fix(py): correct ConstString JSON encoding (#2325)

Author: ss2165

hugr-py/src/hugr/std/prelude.py

@@ -22,11 +22,10 @@ class StringVal(val.ExtensionValue):
 
     def to_value(self) -> val.Extension:
         name = "ConstString"
-        payload = {"value": self.v}
         return val.Extension(
             name,
             typ=STRING_T,
-            val=payload,
+            val=self.v,
         )
 
     def __str__(self) -> str:

hugr-py/tests/test_prelude.py

@@ -1,8 +1,18 @@
+from hugr.build.dfg import Dfg
 from hugr.std.prelude import STRING_T, StringVal
 
+from .conftest import validate
+
 
 def test_string_val():
-    ext_val = StringVal("test").to_value()
+    val = StringVal("test")
+    ext_val = val.to_value()
     assert ext_val.name == "ConstString"
     assert ext_val.typ == STRING_T
-    assert ext_val.val == {"value": "test"}
+    assert ext_val.val == "test"
+
+    dfg = Dfg()
+    v = dfg.load(val)
+    dfg.set_outputs(v)
+
+    validate(dfg.hugr)