Deprecate the condition attribute and related functionality (#13223)

* Deprecate the condition attribute and related functionality

This commit deprecates the Instruction.condition and c_if() method for
removal in 2.0. This functionality has been superseded by the more
sophisiticated `IfElseOp` for some time now. Removing the condition
property will simplify the Qiskit data model as it is implemented in
a kind of ad-hoc manner that adds additional overhead to manually check
it in many places.

For the unittest modifications the deprecation warning for the .condtion
getter is suppressed for the entire suite because this gets triggered
internally by the transpiler and a lot of other places, including from
rust code as until it is removed we need to use it to check that piece
of the data model.

Fixes #9556

* Add missing assertWarns

* Handle deprecation warnings in visual tests too

* Apply suggestions from code review

Co-authored-by: Elena Peña Tapia <57907331+ElePT@users.noreply.github.com>

* Use private attribute in py->rust conversion

* Avoid deprecation warning in non-deprecated code

This commit fixes some places in the code where we were using the
deprecated functionality where it needed a path to persist the behavior
or where the deprecation warning became a performance bottleneck. The
code is updated accordingly and to catch issues like this in the future
the warning filters are adjusted to be more selective.

* Add missing test updates

* Add filter for aer's condition usage and dag drawer

* Fix lint

---------

Co-authored-by: Elena Peña Tapia <57907331+ElePT@users.noreply.github.com>

Author: mtreinish

crates/circuit/src/circuit_instruction.rs

@@ -656,7 +656,7 @@ impl<'py> FromPyObject<'py> for OperationFromPython {
                 ob.getattr(intern!(py, "label"))?.extract()?,
                 duration,
                 unit,
-                ob.getattr(intern!(py, "condition"))?.extract()?,
+                ob.getattr(intern!(py, "_condition"))?.extract()?,
             ))
         };
 

qiskit/circuit/barrier.py

@@ -19,6 +19,7 @@
 from __future__ import annotations
 
 from qiskit.exceptions import QiskitError
+from qiskit.utils import deprecate_func
 from .instruction import Instruction
 
 
@@ -44,5 +45,6 @@ def inverse(self, annotated: bool = False):
         """Special case. Return self."""
         return Barrier(self.num_qubits)
 
+    @deprecate_func(since="1.3.0", removal_timeline="in 2.0.0")
     def c_if(self, classical, val):
         raise QiskitError("Barriers are compiler directives and cannot be conditional.")

qiskit/circuit/controlflow/builder.py

@@ -284,7 +284,7 @@ def _copy_mutable_properties(self, instruction: Instruction) -> Instruction:
             The same instruction instance that was passed, but mutated to propagate the tracked
             changes to this class.
         """
-        instruction.condition = self.condition
+        instruction._condition = self._condition
         return instruction
 
     # Provide some better error messages, just in case something goes wrong during development and
@@ -639,8 +639,8 @@ def update_registers(index, op):
                         # a register is already present, so we use our own tracking.
                         self.add_register(register)
                         out.add_register(register)
-            if getattr(op, "condition", None) is not None:
-                for register in condition_resources(op.condition).cregs:
+            if getattr(op, "_condition", None) is not None:
+                for register in condition_resources(op._condition).cregs:
                     if register not in self.registers:
                         self.add_register(register)
                         out.add_register(register)

qiskit/circuit/controlflow/if_else.py

@@ -87,12 +87,20 @@ def __init__(
 
         super().__init__("if_else", num_qubits, num_clbits, [true_body, false_body], label=label)
 
-        self.condition = validate_condition(condition)
+        self._condition = validate_condition(condition)
 
     @property
     def params(self):
         return self._params
 
+    @property
+    def condition(self):
+        return self._condition
+
+    @condition.setter
+    def condition(self, value):
+        self._condition = value
+
     @params.setter
     def params(self, parameters):
         # pylint: disable=cyclic-import
@@ -152,7 +160,7 @@ def replace_blocks(self, blocks: Iterable[QuantumCircuit]) -> "IfElseOp":
         true_body, false_body = (
             ablock for ablock, _ in itertools.zip_longest(blocks, range(2), fillvalue=None)
         )
-        return IfElseOp(self.condition, true_body, false_body=false_body, label=self.label)
+        return IfElseOp(self._condition, true_body, false_body=false_body, label=self.label)
 
