diffutils: added support for external detection (#19344)

var/spack/repos/builtin/packages/diffutils/package.py

@@ -3,6 +3,8 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+import re
+
 from spack import *
 
 
@@ -10,6 +12,8 @@ class Diffutils(AutotoolsPackage, GNUMirrorPackage):
     """GNU Diffutils is a package of several programs related to finding
     differences between files."""
 
+    executables = [r'^diff$']
+
     homepage = "https://www.gnu.org/software/diffutils/"
     gnu_mirror_path = "diffutils/diffutils-3.7.tar.xz"
 
@@ -24,3 +28,9 @@ def setup_build_environment(self, env):
         if self.spec.satisfies('%fj'):
             env.append_flags('CFLAGS',
                              '-Qunused-arguments')
+
+    @classmethod
+    def determine_version(cls, exe):
+        output = Executable(exe)('--version', output=str, error=str)
+        match = re.search(r'diff \(GNU diffutils\) (\S+)', output)
+        return match.group(1) if match else None