From d4368c8c307f61b5346df540aaf329b8495fe32c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Thu, 17 Feb 2022 16:23:42 +0100
Subject: [PATCH 3/3] guix build: Warn when attempting to build an unsupported
 package.

Fixes <https://issues.guix.gnu.org/51801>.
Reported by Maxim Cournoyer <maxim.cournoyer@gmail.com>.

* guix/scripts/build.scm (options->derivations)[warn-if-unsupported]:
New procedure.
[compute-derivation]: Use it.
* tests/guix-build.sh: Add test.
---
 guix/scripts/build.scm | 22 ++++++++++++++++++++--
 tests/guix-build.sh    | 12 +++++++++++-
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/guix/scripts/build.scm b/guix/scripts/build.scm
index 97e2f5a167..d9cdb6e5e0 100644
--- a/guix/scripts/build.scm
+++ b/guix/scripts/build.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2021 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012-2022 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2013 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2020 Marius Bakke <mbakke@fastmail.com>
 ;;; Copyright © 2020 Ricardo Wurmus <rekado@elephly.net>
@@ -559,11 +559,29 @@ (define systems
   (define things-to-build
     (map transform (options->things-to-build opts)))
 
+  (define warn-if-unsupported
+    (let ((target (assoc-ref opts 'target)))
+      (if target
+          (lambda (package system)
+            ;; We cannot tell whether PACKAGE supports TARGET.
+            package)
+          (lambda (package system)
+            (match package
+              ((? package? package)
+               (unless (supported-package? package system)
+                 (warning (package-location package)
+                          (G_ "package ~a does not support ~a~%")
+                          (package-full-name package) system))
+               package)
+              (x x))))))
+
   (define (compute-derivation obj system)
     ;; Compute the derivation of OBJ for SYSTEM.
     (match obj
       ((? package? p)
-       (let ((p (or (and graft? (package-replacement p)) p)))
+       (let ((p (warn-if-unsupported
+                 (or (and graft? (package-replacement p)) p)
+                 system)))
          (match src
            (#f
             (list (package->derivation store p system)))
diff --git a/tests/guix-build.sh b/tests/guix-build.sh
index 86e41e2927..9cbf8fe26d 100644
--- a/tests/guix-build.sh
+++ b/tests/guix-build.sh
@@ -1,5 +1,5 @@
 # GNU Guix --- Functional package management for GNU
-# Copyright © 2012, 2013, 2014, 2016, 2017, 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
+# Copyright © 2012-2014, 2016-2022 Ludovic Courtès <ludo@gnu.org>
 # Copyright © 2020 Marius Bakke <mbakke@fastmail.com>
 # Copyright © 2021 Chris Marusich <cmmarusich@gmail.com>
 #
@@ -31,6 +31,16 @@ guix build --version
 guix build -e '(@ (gnu packages bootstrap) %bootstrap-glibc)' -S
 test "`guix build -e '(@ (gnu packages bootstrap) %bootstrap-glibc)' -S`" = ""
 
+# Warn when attempting to build an unsupported package.
+case "$(guix build intelmetool -s armhf-linux -v0 -n 2>&1)" in
+    *warning:*intelmetool*support*armhf*)
+	true
+	break;;
+    *)
+	false;
+	break;;
+esac
+
 # Should pass.
 guix build -e '(@@ (gnu packages bootstrap) %bootstrap-guile)' |	\
     grep -e '-guile-'
-- 
2.34.0