fix: trim empty top-level else branches

Symptom: describe could emit an empty top-level `else` when the false branch pointed at a continuation that had already been emitted while traversing the true branch. Re-executing the MDL removed that empty branch, leaving a roundtrip mismatch.

Root cause: top-level IF traversal decided whether to emit `else` only by comparing `falseFlow.DestinationID` to the selected merge. That misses cases where the false destination is not the merge but traversal still emits no statements because the continuation is already visited.

Fix: mirror nested IF traversal: emit the `else` line tentatively, traverse the false branch, and remove the line again if the traversal produced no statements.

Tests: added a synthetic traversal regression test; `go test ./mdl/executor -run 'TopLevelIfRemovesEmptyElse|SequentialIfWithoutElse' -v`; `make build`; `make lint-go`; `make test`.

Author: hjothamendix

mdl/executor/cmd_microflows_show_helpers.go

@@ -724,18 +724,20 @@ func traverseFlow(
 				traverseFlowUntilMerge(ctx, trueFlow.DestinationID, mergeID, activityMap, flowsByOrigin, flowsByDest, splitMergeMap, visited, entityNames, microflowNames, lines, indent+1, sourceMap, headerLineCount, annotationsByTarget)
 			}
 
-			// 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 {
+			if falseFlow != nil {
+				elseLineIdx := len(*lines)
 				*lines = append(*lines, indentStr+"else")
 				visitedFalseBranch := make(map[model.ID]bool)
 				for id := range visited {
 					visitedFalseBranch[id] = true
 				}
 				traverseFlowUntilMerge(ctx, falseFlow.DestinationID, mergeID, activityMap, flowsByOrigin, flowsByDest, splitMergeMap, visitedFalseBranch, entityNames, microflowNames, lines, indent+1, sourceMap, headerLineCount, annotationsByTarget)
+				// Remove empty else block. A false branch can point at a
+				// continuation already emitted through the true branch, so checking
+				// only falseFlow.DestinationID != mergeID is not enough.
+				if len(*lines) == elseLineIdx+1 {
+					*lines = (*lines)[:elseLineIdx]
+				}
 			}
 
 			*lines = append(*lines, indentStr+"end if;")

mdl/executor/cmd_microflows_traverse_test.go

@@ -561,6 +561,63 @@ func TestTraverseFlow_SequentialIfWithoutElseKeepsContinuationOutsideFirstIf(t *
 	}
 }
 
+func TestTraverseFlow_TopLevelIfRemovesEmptyElseAfterVisitedContinuation(t *testing.T) {
+	e := newTestExecutor()
+
+	logAction := func(id, message string) *microflows.ActionActivity {
+		return &microflows.ActionActivity{
+			BaseActivity: microflows.BaseActivity{BaseMicroflowObject: mkObj(id)},
+			Action: &microflows.LogMessageAction{
+				LogLevel:        "Info",
+				LogNodeName:     "'Synthetic'",
+				MessageTemplate: &model.Text{Translations: map[string]string{"en_US": message}},
+			},
+		}
+	}
+
+	activityMap := map[model.ID]microflows.MicroflowObject{
+		mkID("start"): &microflows.StartEvent{BaseMicroflowObject: mkObj("start")},
+		mkID("outer_split"): &microflows.ExclusiveSplit{
+			BaseMicroflowObject: mkObj("outer_split"),
+			SplitCondition:      &microflows.ExpressionSplitCondition{Expression: "$UseNestedPath"},
+		},
+		mkID("inner_split"): &microflows.ExclusiveSplit{
+			BaseMicroflowObject: mkObj("inner_split"),
+			SplitCondition:      &microflows.ExpressionSplitCondition{Expression: "$HasContinuation"},
+		},
+		mkID("inner_return"): &microflows.EndEvent{BaseMicroflowObject: mkObj("inner_return")},
+		mkID("tail_log"):     logAction("tail_log", "shared tail"),
+		mkID("end"):          &microflows.EndEvent{BaseMicroflowObject: mkObj("end")},
+	}
+	flowsByOrigin := map[model.ID][]*microflows.SequenceFlow{
+		mkID("start"): {mkFlow("start", "outer_split")},
+		mkID("outer_split"): {
+			mkBranchFlow("outer_split", "inner_split", &microflows.ExpressionCase{Expression: "true"}),
+			mkBranchFlow("outer_split", "tail_log", &microflows.ExpressionCase{Expression: "false"}),
+		},
+		mkID("inner_split"): {
+			mkBranchFlow("inner_split", "tail_log", &microflows.ExpressionCase{Expression: "true"}),
+			mkBranchFlow("inner_split", "inner_return", &microflows.ExpressionCase{Expression: "false"}),
+		},
+		mkID("tail_log"): {mkFlow("tail_log", "end")},
+	}
+
+	splitMergeMap := map[model.ID]model.ID{
+		mkID("outer_split"): mkID("end"),
+		mkID("inner_split"): mkID("tail_log"),
+	}
+	var lines []string
+	e.traverseFlow(mkID("start"), activityMap, flowsByOrigin, splitMergeMap, make(map[model.ID]bool), nil, nil, &lines, 0, nil, 0, nil)
+
+	out := strings.Join(lines, "\n")
+	if strings.Contains(out, "\nelse\nend if;") {
+		t.Fatalf("empty top-level else should be removed:\n%s", out)
+	}
+	if got := strings.Count(out, "shared tail"); got != 1 {
+		t.Fatalf("shared tail emitted %d times, want once:\n%s", got, out)
+	}
+}
+
 func TestTraverseFlow_GuardBranchWithMultipleActivitiesKeepsContinuationOutsideElse(t *testing.T) {
 	e := newTestExecutor()