depot/third_party/nixpkgs/pkgs/development/libraries/eigen/include-dir.patch

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,5 @@
 # cmake_minimum_require must be the first command of the file
-cmake_minimum_required(VERSION 3.5.0)
+cmake_minimum_required(VERSION 3.7.0)
 
 project(Eigen3)
 
@@ -443,7 +443,7 @@ set(PKGCONFIG_INSTALL_DIR
     CACHE PATH "The directory relative to CMAKE_INSTALL_PREFIX where eigen3.pc is installed"
     )
 
-foreach(var INCLUDE_INSTALL_DIR CMAKEPACKAGE_INSTALL_DIR PKGCONFIG_INSTALL_DIR)
+foreach(var CMAKEPACKAGE_INSTALL_DIR PKGCONFIG_INSTALL_DIR)
   # If an absolute path is specified, make it relative to "{CMAKE_INSTALL_PREFIX}".
   if(IS_ABSOLUTE "${${var}}")
     file(RELATIVE_PATH "${var}" "${CMAKE_INSTALL_PREFIX}" "${${var}}")
@@ -466,13 +466,6 @@ install(FILES
   DESTINATION ${INCLUDE_INSTALL_DIR} COMPONENT Devel
   )
 
-if(EIGEN_BUILD_PKGCONFIG)
-    configure_file(eigen3.pc.in eigen3.pc @ONLY)
-    install(FILES ${CMAKE_CURRENT_BINARY_DIR}/eigen3.pc
-        DESTINATION ${PKGCONFIG_INSTALL_DIR}
-        )
-endif()
-
 install(DIRECTORY Eigen DESTINATION ${INCLUDE_INSTALL_DIR} COMPONENT Devel)
 
 
@@ -593,8 +586,15 @@ set ( EIGEN_VERSION_MAJOR  ${EIGEN_WORLD_VERSION} )
 set ( EIGEN_VERSION_MINOR  ${EIGEN_MAJOR_VERSION} )
 set ( EIGEN_VERSION_PATCH  ${EIGEN_MINOR_VERSION} )
 set ( EIGEN_DEFINITIONS "")
-set ( EIGEN_INCLUDE_DIR "${CMAKE_INSTALL_PREFIX}/${INCLUDE_INSTALL_DIR}" )
 set ( EIGEN_ROOT_DIR ${CMAKE_INSTALL_PREFIX} )
+GNUInstallDirs_get_absolute_install_dir(EIGEN_INCLUDE_DIR INCLUDE_INSTALL_DIR)
+
+if(EIGEN_BUILD_PKGCONFIG)
+    configure_file(eigen3.pc.in eigen3.pc @ONLY)
+    install(FILES ${CMAKE_CURRENT_BINARY_DIR}/eigen3.pc
+        DESTINATION ${PKGCONFIG_INSTALL_DIR}
+        )
+endif()
 
 include (CMakePackageConfigHelpers)
 
--- a/eigen3.pc.in
+++ b/eigen3.pc.in
@@ -6,4 +6,4 @@ Description: A C++ template library for linear algebra: vectors, matrices, and r
 Requires:
 Version: @EIGEN_VERSION_NUMBER@
 Libs:
-Cflags: -I${prefix}/@INCLUDE_INSTALL_DIR@
+Cflags: -I@EIGEN_INCLUDE_DIR@