Don't reject non-const duration in constructors. (#14009)

Originally, I thought it'd make the most sense to reject
construction of operations that'd have a duration type
but also be non-const expressions. But, a user can
currently create a `Var` with a duration type, so this
seems like an incomplete restriction.

Author: kevinhartman

qiskit/circuit/classical/expr/constructors.py

@@ -683,16 +683,8 @@ def mul(left: typing.Any, right: typing.Any) -> Expr:
         left = _coerce_lossless(left, type)
         right = _coerce_lossless(right, type)
     elif left.type.kind is types.Duration and right.type.kind in {types.Uint, types.Float}:
-        if not right.const:
-            raise ValueError(
-                f"multiplying operands '{left}' and '{right}' would result in a non-const '{left.type}'"
-            )
         type = left.type
     elif right.type.kind is types.Duration and left.type.kind in {types.Uint, types.Float}:
-        if not left.const:
-            raise ValueError(
-                f"multiplying operands '{left}' and '{right}' would result in a non-const '{right.type}'"
-            )
         type = right.type
     else:
         raise TypeError(f"invalid types for '{Binary.Op.MUL}': '{left.type}' and '{right.type}'")
@@ -761,10 +753,6 @@ def div(left: typing.Any, right: typing.Any) -> Expr:
             left = _coerce_lossless(left, type)
             right = _coerce_lossless(right, type)
     elif left.type.kind is types.Duration and right.type.kind in {types.Uint, types.Float}:
-        if not right.const:
-            raise ValueError(
-                f"division of '{left}' and '{right}' would result in a non-const '{left.type}'"
-            )
         type = left.type
     else:
         raise TypeError(f"invalid types for '{Binary.Op.DIV}': '{left.type}' and '{right.type}'")

test/python/circuit/classical/test_expr_constructors.py

@@ -808,13 +808,6 @@ def test_mul_forbidden(self):
         with self.assertRaisesRegex(TypeError, "cannot multiply two durations"):
             expr.mul(Duration.dt(1000), Duration.dt(1000))
 
-        # Multiply timing expressions by non-const floats:
-        non_const_float = expr.Var.new("a", types.Float())
-        with self.assertRaisesRegex(ValueError, "would result in a non-const"):
-            expr.mul(Duration.dt(1000), non_const_float)
-        with self.assertRaisesRegex(ValueError, "would result in a non-const"):
-            expr.mul(non_const_float, Duration.dt(1000))
-
     def test_div_explicit(self):
         cr = ClassicalRegister(8, "c")
 
@@ -924,8 +917,3 @@ def test_div_forbidden(self):
             expr.div(255.0, 1)
         with self.assertRaisesRegex(TypeError, "invalid types"):
             expr.div(255.0, Duration.dt(1000))
-
-        # Divide timing expressions by non-const floats:
-        non_const_float = expr.Var.new("a", types.Float())
-        with self.assertRaisesRegex(ValueError, "would result in a non-const"):
-            expr.div(Duration.dt(1000), non_const_float)