[SegFormer] Add deprecation warning (#15889)

* Add deprecation warning

* Remove from docs and hide in kwargs

* Improve implementation
Co-authored-by: Niels Rogge <nielsrogge@Nielss-MacBook-Pro.local>

src/transformers/models/segformer/configuration_segformer.py

@@ -14,6 +14,8 @@
 # limitations under the License.
 """ SegFormer model configuration"""
 
+import warnings
+
 from ...configuration_utils import PretrainedConfig
 from ...utils import logging
 
@@ -78,9 +80,6 @@ class SegformerConfig(PretrainedConfig):
             The epsilon used by the layer normalization layers.
         decoder_hidden_size (`int`, *optional*, defaults to 256):
             The dimension of the all-MLP decode head.
-        reshape_last_stage (`bool`, *optional*, defaults to `True`):
-            Whether to reshape the features of the last stage back to `(batch_size, num_channels, height, width)`. Only
-            required for the semantic segmentation model.
         semantic_loss_ignore_index (`int`, *optional*, defaults to 255):
             The index that is ignored by the loss function of the semantic segmentation model.
 
@@ -122,12 +121,18 @@ class SegformerConfig(PretrainedConfig):
         layer_norm_eps=1e-6,
         decoder_hidden_size=256,
         is_encoder_decoder=False,
-        reshape_last_stage=True,
         semantic_loss_ignore_index=255,
         **kwargs
     ):
         super().__init__(**kwargs)
 
+        if "reshape_last_stage" in kwargs and kwargs["reshape_last_stage"] is False:
+            warnings.warn(
+                "Reshape_last_stage is set to False in this config. This argument is deprecated and will soon be removed, "
+                "as the behaviour will default to that of reshape_last_stage = True.",
+                FutureWarning,
+            )
+
         self.image_size = image_size
         self.num_channels = num_channels
         self.num_encoder_blocks = num_encoder_blocks
@@ -147,5 +152,5 @@ class SegformerConfig(PretrainedConfig):
         self.drop_path_rate = drop_path_rate
         self.layer_norm_eps = layer_norm_eps
         self.decoder_hidden_size = decoder_hidden_size
-        self.reshape_last_stage = reshape_last_stage
+        self.reshape_last_stage = kwargs.get("reshape_last_stage", True)
         self.semantic_loss_ignore_index = semantic_loss_ignore_index

src/transformers/models/segformer/modeling_segformer.py

@@ -45,7 +45,7 @@ _FEAT_EXTRACTOR_FOR_DOC = "SegformerFeatureExtractor"
 
 # Base docstring
 _CHECKPOINT_FOR_DOC = "nvidia/mit-b0"
-_EXPECTED_OUTPUT_SHAPE = [1, 256, 256]
+_EXPECTED_OUTPUT_SHAPE = [1, 256, 16, 16]
 
 # Image classification docstring
 _IMAGE_CLASS_CHECKPOINT = "nvidia/mit-b0"