FIX Bug with handling of active adapters (#1659)

There was a bug for some models like IA3, LoHa, etc., where calling
set_adapter would not correctly update the active_adapter. This is now
fixed.

Note that this is not about the active_adapter attribute on PeftModel or
layers, which are handled separately.

This PR also ensures that LoraModel, IA3Model, etc. consistently use
self.active_adapters, not self.active_adapter. The latter should be
treated more like a private attribute (but this isn't changed for
backwards compatibility).

src/peft/tuners/adalora/model.py

@@ -134,7 +134,7 @@ def _create_and_replace(
         # If it is not an AdaLoraLayer, create a new module, else update it with new adapters
         if not isinstance(target, AdaLoraLayer):
             new_module = self._create_new_module(lora_config, adapter_name, target, **kwargs)
-            if adapter_name != self.active_adapter:
+            if adapter_name not in self.active_adapters:
                 # adding an additional adapter: it is not automatically trainable
                 new_module.requires_grad_(False)
             self._replace_module(parent, target_name, new_module, target)

src/peft/tuners/boft/model.py

@@ -116,7 +116,7 @@ def _create_and_replace(
         # If it is not a BOFTLayer, create a new module, else update it with new adapters
         if not isinstance(target, BOFTLayer):
             new_module = self._create_new_module(boft_config, adapter_name, target, **kwargs)
-            if adapter_name != self.active_adapter:
+            if adapter_name not in self.active_adapters:
                 # adding an additional adapter: it is not automatically trainable
                 new_module.requires_grad_(False)
             self._replace_module(parent, target_name, new_module, target)
@@ -244,6 +244,7 @@ def set_adapter(self, adapter_name):
                     warnings.warn("Adapter cannot be set when the model is merged. Unmerging the model first.")
                     module.unmerge()
                 module.set_adapter(adapter_name)
+        self.active_adapter = adapter_name
 
     @staticmethod
     def _prepare_adapter_config(peft_config, model_config):

src/peft/tuners/ia3/model.py

@@ -179,7 +179,7 @@ def _create_and_replace(
             )
         else:
             new_module = self._create_new_module(ia3_config, adapter_name, target, **kwargs)
-            if adapter_name != self.active_adapter:
+            if adapter_name not in self.active_adapters:
                 # adding an additional adapter: it is not automatically trainable
                 new_module.requires_grad_(False)
             self._replace_module(parent, target_name, new_module, target)
@@ -277,6 +277,7 @@ def set_adapter(self, adapter_name: str | list[str]) -> None:
                     warnings.warn("Adapter cannot be set when the model is merged. Unmerging the model first.")
                     module.unmerge()
                 module.set_adapter(adapter_name)
+        self.active_adapter = adapter_name
 
     def _prepare_adapter_config(self, peft_config, model_config):
         if peft_config.target_modules is None:

src/peft/tuners/lora/model.py

@@ -218,7 +218,7 @@ def _create_and_replace(
             )
         else:
             new_module = self._create_new_module(lora_config, adapter_name, target, **kwargs)
-            if adapter_name != self.active_adapter:
+            if adapter_name not in self.active_adapters:
                 # adding an additional adapter: it is not automatically trainable
                 new_module.requires_grad_(False)
             self._replace_module(parent, target_name, new_module, target)

src/peft/tuners/lycoris_utils.py

@@ -404,6 +404,7 @@ def set_adapter(self, adapter_name: str | list[str]) -> None:
                     warnings.warn("Adapter cannot be set when the model is merged. Unmerging the model first.")
                     module.unmerge()
                 module.set_adapter(adapter_name)
+        self.active_adapter = adapter_name
 
     def delete_adapter(self, adapter_name: str) -> None:
         """

src/peft/tuners/poly/model.py

@@ -57,7 +57,7 @@ def _create_and_replace(
                 adapter_name,
                 target,
             )
-            if adapter_name != self.active_adapter:
+            if adapter_name not in self.active_adapters:
                 # adding an additional adapter: it is not automatically trainable
                 new_module.requires_grad_(False)
             self._replace_module(parent, target_name, new_module, target)

src/peft/tuners/tuners_utils.py

@@ -161,7 +161,7 @@ def __init__(self, model, peft_config: Union[PeftConfig, dict[str, PeftConfig]],
                 # user is adding a dict of PeftConfigs
                 self.peft_config.update(peft_config)
 
-        self.active_adapter = adapter_name
+        self.active_adapter: str | list[str] = adapter_name
         self.inject_adapter(self.model, adapter_name)
 
         # Copy the peft_config in the injected model.
@@ -477,7 +477,7 @@ def disable_adapters(self) -> bool:
         return self._disable_adapters
 
     @property
-    def active_adapter(self) -> str:
+    def active_adapter(self) -> str | list[str]:
         # use a property to ensure that active_adapter is not set directly, instead use the set_adapter method
         return self._active_adapter
 

tests/test_custom_models.py

@@ -945,6 +945,36 @@ def run_with_disable(config_kwargs, bias):
             # This is bad, there was a warning about the bias when there should not have been any.
             self.fail("There should be no warning when bias is set to 'none'")
 
+    @parameterized.expand(TEST_CASES)
+    def test_active_adapter(self, test_name, model_id, config_cls, config_kwargs):
+        model = self.transformers_class.from_pretrained(model_id).to(self.torch_device)
+        config = config_cls(
+            base_model_name_or_path=model_id,
+            **config_kwargs,
+        )
+        model = get_peft_model(model, config)
+        assert model.active_adapters == ["default"]
+        assert model.active_adapter == "default"
+
+        # at this stage, "default" is still the activate adapter, "other" is disabled
+        model.add_adapter("other", config)
+        assert model.active_adapters == ["default"]
+        assert model.active_adapter == "default"
+
+        # set "other" as the active adapter
+        model.set_adapter("other")
+        assert model.active_adapters == ["other"]
+        assert model.active_adapter == "other"
+
+        # set both adapters as active
+        # Note: On the PeftModel, there cannot be multiple active adapters, so we have to go through model.base_model
+        # instead.
+        model.base_model.set_adapter(["default", "other"])
+        # model.active_adapters works, as it delegates to the base_model
+        assert model.active_adapters == ["default", "other"]
+        # model.active_adapter would not work, thus we have to check the base_model directly
+        assert model.base_model.active_adapter == ["default", "other"]
+
     @parameterized.expand(TEST_CASES)
     def test_delete_adapter(self, test_name, model_id, config_cls, config_kwargs):
         self._test_delete_adapter(model_id, config_cls, config_kwargs)