fix: drop empty else branch from describer output

mdl-examples/bug-tests/304-describer-empty-else-branch.mdl

@@ -0,0 +1,57 @@
+-- ============================================================================
+-- Bug #304: Empty `else` branch emitted by DESCRIBE MICROFLOW
+-- ============================================================================
+--
+-- Symptom (before fix):
+--   `describe microflow` printed an `else` line for every IF whose false
+--   branch jumped straight to the merge point (the shape produced by an
+--   `if X then ... end if;` with no else body and a non-terminal true branch).
+--   Output looked like
+--     if $X > 0 then
+--       ...
+--     else
+--     end if;
+--   The empty else block re-parsed as a real branch, breaking
+--   describe → exec → describe fixpoint and creating cosmetic BSON drift.
+--
+-- After fix:
+--   Split traversal in cmd_microflows_show_helpers.go skips the `else`
+--   keyword when the false branch destination is the matching merge point.
+--   Explicit else bodies (with at least one activity) are still emitted.
+--
+-- Usage:
+--   mxcli exec mdl-examples/bug-tests/304-describer-empty-else-branch.mdl -p app.mpr
+--   mxcli -p app.mpr -c "describe microflow BugTest304.MF_IfWithoutElse"
+--   The output must NOT contain an `else` keyword and MUST be a fixpoint
+--   under describe → exec → describe.
+-- ============================================================================
+
+create module BugTest304;
+
+create microflow BugTest304.MF_IfWithoutElse (
+  $value: integer
+)
+begin
+  if $value > 0 then
+    log info node 'BugTest304' 'positive value';
+  end if;
+
+  log info node 'BugTest304' 'always logged';
+end;
+/
+
+-- Negative control: explicit else body MUST still be preserved.
+create microflow BugTest304.MF_IfWithElse (
+  $value: integer
+)
+returns string as $label
+begin
+  declare $label string = empty;
+
+  if $value > 0 then
+    return 'positive';
+  else
+    return 'non-positive';
+  end if;
+end;
+/

mdl/executor/cmd_microflows_show_helpers.go

@@ -531,7 +531,12 @@ func traverseFlow(
 				traverseFlowUntilMerge(ctx, trueFlow.DestinationID, mergeID, activityMap, flowsByOrigin, flowsByDest, splitMergeMap, visited, entityNames, microflowNames, lines, indent+1, sourceMap, headerLineCount, annotationsByTarget)
 			}
 
-			if falseFlow != nil {
+			// Emit the ELSE branch only if it has statements. When the false
+			// flow jumps straight to the merge (the MDL was `if X then ... end if`
+			// with no else), emitting `else` with no body produces an empty
+			// branch that normalizes away on re-parse.
+			falseHasBody := falseFlow != nil && falseFlow.DestinationID != mergeID
+			if falseHasBody {
 				*lines = append(*lines, indentStr+"else")
 				visitedFalseBranch := make(map[model.ID]bool)
 				for id := range visited {

mdl/executor/cmd_microflows_traverse_test.go

@@ -124,6 +124,62 @@ func TestTraverseFlow_IfElse(t *testing.T) {
 	}
 }
 
+// TestTraverseFlow_IfWithoutElse verifies that when the FALSE branch jumps
+// straight to the merge point (as emitted by the builder for `if X then ... end if`),
+// the describer does not print an empty `else` — the previous behavior produced
+// `if X then ... else end if;` which re-parses as an IF with an empty else body
+// that is indistinguishable from the original.
+func TestTraverseFlow_IfWithoutElse(t *testing.T) {
+	e := newTestExecutor()
+
+	activityMap := map[model.ID]microflows.MicroflowObject{
+		mkID("start"): &microflows.StartEvent{BaseMicroflowObject: mkObj("start")},
+		mkID("split"): &microflows.ExclusiveSplit{
+			BaseMicroflowObject: mkObj("split"),
+			SplitCondition:      &microflows.ExpressionSplitCondition{Expression: "$x > 0"},
+		},
+		mkID("true_act"): &microflows.ActionActivity{
+			BaseActivity: microflows.BaseActivity{BaseMicroflowObject: mkObj("true_act")},
+			Action:       &microflows.LogMessageAction{LogLevel: "Info", LogNodeName: "'App'", MessageTemplate: &model.Text{Translations: map[string]string{"en_US": "positive"}}},
+		},
+		mkID("merge"): &microflows.ExclusiveMerge{BaseMicroflowObject: mkObj("merge")},
+		mkID("end"):   &microflows.EndEvent{BaseMicroflowObject: mkObj("end")},
+	}
+
+	flowsByOrigin := map[model.ID][]*microflows.SequenceFlow{
+		mkID("start"): {mkFlow("start", "split")},
+		mkID("split"): {
+			mkBranchFlow("split", "true_act", &microflows.ExpressionCase{Expression: "true"}),
+			mkBranchFlow("split", "merge", &microflows.ExpressionCase{Expression: "false"}),
+		},
+		mkID("true_act"): {mkFlow("true_act", "merge")},
+		mkID("merge"):    {mkFlow("merge", "end")},
+	}
+
+	splitMergeMap := map[model.ID]model.ID{
+		mkID("split"): mkID("merge"),
+	}
+
+	var lines []string
+	visited := make(map[model.ID]bool)
+	e.traverseFlow(mkID("start"), activityMap, flowsByOrigin, splitMergeMap, visited, nil, nil, &lines, 1, nil, 0, nil)
+
+	for _, line := range lines {
+		if contains(line, "else") {
+			t.Errorf("expected no else branch in output, got: %v", lines)
+		}
+	}
+	foundENDIF := false
+	for _, line := range lines {
+		if contains(line, "end if;") {
+			foundENDIF = true
+		}
+	}
+	if !foundENDIF {
+		t.Errorf("expected end if in output: %v", lines)
+	}
+}
+
 // =============================================================================
 // collectErrorHandlerStatements
 // =============================================================================