Add experimental xDSL plugin (#1707)

**Context:** We need a way to find out if we are running passes in xDSL
or in MLIR. Plugins already kind of do this, so let's model xDSL as an
MLIR plugin.

**Description of the Change:** This commit adds a fake MLIR plugin that
denotes the use of xDSL. Its sole purpose is to find out if the user
requests to run passes from xDSL and it is removed before being sent to
the compiler.

Author: erick-xanadu

doc/releases/changelog-dev.md

@@ -78,6 +78,10 @@
 
 <h3>Internal changes ⚙️</h3>
 
+* Add an xDSL MLIR plugin to denote whether we will be using xDSL to execute some passes.
+  This changelog entry may be moved to new features once all branches are merged together.
+  [(#1707)](https://github.com/PennyLaneAI/catalyst/pull/1707)
+
 * Creates a function that allows developers to register an equivalent MLIR transform for a given
   PLxPR transform.
   [(#1705)](https://github.com/PennyLaneAI/catalyst/pull/1705)

frontend/catalyst/compiler.py

@@ -467,6 +467,29 @@ def run_from_ir(self, ir: str, module_name: str, workspace: Directory):
 
         return output_object_name, out_IR
 
+    @debug_logger
+    def is_using_python_compiler(self):
+        """Returns true if we detect that there is an xdsl plugin in use.
+
+        Will also modify self.options.pass_plugins and self.options.dialect_plugins to remove
+        the xdsl plugin.
+        """
+        xdsl_path = pathlib.Path("xdsl-does-not-use-a-real-path")
+        if not (
+            xdsl_path in self.options.pass_plugins or xdsl_path in self.options.dialect_plugins
+        ):
+            return False
+
+        if xdsl_path in self.options.pass_plugins:
+            plugins = self.options.pass_plugins
+            self.options.pass_plugins = tuple(elem for elem in plugins if elem != xdsl_path)
+
+        if xdsl_path in self.options.dialect_plugins:
+            plugins = self.options.dialect_plugins
+            self.options.dialect_plugins = tuple(elem for elem in plugins if elem != xdsl_path)
+
+        return True
+
     @debug_logger
     def run(self, mlir_module, *args, **kwargs):
         """Compile an MLIR module to a shared object.
@@ -483,6 +506,8 @@ def run(self, mlir_module, *args, **kwargs):
             (str): filename of shared object
         """
 
+        self.is_using_python_compiler()
+
         return self.run_from_ir(
             mlir_module.operation.get_asm(
                 binary=False, print_generic_op_form=False, assume_verified=True

frontend/catalyst/passes/xdsl_plugin/__init__.py

@@ -0,0 +1,45 @@
+# Copyright 2025 Xanadu Quantum Technologies Inc.
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""XDSL Plugin Interface"""
+
+# This file contains what looks like a plugin
+# but in reality it is just not a "real" MLIR plugin.
+# It just follows the same convention to be able to add passes
+# that are implemented in xDSL
+
+import importlib.util
+from pathlib import Path
+
+
+def getXDSLPluginAbsolutePath():
+    """Returns a fake path"""
+    try:
+        # pylint: disable-next=import-outside-toplevel,unused-import
+        import xdsl
+    except ImportError as e:
+        # pragma: nocover
+        msg = "The xdsl plugin requires the xdsl package to be installed"
+        raise ImportError(msg) from e
+
+    return Path("xdsl-does-not-use-a-real-path")
+
+
+def name2pass(name):
+    """Identity function
+
+    This function is useful if we want a map from user-facing pass name
+    to mlir-facing pass names.
+    """
+    return getXDSLPluginAbsolutePath(), name

frontend/test/pytest/test_mlir_plugin_interface.py

@@ -91,3 +91,15 @@ def test_get_options():
         == "an-option bn-option"
     )
     assert catalyst.passes.Pass("example-pass", option=True).get_options() == "option=True"
+
+
+def test_xdsl_plugin():
+    """Here, we just test that we are able to run."""
+
+    @catalyst.qjit
+    @catalyst.passes.apply_pass("catalyst_xdsl_plugin.remove-chained-self-inverse")
+    @qml.qnode(qml.device("null.qubit", wires=1))
+    def example():
+        return qml.state()
+
+    example()

requirements.txt

@@ -29,3 +29,4 @@ nbmake
 # optional rt/test dependencies
 pennylane-lightning-kokkos
 amazon-braket-pennylane-plugin>1.27.1
+xdsl

setup.py

@@ -147,6 +147,7 @@ def parse_dep_versions():
         "cuda_quantum.ops = catalyst.api_extensions",
         "cuda_quantum.qjit = catalyst.third_party.cuda:cudaqjit",
     ],
+    "catalyst.passes_resolution": ["catalyst_xdsl_plugin.passes = catalyst.passes.xdsl_plugin"],
 }
 
 classifiers = [