Fix up Perl-to-Postgres datatype conversions in pl/perl.

This patch restores the pre-9.1 behavior that pl/perl functions returning
VOID ignore the result value of their last Perl statement.  9.1.0
unintentionally threw an error if the last statement returned a reference,
as reported by Amit Khandekar.

Also, make sure it works to return a string value for a composite type,
so long as the string meets the type's input format.  We already allowed
the equivalent behavior for arrays, so it seems inconsistent to not allow
it for composites.

In addition, ensure we throw errors for attempts to return arrays or hashes
when the function's declared result type is not an array or composite type,
respectively.  Pre-9.1 versions rather uselessly returned strings like
ARRAY(0x221a9a0) or HASH(0x221aa90), while 9.1.0 threw an error for the
hash case and returned a garbage value for the array case.

Also, clean up assorted grotty coding in Perl array conversion, including
use of a session-lifespan memory context to accumulate the array value
(resulting in session-lifespan memory leak on error), failure to apply the
declared typmod if any, and failure to detect some cases of non-rectangular
multi-dimensional arrays.

Alex Hunsaker and Tom Lane

src/pl/plperl/sql/plperl.sql

@@ -50,6 +50,13 @@ $$ LANGUAGE plperl;
 SELECT perl_row();
 SELECT * FROM perl_row();
 
+-- test returning a composite literal
+CREATE OR REPLACE FUNCTION perl_row_lit() RETURNS testrowperl AS $$
+    return '(1,hello,world,"({{1}})")';
+$$ LANGUAGE plperl;
+
+SELECT perl_row_lit();
+
 
 CREATE OR REPLACE FUNCTION perl_set() RETURNS SETOF testrowperl AS $$
     return undef;
@@ -415,3 +422,43 @@ DO $do$ use strict; my $name = "foo"; my $ref = $$name; $do$ LANGUAGE plperl;
 -- check that we can "use warnings" (in this case to turn a warn into an error)
 -- yields "ERROR:  Useless use of sort in scalar context."
 DO $do$ use warnings FATAL => qw(void) ; my @y; my $x = sort @y; 1; $do$ LANGUAGE plperl;
+
+-- make sure functions marked as VOID without an explicit return work
+CREATE OR REPLACE FUNCTION myfuncs() RETURNS void AS $$
+   $_SHARED{myquote} = sub {
+       my $arg = shift;
+       $arg =~ s/(['\\])/\\$1/g;
+       return "'$arg'";
+   };
+$$ LANGUAGE plperl;
+
+SELECT myfuncs();
+
+-- make sure we can't return an array as a scalar
+CREATE OR REPLACE FUNCTION text_arrayref() RETURNS text AS $$
+	return ['array'];
+$$ LANGUAGE plperl;
+
+SELECT text_arrayref();
+
+--- make sure we can't return a hash as a scalar
+CREATE OR REPLACE FUNCTION text_hashref() RETURNS text AS $$
+	return {'hash'=>1};
+$$ LANGUAGE plperl;
+
+SELECT text_hashref();
+
+---- make sure we can't return a blessed object as a scalar
+CREATE OR REPLACE FUNCTION text_obj() RETURNS text AS $$
+	return bless({}, 'Fake::Object');
+$$ LANGUAGE plperl;
+
+SELECT text_obj();
+
+----- make sure we can't return a scalar ref
+CREATE OR REPLACE FUNCTION text_scalarref() RETURNS text AS $$
+	my $str = 'str';
+	return \$str;
+$$ LANGUAGE plperl;
+
+SELECT text_scalarref();