Enable HF pretrained backbones (#31145)

* Enable load HF or tim backbone checkpoints

* Fix up

* Fix test - pass in proper out_indices

* Update docs

* Fix tvp tests

* Fix doc examples

* Fix doc examples

* Try to resolve DPT backbone param init

* Don't conditionally set to None

* Add condition based on whether backbone is defined

* Address review comments

tests/models/mask2former/test_modeling_mask2former.py

@@ -21,6 +21,7 @@ import numpy as np
 from tests.test_modeling_common import floats_tensor
 from transformers import Mask2FormerConfig, is_torch_available, is_vision_available
 from transformers.testing_utils import (
+    require_timm,
     require_torch,
     require_torch_accelerator,
     require_torch_fp16,
@@ -317,6 +318,37 @@ class Mask2FormerModelTest(ModelTesterMixin, PipelineTesterMixin, unittest.TestC
         self.assertIsNotNone(transformer_decoder_hidden_states.grad)
         self.assertIsNotNone(attentions.grad)
 
+    @require_timm
+    def test_backbone_selection(self):
+        config, inputs = self.model_tester.prepare_config_and_inputs_for_common()
+
+        config.backbone_config = None
+        config.backbone_kwargs = {"out_indices": [1, 2, 3]}
+        config.use_pretrained_backbone = True
+
+        # Load a timm backbone
+        # We can't load transformer checkpoint with timm backbone, as we can't specify features_only and out_indices
+        config.backbone = "resnet18"
+        config.use_timm_backbone = True
+
+        for model_class in self.all_model_classes:
+            model = model_class(config).to(torch_device).eval()
+            if model.__class__.__name__ == "Mask2FormerModel":
+                self.assertEqual(model.pixel_level_module.encoder.out_indices, [1, 2, 3])
+            elif model.__class__.__name__ == "Mask2FormerForUniversalSegmentation":
+                self.assertEqual(model.model.pixel_level_module.encoder.out_indices, [1, 2, 3])
+
+        # Load a HF backbone
+        config.backbone = "microsoft/resnet-18"
+        config.use_timm_backbone = False
+
+        for model_class in self.all_model_classes:
+            model = model_class(config).to(torch_device).eval()
+            if model.__class__.__name__ == "Mask2FormerModel":
+                self.assertEqual(model.pixel_level_module.encoder.out_indices, [1, 2, 3])
+            elif model.__class__.__name__ == "Mask2FormerForUniversalSegmentation":
+                self.assertEqual(model.model.pixel_level_module.encoder.out_indices, [1, 2, 3])
+
 
 TOLERANCE = 1e-4