     def c_if(self, classical, val):
         raise NotImplementedError(
@@ -200,7 +208,7 @@ def __init__(
             "if_else", len(self.__resources.qubits), len(self.__resources.clbits), [], label=label
         )
         # Set the condition after super().__init__() has initialized it to None.
-        self.condition = validate_condition(condition)
+        self._condition = validate_condition(condition)
 
     def with_false_block(self, false_block: ControlFlowBuilderBlock) -> "IfElsePlaceholder":
         """Return a new placeholder instruction, with the false block set to the given value,
@@ -225,7 +233,7 @@ def with_false_block(self, false_block: ControlFlowBuilderBlock) -> "IfElsePlace
         false_bits = false_block.qubits() | false_block.clbits()
         true_block.add_bits(false_bits - true_bits)
         false_block.add_bits(true_bits - false_bits)
-        return type(self)(self.condition, true_block, false_block, label=self.label)
+        return type(self)(self._condition, true_block, false_block, label=self.label)
 
     def registers(self):
         """Get the registers used by the interior blocks."""
@@ -288,7 +296,7 @@ def concrete_instruction(self, qubits, clbits):
             )
         return (
             self._copy_mutable_properties(
-                IfElseOp(self.condition, true_body, false_body, label=self.label)
+                IfElseOp(self._condition, true_body, false_body, label=self.label)
             ),
             InstructionResources(
                 qubits=tuple(true_body.qubits),

qiskit/circuit/controlflow/while_loop.py

@@ -53,12 +53,20 @@ def __init__(
         num_clbits = body.num_clbits
 
         super().__init__("while_loop", num_qubits, num_clbits, [body], label=label)
-        self.condition = validate_condition(condition)
+        self._condition = validate_condition(condition)
 
     @property
     def params(self):
         return self._params
 
+    @property
+    def condition(self):
+        return self._condition
+
+    @condition.setter
+    def condition(self, value):
+        self._condition = value
+
     @params.setter
     def params(self, parameters):
         # pylint: disable=cyclic-import
@@ -88,7 +96,7 @@ def blocks(self):
 
     def replace_blocks(self, blocks):
         (body,) = blocks
-        return WhileLoopOp(self.condition, body, label=self.label)
+        return WhileLoopOp(self._condition, body, label=self.label)
 
     def c_if(self, classical, val):
         raise NotImplementedError(

qiskit/circuit/delay.py

@@ -19,6 +19,7 @@
 from qiskit.circuit.gate import Gate
 from qiskit.circuit import _utils
 from qiskit.circuit.parameterexpression import ParameterExpression
+from qiskit.utils import deprecate_func
 
 
 @_utils.with_gate_array(np.eye(2, dtype=complex))
@@ -46,6 +47,7 @@ def inverse(self, annotated: bool = False):
         """Special case. Return self."""
         return self
 
+    @deprecate_func(since="1.3.0", removal_timeline="in 2.0.0")
     def c_if(self, classical, val):
         raise CircuitError("Conditional Delay is not yet implemented.")
 

qiskit/circuit/instruction.py

@@ -176,6 +176,7 @@ def to_mutable(self):
         return self.copy()
 
     @property
+    @deprecate_func(since="1.3.0", removal_timeline="in 2.0.0", is_property=True)
     def condition(self):
         """The classical condition on the instruction."""
         return self._condition
@@ -410,8 +411,8 @@ def _assemble(self):
         # Add condition parameters for assembler. This is needed to convert
         # to a qobj conditional instruction at assemble time and after
         # conversion will be deleted by the assembler.
-        if self.condition:
-            instruction._condition = self.condition
+        if self._condition:
+            instruction._condition = self._condition
         return instruction
 
     @property
@@ -517,6 +518,7 @@ def inverse(self, annotated: bool = False):
         inverse_gate.definition = inverse_definition
         return inverse_gate
 
+    @deprecate_func(since="1.3.0", removal_timeline="in 2.0.0")
     def c_if(self, classical, val):
         """Set a classical equality condition on this instruction between the register or cbit
         ``classical`` and value ``val``.
@@ -632,26 +634,27 @@ def repeat(self, n):
             qargs = tuple(qc.qubits)
             cargs = tuple(qc.clbits)
             base = self.copy()
-            if self.condition:
+            if self._condition:
                 # Condition is handled on the outer instruction.
                 base = base.to_mutable()
                 base.condition = None
             for _ in [None] * n:
                 qc._append(CircuitInstruction(base, qargs, cargs))
 
             instruction.definition = qc
-        if self.condition:
-            instruction = instruction.c_if(*self.condition)
+        if self._condition:
+            instruction = instruction.c_if(*self._condition)
         return instruction
 
