Fix target matching for fused layers with compressed-tensors (vllm-pr…

…oject#12617)

Without this PR
---------------
Quantizing models with llm-compressor and a recipe that explicitly lists
names of layers produces a model that is not loadable by vLLM (i.e.
`vllm serve <model>` fails with `raise ValueError(f"Unable to find
matching target for {module} in the ...`).

Example recipe:
```
recipe = """
quantization_stage:
  run_type: oneshot
  quantization_modifiers:
    GPTQModifier:
      ignore: ["lm_head"]
      config_groups:
        group_0:
          weights:
            num_bits: 4
            type: "int"
            symmetric: true
            strategy: "group"
            group_size: 128
          targets: [
            "model.layers.0.mlp.down_proj",
            "model.layers.2.mlp.down_proj",
            "model.layers.3.mlp.down_proj",
            "model.layers.4.mlp.down_proj",
            "model.layers.5.mlp.down_proj",
            "model.layers.6.mlp.down_proj",
            "model.layers.7.mlp.down_proj",
            "model.layers.8.mlp.down_proj",
            "model.layers.9.mlp.down_proj",
            "model.layers.10.mlp.down_proj",
            "model.layers.11.mlp.down_proj",
            "model.layers.12.mlp.down_proj",
            "model.layers.13.mlp.down_proj",
            "model.layers.14.mlp.down_proj",
            "model.layers.15.mlp.down_proj",
            "model.layers.16.mlp.down_proj",
            "model.layers.17.mlp.down_proj",
            "model.layers.19.mlp.down_proj",
            "model.layers.21.mlp.down_proj",
            "model.layers.22.mlp.down_proj",
            .
            .
            .
          ]
"""
```

To reproduce the vLLM error: 
```bash
vllm serve nm-testing/eldar-test
```

With this PR
------------
Models are loaded correctly without any errors.

vllm/model_executor/layers/quantization/compressed_tensors/utils.py

@@ -103,7 +103,8 @@ def find_matched_target(layer_name: Optional[str], module: Module,
 
     matched_target = (_find_first_match(layer_name, targets)
                       or _find_first_match(module.__class__.__name__, targets,
-                                           True))
+                                           True)
+                      or _match_fused_layer(layer_name, targets))
 
     if matched_target is None:
         raise ValueError(f"Unable to find matching target for {module} in the "
@@ -152,3 +153,41 @@ def _is_equal_or_regex_match(value: str,
     elif target == value:
         return True
     return False
+
+
+def _match_fused_layer(layer_name: str,
+                       target_layers: Iterable[str]) -> Optional[str]:
+    """
+    Match a fused layer name to its corresponding individual layer in 
+    target_layers.
+
+    Examples:
+        layer_name = "model.layers.0.self_attn.qkv_proj"
+        target_layers = ["model.layers.0.self_attn.q_proj",
+                        "model.layers.0.self_attn.k_proj",
+                        "model.layers.0.self_attn.v_proj"]
+    """
+    # Split into parent path and layer type
+    # e.g., "model.layers.0.self_attn" and "qkv_proj"
+    parent_path = ".".join(layer_name.split(".")[:-1])
+    layer_type = layer_name.split(".")[-1]
+
+    if layer_type not in FUSED_LAYER_NAME_MAPPING:
+        return None
+
+    possible_layer_types = FUSED_LAYER_NAME_MAPPING[layer_type]
+
+    # Look for a target layer that:
+    # 1. Has the same parent path
+    # 2. Ends with one of the possible individual layer types
+    for target in target_layers:
+        is_same_parent = parent_path in target
+        is_matching_type = any(type_suffix in target
+                               for type_suffix in possible_layer_types)
+
+        if is_same_parent and is_matching_type and all(
+                '.'.join([parent_path, type_suffix])
+                for type_suffix in possible_layer_types):
+            return target
+
+    return None