From cf29fa18c8f0e7e482a0668ac1f36d1928080214 Mon Sep 17 00:00:00 2001
From: Brad King <brad.king@kitware.com>
Date: Fri, 30 Aug 2019 14:03:59 -0400
Subject: FindBoost: Unwrap compatibility INTERFACE targets for legacy
 variables

Since commit 0dd6772a89 (FindBoost: Add legacy variables and targets for
compatibility, 2019-06-14, v3.15.0-rc2~3^2~1) we extract information
from imported targets provided by upstream `BoostConfig.cmake` files.
However, upstream Boost 1.71 provides some imported targets only for
compatibility.  They are just INTERFACE libraries that wrap around the
real target named by `INTERFACE_LINK_LIBRARIES`.  Unwrap this layer so
we can extract the real imported location.

Fixes: #19656
---
 Modules/FindBoost.cmake                                   | 15 +++++++++++++++
 .../RunCMake/FindBoost/CMakePackage_New/BoostConfig.cmake |  5 +++++
 2 files changed, 20 insertions(+)

diff --git a/Modules/FindBoost.cmake b/Modules/FindBoost.cmake
index d260ff2..5d20a84 100644
--- a/Modules/FindBoost.cmake
+++ b/Modules/FindBoost.cmake
@@ -266,6 +266,21 @@ function(_boost_get_existing_target component target_var)
   foreach(prefix Boost boost)
     foreach(name IN LISTS names)
       if(TARGET "${prefix}::${name}")
+        # The target may be an INTERFACE library that wraps around a single other
+        # target for compatibility.  Unwrap this layer so we can extract real info.
+        if("${name}" MATCHES "^(python|numpy|mpi_python)([1-9])([0-9])$")
+          set(name_nv "${CMAKE_MATCH_1}")
+          if(TARGET "${prefix}::${name_nv}")
+            get_property(type TARGET "${prefix}::${name}" PROPERTY TYPE)
+            if(type STREQUAL "INTERFACE_LIBRARY")
+              get_property(lib TARGET "${prefix}::${name}" PROPERTY INTERFACE_LINK_LIBRARIES)
+              if("${lib}" STREQUAL "${prefix}::${name_nv}")
+                set(${target_var} "${prefix}::${name_nv}" PARENT_SCOPE)
+                return()
+              endif()
+            endif()
+          endif()
+        endif()
         set(${target_var} "${prefix}::${name}" PARENT_SCOPE)
         return()
       endif()
diff --git a/Tests/RunCMake/FindBoost/CMakePackage_New/BoostConfig.cmake b/Tests/RunCMake/FindBoost/CMakePackage_New/BoostConfig.cmake
index 3a88f26..1151514 100644
--- a/Tests/RunCMake/FindBoost/CMakePackage_New/BoostConfig.cmake
+++ b/Tests/RunCMake/FindBoost/CMakePackage_New/BoostConfig.cmake
@@ -8,6 +8,7 @@ set_target_properties(Boost::date_time PROPERTIES
   IMPORTED_CONFIGURATIONS RELEASE
   IMPORTED_LOCATION_RELEASE "${CMAKE_CURRENT_LIST_DIR}/lib/libboost_date_time.a"
   )
+
 set(Boost_python37_FOUND 1)
 add_library(Boost::python UNKNOWN IMPORTED)
 set_target_properties(Boost::python PROPERTIES
@@ -15,6 +16,10 @@ set_target_properties(Boost::python PROPERTIES
   IMPORTED_LOCATION_RELEASE "${CMAKE_CURRENT_LIST_DIR}/lib/libboost_python_release.a"
   IMPORTED_LOCATION_DEBUG "${CMAKE_CURRENT_LIST_DIR}/lib/libboost_python.a"
   )
+# Versioned target alias for compatibility (added by upstream BoostConfig).
+add_library(Boost::python37 INTERFACE IMPORTED)
+set_property(TARGET Boost::python37 APPEND PROPERTY INTERFACE_LINK_LIBRARIES Boost::python)
+
 set(Boost_mpi_python2_FOUND 1)
 add_library(Boost::mpi_python UNKNOWN IMPORTED)
 set_target_properties(Boost::mpi_python PROPERTIES
-- 
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