Add resource config class to Pennylane core (#8259)

**Context:**
We are moving the resource config class from labs to pennylane.

**Description of the Change:**
Add resource_config.py and test_resource_config.py to
pennylane.estimator. Since we do not have the templates, we do not add
them and their related tests.

**Benefits:**

**Possible Drawbacks:**

**Related GitHub Issues:**
[sc-96876]

---------

Co-authored-by: Diksha Dhawan <[email protected]>
Co-authored-by: Diksha Dhawan <[email protected]>
Co-authored-by: Astral Cai <[email protected]>
Co-authored-by: Christina Lee <[email protected]>
Co-authored-by: Andrija Paurevic <[email protected]>
Co-authored-by: Soran Jahangiri <[email protected]>
Co-authored-by: ANT0N <[email protected]>
Co-authored-by: obliviateandsurrender <[email protected]>

Author: 8 people

doc/releases/changelog-dev.md

@@ -21,6 +21,8 @@
     [(#8205)](https://github.com/PennyLaneAI/pennylane/pull/8205)
   * The test files were renamed to avoid the dual definition error with labs module.
     [(#8261)](https://github.com/PennyLaneAI/pennylane/pull/8261)
+  * Added a new `ResourceConfig` class to store the configuration used for resource estimation, including operator precisions and custom decompositions.
+    [(#8259)](https://github.com/PennyLaneAI/pennylane/pull/8259)
 
 * Dynamic wire allocation with `qml.allocation.allocate` can now be executed on `default.qubit`.
   [(#7718)](https://github.com/PennyLaneAI/pennylane/pull/7718)

pennylane/estimator/__init__.py

@@ -33,6 +33,7 @@
     :toctree: api
 
     ~Resources
+    ~ResourceConfig
     ~ResourceOperator
     ~CompressedResourceOp
     ~GateCount
@@ -44,6 +45,8 @@
 
 from .resources_base import Resources
 
+from .resource_config import ResourceConfig
+
 from .resource_operator import (
     ResourceOperator,
     CompressedResourceOp,

pennylane/estimator/resource_config.py

@@ -0,0 +1,253 @@
+# 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.
+r"""This module contains the ResourceConfig class, which tracks the configuration for resource estimation"""
+
+from __future__ import annotations
+
+from collections.abc import Callable
+from enum import StrEnum
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from pennylane.estimator.resource_operator import ResourceOperator
+
+
+class DecompositionType(StrEnum):
+    """Specifies the type of decomposition to override."""
+
+    ADJOINT = "adj"
+    CONTROLLED = "ctrl"
+    POW = "pow"
+    BASE = "base"
+
+
+class ResourceConfig:
+    """A container to track the configuration for precisions and custom decompositions for the
+    resource estimation pipeline.
+    """
+
+    def __init__(self) -> None:
+        _DEFAULT_PRECISION = 1e-9
+        _DEFAULT_BIT_PRECISION = 15
+        self.resource_op_precisions = {}
+        self._custom_decomps = {}
+        self._adj_custom_decomps = {}
+        self._ctrl_custom_decomps = {}
+        self._pow_custom_decomps = {}
+
+    def __str__(self) -> str:
+        decomps = [op.__name__ for op in self._custom_decomps]
+        adj_decomps = [f"Adjoint({op.__name__})" for op in self._adj_custom_decomps]
+        ctrl_decomps = [f"Controlled({op.__name__})" for op in self._ctrl_custom_decomps]
+        pow_decomps = [f"Pow({op.__name__})" for op in self._pow_custom_decomps]
+
+        all_op_strings = decomps + adj_decomps + ctrl_decomps + pow_decomps
+        op_names = ", ".join(all_op_strings)
+
+        dict_items_str = ",\n".join(
+            f"    {key.__name__}: {value!r}" for key, value in self.resource_op_precisions.items()
+        )
+
+        formatted_dict = f"{{\n{dict_items_str}\n}}"
+
+        return (
+            f"ResourceConfig(\n"
+            f"  precisions = {formatted_dict},\n"
+            f"  custom decomps = [{op_names}]\n)"
+        )
+
+    def __repr__(self) -> str:
+        return f"ResourceConfig(precisions = {self.resource_op_precisions}, custom_decomps = {self._custom_decomps}, adj_custom_decomps = {self._adj_custom_decomps}, ctrl_custom_decomps = {self._ctrl_custom_decomps}, pow_custom_decomps = {self._pow_custom_decomps})"
+
+    def set_precision(self, op_type: type[ResourceOperator], precision: float) -> None:
+        r"""Sets the precision for a given resource operator.
+
+        This method updates the precision value for operators that use a single
+        tolerance parameter (e.g., for synthesis error). It will raise an error
+        if you attempt to set the precision for an operator that is not
+        configurable or uses bit-precisions. A negative precision will also raise an error.
+
+        Args:
+            op_type (type[ResourceOperator]): the operator class for which
+                to set the precision
+            precision (float): The desired precision tolerance. A smaller
+                value corresponds to a higher precision compilation, which may
+                increase the required gate counts. Must be greater than 0.
+
+        Raises:
+            ValueError: If ``op_type`` is not a configurable operator or if setting
+                the precision for it is not supported, or if ``precision`` is negative.
+
+        **Example**
+
+        .. code-block:: python
+
+            import pennylane.estimator as qre
+
+            config = qre.ResourceConfig()
+
+            # Check the default precision
+            default = config.resource_op_precisions[qre.SelectPauliRot]['precision']
+            print(f"Default precision for SelectPauliRot: {default}")
+
+            # Set a new precision
+            config.set_precision(qre.SelectPauliRot, precision=1e-5)
+            new = config.resource_op_precisions[qre.SelectPauliRot]['precision']
+            print(f"New precision for SelectPauliRot: {new}")
+
+        .. code-block:: pycon
+
+            Default precision for SelectPauliRot: 1e-09
+            New precision for SelectPauliRot: 1e-05
+        """
+        if precision < 0:
+            raise ValueError(f"Precision must be a non-negative value, but got {precision}.")
+
+        if op_type not in self.resource_op_precisions:
+            configurable_ops = sorted(
+                [
+                    op.__name__
+                    for op, params in self.resource_op_precisions.items()
+                    if "precision" in params
+                ]
+            )
+            raise ValueError(
+                f"{op_type.__name__} is not a configurable operator. "
+                f"Configurable operators are: {', '.join(configurable_ops)}"
+            )
+
+        if "precision" not in self.resource_op_precisions[op_type]:
+            raise ValueError(f"Setting precision for {op_type.__name__} is not supported.")
+
+        self.resource_op_precisions[op_type]["precision"] = precision
+
+    def set_single_qubit_rot_precision(self, precision: float) -> None:
+        r"""Sets the synthesis precision for all single-qubit rotation gates.
+
+        This is a convenience method to update the synthesis precision tolerance
