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plpgsql unreachable code (was BUG #1329: Bug in IF-ELSEIF-ELSE construct)

From: Neil Conway <neilc(at)samurai(dot)com>
To: PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Rico Wind <rw(at)rico-wind(dot)dk>,pgsql-bugs(at)postgresql(dot)org
Subject: plpgsql unreachable code (was BUG #1329: Bug in IF-ELSEIF-ELSE construct)
Date: 2004-11-27 13:56:31
Message-ID: 41A8878F.3020808@samurai.com (view raw or flat)
Thread:
Lists: pgsql-bugspgsql-patches
Neil Conway wrote:
> (BTW, another thing this example exposes is that we don't issue warnings 
> about trivially-dead-code, such as statements in a basic block that 
> follow a RETURN. This would probably be also worth doing.)

Attached is a patch that implements this. Specifically, if there are any 
statements in the same block that follow a RETURN, EXIT (without 
condition) or RAISE EXCEPTION statement, we issue a warning at CREATE 
FUNCTION time:

create function exit_warn() returns int as $$
declare x int;
begin
     x := 5;
     loop
         x := x + 1;
         exit;
         x := x + 2;
     end loop;
     x := x + 3;
     return x;
end;$$ language 'plpgsql';
WARNING:  assignment is unreachable, due to exit near line 6
CONTEXT:  compile of PL/pgSQL function "exit_warn" near line 7

No warning is issued if check_function_bodies is false.

AFAICS there is no current infrastructure for walking a PL/PgSQL 
function's parse tree, so I did this manually (which is easy enough, of 
course). In the future it might be a good idea to refactor this to use 
something akin to the "walker" infrastructure in the backend (for one 
thing the PL/PgSQL function dumping code could use this as well).

(BTW this patch is intended for 8.1, of course.)

-Neil

Attachment: plpgsql-unreachable-1.patch
Description: text/plain (10.8 KB)

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