fix: issue 3840 (#3845)

core/mapping/unmarshaler.go

@@ -625,7 +625,12 @@ func (u *Unmarshaler) processFieldPrimitiveWithJSONNumber(fieldType reflect.Type
 			return err
 		}
 
-		if value.OverflowFloat(fValue) {
+		// if value is a pointer, we need to check overflow with the pointer's value.
+		overflowValidator := value
+		if overflowValidator.Type().Kind() == reflect.Ptr {
+			overflowValidator = overflowValidator.Elem()
+		}
+		if overflowValidator.OverflowFloat(fValue) {
 			return fmt.Errorf("parsing %q as float32: value out of range", v.String())
 		}
 

core/mapping/unmarshaler_test.go

@@ -1339,8 +1339,20 @@ func TestUnmarshalNullableSlice(t *testing.T) {
 		"slice": `[null,2]`,
 	}
 
-	ast := assert.New(t)
-	ast.Equal(UnmarshalKey(m, &v), errNilSliceElement)
+	assert.New(t).Equal(UnmarshalKey(m, &v), errNilSliceElement)
+}
+
+func TestUnmarshalWithFloatPtr(t *testing.T) {
+	var v struct {
+		WeightFloat32 *float32 `key:"weightFloat32,optional"`
+	}
+	m := map[string]any{
+		"weightFloat32": json.Number("3.2"),
+	}
+
+	if assert.NoError(t, UnmarshalKey(m, &v)) {
+		assert.Equal(t, float32(3.2), *v.WeightFloat32)
+	}
 }
 
 func TestUnmarshalIntSlice(t *testing.T) {