From 3d776e0077d62000f20d23a1b42b32fef718a503 Mon Sep 17 00:00:00 2001
From: "Jan (janneke) Nieuwenhuizen" <janneke@gnu.org>
Date: Sat, 18 Apr 2020 19:49:54 +0200
Subject: [PATCH] gnu: autoconf: Support cross-build.

Autoconf cannot be cross-built properly: it lacks the concept of
<tool>-for-build.  It runs the host `autom4te' (a perl script) during build.

* gnu/packages/autotools.scm (autoconf)[inputs]: When cross-building, add perl
and m4.
[native-inputs]: when cross-building, use -for-build names.
[arguments]: When cross-building, add `fake-cross-build' phase to substitute
m4 and perl.
---
 gnu/packages/autotools.scm | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/gnu/packages/autotools.scm b/gnu/packages/autotools.scm
index 99ca52730e..fa3ced182f 100644
--- a/gnu/packages/autotools.scm
+++ b/gnu/packages/autotools.scm
@@ -55,12 +55,38 @@
        (base32
         "113nlmidxy9kjr45kg9x3ngar4951mvag1js2a3j8nxcz34wxsv4"))))
     (build-system gnu-build-system)
+    (inputs
+     ;; TODO: remove `if' in the next rebuild cycle.
+     (if (%current-target-system)
+         `(("perl" ,perl)
+           ("m4" ,m4))
+         '()))
     (native-inputs
      `(("perl" ,perl)
        ("m4" ,m4)))
     ;; XXX: testsuite: 209 and 279 failed. The latter is an impurity. It
     ;; should use our own "cpp" instead of "/lib/cpp".
-    (arguments `(#:tests? #f))
+    (arguments
+     `(#:tests? #f
+       ,@(if (%current-target-system)
+             `(#:phases
+               (modify-phases %standard-phases
+                 ;; `patch-shebangs' patches shebangs only, and the Perl
+                 ;; scripts use a re-exec feature that references the build
+                 ;; hosts' perl.  Also, M4 store references hide in the
+                 ;; scripts.
+                 (add-after 'install 'patch-non-shebang-references
+                   (lambda* (#:key build inputs outputs #:allow-other-keys)
+                     (let ((m4 (assoc-ref inputs "m4"))
+                           (perl (assoc-ref inputs "perl"))
+                           (out  (assoc-ref outputs "out"))
+                           (store-directory (%store-directory)))
+                      (substitute* (find-files (string-append out "/bin"))
+                        (((string-append store-directory "/[^/]*-m4-[^/]*")) m4)
+                        (((string-append store-directory "/[^/]*-perl-[^/]*"))
+                         perl))
+                      #t)))))
+             '())))
     (home-page "https://www.gnu.org/software/autoconf/")
     (synopsis "Create source code configuration scripts")
     (description
-- 
2.26.0