From d2a0235d4b9f31a5af9f407ab2c2d1ee4c1a6e48 Mon Sep 17 00:00:00 2001
From: iarspider <iarspider@gmail.com>
Date: Tue, 16 Feb 2021 16:57:02 +0100
Subject: [PATCH] gruff: add support for external detection  (#21646)

---
 var/spack/repos/builtin/packages/groff/package.py | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/var/spack/repos/builtin/packages/groff/package.py b/var/spack/repos/builtin/packages/groff/package.py
index 450c4794c0..63c8bf1c4f 100644
--- a/var/spack/repos/builtin/packages/groff/package.py
+++ b/var/spack/repos/builtin/packages/groff/package.py
@@ -4,6 +4,7 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
 from spack import *
+import re
 
 
 class Groff(AutotoolsPackage, GNUMirrorPackage):
@@ -40,6 +41,14 @@ class Groff(AutotoolsPackage, GNUMirrorPackage):
     patch('BuildFoundries.patch')
     patch('pdfmom.patch')
 
+    executables = ['^groff$']
+
+    @classmethod
+    def determine_version(cls, exe):
+        output = Executable(exe)('--version', output=str, error=str)
+        match = re.search(r'GNU groff version\s+(\S+)', output)
+        return match.group(1) if match else None
+
     def configure_args(self):
         args = [
             "--without-x"