Don't validate if the field shouldn't be shown

src/collective/volto/formsupport/restapi/services/submit_form/field.py

@@ -5,6 +5,30 @@
 validation_message_matcher = re.compile("Validation failed\(([^\)]+)\): ")
 
 
+def always():
+    return True
+
+
+def value_is(value, target_value):
+    if isinstance(target_value, list):
+        return value in target_value
+    return value == target_value
+
+
+def value_is_not(value, target_value):
+    if isinstance(target_value, list):
+        return value not in target_value
+    return value != target_value
+
+
+show_when_validators = {
+    "": always,
+    "always": always,
+    "value_is": value_is,
+    "value_is_not": value_is_not,
+}
+
+
 class Field:
     def __init__(self, field_data):
         def _attribute(attribute_name: str):
@@ -37,6 +61,15 @@ def value(self):
     def value(self, value):
         self._value = value
 
+    def should_show(self, show_when_is, target_value):
+        always_show_validator = show_when_validators['always']
+        if not show_when_is:
+            return always_show_validator()
+        show_when_validator = show_when_validators[show_when_is]
+        if not show_when_validator:
+            return always_show_validator
+        return show_when_validator(value=self.value, target_value=target_value)
+
     @property
     def label(self):
         return self._label if self._label else self.field_id

src/collective/volto/formsupport/restapi/services/submit_form/post.py

@@ -105,7 +105,21 @@ def reply(self):
 
         errors = {}
         for field in self.fields:
-            field_errors = field.validate()
+            show_when = field.show_when_when
+            should_show = True
+            if show_when and show_when != "always":
+                target_field = [
+                    val for val in self.fields if val.id == field.show_when_when
+                ][0]
+                should_show = (
+                    target_field.should_show(
+                        show_when_is=field.show_when_is, target_value=field.show_when_to
+                    )
+                    if target_field
+                    else True
+                )
+            if should_show:
+                field_errors = field.validate()
 
             if field_errors:
                 errors[field.field_id] = field_errors