fix(lmp): link torch for builtin shared builds

source/cmake/Config.cmake.in

@@ -1,5 +1,10 @@
 @PACKAGE_INIT@
 include(CMakeFindDependencyMacro)
 
+set(@CMAKE_PROJECT_NAME@_ENABLE_PYTORCH "@ENABLE_PYTORCH@")
+set(@CMAKE_PROJECT_NAME@_TORCH_DIR "@Torch_DIR@")
+set(@CMAKE_PROJECT_NAME@_TORCH_VERSION "@Torch_VERSION@")
+set(@CMAKE_PROJECT_NAME@_TORCH_CXX11_ABI "@OP_CXX_ABI_PT@")
+
 include("${CMAKE_CURRENT_LIST_DIR}/@targets_export_name@.cmake")
 check_required_components("@CMAKE_PROJECT_NAME@")

source/lmp/builtin.cmake

@@ -58,6 +58,92 @@ configure_file("${CMAKE_CURRENT_LIST_DIR}/deepmd_version.h.in"
 file(GLOB DEEPMD_LMP_SRC ${CMAKE_CURRENT_LIST_DIR}/*.cpp)
 
 find_package(DeePMD REQUIRED)
+
+function(_deepmd_lammps_link_torch target_name)
+  if(NOT DeePMD_ENABLE_PYTORCH)
+    return()
+  endif()
+
+  set(_deepmd_torch_from_recorded_dir FALSE)
+  if(Torch_FOUND)
+    # A parent project may already have loaded Torch. Validate it below rather
+    # than attempting to redefine its imported targets from another package.
+  elseif(DeePMD_TORCH_DIR)
+    find_package(
+      Torch
+      CONFIG
+      QUIET
+      PATHS "${DeePMD_TORCH_DIR}"
+      NO_DEFAULT_PATH)
+    if(Torch_FOUND)
+      set(_deepmd_torch_from_recorded_dir TRUE)
+    endif()
+  endif()
+
+  if(NOT Torch_FOUND)
+    # The recorded package may have moved or been removed. A caller-provided
+    # installation is acceptable only after the compatibility checks below.
+    unset(Torch_DIR CACHE)
+    unset(Torch_DIR)
+    find_package(Torch CONFIG QUIET)
+  endif()
+
+  if(NOT Torch_FOUND)
+    message(
+      WARNING
+        "DeePMD-kit was built with the PyTorch backend, but Torch was not "
+        "found while configuring LAMMPS. Install the same Torch package or "
+        "set Torch_DIR to its CMake configuration directory.")
+    return()
+  endif()
+
+  string(REGEX MATCH "_GLIBCXX_USE_CXX11_ABI=([0-9]+)"
+               _deepmd_torch_abi_match "${TORCH_CXX_FLAGS}")
+  set(_deepmd_torch_abi "")
+  if(_deepmd_torch_abi_match)
+    set(_deepmd_torch_abi "${CMAKE_MATCH_1}")
+  elseif(UNIX AND NOT APPLE AND Torch_VERSION VERSION_GREATER_EQUAL "2.8.0")
+    # Recent Linux Torch packages no longer publish the ABI in
+    # TORCH_CXX_FLAGS and use the C++11 ABI unconditionally.
+    set(_deepmd_torch_abi "1")
+  else()
+    # Match DeePMD's build-time fallback for platforms and older packages that
+    # do not expose a libstdc++ ABI flag.
+    set(_deepmd_torch_abi "0")
+  endif()
+
+  if(NOT _deepmd_torch_from_recorded_dir
+     AND ("${DeePMD_TORCH_VERSION}" STREQUAL ""
+          OR "${DeePMD_TORCH_CXX11_ABI}" STREQUAL ""))
+    message(
+      WARNING
+        "DeePMD-kit did not record enough Torch compatibility metadata to "
+        "validate a different installation; refusing to link it into LAMMPS.")
+    return()
+  endif()
+  if(NOT "${DeePMD_TORCH_VERSION}" STREQUAL ""
+     AND NOT "${Torch_VERSION}" STREQUAL "${DeePMD_TORCH_VERSION}")
+    message(
+      FATAL_ERROR
+        "Torch version mismatch: DeePMD-kit was built with "
+        "${DeePMD_TORCH_VERSION}, but LAMMPS found ${Torch_VERSION}.")
+  endif()
+  if(NOT "${DeePMD_TORCH_CXX11_ABI}" STREQUAL ""
+     AND NOT "${_deepmd_torch_abi}" STREQUAL "${DeePMD_TORCH_CXX11_ABI}")
+    message(
+      FATAL_ERROR
+        "Torch C++ ABI mismatch: DeePMD-kit was built with "
+        "_GLIBCXX_USE_CXX11_ABI=${DeePMD_TORCH_CXX11_ABI}, but LAMMPS found "
+        "${_deepmd_torch_abi}.")
+  endif()
+
+  # LAMMPS exports this target as LAMMPS::lammps. Torch is needed to resolve
+  # the in-tree executable's transitive DeePMD symbols, but must not leak
+  # imported targets or absolute paths into the installed LAMMPS interface.
+  target_link_libraries(${target_name}
+                        PUBLIC "$<BUILD_INTERFACE:${TORCH_LIBRARIES}>")
+endfunction()
+
 target_sources(
   lammps
   PRIVATE ${DEEPMD_LMP_SRC}
@@ -69,6 +155,7 @@ target_sources(
           ${LAMMPS_SOURCE_DIR}/EXTRA-FIX/fix_ttm.cpp # for ttm
 )
 target_link_libraries(lammps PUBLIC DeePMD::deepmd_c)
+_deepmd_lammps_link_torch(lammps)
 target_include_directories(
   lammps PRIVATE ${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_CURRENT_LIST_DIR}
                  ${LAMMPS_SOURCE_DIR}/KSPACE ${LAMMPS_SOURCE_DIR}/EXTRA-FIX)