+        for all standard single-qubit rotation gates (and their
+        controlled versions) at once. The synthesis precision dictates the precision
+        for compiling rotation gates into a discrete gate set, which in turn
+        affects the number of gates required.
+
+        This method updates the ``precision`` value for the following operators:
+        :class:`~.pennylane.estimator.RX`, :class:`~.pennylane.estimator.RY`,
+        :class:`~.pennylane.estimator.RZ`, :class:`~.pennylane.estimator.CRX`,
+        :class:`~.pennylane.estimator.CRY`, :class:`~.pennylane.estimator.CRZ`.
+
+        Args:
+            precision (float): The desired synthesis precision tolerance. A smaller
+                value corresponds to a higher precision compilation, which may
+                increase the required gate counts. Must be greater than ``0``.
+
+        Raises:
+            ValueError: If ``precision`` is a negative value.
+
+        **Example**
+
+        .. code-block:: python
+
+            import pennylane.estimator as qre
+
+            config = qre.ResourceConfig()
+            print(f"Default RX precision: {config.resource_op_precisions[qre.RX]['precision']}")
+            print(f"Default RY precision: {config.resource_op_precisions[qre.RY]['precision']}")
+            print(f"Default RZ precision: {config.resource_op_precisions[qre.RZ]['precision']}")
+
+            config.set_single_qubit_rot_precision(1e-5)
+            print(f"Updated RX precision: {config.resource_op_precisions[qre.RX]['precision']}")
+            print(f"Updated RY precision: {config.resource_op_precisions[qre.RY]['precision']}")
+            print(f"Updated RZ precision: {config.resource_op_precisions[qre.RZ]['precision']}")
+
+        .. code-block:: pycon
+
+            Default RX precision: 1e-09
+            Default RY precision: 1e-09
+            Default RZ precision: 1e-09
+            Updated RX precision: 1e-05
+            Updated RY precision: 1e-05
+            Updated RZ precision: 1e-05
+        """
+        if precision < 0:
+            raise ValueError(f"Precision must be a non-negative value, but got {precision}.")
+
+    def set_decomp(
+        self,
+        op_type: type[ResourceOperator],
+        decomp_func: Callable,
+        decomp_type: DecompositionType | None = DecompositionType.BASE,
+    ) -> None:
+        """Sets a custom function to override the default resource decomposition.
+
+        Args:
+            op_type (type[ResourceOperator]): the operator class whose decomposition is being overriden.
+            decomp_func (Callable): the new resource decomposition function to be set as default.
+            decomp_type (None | DecompositionType): the decomposition type to override. Options are
+                ``"adj"``, ``"pow"``, ``"ctrl"``,
+                and ``"base"``. Default is ``"base"``.
+
+        Raises:
+            ValueError: If ``decomp_type`` is not a valid decomposition type.
+
+        .. note::
+
+            The new decomposition function ``decomp_func`` should have the same signature as the one it replaces.
+            Specifically, the signature should match the :code:`resource_keys` of the base resource
+            operator class being overriden.
+
+        **Example**
+
+        .. code-block:: python
+
+            import pennylane.estimator as qre
+
+            def custom_res_decomp(**kwargs):
+                h = qre.resource_rep(qre.Hadamard)
+                s = qre.resource_rep(qre.S)
+                return [qre.GateCount(h, 1), qre.GateCount(s, 2)]
+
+        .. code-block:: pycon
+
+            >>> print(qre.estimate_resources(qre.X(), gate_set={"Hadamard", "Z", "S"}))
+            --- Resources: ---
+            Total qubits: 1
+            Total gates : 4
+            Qubit breakdown:
+              clean qubits: 0, dirty qubits: 0, algorithmic qubits: 1
+            Gate breakdown:
+              {'Hadamard': 2, 'S': 2}
+            >>> config = qre.ResourceConfig()
+            >>> config.set_decomp(qre.X, custom_res_decomp)
+            >>> print(qre.estimate_resources(qre.X(), gate_set={"Hadamard", "Z", "S"}, config=config))
+            --- Resources: ---
+            Total qubits: 1
+            Total gates : 3
+            Qubit breakdown:
+              clean qubits: 0, dirty qubits: 0, algorithmic qubits: 1
+            Gate breakdown:
+              {'S': 1, 'Hadamard': 2}
+        """
+        if decomp_type is None:
+            decomp_type = DecompositionType("base")
+        else:
+            decomp_type = DecompositionType(decomp_type)
+
+        if decomp_type == DecompositionType.ADJOINT:
+            self._adj_custom_decomps[op_type] = decomp_func
+        elif decomp_type == DecompositionType.CONTROLLED:
+            self._ctrl_custom_decomps[op_type] = decomp_func
+        elif decomp_type == DecompositionType.POW:
+            self._pow_custom_decomps[op_type] = decomp_func
+        elif decomp_type is None or decomp_type == DecompositionType.BASE:
+            self._custom_decomps[op_type] = decomp_func