     @property
+    @deprecate_func(since="1.3.0", removal_timeline="in 2.0.0", is_property=True)
     def condition_bits(self) -> List[Clbit]:
         """Get Clbits in condition."""
         from qiskit.circuit.controlflow import condition_resources  # pylint: disable=cyclic-import
 
-        if self.condition is None:
+        if self._condition is None:
             return []
-        return list(condition_resources(self.condition).clbits)
+        return list(condition_resources(self._condition).clbits)
 
     @property
     def name(self):

qiskit/circuit/instructionset.py

@@ -20,6 +20,7 @@
 from typing import Callable
 
 from qiskit.circuit.exceptions import CircuitError
+from qiskit.utils import deprecate_func
 from .classicalregister import Clbit, ClassicalRegister
 from .operation import Operation
 from .quantumcircuitdata import CircuitInstruction
@@ -105,6 +106,7 @@ def inverse(self, annotated: bool = False):
                 )
         return self
 
+    @deprecate_func(since="1.3.0", removal_timeline="in 2.0.0")
     def c_if(self, classical: Clbit | ClassicalRegister | int, val: int) -> "InstructionSet":
         """Set a classical equality condition on all the instructions in this set between the
         :obj:`.ClassicalRegister` or :obj:`.Clbit` ``classical`` and value ``val``.

qiskit/circuit/quantumcircuit.py

@@ -2102,14 +2102,14 @@ def map_vars(op):
                 is_control_flow = isinstance(n_op, ControlFlowOp)
                 if (
                     not is_control_flow
-                    and (condition := getattr(n_op, "condition", None)) is not None
+                    and (condition := getattr(n_op, "_condition", None)) is not None
                 ):
                     n_op = n_op.copy() if n_op is op and copy else n_op
                     n_op.condition = variable_mapper.map_condition(condition)
                 elif is_control_flow:
                     n_op = n_op.replace_blocks(recurse_block(block) for block in n_op.blocks)
                     if isinstance(n_op, (IfElseOp, WhileLoopOp)):
-                        n_op.condition = variable_mapper.map_condition(n_op.condition)
+                        n_op.condition = variable_mapper.map_condition(n_op._condition)
                     elif isinstance(n_op, SwitchCaseOp):
                         n_op.target = variable_mapper.map_target(n_op.target)
                 elif isinstance(n_op, Store):
@@ -3520,7 +3520,7 @@ def update_from_expr(objects, node):
 
         for instruction in self._data:
             objects = set(itertools.chain(instruction.qubits, instruction.clbits))
-            if (condition := getattr(instruction.operation, "condition", None)) is not None:
+            if (condition := getattr(instruction.operation, "_condition", None)) is not None:
                 objects.update(_builder_utils.condition_resources(condition).clbits)
                 if isinstance(condition, expr.Expr):
                     update_from_expr(objects, condition)
@@ -3623,7 +3623,7 @@ def num_connected_components(self, unitary_only: bool = False) -> int:
             else:
                 args = instruction.qubits + instruction.clbits
                 num_qargs = len(args) + (
-                    1 if getattr(instruction.operation, "condition", None) else 0
+                    1 if getattr(instruction.operation, "_condition", None) else 0
                 )
 
             if num_qargs >= 2 and not getattr(instruction.operation, "_directive", False):

qiskit/circuit/singleton.py

@@ -251,6 +251,7 @@ class XGate(Gate, metaclass=_SingletonMeta, overrides=_SingletonGateOverrides):
 
 import functools
 
+from qiskit.utils import deprecate_func
 from .instruction import Instruction
 from .gate import Gate
 from .controlledgate import ControlledGate, _ctrl_state_to_int
@@ -489,6 +490,7 @@ class they are providing overrides for has more lazy attributes or user-exposed
         instruction._params = _frozenlist(instruction._params)
         return instruction
 
+    @deprecate_func(since="1.3.0", removal_timeline="in 2.0.0")
     def c_if(self, classical, val):
         return self.to_mutable().c_if(classical, val)