Add bundled Eigen3 as an internal dependency

cmake/libint2-config.cmake.in

@@ -55,15 +55,26 @@ list(PREPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_LIST_DIR})
 # check library language component
 include(CMakeFindDependencyMacro)
 
-    if(NOT TARGET Eigen3::Eigen)
-      set(Eigen3_CONFIG @Eigen3_CONFIG@)
-      if (NOT Eigen3_CONFIG OR NOT EXISTS ${Eigen3_CONFIG})
-        message(WARNING "Libint2 library was built with Eigen3Config.cmake detected at ${Eigen3_CONFIG}, but this path is no longer valid; directory moved since Libint2 library build?")
-        find_dependency(Eigen3 REQUIRED)
-      else()
-        get_filename_component(Eigen3_DIR "${Eigen3_CONFIG}" DIRECTORY)
-        find_dependency(Eigen3 REQUIRED HINTS "${Eigen3_DIR}")
-      endif()
+    get_filename_component(_LIBINT_PREFIX "${CMAKE_CURRENT_LIST_DIR}/../../../" ABSOLUTE)
+    if(EXISTS "${_LIBINT_PREFIX}/include/libint2/eigen3/Eigen/Core")
+        if(NOT TARGET Eigen3::Eigen)
+            add_library(Eigen3::Eigen INTERFACE IMPORTED)
+            set_target_properties(Eigen3::Eigen PROPERTIES
+                INTERFACE_INCLUDE_DIRECTORIES "${_LIBINT_PREFIX}/include/libint2/eigen3"
+            )
+        endif()
+    else()
+        if(NOT TARGET Eigen3::Eigen)
+            set(Eigen3_CONFIG @Eigen3_CONFIG@)
+            if (NOT Eigen3_CONFIG OR NOT EXISTS ${Eigen3_CONFIG})
+                include(CMakeFindDependencyMacro)
+                find_dependency(Eigen3 REQUIRED)
+            else()
+                include(CMakeFindDependencyMacro)
+                get_filename_component(Eigen3_DIR "${Eigen3_CONFIG}" DIRECTORY)
+                find_dependency(Eigen3 REQUIRED HINTS "${Eigen3_DIR}")
+            endif()
+        endif()
     endif()
 
     if (@LIBINT_HAS_SYSTEM_BOOST_PREPROCESSOR_VARIADICS@)  # LIBINT_HAS_SYSTEM_BOOST_PREPROCESSOR_VARIADICS

export/CMakeLists.txt.export

@@ -58,6 +58,8 @@ option_with_print(LIBINT2_LOCAL_Eigen3_INSTALL
   "Install an exported target with hard-coded Eigen3 dependency paths. This is potentially useful and important when consuming the compiled C++11 interface library so that the Libint library build and Libint consumer build use the same Eigen3 installation & ABI. This is at most a convenience when consuming the header-only C++11 interface library. In consumer build, set `LIBINT2_LOCAL_Eigen3_FIND=ON` before `find_package(Libint2) to load the exported Eigen3." OFF)
 option_with_print(CMAKE_DISABLE_FIND_PACKAGE_Boost
   "When Boost required for C++11 API, disable its detection, thereby forcing use of bundled Boost (Standard CMake variable: https://cmake.org/cmake/help/latest/variable/CMAKE_DISABLE_FIND_PACKAGE_PackageName.html)" OFF)
+option_with_print(CMAKE_DISABLE_FIND_PACKAGE_Eigen3
+  "Disable Eigen3 detection, thereby forcing use of bundled Eigen3" OFF)
 
 check_function_exists(posix_memalign HAVE_POSIX_MEMALIGN)
 if (HAVE_POSIX_MEMALIGN)
@@ -167,7 +169,9 @@ if (LIBINT2_REQUIRE_CXX_API)
     endif()
 endif()
 
