Adding BlockCollector classes to documentation (Qiskit#14575) (Qiskit#14579)

(cherry picked from commit 19a1fd1)

Co-authored-by: Alexander Ivrii <[email protected]>

Author: mergify[bot]

qiskit/dagcircuit/__init__.py

@@ -36,7 +36,18 @@
 
 .. autoexception:: DAGCircuitError
 .. autoexception:: DAGDependencyError
+
+Utilities
+=========
+
+.. autosummary::
+   :toctree: ../stubs/
+
+   BlockCollapser
+   BlockCollector
+   BlockSplitter
 """
+from .collect_blocks import BlockCollapser, BlockCollector, BlockSplitter
 from .dagcircuit import DAGCircuit
 from .dagnode import DAGNode, DAGOpNode, DAGInNode, DAGOutNode
 from .dagdepnode import DAGDepNode

qiskit/dagcircuit/collect_blocks.py

@@ -17,11 +17,12 @@
 
 from collections.abc import Iterable, Callable
 
-from qiskit.dagcircuit import DAGDepNode
-
 from qiskit.circuit import QuantumCircuit, CircuitInstruction, ClassicalRegister, Bit
 from qiskit.circuit.controlflow import condition_resources
-from . import DAGOpNode, DAGCircuit, DAGDependency
+from qiskit.dagcircuit.dagcircuit import DAGCircuit
+from qiskit.dagcircuit.dagdependency import DAGDependency
+from qiskit.dagcircuit.dagnode import DAGOpNode
+from qiskit.dagcircuit.dagdepnode import DAGDepNode
 from .exceptions import DAGCircuitError
 
 
@@ -323,15 +324,18 @@ def split_block_into_layers(block: list[DAGOpNode | DAGDepNode]):
 
 class BlockCollapser:
     """This class implements various strategies of consolidating blocks of nodes
-     in a DAG (direct acyclic graph). It works both with the
-    :class:`~qiskit.dagcircuit.DAGCircuit` and
-    :class:`~qiskit.dagcircuit.DAGDependency` DAG representations.
+    in a DAG (direct acyclic graph). It works both with
+    the :class:`~qiskit.dagcircuit.DAGCircuit`
+    and :class:`~qiskit.dagcircuit.DAGDependency` DAG representations.
     """
 
     def __init__(self, dag):
         """
         Args:
             dag (Union[DAGCircuit, DAGDependency]): The input DAG.
+
+        Raises:
+            DAGCircuitError: the input object is not a DAG.
         """
 
         self.dag = dag