Revert "[BE] Make Eigen an optional dependency (#155955)"

This reverts commit 1b50c12584909bda00009f4f0fd0d38ec792d019.

Reverted https://github.com/pytorch/pytorch/pull/155955 on behalf of https://github.com/atalman due to need to revert eigen test ([comment](https://github.com/pytorch/pytorch/pull/155955#issuecomment-2992512124))

.gitmodules

@@ -2,6 +2,10 @@
     ignore = dirty
     path = third_party/pybind11
     url = https://github.com/pybind/pybind11.git
+[submodule "third_party/eigen"]
+    ignore = dirty
+    path = third_party/eigen
+    url = https://gitlab.com/libeigen/eigen.git
 [submodule "third_party/googletest"]
     ignore = dirty
     path = third_party/googletest

cmake/Dependencies.cmake

@@ -778,6 +778,25 @@ elseif(NOT TARGET fp16 AND USE_SYSTEM_FP16)
 endif()
 list(APPEND Caffe2_DEPENDENCY_LIBS fp16)
 
+# ---[ EIGEN
+# Due to license considerations, we will only use the MPL2 parts of Eigen.
+set(EIGEN_MPL2_ONLY 1)
+if(USE_SYSTEM_EIGEN_INSTALL)
+  find_package(Eigen3)
+  if(EIGEN3_FOUND)
+    message(STATUS "Found system Eigen at " ${EIGEN3_INCLUDE_DIR})
+  else()
+    message(STATUS "Did not find system Eigen. Using third party subdirectory.")
+    set(EIGEN3_INCLUDE_DIR ${CMAKE_CURRENT_LIST_DIR}/../third_party/eigen)
+    caffe2_update_option(USE_SYSTEM_EIGEN_INSTALL OFF)
+  endif()
+else()
+  message(STATUS "Using third party subdirectory Eigen.")
+  set(EIGEN3_INCLUDE_DIR ${CMAKE_CURRENT_LIST_DIR}/../third_party/eigen)
+endif()
+include_directories(SYSTEM ${EIGEN3_INCLUDE_DIR})
+
+
 # ---[ Python Interpreter
 # If not given a Python installation, then use the current active Python
 if(NOT Python_EXECUTABLE)
@@ -791,29 +810,6 @@ if(NOT Python_EXECUTABLE)
   endif()
 endif()
 
-
-# ---[ EIGEN
-# Due to license considerations, we will only use the MPL2 parts of Eigen.
-set(EIGEN_MPL2_ONLY 1)
-if(USE_SYSTEM_EIGEN_INSTALL)
-  find_package(Eigen3)
-  if(EIGEN3_FOUND)
-    message(STATUS "Found system Eigen at " ${EIGEN3_INCLUDE_DIR})
-  else()
-    message(STATUS "Did not find system Eigen. Using third party subdirectory.")
-    execute_process(COMMAND ${Python_EXECUTABLE} ../tools/optional_modules.py checkout_eigen
-                    WORKING_DIRECTORY ${CMAKE_CURRENT_LIST_DIR})
-
-    set(EIGEN3_INCLUDE_DIR ${CMAKE_CURRENT_LIST_DIR}/../third_party/eigen)
-    caffe2_update_option(USE_SYSTEM_EIGEN_INSTALL OFF)
-  endif()
-else()
-  message(STATUS "Using third party subdirectory Eigen.")
-  set(EIGEN3_INCLUDE_DIR ${CMAKE_CURRENT_LIST_DIR}/../third_party/eigen)
-endif()
-include_directories(SYSTEM ${EIGEN3_INCLUDE_DIR})
-
-
 if(BUILD_PYTHON)
   set(PYTHON_COMPONENTS Development.Module)
   if(USE_NUMPY)

third_party/eigen_pin.txt

@@ -1 +0,0 @@
-3.4.0

tools/optional_submodules.py

@@ -43,21 +43,5 @@ def checkout_nccl() -> None:
         _checkout_by_tag("https://github.com/NVIDIA/nccl", release_tag)
 
 
-def checkout_eigen() -> None:
-    eigen_tag = _read_file(third_party_path / "eigen_pin.txt")
-    print(f"-- Checkout Eigen release tag: {eigen_tag}")
-    eigen_basedir = third_party_path / "eigen"
-    if not eigen_basedir.exists():
-        _checkout_by_tag("https://gitlab.com/libeigen/eigen", eigen_tag)
-
-
 if __name__ == "__main__":
-    import sys
+    checkout_nccl()
-
-    if len(sys.argv) == 1:
-        # If no arguments are given checkout all optional dependency
-        checkout_nccl()
-        checkout_eigen()
-    else:
-        # Otherwise just call top-level function of choice
-        globals()[sys.argv[1]]()