Improve repr of _BaseAncillaQid classes with prefix (#6555)

* Add failing repr tests for CleanQubit and BorrowableQubit with prefix

* Quote prefix string in repr of `_BaseAncillaQid` classes

Author: pavoljuhas

cirq-core/cirq/ops/qubit_manager.py

@@ -53,7 +53,7 @@ def with_dimension(self, dimension: int) -> '_BaseAncillaQid':
 
     def __repr__(self) -> str:
         dim_str = f', dim={self.dim}' if self.dim != 2 else ''
-        prefix_str = f', prefix={self.prefix}' if self.prefix != '' else ''
+        prefix_str = f', prefix={self.prefix!r}' if self.prefix != '' else ''
         return f"cirq.ops.{type(self).__name__}({self.id}{dim_str}{prefix_str})"
 
 

cirq-core/cirq/ops/qubit_manager_test.py

@@ -31,6 +31,10 @@ def test_clean_qubits():
     assert str(q) == '_c(2) (d=3)'
     assert repr(q) == 'cirq.ops.CleanQubit(2, dim=3)'
 
+    q = cqi.CleanQubit(3, dim=4, prefix="a")
+    assert str(q) == 'a_c(3) (d=4)'
+    assert repr(q) == "cirq.ops.CleanQubit(3, dim=4, prefix='a')"
+
     assert cqi.CleanQubit(1) < cqi.CleanQubit(2)
 
 
@@ -58,6 +62,10 @@ def test_borrow_qubits():
     assert str(q) == '_b(20) (d=4)'
     assert repr(q) == 'cirq.ops.BorrowableQubit(20, dim=4)'
 
+    q = cqi.BorrowableQubit(30, dim=4, prefix="a")
+    assert str(q) == 'a_b(30) (d=4)'
+    assert repr(q) == "cirq.ops.BorrowableQubit(30, dim=4, prefix='a')"
+
     assert cqi.BorrowableQubit(1) < cqi.BorrowableQubit(2)