prevent panic on triggers with declare statements

enginetest/queries/trigger_queries.go

@@ -2204,6 +2204,23 @@ INSERT INTO t0 (v1, v2) VALUES (i, s); END;`,
 			},
 		},
 	},
+
+	{
+		Name: "delete me",
+		SetUpScript: []string{
+			"create table t (i int primary key);",
+		},
+		Assertions: []ScriptTestAssertion{
+			{
+				Query:       "create trigger trig1 before insert on t for each row begin declare x int; select new.i + 10 into x; set new.i = x; end;",
+				ExpectedErr: sql.ErrUnsupportedFeature,
+			},
+			{
+				Query:       "create trigger trig2 before insert on t for each row begin declare x int; set x = new.i * 10; set new.i = x; end;",
+				ExpectedErr: sql.ErrUnsupportedFeature,
+			},
+		},
+	},
 }
 
 // RollbackTriggerTests are trigger tests that require rollback logic to work correctly

sql/expression/procedurereference.go

@@ -60,6 +60,9 @@ type ProcedureReferencable interface {
 
 // InitializeVariable sets the initial value for the variable.
 func (ppr *ProcedureReference) InitializeVariable(name string, sqlType sql.Type, val interface{}) error {
+	if ppr == nil || ppr.InnermostScope == nil {
+		return fmt.Errorf("cannot initialize variable `%s` in an empty procedure reference", name)
+	}
 	convertedVal, _, err := sqlType.Convert(val)
 	if err != nil {
 		return err
@@ -271,7 +274,11 @@ var _ sql.CollationCoercible = (*ProcedureParam)(nil)
 
 // NewProcedureParam creates a new ProcedureParam expression.
 func NewProcedureParam(name string, typ sql.Type) *ProcedureParam {
-	return &ProcedureParam{name: strings.ToLower(name), typ: typ}
+	return &ProcedureParam{
+		name: strings.ToLower(name),
+		typ:  typ,
+		//pRef: NewProcedureReference(),
+	}
 }
 
 // Children implements the sql.Expression interface.

sql/planbuilder/create_ddl.go

@@ -108,6 +108,16 @@ func (b *Builder) buildCreateTrigger(inScope *scope, query string, c *ast.DDL) (
 		}
 	}
 
+	// TODO: https://github.com/dolthub/dolt/issues/7720
+	if block, isBEBlock := bodyScope.node.(*plan.BeginEndBlock); isBEBlock {
+		for _, child := range block.Children() {
+			if _, ok := child.(*plan.DeclareVariables); ok {
+				err := sql.ErrUnsupportedFeature.New("DECLARE in BEGIN END block")
+				b.handleErr(err)
+			}
+		}
+	}
+
 	outScope.node = plan.NewCreateTrigger(
 		db,
 		c.TriggerSpec.TrigName.Name.String(),