From df2050343486e784dfbfd651eb766d0677554b14 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Thu, 9 Feb 2023 07:44:40 -0500
Subject: [PATCH] make fallback url function available to plugin compilations

---
 cmake/Modules/LAMMPSInterfacePlugin.cmake | 12 ++++++++++++
 cmake/Modules/LAMMPSUtils.cmake           |  1 +
 2 files changed, 13 insertions(+)

diff --git a/cmake/Modules/LAMMPSInterfacePlugin.cmake b/cmake/Modules/LAMMPSInterfacePlugin.cmake
index 79e9a0955c..c1cc613496 100644
--- a/cmake/Modules/LAMMPSInterfacePlugin.cmake
+++ b/cmake/Modules/LAMMPSInterfacePlugin.cmake
@@ -88,6 +88,18 @@ function(get_lammps_version version_header variable)
     set(${variable} "${date}" PARENT_SCOPE)
 endfunction()
 
+# determine canonical URL for downloading backup copy from download.lammps.org/thirdparty
+function(GetFallbackURL input output)
+  string(REPLACE "_URL" "" _tmp ${input})
+  string(TOLOWER ${_tmp} libname)
+  string(REGEX REPLACE "^https://.*/([^/]+gz)" "${LAMMPS_THIRDPARTY_URL}/${libname}-\\1" newurl "${${input}}")
+  if ("${newurl}" STREQUAL "${${input}}")
+    set(${output} "" PARENT_SCOPE)
+  else()
+    set(${output} ${newurl} PARENT_SCOPE)
+  endif()
+endfunction(GetFallbackURL)
+
 #################################################################################
 # LAMMPS C++ interface. We only need the header related parts except on windows.
 add_library(lammps INTERFACE)
diff --git a/cmake/Modules/LAMMPSUtils.cmake b/cmake/Modules/LAMMPSUtils.cmake
index 9dd123e55a..03ac8a3258 100644
--- a/cmake/Modules/LAMMPSUtils.cmake
+++ b/cmake/Modules/LAMMPSUtils.cmake
@@ -150,6 +150,7 @@ if((CMAKE_SYSTEM_NAME STREQUAL "Linux") AND (EXISTS /etc/os-release))
   set(CMAKE_DISTRO_VERSION ${disversion})
 endif()
 
+# determine canonical URL for downloading backup copy from download.lammps.org/thirdparty
 function(GetFallbackURL input output)
   string(REPLACE "_URL" "" _tmp ${input})
   string(TOLOWER ${_tmp} libname)