From b4307e235447821b6893e33ac87cb8a222f08e22 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Wed, 29 Sep 2021 09:01:01 -0400
Subject: [PATCH] only need Tcl not Tk to compile Tcl swig wrapper

---
 tools/swig/CMakeLists.txt | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/swig/CMakeLists.txt b/tools/swig/CMakeLists.txt
index 204b351ed6..b3397c5dc9 100644
--- a/tools/swig/CMakeLists.txt
+++ b/tools/swig/CMakeLists.txt
@@ -90,7 +90,10 @@ if(BUILD_SWIG_TCL)
   # build loadable Tcl module
   set_property(SOURCE lammps.i PROPERTY SWIG_MODULE_NAME tcllammps)
   swig_add_library(tcllammps TYPE MODULE LANGUAGE tcl SOURCES lammps.i)
-  find_package(TCL REQUIRED)
+  find_package(TCL)
+  if(NOT TCL_FOUND)
+    message(FATAL_ERROR "Tcl development headers and libraries are required")
+  endif()
   target_include_directories(tcllammps PRIVATE ${TCL_INCLUDE_PATH})
   swig_link_libraries(tcllammps PRIVATE lammps ${TCL_LIBRARY})
   # build extended Tcl shell binary