CONTAINER Action: nanoflow does not support explicit parameter binding — CE1571

[acarum]

When a CONTAINER widget inside a DataGrid 2 controlbar has Action: nanoflow Module.NF, and that nanoflow declares a required entity parameter, Mendix raises CE1571 ("No argument has been selected for parameter") because there
is no MDL syntax to pass the datagrid's selection context into the nanoflow through a container action.

Environment

• Mendix: 11.12.0
• mxcli: local binary (.0.21.0)
• Widget: DataGrid 2 (datagrid) controlbar, CONTAINER with Action: nanoflow

Steps to Reproduce

1. Create a nanoflow with an entity parameter:
   CREATE OR MODIFY NANOFLOW CustomModule.ACT_UnLinkMaterialDefinition_NF (
   $LogisticWhitelist: CustomModule.LogisticWhitelist
   )
   BEGIN
   -- ... uses $LogisticWhitelist
   END;
   /

2. Reference it from a container inside a datagrid controlbar:
   datagrid dgMaterials (
   DataSource: database from CustomModule.LogisticWhitelist where [...],
   Selection: Single
   ) {
   -- Context: $currentObject (CustomModule.LogisticWhitelist), $dgMaterials (selection)
   controlbar controlBar1 {
   container containerUnlinkMat (
   Class: 'command',
   Action: nanoflow CustomModule.ACT_UnLinkMaterialDefinition_NF
   ) {
   actionbutton btnUnlink (Caption: 'Unlink', Icon: 'Atlas_Core.Atlas_Filled.trash-can')
   }
   }
   }

3. Run mx check:
   [error] [CE1571] "No argument has been selected for parameter 'LogisticWhitelist'
   and no default is available. Please select an argument manually."
   at Container 'containerUnlinkMat'

Root Cause

The CONTAINER widget's Action: clause in MDL does not support explicit parameter binding. It accepts only Action: nanoflow Module.NF (no argument list). This means there is no way in MDL to pass $currentObject or the datagrid
selection variable ($dgMaterials) to a parameterised nanoflow via a container action.

In contrast, ACTIONBUTTON supports explicit binding:
actionbutton btnUnlink (
Caption: 'Unlink',
Action: nanoflow CustomModule.ACT_UnLinkMaterialDefinition_NF ($LogisticWhitelist = $dgMaterials)
)
This compiles and runs correctly.

The DESCRIBE output confirms the datagrid exposes the selection context:
-- Context: $currentObject (CustomModule.LogisticWhitelist), $dgMaterials (selection)
Both $currentObject and $dgMaterials are in scope, but neither can be forwarded through a CONTAINER action.

Expected Behaviour

Either:

• Option A: MDL should support explicit parameter binding on CONTAINER Action: nanoflow, e.g.:
  Action: nanoflow Module.NF ($Param = $dgMaterials)
• Option B: When the nanoflow has exactly one parameter whose type matches $currentObject's type, the runtime should automatically bind it — consistent with how Studio Pro resolves context in containers.

Actual Behaviour

CE1571 at build time. The only workaround is to replace the CONTAINER with an ACTIONBUTTON with an explicit ($Param = $dgWidgetName) binding — which changes the visual rendering (command-style container pattern cannot be
used).