From 4b2a61946fdb77ab37b66b1d2b81d2d77453ca5d Mon Sep 17 00:00:00 2001
From: Brad King <brad.king@kitware.com>
Date: Thu, 22 Oct 2020 10:36:20 -0400
Subject: FindBoost: Honor BOOST_ROOT when finding upstream BoostConfig

Fixes: #21200
---
 Modules/FindBoost.cmake | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Modules/FindBoost.cmake b/Modules/FindBoost.cmake
index f27666d..77868f4 100644
--- a/Modules/FindBoost.cmake
+++ b/Modules/FindBoost.cmake
@@ -450,7 +450,13 @@ if (NOT Boost_NO_BOOST_CMAKE)
   # Do the same find_package call but look specifically for the CMake version.
   # Note that args are passed in the Boost_FIND_xxxxx variables, so there is no
   # need to delegate them to this find_package call.
+  cmake_policy(PUSH)
+  if(BOOST_ROOT AND NOT Boost_ROOT)
+    cmake_policy(SET CMP0074 NEW)
+    set(Boost_ROOT "${BOOST_ROOT}")
+  endif()
   find_package(Boost QUIET NO_MODULE ${_boost_FIND_PACKAGE_ARGS})
+  cmake_policy(POP)
   if (DEFINED Boost_DIR)
     mark_as_advanced(Boost_DIR)
   endif ()
-- 
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