[CI] Fix doctest job if build without distributed (#165449)

Guard test with `TORCH_DOCTEST_DISTRIBUTED` and set it to true in
run_test.py to be able to pass doctest for PyTorch build without
distribtued support. This is a regression introduced by https://github.com/pytorch/pytorch/pull/164806

Fixes https://github.com/pytorch/pytorch/issues/165343

Pull Request resolved: https://github.com/pytorch/pytorch/pull/165449
Approved by: https://github.com/seemethere

test/run_test.py

@@ -1123,6 +1123,9 @@ def run_doctests(test_module, test_directory, options):
     if torch.mps.is_available():
         os.environ["TORCH_DOCTEST_MPS"] = "1"
 
+    if torch.distributed.is_available():
+        os.environ["TORCH_DOCTEST_DISTRIBUTED"] = "1"
+
     if 0:
         # TODO: could try to enable some of these
         os.environ["TORCH_DOCTEST_QUANTIZED_DYNAMIC"] = "1"

torch/distributed/tensor/_dtensor_spec.py

@@ -27,6 +27,7 @@ class ShardOrderEntry(NamedTuple):
                    second, etc. This tuple is guaranteed to be non-empty.
 
     Examples:
+        >>> # xdoctest: +REQUIRES(env:TORCH_DOCTEST_DISTRIBUTED)
         >>> # Tensor dim 1 sharded across mesh dim 2, then mesh dim 0
         >>> ShardOrderEntry(tensor_dim=1, mesh_dims=(2, 0))