Re: Clobbered parameter names via DECLARE in PL/PgSQL

2012/4/15 Brendan Jurd <direvus(at)gmail(dot)com>:
> Hello hackers,
>
> It turns out that in a PL/PgSQL function, you can DECLARE a variable
> using the same name as one of the function parameters.  This has the
> effect of clobbering the parameter, for example:
>
> CREATE OR REPLACE FUNCTION declare_clobber(foo int)
> RETURNS int LANGUAGE plpgsql AS $$
>        DECLARE
>                foo text;
>        BEGIN
>                RETURN foo;
>        END;
> $$;
>
> SELECT declare_clobber(1);
> ==> NULL
>
> On the other hand, PL/PgSQL does protect against duplicate definitions
> within DECLARE:
>
> CREATE OR REPLACE FUNCTION declare_clobber(foo int)
> RETURNS int LANGUAGE plpgsql AS $$
>        DECLARE
>                foo int;
>                foo text;
>        BEGIN
>                RETURN foo;
>        END;
> $$;
> ==> ERROR:  duplicate declaration at or near "foo"
>
> And it also protects against using a DECLAREd name as a parameter alias:
>
> CREATE OR REPLACE FUNCTION declare_clobber(foo int)
> RETURNS int LANGUAGE plpgsql AS $$
>        DECLARE
>                bar int;
>                bar ALIAS FOR $1;
>        BEGIN
>                RETURN bar;
>        END;
> $$;
> ==> ERROR:  duplicate declaration at or near "bar"
>
> I would suggest that if the user DECLAREs a variable with the same
> name as a parameter, it is very evidently a programming error, and we
> should raise the same "duplicate declaration" error.  I haven't yet
> looked at how difficult this would be to fix, but if there are no
> objections I would like to attempt a patch.
>

I disagree - variables and parameters are in different namespace so
you can exactly identify variable and parameter. More - it is
compatibility break.

If plpgsql_check_function exists, then this check can be implemented
as warning.

Regards

Pavel

> Cheers,
> BJ
>
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