transforms.iodelay_estimator: fix handling of `with sequential`.

artiq/compiler/transforms/iodelay_estimator.py

@@ -216,7 +216,7 @@ class IODelayEstimator(algorithm.Visitor):
                 self.current_delay = old_delay
 
             self.current_delay += iodelay.Max(delays)
-        elif len(node.items) == 1 and types.is_builtin(context_expr.type, "serial"):
+        elif len(node.items) == 1 and types.is_builtin(context_expr.type, "sequential"):
             self.visit(node.body)
         else:
             self.abort("with statement cannot be interleaved", node.loc)

lit-test/test/iodelay/sequential.py

@@ -0,0 +1,8 @@
+# RUN: %python -m artiq.compiler.testbench.signature %s >%t
+# RUN: OutputCheck %s --file-to-check=%t
+
+# CHECK-L: f: (a:int(width=64), b:int(width=64))->NoneType delay(a + b mu)
+def f(a, b):
+    with sequential:
+        delay_mu(a)
+        delay_mu(b)