utils: Define ‘search-input-file’ procedure.

The procedure ‘which’ from (guix build utils)
is used for two different purposes:

  1. for finding the absolute file name of a binary
     that needs to run during the build process

  2. for finding the absolute file name of a binary,
     for the target system (as in --target=TARGET),
     e.g. for substituting sh->/gnu/store/.../bin/sh,
     python->/gnu/store/.../bin/python.

When compiling natively (target=#f in Guix parlance),
this is perfectly fine.

However, when cross-compiling, there is a problem.
"which" looks in $PATH for binaries.  That's good for purpose (1),
but incorrect for (2), as the $PATH contains binaries from native-inputs
instead of inputs.

This commit defines a ‘search-input-file’ procedure. It functions
like 'which', but instead of searching in $PATH, it searches in
the 'inputs' of the build phase, which must be passed to
‘search-input-file’ as an argument. Also, the file name must
include "bin/" or "sbin/" as appropriate.

* guix/build/utils.scm (search-input-file): New procedure.
* tests/build-utils.scm
  ("search-input-file: exception if not found")
  ("search-input-file: can find if existent"): Test it.
* doc/guix.texi (File Search): Document it.

Partially-Fixes: <https://issues.guix.gnu.org/47869>
Co-Authored-By: Ludovic Courtès <ludo@gnu.org>
Signed-off-by: Ludovic Courtès <ludo@gnu.org>

1 files changed, 25 insertions, 0 deletions

diff --git a/tests/build-utils.scm b/tests/build-utils.scm
index 31be7ff80f..6b131c0af8 100644
--- a/tests/build-utils.scm
+++ b/tests/build-utils.scm
@@ -2,6 +2,7 @@
 ;;; Copyright © 2012, 2015, 2016, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2019 Ricardo Wurmus <rekado@elephly.net>
 ;;; Copyright © 2021 Maxim Cournoyer <maxim.cournoyer@gmail.com>
+;;; Copyright © 2021 Maxime Devos <maximedevos@telenet.be>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -263,4 +264,28 @@ print('hello world')"))
          (lambda _
            (get-string-all (current-input-port))))))))
 
+(test-equal "search-input-file: exception if not found"
+  `((path)
+    (file . "does-not-exist"))
+  (guard (e ((search-error? e)
+             `((path . ,(search-error-path e))
+               (file . ,(search-error-file e)))))
+    (search-input-file '() "does-not-exist")))
+
+(test-equal "search-input-file: can find if existent"
+  (which "guile")
+  (search-input-file
+    `(("guile/bin" . ,(dirname (which "guile"))))
+    "guile"))
+
+(test-equal "search-input-file: can search in multiple directories"
+  (which "guile")
+  (call-with-temporary-directory
+    (lambda (directory)
+      (search-input-file
+        `(("irrelevant" . ,directory)
+          ("guile/bin" . ,(dirname (which "guile"))))
+        "guile"))))
+
+
 (test-end)