File Uploader: an `allowedfileformat` in `configMode: 'simple'` passes check and exec, then fails `mx check` with CE0463 — hidden TextTemplates inside object-list items are never nulled

[MendixMau]

Environment: mxcli v0.24.0 (2026-09-24T05:44:35Z), same result on v0.23.0. Mendix 11.12.2 (mx check from mxbuild 11.12.2). Widget: Mendix File Uploader 2.5.0 (com.mendix.widget.web.FileUploader.mpk, taken from the Marketplace module package). Fresh app from mxcli new App --version 11.12.2, macOS. Upstream main at d3adfa43 has no changes to mdl/backend/widgetobj/ since v0.24.0.

Summary: An allowedfileformat item in the widget's default configMode: 'simple' (with predefinedType) is accepted by mxcli check and written by exec with 0 errors, but mx check then reports CE0463 "The definition of this widget has changed". The same widget with every item in configMode: 'advanced' is 0 errors, and uploads work end to end at runtime, so the widget and module setup are fine. Only the simple-mode item triggers it.

Steps to reproduce

1. mxcli new App --version 11.12.2, copy com.mendix.widget.web.FileUploader.mpk (2.5.0) into widgets/, run mxcli widget init -p App.mpr.
2. Create a context entity, a System.FileDocument specialisation with a reference to it, a create microflow (createFileAction) and a delete microflow (onUploadFailureFile), with grants.
3. Put this uploader in a dataview on the context entity:

fileuploader "upFiles" (
  uploadMode: 'files',
  associatedFiles: association $currentObject/Uploads.Attachment_UploadRequest,
  readOnlyMode: false,
  createFileAction: microflow Uploads.ACT_CreateAttachment,
  onUploadFailureFile: microflow Uploads.ACT_DeleteAttachment,
  maxFileSize: 5,
  objectCreationTimeout: 10,
  enableCustomButtons: false
) {
  allowedfileformat "fmtTxt" (configMode: 'simple', predefinedType: 'plainTextFile')
  allowedfileformat "fmtZip" (configMode: 'advanced', mimeType: 'application/zip', extensions: '.zip', typeFormatDescription: 'ZIP archive')
}

4. mxcli exec the page, then mx check App.mpr.

Actual

$ mxcli exec 02-simple-mode.mdl -p App.mpr
1 issues: 0 errors, 1 warnings, 0 info        (the warning is MPR010, layout grid, unrelated)
Replaced page Uploads.UploadRequest_NewEdit
$ mx check App.mpr
[error] [CE0463] "The definition of this widget has changed. Update this widget by right-clicking it and selecting 'Update widget', or select 'Update all widgets' to update all widgets in the app." at File uploader 'upFiles'
The app contains: 1 errors.

Expected: 0 errors, as with fmtTxt written as configMode: 'advanced', mimeType: 'text/plain', extensions: '.txt', typeFormatDescription: 'Text file' (that variant: The app contains: 0 errors.).

Cause (from reading main): the File Uploader's editorConfig hides the item's typeFormatDescription (a TextTemplate), via hideNestedPropertiesIn(..., "allowedFileFormats", n, ["mimeType","extensions","typeFormatDescription"]), when configMode is simple. editorconfig_extract.go does extract that rule with ListPropertyKey: "allowedFileFormats". But ApplyVisibilityRules (mdl/backend/widgetobj/builder.go) only looks rules up in the widget's top-level propertyTypeIDs and never reads ListPropertyKey. So a hidden TextTemplate inside an object-list item keeps its default-filled ClientTemplate, where the type definition expects null. It is the #574 nulling, not yet applied one level down.

Suggested fixes, ranked

1. In ApplyVisibilityRules (or a sibling called from the object-list item build), apply rules with ListPropertyKey set per item: evaluate the rule's condition against that item's own primitive values (configMode), and null the item's hidden TextTemplate. We verified locally that writing null for the hidden typeFormatDescription gives mx check 0 errors and a working upload (the predefined type reaches the widget at runtime: the rejection message names "Plain Text (.txt)").
2. At minimum, have check/exec warn when an object-list item sets a configMode whose nested visibility rules are not applied, so the CE0463 is not a surprise at mx check.

Workaround: write every format as configMode: 'advanced' with mimeType, extensions and typeFormatDescription.

Retest: steps 1–4 on a fresh app. Pass = mx check says The app contains: 0 errors. with the simple-mode item in place.

Related: #574 (top-level conditional visibility, closed), #999 (object-list item parsing for this widget, closed).

[MendixMau]

Companion issue with the same widget but a different root cause: #1199 (DESCRIBE → exec round trip).