fix: preserve commit error handling through describe/exec/describe

mdl-examples/bug-tests/308-commit-on-error-rollback-roundtrip.mdl

@@ -0,0 +1,53 @@
+-- ============================================================================
+-- Bug #308: `commit ... on error rollback` lost during describe → exec → describe
+-- ============================================================================
+--
+-- Symptom (before fix):
+--   Authoring `commit $X on error rollback;` and then re-executing the
+--   describe output silently dropped the `on error rollback` clause —
+--   subsequent describes printed plain `commit $X;`. In Studio Pro the
+--   "Action call action" still showed Rollback, but mxcli's view of the
+--   model diverged from the BSON, so any further mutation could mis-write
+--   the field.
+--
+-- Root cause:
+--   The commit writer omitted `ErrorHandlingType` when its value was
+--   Rollback (treating Rollback as implicit). The parser then left the
+--   absent field as the empty string, so the describer printed `commit $X`
+--   without a clause.
+--
+-- After fix:
+--   Parser defaults absent commit `ErrorHandlingType` to Rollback; the
+--   writer always emits the field, defaulting to Rollback. The behaviour
+--   is symmetric and round-trips cleanly.
+--
+-- Usage:
+--   mxcli exec mdl-examples/bug-tests/308-commit-on-error-rollback-roundtrip.mdl -p app.mpr
+--   mxcli -p app.mpr -c "describe microflow BugTest308.MF_CommitRollback"
+--   The output must contain `on error rollback` and must be a fixpoint
+--   under describe → exec → describe.
+-- ============================================================================
+
+create module BugTest308;
+
+create entity BugTest308.Item (
+  Name : string(100)
+);
+/
+
+create microflow BugTest308.MF_CommitRollback (
+  $Item: BugTest308.Item
+)
+begin
+  commit $Item on error rollback;
+end;
+/
+
+-- Negative control: explicit `on error continue` must survive equally.
+create microflow BugTest308.MF_CommitContinue (
+  $Item: BugTest308.Item
+)
+begin
+  commit $Item on error continue;
+end;
+/

sdk/mpr/parser_microflow.go

@@ -714,8 +714,9 @@ func parseCommitAction(raw map[string]any) *microflows.CommitObjectsAction {
 	action.CommitVariable = extractString(raw["CommitVariableName"])
 	action.WithEvents = extractBool(raw["WithEvents"], false)
 	action.RefreshInClient = extractBool(raw["RefreshInClient"], false)
-	if errType, ok := raw["ErrorHandlingType"].(string); ok {
-		action.ErrorHandlingType = microflows.ErrorHandlingType(errType)
+	action.ErrorHandlingType = microflows.ErrorHandlingType(extractString(raw["ErrorHandlingType"]))
+	if action.ErrorHandlingType == "" {
+		action.ErrorHandlingType = microflows.ErrorHandlingTypeRollback
 	}
 	return action
 }

sdk/mpr/parser_microflow_test.go

@@ -47,3 +47,37 @@ func TestParseSequenceFlow_NewCaseValueNoCase(t *testing.T) {
 		t.Fatalf("expected *NoCase, got %T", flow.CaseValue)
 	}
 }
+
+func TestParseCommitAction_ErrorHandlingTypeExplicit(t *testing.T) {
+	action := parseCommitAction(map[string]any{
+		"$ID":                "commit-1",
+		"CommitVariableName": "Order",
+		"WithEvents":         true,
+		"RefreshInClient":    false,
+		"ErrorHandlingType":  "Continue",
+	})
+
+	if action.ErrorHandlingType != microflows.ErrorHandlingTypeContinue {
+		t.Errorf("expected Continue, got %q", action.ErrorHandlingType)
+	}
+	if action.CommitVariable != "Order" {
+		t.Errorf("expected CommitVariable Order, got %q", action.CommitVariable)
+	}
+}
+
+func TestParseCommitAction_ErrorHandlingTypeDefaultsToRollback(t *testing.T) {
+	// When ErrorHandlingType is absent from BSON, the describer must still
+	// emit "on error rollback" — matching Mendix Studio Pro's default.
+	// Without this default, describe → exec → describe drops the suffix
+	// because the writer omits the field when it equals Rollback.
+	action := parseCommitAction(map[string]any{
+		"$ID":                "commit-1",
+		"CommitVariableName": "Order",
+		"WithEvents":         false,
+		"RefreshInClient":    false,
+	})
+
+	if action.ErrorHandlingType != microflows.ErrorHandlingTypeRollback {
+		t.Errorf("expected default Rollback, got %q", action.ErrorHandlingType)
+	}
+}

sdk/mpr/writer_microflow_actions.go

@@ -126,17 +126,14 @@ func serializeMicroflowAction(action microflows.MicroflowAction) bson.D {
 		return doc
 
 	case *microflows.CommitObjectsAction:
-		doc := bson.D{
+		return bson.D{
 			{Key: "$ID", Value: idToBsonBinary(string(a.ID))},
 			{Key: "$Type", Value: "Microflows$CommitAction"},
 			{Key: "CommitVariableName", Value: a.CommitVariable},
+			{Key: "ErrorHandlingType", Value: stringOrDefault(string(a.ErrorHandlingType), "Rollback")},
+			{Key: "RefreshInClient", Value: a.RefreshInClient},
+			{Key: "WithEvents", Value: a.WithEvents},
 		}
-		if a.ErrorHandlingType != "" && a.ErrorHandlingType != microflows.ErrorHandlingTypeRollback {
-			doc = append(doc, bson.E{Key: "ErrorHandlingType", Value: string(a.ErrorHandlingType)})
-		}
-		doc = append(doc, bson.E{Key: "RefreshInClient", Value: a.RefreshInClient})
-		doc = append(doc, bson.E{Key: "WithEvents", Value: a.WithEvents})
-		return doc
 
 	case *microflows.DeleteObjectAction:
 		return bson.D{