From 936d538edb53f37366637180c4e0ed205489ed2d Mon Sep 17 00:00:00 2001
From: "Hans J. Johnson" <hans-johnson@uiowa.edu>
Date: Tue, 22 Sep 2026 13:51:41 -0500
Subject: [PATCH] BUG: Give the installed itkTestDriver an RPATH to ITK's
 libraries

ITK's libraries are installed with @rpath install names, but the installed
itkTestDriver carries no RPATH, so on macOS it fails to load
libITKTestKernel from <prefix>/lib and every external module test that runs
through ITK_TEST_DRIVER aborts unless DYLD_LIBRARY_PATH is set. Set the
install RPATH to the library directory relative to the runtime directory,
which also covers Linux installs that do not add <prefix>/lib to the loader
path.
---
 Modules/Core/TestKernel/src/CMakeLists.txt | 35 ++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/Modules/Core/TestKernel/src/CMakeLists.txt b/Modules/Core/TestKernel/src/CMakeLists.txt
index 966d3d19963..64cce78bff3 100644
--- a/Modules/Core/TestKernel/src/CMakeLists.txt
+++ b/Modules/Core/TestKernel/src/CMakeLists.txt
@@ -22,6 +22,41 @@ if(NOT DO_NOT_BUILD_ITK_TEST_DRIVER)
   )
 
   if(NOT DO_NOT_INSTALL_ITK_TEST_DRIVER) # used only by vcpkg
+    if(
+      IS_ABSOLUTE
+        "${ITK_INSTALL_RUNTIME_DIR}"
+      OR
+        IS_ABSOLUTE
+          "${ITK_INSTALL_LIBRARY_DIR}"
+    )
+      # ITKModuleMacros assumes relative too, so the install tree is already
+      # wrong by this point (issue #6896).
+      message(
+        FATAL_ERROR
+        "ITK_INSTALL_RUNTIME_DIR ('${ITK_INSTALL_RUNTIME_DIR}') and ITK_INSTALL_LIBRARY_DIR ('${ITK_INSTALL_LIBRARY_DIR}') must be relative to CMAKE_INSTALL_PREFIX."
+      )
+    else()
+      file(
+        RELATIVE_PATH
+        _itk_test_driver_rpath
+        "${CMAKE_INSTALL_PREFIX}/${ITK_INSTALL_RUNTIME_DIR}"
+        "${CMAKE_INSTALL_PREFIX}/${ITK_INSTALL_LIBRARY_DIR}"
+      )
+      if(APPLE)
+        set(_itk_test_driver_rpath "@loader_path/${_itk_test_driver_rpath}")
+      else()
+        set(_itk_test_driver_rpath "$ORIGIN/${_itk_test_driver_rpath}")
+      endif()
+      set_property(
+        TARGET
+          itkTestDriver
+        APPEND
+        PROPERTY
+          INSTALL_RPATH
+            "${_itk_test_driver_rpath}"
+      )
+      unset(_itk_test_driver_rpath)
+    endif()
     itk_module_target_install(itkTestDriver)
   endif()
 endif()