Keep floats in int and float unions when decoding typed JSON payloads

changelog/fixed/tumbling-toucan.md

@@ -0,0 +1 @@
+Typed JSON payload conversion no longer truncates a float to an `int` when the type hint is a union of `int` and `float`, such as `int | float`.

temporalio/converter/_payload_converter.py

@@ -900,6 +900,10 @@ def value_to_type(
 
     # Union
     if is_union:
+        # The int conversion accepts a float and truncates it, so give a float
+        # to a float member before trying an earlier int member
+        if isinstance(value, float) and float in type_args:
+            return value_to_type(float, value, custom_converters)
         # Try each one. Note, Optional is just a union w/ none.
         for arg in type_args:
             try:

tests/test_converter.py

@@ -675,6 +675,11 @@ def fail(hint: Any, value: Any) -> None:
     fail(int | None, "1")
     ok(MyDataClass | NestedDataClass, MyDataClass("foo", 5, SerializableEnum.FOO))
     ok(MyDataClass | NestedDataClass, NestedDataClass("foo"))
+    # An earlier int member must not truncate a float
+    ok(int | float, 5)
+    ok(int | float, 5.5)
+    ok(int | float | None, 5.5)
+    ok(list[int | float], [5, 5.5])
 
     # NewType
     ok(NewIntType, 5)