return
+PACKAGE.
+
+The goal is to avoid duplication in cases like GUILE-FINAL vs. GUILE-2.0,
+COREUTILS-FINAL vs. COREUTILS, etc."
+      ;; XXX: This doesn't handle dependencies of the final inputs, such as
+      ;; libunistring, GMP, etc.
+      (match (vhash-assoc (package-full-name package) name->package)
+        ((_ . canon)
+         ;; In general we want CANON, except if we're cross-compiling: CANON
+         ;; uses explicit inputs, so it is "anchored" in the bootstrapped
+         ;; process, with dependencies on things that cannot be
+         ;; cross-compiled.
+         (if (%current-target-system)
+             package
+             canon))
+        (_ package)))))
+
+
+;;;
+;;; GCC toolchain.
+;;;
+
 (define (gcc-toolchain gcc)
   "Return a complete toolchain for GCC."
   (package

gnu/system.scm

@@ -216,12 +216,16 @@ explicitly appear in OS."
 (define %base-packages
   ;; Default set of packages globally visible.  It should include anything
   ;; required for basic administrator tasks.
-  (list bash coreutils findutils grep sed
-        procps psmisc less zile
-        guile-final (@ (gnu packages admin) dmd) guix
-        util-linux inetutils isc-dhcp
-        net-tools                        ; XXX: remove when Inetutils suffices
-        module-init-tools kbd))
+  (cons* procps psmisc less zile
+         guile-final (@ (gnu packages admin) dmd) guix
+         util-linux inetutils isc-dhcp
+         net-tools                        ; XXX: remove when Inetutils suffices
+         module-init-tools kbd
+
+         ;; The packages below are also in %FINAL-INPUTS, so take them from
+         ;; there to avoid duplication.
+         (map canonical-package
+              (list bash coreutils findutils grep sed))))
 
 (define %default-issue
   ;; Default contents for /etc/issue.