data: support stepless updating compositions

1 files changed, 6 insertions, 4 deletions

diff --git a/src/data/things/composite.js b/src/data/things/composite.js
index 51525bc..c3b08f8 100644
--- a/src/data/things/composite.js
+++ b/src/data/things/composite.js
@@ -802,8 +802,8 @@ export function compositeFrom(description) {
     });
   }
 
-  if (!compositionNests && !anyStepsCompute && !anyStepsTransform) {
-    aggregate.push(new TypeError(`Expected at least one step to compute or transform`));
+  if (!compositionNests && !compositionUpdates && !anyStepsCompute) {
+    aggregate.push(new TypeError(`Expected at least one step to compute`));
   }
 
   aggregate.close();
@@ -1241,8 +1241,10 @@ export function compositeFrom(description) {
         expose.cache = base.cacheComposition;
       }
     } else if (compositionUpdates) {
-      expose.transform = (value, dependencies) =>
-        _wrapper(value, null, dependencies);
+      if (!empty(steps)) {
+        expose.transform = (value, dependencies) =>
+          _wrapper(value, null, dependencies);
+      }
     } else {
       expose.compute = (dependencies) =>
         _wrapper(noTransformSymbol, null, dependencies);