gnu: racket: fix `raco exe` with non-minimal Racket

This commit backports an upstream repair for a bug exposed by Guix's
change in Racket 8.2 to make the `racket` package a layered/tethered
installation that chains to the `racket-minimal` package. When using a
layered/tethered installation, the `setup/variant` library would fail to
recognize the default Racet variant (CS, 3M, or CGC), leading to
confusing failures from `raco exe`, `create-embedding-executable`, and
other clients.

For further details, see <https://issues.guix.gnu.org/50118> and
<https://github.com/racket/racket/issues/3969>.

* gnu/packages/patches/racket-minimal-backport-1629887.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/racket.scm (racket-minimal)[source]: Use it.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu/local.mk

@@ -1703,6 +1703,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/ripperx-missing-file.patch		\
   %D%/packages/patches/rpcbind-CVE-2017-8779.patch		\
   %D%/packages/patches/rtags-separate-rct.patch			\
+  %D%/packages/patches/racket-minimal-backport-1629887.patch    \
   %D%/packages/patches/racket-minimal-sh-via-rktio.patch	\
   %D%/packages/patches/remake-impure-dirs.patch			\
   %D%/packages/patches/restic-0.9.6-fix-tests-for-go1.15.patch	\

gnu/packages/patches/racket-minimal-backport-1629887.patch

@@ -0,0 +1,28 @@
+From fb1a6ab205fd63a46669a463931af473e2ac0c87 Mon Sep 17 00:00:00 2001
+From: Matthew Flatt <mflatt@racket-lang.org>
+Date: Sat, 21 Aug 2021 15:29:59 -0600
+Subject: [PATCH] setup/variant: recognize starter executables
+
+Related to #3969
+
+(cherry picked from commit 1629887071fe3cc8fe8af0a7aa0d3912509cb058)
+---
+ racket/collects/setup/variant.rkt | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/racket/collects/setup/variant.rkt b/racket/collects/setup/variant.rkt
+index 81da6f5701..b23131e481 100644
+--- a/racket/collects/setup/variant.rkt
++++ b/racket/collects/setup/variant.rkt
+@@ -25,7 +25,7 @@
+         (and (file-exists? f)
+              (with-input-from-file f
+                (lambda ()
+-                 (define m (regexp-match #rx#"bINARy tYPe:..(.)"
++                 (define m (regexp-match #rx#"bINARy tYPe:e?..(.)"
+                                          (current-input-port)))
+                  (cond
+                    [(not m) '3m]
+-- 
+2.30.2
+

gnu/packages/racket.scm

@@ -138,7 +138,9 @@
        (sha256
         "061bhiyjlvazph0dj9i3i3x2q5z53rp8h5cjwg3frjimkr45lncn")
        (file-name (git-file-name name version))
-       (patches (search-patches "racket-minimal-sh-via-rktio.patch"))
+       (patches (search-patches "racket-minimal-sh-via-rktio.patch"
+                                ;; Remove the following in version 8.3:
+                                "racket-minimal-backport-1629887.patch"))
        (modules '((guix build utils)))
        (snippet
         (with-imported-modules '((guix build utils))