-find_package(Eigen3 MODULE)
+if (NOT TARGET Eigen3::Eigen AND NOT CMAKE_DISABLE_FIND_PACKAGE_Eigen3)
+    find_package(Eigen3 MODULE)
+endif()
 
 set(LIBINT2_CXX_STANDARD 11)
 if (TARGET Eigen3::Eigen)
@@ -177,6 +181,27 @@ if (TARGET Eigen3::Eigen)
         set(LIBINT2_CXX_STANDARD 14)
         message(STATUS "Eigen ${EIGEN3_VERSION} requires C++14; setting LIBINT2_CXX_STANDARD=14")
     endif()
+else()
+    if (LIBINT2_REQUIRE_CXX_API)
+        message(STATUS "Unpacking bundled Eigen3...")
+        file(MAKE_DIRECTORY ${PROJECT_BINARY_DIR}/include/libint2)
+        execute_process(
+            COMMAND ${CMAKE_COMMAND} -E tar xzf ${PROJECT_SOURCE_DIR}/external/eigen3.tar.gz
+            WORKING_DIRECTORY ${PROJECT_BINARY_DIR}/include/libint2
+            RESULT_VARIABLE UNPACK_EIGEN_RESULT
+            OUTPUT_VARIABLE UNPACK_EIGEN_OUTPUT
+            ERROR_VARIABLE UNPACK_EIGEN_OUTPUT
+            )
+        if (NOT UNPACK_EIGEN_RESULT EQUAL 0)
+            message(FATAL_ERROR "Failed to unpack the bundled Eigen3!\nThe tar command output:\n${UNPACK_EIGEN_OUTPUT}")
+        endif()
+        add_library(Eigen3::Eigen INTERFACE IMPORTED)
+        set_target_properties(Eigen3::Eigen PROPERTIES
+            INTERFACE_INCLUDE_DIRECTORIES "${PROJECT_BINARY_DIR}/include/libint2/eigen3"
+        )
+        set(LIBINT_HAS_EIGEN 1)
+        set(LIBINT_HAS_BUNDLED_EIGEN 1)
+    endif()
 endif()
 if (LIBINT2_REQUIRE_CXX_API AND NOT LIBINT_HAS_EIGEN)
     message(FATAL_ERROR "C++ API cannot be built without Eigen3; configure (via CMake) and install Eigen3 and add the install prefix to CMAKE_PREFIX_PATH, or add -D LIBINT2_REQUIRE_CXX_API=OFF to the CMake command line if the C++ API is not required")
@@ -792,13 +817,21 @@ install(CODE "
 ")
 
 # install bundled Boost headers if needed
-if (NOT LIBINT_HAS_SYSTEM_BOOST_PREPROCESSOR_VARIADICS)
+if (LIBINT2_REQUIRE_CXX_API AND NOT LIBINT_HAS_SYSTEM_BOOST_PREPROCESSOR_VARIADICS)
     install(
       DIRECTORY ${PROJECT_BINARY_DIR}/include/libint2/boost
       DESTINATION "${LIBINT2_INSTALL_INCLUDEDIR}/libint2"
       )
 endif()
 
+# install bundled Eigen3 headers if needed
+if (LIBINT_HAS_BUNDLED_EIGEN)
+    install(
+      DIRECTORY ${PROJECT_BINARY_DIR}/include/libint2/eigen3
+      DESTINATION "${LIBINT2_INSTALL_INCLUDEDIR}/libint2"
+      )
+endif()
+
 # install basis set library
 install(
   DIRECTORY ${PROJECT_SOURCE_DIR}/lib/basis

src/lib/libint/populate.cmake

@@ -120,6 +120,7 @@ file(
 file(
   INSTALL
     "${PROJECT_SOURCE_DIR}/external/boost.tar.gz"
+    "${PROJECT_SOURCE_DIR}/external/eigen3.tar.gz"
   DESTINATION "${EXPORT_STAGE_DIR}/external"
   )