fix: issue with default field values that can override payload field values

huma.go

@@ -1293,12 +1293,22 @@ func Register[I, O any](api API, op Operation, handler func(context.Context, *I)
 								})
 							}
 						} else {
-							// Set defaults for any fields that were not in the input.
+							// Set defaults for any fields that were not in the input:
+							atLeastOneFieldIsOverridden := false
 							defaults.Every(v, func(item reflect.Value, def any) {
-								if item.IsZero() {
+								if item.IsZero() && !reflect.ValueOf(def).IsZero() {
+									// There is one caveat here:
+									//     - IF the default value is not the 'zero' of the field type
+									//     - AND the 'zero' of the field type is a valid value specified in the input
+									//     - THEN the input required field value is overridden with a different value
 									item.Set(reflect.Indirect(reflect.ValueOf(def)))
+									atLeastOneFieldIsOverridden = true
 								}
 							})
+							// Restore wrongly overridden input values if any
+							if atLeastOneFieldIsOverridden {
+								_ = api.Unmarshal(ctx.Header("Content-Type"), body, f.Addr().Interface())
+							}
 						}
 					}
 

huma_test.go

@@ -627,14 +627,17 @@ func TestFeatures(t *testing.T) {
 					assert.Equal(t, 5, input.Body.Count)
 					assert.Equal(t, []string{"foo", "bar"}, input.Body.Tags)
 					assert.Equal(t, []int{1, 2, 3}, input.Body.Numbers)
+					assert.Len(t, input.Body.Items, 2)
 					assert.Equal(t, 1, input.Body.Items[0].ID)
 					assert.True(t, input.Body.Items[0].Verified)
+					assert.Equal(t, 1, input.Body.Items[1].ID)
+					assert.False(t, input.Body.Items[1].Verified)
 					return nil, nil
 				})
 			},
 			Method: http.MethodPut,
 			URL:    "/body",
-			Body:   `{"items": [{"id": 1}]}`,
+			Body:   `{"items": [{"id": 1}, {"id": 1, "verified": false}]}`,
 		},
 		{
 			Name: "request-body-required",