Pluggable object-list properties (FileUploader allowedFileFormats / customButtons): multi-key entries unparseable, single-key entries pass check+exec then are SILENTLY DROPPED

[MohamedGamalEzzatAli]

mxcli version: v0.20.0 (release 2026-08-28) · Mendix 11.12.1 bench project, FileUploader .mpk present (widget defs derive fine — scaffolding works)

FileUploader declares repeatable object properties in its widget XML — allowedFileFormats (children: configMode, predefinedType, mimeType, extensions, …) and customButtons (children: buttonCaption, buttonIcon, buttonActionFile, …). MDL has no working surface for them, and the failure mode splits into a parse error and a silent drop:

Repro A — multi-key entry: unparseable

CREATE OR REPLACE PAGE MyModule.UploadPage (Layout: Atlas_Core.Atlas_Default) {
  PLUGGABLEWIDGET 'com.mendix.widget.web.fileuploader.FileUploader' fileUploader1 (maxFileSize: 25, allowedFileFormats: [(configMode: simple, predefinedType: pdfFile)])
};

Syntax errors found:
  - line 2:140 missing ')' at ','
  - line 2:165 extraneous input ')' expecting {',', ']'}

(Adjacent-parens variant [(configMode: simple) (predefinedType: pdfFile)] also fails: mismatched input '(' expecting {',', ']'}.)

Repro B — single-key entry: parses, execs, silently dropped

CREATE OR REPLACE PAGE MyModule.UploadPage (Layout: Atlas_Core.Atlas_Default) {
  PLUGGABLEWIDGET 'com.mendix.widget.web.fileuploader.FileUploader' fileUploader1 (allowedFileFormats: [(configMode: simple)])
};

mxcli check → ✓ Syntax OK (1 statements)
mxcli exec  → Replaced page MyModule.UploadPage

Then:

mxcli describe page MyModule.UploadPage --format mdl  → no allowedFileFormats anywhere
mxcli describe page MyModule.UploadPage --format json | grep -c allowedFileFormats  → 0

The property vanishes without any warning — check-clean, exec-success, zero trace in storage.

(The map-style form allowedFileFormats: ['configMode': 'simple'] also parses; not exec-probed further.)

Control — scalar pluggable props are fine

maxFileSize: 20 at CREATE-level and SET 'maxFileSize' = 25 ON fileUploader1 via ALTER both land and round-trip in describe. The gap is specifically the object-list (repeatable object) property type.

Impact

This is the check/exec-pass-then-discard class (#852's family): a script that lints and applies cleanly leaves the widget missing required configuration with no signal. For FileUploader specifically, allowedFileFormats is how upload restrictions are enforced — a silently-dropped restriction is a correctness and mild security issue for the generated app.

Expected

Either a real grammar + writer for object-list entries (multi-key [(k: v, k: v), (…)] storing Object.Properties[] children), or a hard parse/exec error — anything but silent success.