Add compatibility checks for C++ extensions (#2467)

* Add compatibility checks for C++ extensions

* Fix lint

torchvision/extension.py

 _HAS_OPS = False
 
 
+def _has_ops():
+    return False
+
+
 def _register_extensions():
     import os
     import importlib
@@ -23,10 +27,26 @@ def _register_extensions():
 try:
     _register_extensions()
     _HAS_OPS = True
+
+    def _has_ops():  # noqa: F811
+        return True
 except (ImportError, OSError):
     pass
 
 
+def _assert_has_ops():
+    if not _has_ops():
+        raise RuntimeError(
+            "Couldn't load custom C++ ops. This can happen if your PyTorch and "
+            "torchvision versions are incompatible, or if you had errors while compiling "
+            "torchvision from source. For further information on the compatible versions, check "
+            "https://github.com/pytorch/vision#installation for the compatibility matrix. "
+            "Please check your PyTorch version with torch.__version__ and your torchvision "
+            "version with torchvision.__version__ and verify if they are compatible, and if not "
+            "please reinstall torchvision so that it matches your PyTorch install."
+        )
+
+
 def _check_cuda_version():
     """
     Make sure that CUDA versions match between the pytorch install and torchvision install

torchvision/ops/boxes.py

@@ -3,6 +3,7 @@ from torch.jit.annotations import Tuple
 from torch import Tensor
 from ._box_convert import _box_cxcywh_to_xyxy, _box_xyxy_to_cxcywh, _box_xywh_to_xyxy, _box_xyxy_to_xywh
 import torchvision
+from torchvision.extension import _assert_has_ops
 
 
 def nms(boxes: Tensor, scores: Tensor, iou_threshold: float) -> Tensor:
@@ -37,6 +38,7 @@ def nms(boxes: Tensor, scores: Tensor, iou_threshold: float) -> Tensor:
         of the elements that have been kept
         by NMS, sorted in decreasing order of scores
     """
+    _assert_has_ops()
     return torch.ops.torchvision.nms(boxes, scores, iou_threshold)
 
 

torchvision/ops/deform_conv.py

@@ -6,6 +6,7 @@ from torch.nn import init
 from torch.nn.parameter import Parameter
 from torch.nn.modules.utils import _pair
 from torch.jit.annotations import Optional, Tuple
+from torchvision.extension import _assert_has_ops
 
 
 def deform_conv2d(
@@ -51,6 +52,7 @@ def deform_conv2d(
         >>>  torch.Size([4, 5, 8, 8])
     """
 
+    _assert_has_ops()
     out_channels = weight.shape[0]
     if bias is None:
         bias = torch.zeros(out_channels, device=input.device, dtype=input.dtype)

torchvision/ops/ps_roi_align.py

@@ -4,6 +4,7 @@ from torch import nn, Tensor
 from torch.nn.modules.utils import _pair
 from torch.jit.annotations import List, Tuple
 
+from torchvision.extension import _assert_has_ops
 from ._utils import convert_boxes_to_roi_format, check_roi_boxes_shape
 
 
@@ -38,6 +39,7 @@ def ps_roi_align(
     Returns:
         output (Tensor[K, C, output_size[0], output_size[1]])
     """
+    _assert_has_ops()
     check_roi_boxes_shape(boxes)
     rois = boxes
     output_size = _pair(output_size)

torchvision/ops/ps_roi_pool.py

@@ -4,6 +4,7 @@ from torch import nn, Tensor
 from torch.nn.modules.utils import _pair
 from torch.jit.annotations import List, Tuple
 
+from torchvision.extension import _assert_has_ops
 from ._utils import convert_boxes_to_roi_format, check_roi_boxes_shape
 
 
@@ -32,6 +33,7 @@ def ps_roi_pool(
     Returns:
         output (Tensor[K, C, output_size[0], output_size[1]])
     """
+    _assert_has_ops()
     check_roi_boxes_shape(boxes)
     rois = boxes
     output_size = _pair(output_size)

torchvision/ops/roi_align.py

@@ -4,6 +4,7 @@ from torch import nn, Tensor
 from torch.nn.modules.utils import _pair
 from torch.jit.annotations import List, BroadcastingList2
 
+from torchvision.extension import _assert_has_ops
 from ._utils import convert_boxes_to_roi_format, check_roi_boxes_shape
 
 
@@ -41,6 +42,7 @@ def roi_align(
     Returns:
         output (Tensor[K, C, output_size[0], output_size[1]])
     """
+    _assert_has_ops()
     check_roi_boxes_shape(boxes)
     rois = boxes
     output_size = _pair(output_size)

torchvision/ops/roi_pool.py

@@ -4,6 +4,7 @@ from torch import nn, Tensor
 from torch.nn.modules.utils import _pair
 from torch.jit.annotations import List, BroadcastingList2
 
+from torchvision.extension import _assert_has_ops
 from ._utils import convert_boxes_to_roi_format, check_roi_boxes_shape
 
 
@@ -31,6 +32,7 @@ def roi_pool(
     Returns:
         output (Tensor[K, C, output_size[0], output_size[1]])
     """
+    _assert_has_ops()
     check_roi_boxes_shape(boxes)
     rois = boxes
     output_size = _pair(output_size)