BUG #18403: PL/pgSQL is reporting unexpected errors when processing DECLARE blocks with <<label>>

On Wednesday, March 20, 2024, PG Bug reporting form <noreply(at)postgresql(dot)org>
wrote:

> The following bug has been logged on the website:
>
> Bug reference: 18403
> Logged by: Jiangshan Liu
> Email address: jiangshan(dot)liu(at)tju(dot)edu(dot)cn
> PostgreSQL version: 15.2
> Operating system: Ubuntu
> Description:
>
> Hi, I think PL/pgSQL is reporting unexpected errors when dealing with
> DECLARE blocks paired with <<label>>.
> I have approximated the program to a clean situation. When I execute this
> program, the PL/pgSQL engine does not report errors to me:
>
> DO $$
> DECLARE
> DECLARE
> var1 INT = 1;
> BEGIN
> RAISE NOTICE '%', var1;
> END;
> $$;

The failure to report an error here seems contrary to the documentation.
When the end of the DO text is reached and only a single begin/end pair is
seen the parser is being loose in being OK that one of the declares was not
associated with a full block.

David J.