From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
cc: ilmari@ilmari.org (Dagfinn Ilmari =?utf-8?Q?Manns=C3=A5ker?=),
        Alvaro Herrera <alvherre@2ndquadrant.com>,
        Pavel Stehule <pavel.stehule@gmail.com>,
        Nikita Glukhov <n.gluhov@postgrespro.ru>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Transform for pl/perl
In-reply-to: <27213.1528475947@sss.pgh.pa.us>
References: <20180606161453.tvp4ltavlcvejmmz@alvherre.pgsql>
 <e5130c85-23da-5d11-ca74-6a050cc5fa85@2ndquadrant.com>
 <d8jlgbq66t9.fsf@dalvik.ping.uio.no> <28336.1528393969@sss.pgh.pa.us>
 <27213.1528475947@sss.pgh.pa.us>
Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Fri, 08 Jun 2018 12:39:07 -0400"
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Date: Fri, 08 Jun 2018 17:05:29 -0400
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I wrote:
> I'm inclined to think that auto-dereference is indeed a good idea,
> and am tempted to go make that change to make all this consistent.
> Comments?

Here's a draft patch for that.  I ended up only changing
plperl_sv_to_datum.  There is maybe a case for doing something
similar in plperl_return_next_internal's fn_retistuple code path,
so that you can return a reference-to-reference-to-hash there;
but I was unable to muster much enthusiasm for touching that.

			regards, tom lane


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diff --git a/src/pl/plperl/expected/plperl.out b/src/pl/plperl/expected/pl=
perl.out
index ebfba3e..d8a1ff5 100644
*** a/src/pl/plperl/expected/plperl.out
--- b/src/pl/plperl/expected/plperl.out
*************** $$ LANGUAGE plperl;
*** 763,776 ****
  SELECT text_obj();
  ERROR:  cannot convert Perl hash to non-composite type text
  CONTEXT:  PL/Perl function "text_obj"
! ----- make sure we can't return a scalar ref
  CREATE OR REPLACE FUNCTION text_scalarref() RETURNS text AS $$
  	my $str =3D 'str';
  	return \$str;
  $$ LANGUAGE plperl;
  SELECT text_scalarref();
! ERROR:  PL/Perl function must return reference to hash or array
! CONTEXT:  PL/Perl function "text_scalarref"
  -- check safe behavior when a function body is replaced during execution
  CREATE OR REPLACE FUNCTION self_modify(INTEGER) RETURNS INTEGER AS $$
     spi_exec_query('CREATE OR REPLACE FUNCTION self_modify(INTEGER) RETUR=
NS INTEGER AS \'return $_[0] * 3;\' LANGUAGE plperl;');
--- 763,779 ----
  SELECT text_obj();
  ERROR:  cannot convert Perl hash to non-composite type text
  CONTEXT:  PL/Perl function "text_obj"
! -- test looking through a scalar ref
  CREATE OR REPLACE FUNCTION text_scalarref() RETURNS text AS $$
  	my $str =3D 'str';
  	return \$str;
  $$ LANGUAGE plperl;
  SELECT text_scalarref();
!  text_scalarref =

! ----------------
!  str
! (1 row)
! =

  -- check safe behavior when a function body is replaced during execution
  CREATE OR REPLACE FUNCTION self_modify(INTEGER) RETURNS INTEGER AS $$
     spi_exec_query('CREATE OR REPLACE FUNCTION self_modify(INTEGER) RETUR=
NS INTEGER AS \'return $_[0] * 3;\' LANGUAGE plperl;');
diff --git a/src/pl/plperl/plperl.c b/src/pl/plperl/plperl.c
index 4342c02..4cfc506 100644
*** a/src/pl/plperl/plperl.c
--- b/src/pl/plperl/plperl.c
*************** plperl_sv_to_datum(SV *sv, Oid typid, in
*** 1402,1412 ****
  			return ret;
  		}
  =

! 		/* Reference, but not reference to hash or array ... */
! 		ereport(ERROR,
! 				(errcode(ERRCODE_DATATYPE_MISMATCH),
! 				 errmsg("PL/Perl function must return reference to hash or array")))=
;
! 		return (Datum) 0;		/* shut up compiler */
  	}
  	else
  	{
--- 1402,1414 ----
  			return ret;
  		}
  =

! 		/*
! 		 * If it's a reference to something else, such as a scalar, just
! 		 * recursively look through the reference.
! 		 */
! 		return plperl_sv_to_datum(SvRV(sv), typid, typmod,
! 								  fcinfo, finfo, typioparam,
! 								  isnull);
  	}
  	else
  	{
diff --git a/src/pl/plperl/sql/plperl.sql b/src/pl/plperl/sql/plperl.sql
index c36da0f..b0d950b 100644
*** a/src/pl/plperl/sql/plperl.sql
--- b/src/pl/plperl/sql/plperl.sql
*************** $$ LANGUAGE plperl;
*** 504,510 ****
  =

  SELECT text_obj();
  =

! ----- make sure we can't return a scalar ref
  CREATE OR REPLACE FUNCTION text_scalarref() RETURNS text AS $$
  	my $str =3D 'str';
  	return \$str;
--- 504,510 ----
  =

  SELECT text_obj();
  =

! -- test looking through a scalar ref
  CREATE OR REPLACE FUNCTION text_scalarref() RETURNS text AS $$
  	my $str =3D 'str';
  	return \$str;

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