`qml.estimator.estimate` should raise a better error message when the `gate_set` cannot be targeted

[isaacdevlugt]

Feature details

The error message raised by estimate should explain why the error happened and instruct the user what they need to change to get something running.

Implementation

The error raised should be similar to what the decomposition transform says when the user supplies a gate set that cannot be targeted.

How important would you say this feature is?

2: Somewhat important. Needed this quarter.

Additional information

import pennylane as qml
import pennylane.estimator as qre

def circuit(n):
    qre.Hadamard()
    qre.BasisRotation(n)
    mrx = qre.MultiRZ(2)
    qre.Controlled(mrx, num_ctrl_wires=1, num_zero_ctrl=1)
    qre.PhaseShift()
    return 

print(qml.estimator.estimate(circuit, gate_set={'RZ', 'CNOT'})(3))

---------------------------------------------------------------------------
ResourcesUndefinedError                   Traceback (most recent call last)
Cell In[10], [line 12](vscode-notebook-cell:?execution_count=10&line=12)
      9     qre.PhaseShift()
     10     return 
---> [12](vscode-notebook-cell:?execution_count=10&line=12) print(qml.estimator.estimate(circuit, gate_set={'RZ', 'CNOT'})(3))

File python3.13/site-packages/pennylane/estimator/estimate.py:314, in _resources_from_qfunc.<locals>.wrapper(*args, **kwargs)
    312 gate_counts = defaultdict(int)
    313 for cmp_rep_op in compressed_res_ops_list:
--> [314](python3.13/site-packages/pennylane/estimator/estimate.py:314)     _update_counts_from_compressed_res_op(
    315         cmp_rep_op, gate_counts, wire_manager=wire_manager, gate_set=gate_set, config=config
    316     )
    317 return Resources(
    318     zeroed_wires=wire_manager.zeroed,
    319     any_state_wires=wire_manager.any_state,
    320     algo_wires=wire_manager.algo_wires,
    321     gate_types=gate_counts,
    322 )

File python3.13/site-packages/pennylane/estimator/estimate.py:437, in _update_counts_from_compressed_res_op(comp_res_op, gate_counts_dict, wire_manager, gate_set, scalar, config)
    435 params = {key: value for key, value in comp_res_op.params.items() if value is not None}
    436 filtered_kwargs = {key: value for key, value in kwargs.items() if key not in params}
--> [437](python3.13/site-packages/pennylane/estimator/estimate.py:437) resource_decomp = decomp_func(**params, **filtered_kwargs)
    438 qubit_alloc_sum = _sum_allocated_wires(resource_decomp)
    440 for action in resource_decomp:

File python3.13/site-packages/pennylane/estimator/ops/qubit/non_parametric_ops.py:63, in Hadamard.resource_decomp(cls)
     51 @classmethod
     52 def resource_decomp(cls) -> list[GateCount]:
     53     r"""Returns a list representing the resources of the operator. Each object represents a quantum gate
     54     and the number of times it occurs in the decomposition.
     55 
   (...)     61         ResourcesUndefinedError: This gate is fundamental, no further decomposition defined.
     62     """
---> [63](python3.13/site-packages/pennylane/estimator/ops/qubit/non_parametric_ops.py:63)     raise ResourcesUndefinedError

ResourcesUndefinedError: