add error message for pruning global mode schema error (#4440)

nni/algorithms/compression/v2/pytorch/pruning/basic_pruner.py

@@ -5,7 +5,7 @@ from copy import deepcopy
 import logging
 from typing import List, Dict, Tuple, Callable, Optional
 
-from schema import And, Or, Optional as SchemaOptional
+from schema import And, Or, Optional as SchemaOptional, SchemaError
 import torch
 from torch import Tensor
 import torch.nn as nn
@@ -412,7 +412,12 @@ class SlimPruner(BasicPruner):
             sub_shcema[SchemaOptional('op_types')] = ['BatchNorm2d']
         schema = CompressorSchema(schema_list, model, _logger)
 
-        schema.validate(config_list)
+        try:
+            schema.validate(config_list)
+        except SchemaError as e:
+            if "Missing key: 'total_sparsity'" in str(e):
+                _logger.error('`config_list` validation failed. If global mode is set in this pruner, `sparsity_per_layer` and `sparsity` are not supported, make sure `total_sparsity` is set in config_list.')
+            raise e
 
     def criterion_patch(self, criterion: Callable[[Tensor, Tensor], Tensor]) -> Callable[[Tensor, Tensor], Tensor]:
         def patched_criterion(input_tensor: Tensor, target: Tensor):
@@ -664,7 +669,12 @@ class TaylorFOWeightPruner(BasicPruner):
             sub_shcema[SchemaOptional('op_types')] = ['Conv2d', 'Linear']
         schema = CompressorSchema(schema_list, model, _logger)
 
-        schema.validate(config_list)
+        try:
+            schema.validate(config_list)
+        except SchemaError as e:
+            if "Missing key: 'total_sparsity'" in str(e):
+                _logger.error('`config_list` validation failed. If global mode is set in this pruner, `sparsity_per_layer` and `sparsity` are not supported, make sure `total_sparsity` is set in config_list.')
+            raise e
 
     def _collector(self, buffer: List, weight_tensor: Tensor) -> Callable[[Tensor], None]:
         assert len(buffer) == 0, 'Buffer pass to taylor pruner collector is not empty.'