execute round trip negates a decision and swaps its outcomes #1742

mxcli: v0.29.0 (2026-10-30) · Mendix: 11.12.4 (also seen on 10.24.11)

Summary

When a decision's true branch has no activities and its false branch does,
DESCRIBE MICROFLOW renders it as if not(<condition>) then <false branch> end if;.
Executing that description stores the decision literally as not(<condition>) with the
true/false outcomes swapped. Behaviour is unchanged, but the model is changed: a different
expression and swapped outcome labels in Studio Pro. So describe → execute is not a
round trip for this shape.

Steps to reproduce

1. Create the flow (true branch empty, false branch sets $Valid = false):

mdl 1;
create microflow SourceExamplesModule.Repro_DecisionNegation ($Value: String)
returns Boolean
begin
declare $Valid Boolean = true;
@caption 'Value filled?'
if $Value != empty then
else
set $Valid = false;
end if;
return $Valid;
end;

2. DESCRIBE MICROFLOW SourceExamplesModule.Repro_DecisionNegation gives (layout lines omitted):

if not($Value != empty) then
set $Valid = false;
end if;

3. Execute that description unchanged under a new name
   (SourceExamplesModule.Repro_DecisionNegation_RoundTrip).

Result (mxcli bson dump)

Expected

The round-tripped flow stores the decision as $Value != empty with the original
outcomes. For example, DESCRIBE could emit if <condition> then else <branch> end if;
(the form step 1 accepts), or execution could normalise not(...) with a then-only branch
back to the original orientation.

Impact

Conversion scripts generated from DESCRIBE output rewrite every such decision. In one app
this turned all five validation decisions of a single microflow into not(...) with
swapped outcomes. It also occurs in the Marketplace module FeedbackModule.VAL_Feedback
(3 decisions described as if not(...)).