fix declare cursors in triggers (#2865)

Author: jycor

enginetest/queries/trigger_queries.go

@@ -3389,6 +3389,38 @@ for each row
 			},
 		},
 	},
+
+	{
+		Name: "trigger with cursor",
+		SetUpScript: []string{
+			"create table t1 (i int, j int);",
+			"insert into t1 values (1, 2);",
+			"create table t2 (i int, j int);",
+			`
+create trigger trig before insert on t2
+for each row
+begin
+  declare v1 int;
+  declare cur cursor for select i from t1;
+  open cur;
+  fetch cur into v1;
+  set new.j = v1;
+end;
+`,
+		},
+		Assertions: []ScriptTestAssertion{
+			{
+				Query: "insert into t2 values (1, 0);",
+				Expected: []sql.Row{
+					{types.NewOkResult(1)},
+				},
+			},
+			{
+				Query:    "select * from t2;",
+				Expected: []sql.Row{{1, 1}},
+			},
+		},
+	},
 }
 
 var TriggerCreateInSubroutineTests = []ScriptTest{

sql/analyzer/triggers.go

@@ -339,7 +339,12 @@ func applyTrigger(ctx *sql.Context, a *Analyzer, originalNode, n sql.Node, scope
 				}
 				return n.WithSource(newSource), transform.NewTree, nil
 			case expression.ProcedureReferencable:
-				return n.WithParamReference(pRef), transform.NewTree, nil
+				newParamRef := n.WithParamReference(pRef)
+				newNode, _, err := transform.NodeWithOpaque(newParamRef, assignProcRef)
+				if err != nil {
+					return nil, transform.SameTree, err
+				}
+				return newNode, transform.NewTree, nil
 			default:
 				return assignProcRef(node)
 			}

sql/rowexec/dml_iters.go

@@ -193,7 +193,7 @@ func prependRowInPlanForTriggerExecution(row sql.Row) func(c transform.Context)
 		case *plan.Project:
 			// Only prepend rows for projects that aren't the input to inserts and other triggers
 			switch c.Parent.(type) {
-			case *plan.InsertInto, *plan.Into, *plan.TriggerExecutor:
+			case *plan.InsertInto, *plan.Into, *plan.TriggerExecutor, *plan.DeclareCursor:
 				return n, transform.SameTree, nil
 			default:
 				return plan.NewPrependNode(n, row), transform.NewTree, nil