No torch requirement

We now only require torch to build, not installed to run monarch. (Though you need it if you want to use tensors in the tensor worker).

Differential Revision: [D88912346](https://our.internmc.facebook.com/intern/diff/D88912346/)

**NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D88912346/)!

ghstack-source-id: 328596707
Pull Request resolved: #2114

Author: zdevito

requirements.txt

@@ -1,5 +1,3 @@
-torch
-torchshow
 pyzmq
 requests
 numpy

setup.py

@@ -4,54 +4,134 @@
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
 
+import importlib.util
 import os
-
 import shutil
 import subprocess
 import sys
 import sysconfig
 
-import torch
-
 from setuptools import Command, find_packages, setup
+from setuptools.command.build_ext import build_ext
+from setuptools.extension import Extension
 
 from setuptools_rust import Binding, RustBin, RustExtension
-from torch.utils.cpp_extension import (
-    BuildExtension,
-    CppExtension,
-    CUDA_HOME,
-    include_paths as torch_include_paths,
-    TORCH_LIB_PATH,
-)
+
+
+# Helper functions to find torch without importing it
+def find_torch_paths():
+    """Find torch installation paths without importing torch"""
+    spec = importlib.util.find_spec("torch")
+    if not spec or not spec.origin:
+        raise RuntimeError("torch not found - please install PyTorch first")
+
+    base = os.path.dirname(spec.origin)
+    lib_path = os.path.join(base, "lib")
+    include_path = os.path.join(base, "include")
+
+    # Get all include paths (similar to torch.utils.cpp_extension.include_paths())
+    include_paths = [include_path]
+
+    # Add torch/csrc includes if available
+    torch_csrc_include = os.path.join(include_path, "torch", "csrc", "api", "include")
+    if os.path.exists(torch_csrc_include):
+        include_paths.append(torch_csrc_include)
+
+    return {"lib_path": lib_path, "include_paths": include_paths}
+
+
+def find_cuda_home():
+    """Find CUDA installation without importing torch"""
+    # Check environment variable first
+    cuda_home = os.environ.get("CUDA_HOME") or os.environ.get("CUDA_PATH")
+
+    if cuda_home and os.path.exists(cuda_home):
+        return cuda_home
+
+    # Try to find nvcc
+    try:
+        nvcc_path = subprocess.run(
+            ["which", "nvcc"], capture_output=True, text=True, timeout=5
+        )
+        if nvcc_path.returncode == 0:
+            # Get directory containing bin/nvcc
+            nvcc = nvcc_path.stdout.strip()
+            cuda_home = os.path.dirname(os.path.dirname(nvcc))
+            return cuda_home
+    except (subprocess.TimeoutExpired, FileNotFoundError):
+        pass
+
+    # Check common locations
+    for path in ["/usr/local/cuda", "/usr/cuda"]:
+        if os.path.exists(path):
+            return path
+
+    return None
+
+
+def detect_cxx11_abi():
+    """Detect if torch uses C++11 ABI by examining library symbols"""
+    paths = find_torch_paths()
+    lib_path = paths["lib_path"]
+
+    # Try to find a torch library to check
+    for lib_name in ["libtorch_cpu.so", "libtorch.so", "libc10.so"]:
+        lib_file = os.path.join(lib_path, lib_name)
+        if os.path.exists(lib_file):
+            try:
+                result = subprocess.run(
+                    ["nm", "-D", lib_file], capture_output=True, text=True, timeout=10
+                )
+                if result.returncode == 0:
+                    # Check for __cxx11 namespace which indicates new ABI
+                    if "__cxx11" in result.stdout:
+                        return 1  # New ABI
+                    else:
+                        return 0  # Old ABI
+            except (subprocess.TimeoutExpired, FileNotFoundError):
+                pass
+
+    # Default to new ABI if we can't determine
+    return 1
+
+
+# Get torch paths and settings
+torch_paths = find_torch_paths()
+TORCH_LIB_PATH = torch_paths["lib_path"]
+torch_include_paths = torch_paths["include_paths"]
+CUDA_HOME = find_cuda_home()
+cxx11_abi = detect_cxx11_abi()
 
 USE_CUDA = CUDA_HOME is not None
 USE_TENSOR_ENGINE = os.environ.get("USE_TENSOR_ENGINE", "1") == "1"
 
-monarch_cpp_src = ["python/monarch/common/init.cpp"]
 
-if USE_CUDA:
-    monarch_cpp_src.append("python/monarch/common/mock_cuda.cpp")
+def create_torch_extension(name, sources):
+    """Helper to create a C++ extension with torch dependencies"""
+    return Extension(
+        name,
+        sources,
+        extra_compile_args=["-g", "-O3"],
+        libraries=["dl", "c10", "torch", "torch_cpu", "torch_python"],
+        library_dirs=[TORCH_LIB_PATH],
+        include_dirs=[
+            os.path.dirname(os.path.abspath(__file__)),
+            sysconfig.get_config_var("INCLUDEDIR"),
+        ]
+        + torch_include_paths,
+        runtime_library_dirs=[TORCH_LIB_PATH] if sys.platform != "win32" else [],
+    )
 
-common_C = CppExtension(
-    "monarch.common._C",
-    monarch_cpp_src,
-    extra_compile_args=["-g", "-O3"],
-    libraries=["dl"],
-    include_dirs=[
-        os.path.dirname(os.path.abspath(__file__)),
-        sysconfig.get_config_var("INCLUDEDIR"),
-    ],
-)
 
+monarch_cpp_src = ["python/monarch/common/init.cpp"]
+if USE_CUDA:
+    monarch_cpp_src.append("python/monarch/common/mock_cuda.cpp")
 
-controller_C = CppExtension(
+# Create C++ extensions using standard Extension instead of CppExtension
+common_C = create_torch_extension("monarch.common._C", monarch_cpp_src)
+controller_C = create_torch_extension(
     "monarch.gradient._gradient_generator",
     ["python/monarch/gradient/_gradient_generator.cpp"],
-    extra_compile_args=["-g", "-O3"],
-    include_dirs=[
-        os.path.dirname(os.path.abspath(__file__)),
-        sysconfig.get_config_var("INCLUDEDIR"),
-    ],
 )
 
 ENABLE_MSG_LOGGING = (
@@ -64,13 +144,13 @@
 
 os.environ.update(
     {
-        "CXXFLAGS": f"-D_GLIBCXX_USE_CXX11_ABI={int(torch._C._GLIBCXX_USE_CXX11_ABI)}",
+        "CXXFLAGS": f"-D_GLIBCXX_USE_CXX11_ABI={cxx11_abi}",
         "RUSTFLAGS": " ".join(
             ["-Zthreads=16", ENABLE_MSG_LOGGING, ENABLE_TRACING_UNSTABLE]
         ),
         "LIBTORCH_LIB": TORCH_LIB_PATH,
-        "LIBTORCH_INCLUDE": ":".join(torch_include_paths()),
-        "_GLIBCXX_USE_CXX11_ABI": str(int(torch._C._GLIBCXX_USE_CXX11_ABI)),
+        "LIBTORCH_INCLUDE": ":".join(torch_include_paths),
+        "_GLIBCXX_USE_CXX11_ABI": str(cxx11_abi),
         "TORCH_SYS_USE_PYTORCH_APIS": "0",
     }
 )
@@ -229,7 +309,7 @@ def run(self):
     },
     rust_extensions=rust_extensions,
     cmdclass={
-        "build_ext": BuildExtension.with_options(no_python_abi_suffix=True),
+        "build_ext": build_ext,
         "clean": Clean,
     },
 )