Remove _C pyre fixmes

Summary:
Get rid of pyre fixmes related to importing a native module:
- add stub file for the `_C` native extension to the internal typeshed
- add initial annotations to the new stub file
- remove the now unnecessary pyre ignores

Reviewed By: nikhilaravi

Differential Revision: D28929467

fbshipit-source-id: 6525e15c8f27215a3ff6f78392925fd0ed6ec2ac

Author: patricklabatut

pytorch3d/loss/mesh_normal_consistency.py

@@ -5,7 +5,7 @@
 # LICENSE file in the root directory of this source tree.
 
 import torch
-from pytorch3d import _C  # pyre-fixme[21]: Could not find name `_C` in `pytorch3d`.
+from pytorch3d import _C
 
 
 def mesh_normal_consistency(meshes):

pytorch3d/loss/point_mesh_distance.py

@@ -4,7 +4,6 @@
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
 
-# pyre-fixme[21]: Could not find name `_C` in `pytorch3d`.
 from pytorch3d import _C
 from pytorch3d.structures import Meshes, Pointclouds
 from torch.autograd import Function

pytorch3d/ops/graph_conv.py

@@ -7,7 +7,7 @@
 
 import torch
 import torch.nn as nn
-from pytorch3d import _C  # pyre-fixme[21]: Could not find name `_C` in `pytorch3d`.
+from pytorch3d import _C
 from torch.autograd import Function
 from torch.autograd.function import once_differentiable
 

pytorch3d/ops/interp_face_attrs.py

@@ -5,7 +5,7 @@
 # LICENSE file in the root directory of this source tree.
 
 import torch
-from pytorch3d import _C  # pyre-fixme[21]: Could not find name `_C` in `pytorch3d`.
+from pytorch3d import _C
 from torch.autograd import Function
 from torch.autograd.function import once_differentiable
 

pytorch3d/ops/knn.py

@@ -8,7 +8,7 @@
 from typing import Union
 
 import torch
-from pytorch3d import _C  # pyre-fixme[21]: Could not find name `_C` in `pytorch3d`.
+from pytorch3d import _C
 from torch.autograd import Function
 from torch.autograd.function import once_differentiable
 
@@ -58,7 +58,6 @@ def forward(
                 in p2 has fewer than K points and where a cloud in p1 has fewer than P1 points.
         """
 
-        # pyre-fixme[16]: Module `pytorch3d` has no attribute `_C`.
         idx, dists = _C.knn_points_idx(p1, p2, lengths1, lengths2, K, version)
 
         # sort KNN in ascending order if K > 1
@@ -74,6 +73,7 @@ def forward(
                 dists[mask] = 0
             else:
                 dists, sort_idx = dists.sort(dim=2)
+            # pyre-fixme[16]: `Tensor` has no attribute `gather`.
             idx = idx.gather(2, sort_idx)
 
         ctx.save_for_backward(p1, p2, lengths1, lengths2, idx)

pytorch3d/ops/mesh_face_areas_normals.py

@@ -5,7 +5,7 @@
 # LICENSE file in the root directory of this source tree.
 
 import torch
-from pytorch3d import _C  # pyre-fixme[21]: Could not find name `_C` in `pytorch3d`.
+from pytorch3d import _C
 from torch.autograd import Function
 from torch.autograd.function import once_differentiable
 

pytorch3d/ops/packed_to_padded.py

@@ -5,7 +5,7 @@
 # LICENSE file in the root directory of this source tree.
 
 import torch
-from pytorch3d import _C  # pyre-fixme[21]: Could not find name `_C` in `pytorch3d`.
+from pytorch3d import _C
 from torch.autograd import Function
 from torch.autograd.function import once_differentiable
 

pytorch3d/renderer/blending.py

@@ -8,7 +8,7 @@
 from typing import NamedTuple, Sequence, Union
 
 import torch
-from pytorch3d import _C  # pyre-fixme[21]: Could not find name `_C` in `pytorch3d`.
+from pytorch3d import _C
 
 
 # Example functions for blending the top K colors per pixel using the outputs

pytorch3d/renderer/compositing.py

@@ -5,7 +5,7 @@
 # LICENSE file in the root directory of this source tree.
 
 import torch
-from pytorch3d import _C  # pyre-fixme[21]: Could not find name `_C` in `pytorch3d`.
+from pytorch3d import _C
 
 
 # Example functions for blending the top K features per pixel using the outputs

pytorch3d/renderer/mesh/rasterize_meshes.py

@@ -9,7 +9,7 @@
 
 import numpy as np
 import torch
-from pytorch3d import _C  # pyre-fixme[21]: Could not find name `_C` in `pytorch3d`.
+from pytorch3d import _C
 
 from .clip import (
     ClipFrustum,