Fix missing quant_method value

src/compressed_tensors/base.py

@@ -17,3 +17,4 @@
 COMPRESSION_CONFIG_NAME = "compression_config"
 KV_CACHE_SCHEME_NAME = "kv_cache_scheme"
 COMPRESSION_VERSION_NAME = "version"
+QUANTIZATION_METHOD_NAME = "quant_method"

src/compressed_tensors/compressors/model_compressor.py

@@ -20,18 +20,20 @@
 from copy import deepcopy
 from typing import Any, Dict, Optional, Union
 
+import compressed_tensors
 import torch
 import transformers
-import compressed_tensors
 from compressed_tensors.base import (
     COMPRESSION_CONFIG_NAME,
     COMPRESSION_VERSION_NAME,
     QUANTIZATION_CONFIG_NAME,
+    QUANTIZATION_METHOD_NAME,
     SPARSITY_CONFIG_NAME,
 )
 from compressed_tensors.compressors import Compressor
 from compressed_tensors.config import CompressionFormat, SparsityCompressionConfig
 from compressed_tensors.quantization import (
+    DEFAULT_QUANTIZATION_METHOD,
     QuantizationConfig,
     QuantizationStatus,
     apply_quantization_config,
@@ -186,7 +188,17 @@ def parse_sparsity_config(compression_config: Dict) -> Union[Dict, None]:
         return compression_config.get(SPARSITY_CONFIG_NAME, None)
 
     @staticmethod
-    def parse_quantization_config(compression_config: Dict) -> Union[Dict, None]:
+    def parse_quantization_config(
+        compression_config: Dict[str, Any]
+    ) -> Union[Dict[str, Any], None]:
+        """
+        Parse quantization config from quantization/compression config. The
+        quantization are all the fields that are not the sparsity config or
+        metadata fields
+
+        :param compression_config: quantization/compression config
+        :return: quantization config without sparsity config or metadata fields
+        """
         if compression_config is None:
             return None
 
@@ -201,9 +213,20 @@ def parse_quantization_config(compression_config: Dict) -> Union[Dict, None]:
         # SparseAutoModel format
         quantization_config = deepcopy(compression_config)
         quantization_config.pop(SPARSITY_CONFIG_NAME, None)
-        quantization_config.pop(COMPRESSION_VERSION_NAME, None)
+
+        # some fields are required, even if a qconfig is not present
+        # pop them off and if nothing remains, then there is no qconfig
+        quant_method = quantization_config.pop(QUANTIZATION_METHOD_NAME, None)
+        _ = quantization_config.pop(COMPRESSION_VERSION_NAME, None)
+
         if len(quantization_config) == 0:
-            quantization_config = None
+            return None
+
+        # replace popped off values
+        # note that version is discarded for now
+        if quant_method is not None:
+            quantization_config[QUANTIZATION_METHOD_NAME] = quant_method
+
         return quantization_config
 
     def __init__(
@@ -216,7 +239,6 @@ def __init__(
         self.sparsity_compressor = None
         self.quantization_compressor = None
 
-
         if sparsity_config and sparsity_config.format == CompressionFormat.dense.value:
             # ignore dense sparsity config
             self.sparsity_config = None
@@ -300,6 +322,9 @@ def update_config(self, save_directory: str):
 
         :param save_directory: path to a folder containing a HF model config
         """
+        if self.quantization_config is None and self.sparsity_config is None:
+            return
+
         config_file_path = os.path.join(save_directory, CONFIG_NAME)
         if not os.path.exists(config_file_path):
             _LOGGER.warning(
@@ -311,7 +336,20 @@ def update_config(self, save_directory: str):
         with open(config_file_path, "r") as config_file:
             config_data = json.load(config_file)
 
+        # required metadata whenever a quantization or sparsity config is present
+        # overwrite previous config and version if already existing
         config_data[QUANTIZATION_CONFIG_NAME] = {}
+        config_data[QUANTIZATION_CONFIG_NAME][
+            COMPRESSION_VERSION_NAME
+        ] = compressed_tensors.__version__
+        if self.quantization_config is not None:
+            self.quantization_config.quant_method = DEFAULT_QUANTIZATION_METHOD
+        else:
+            config_data[QUANTIZATION_CONFIG_NAME][
+                QUANTIZATION_METHOD_NAME
+            ] = DEFAULT_QUANTIZATION_METHOD
+
+        # quantization and sparsity configs
         if self.quantization_config is not None:
             quant_config_data = self.quantization_config.model_dump()
             config_data[QUANTIZATION_CONFIG_NAME] = quant_config_data

src/compressed_tensors/quantization/quant_scheme.py

@@ -211,7 +211,7 @@ def is_preset_scheme(name: str) -> bool:
     "W4A16": W4A16,
     # Integer weight and activation schemes
     "W8A8": INT8_W8A8,
-    "INT8": INT8_W8A8, # alias for W8A8
+    "INT8": INT8_W8A8,  # alias for W8A8
     "W4A8": INT8_W4A8,
     # Float weight and activation schemes
     "FP8": FP8,