Create contrib/bool_plperl to provide a bool transform for PL/Perl[U].

plperl's default handling of bool arguments or results is not terribly
satisfactory, since Perl doesn't consider the string 'f' to be false.
Ideally we'd just fix that, but the backwards-compatibility hazard
would be substantial.  Instead, build a TRANSFORM module that can
be optionally applied to provide saner semantics.

Perhaps usefully, this is also about the minimum possible skeletal
example of a plperl transform module; so it might be a better starting
point for user-written transform modules than hstore_plperl or
jsonb_plperl.

Ivan Panchenko

Discussion: https://postgr.es/m/1583013317.881182688@f390.i.mail.ru

contrib/Makefile

@@ -75,9 +75,9 @@ ALWAYS_SUBDIRS += sepgsql
 endif
 
 ifeq ($(with_perl),yes)
-SUBDIRS += hstore_plperl jsonb_plperl
+SUBDIRS += bool_plperl hstore_plperl jsonb_plperl
 else
-ALWAYS_SUBDIRS += hstore_plperl jsonb_plperl
+ALWAYS_SUBDIRS += bool_plperl hstore_plperl jsonb_plperl
 endif
 
 ifeq ($(with_python),yes)

contrib/bool_plperl/.gitignore

+# Generated subdirectories
+/log/
+/results/
+/tmp_check/

contrib/bool_plperl/Makefile

+# contrib/bool_plperl/Makefile
+
+MODULE_big = bool_plperl
+OBJS = \
+	$(WIN32RES) \
+	bool_plperl.o
+PGFILEDESC = "bool_plperl - bool transform for plperl"
+
+PG_CPPFLAGS = -I$(top_srcdir)/src/pl/plperl
+
+EXTENSION = bool_plperlu bool_plperl
+DATA = bool_plperlu--1.0.sql bool_plperl--1.0.sql
+
+REGRESS = bool_plperl bool_plperlu
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = contrib/bool_plperl
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
+
+# We must link libperl explicitly
+ifeq ($(PORTNAME), win32)
+# these settings are the same as for plperl
+override CPPFLAGS += -DPLPERL_HAVE_UID_GID -Wno-comment
+# ... see silliness in plperl Makefile ...
+SHLIB_LINK_INTERNAL += $(sort $(wildcard ../../src/pl/plperl/libperl*.a))
+else
+rpathdir = $(perl_archlibexp)/CORE
+SHLIB_LINK += $(perl_embed_ldflags)
+endif
+
+# As with plperl we need to include the perl_includespec directory last.
+override CPPFLAGS := $(CPPFLAGS) $(perl_embed_ccflags) $(perl_includespec)

contrib/bool_plperl/bool_plperl--1.0.sql

+/* contrib/bool_plperl/bool_plperl--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION bool_plperl" to load this file. \quit
+
+CREATE FUNCTION bool_to_plperl(val internal) RETURNS internal
+LANGUAGE C STRICT IMMUTABLE
+AS 'MODULE_PATHNAME';
+
+CREATE FUNCTION plperl_to_bool(val internal) RETURNS bool
+LANGUAGE C STRICT IMMUTABLE
+AS 'MODULE_PATHNAME';
+
+CREATE TRANSFORM FOR bool LANGUAGE plperl (
+    FROM SQL WITH FUNCTION bool_to_plperl(internal),
+    TO SQL WITH FUNCTION plperl_to_bool(internal)
+);
+
+COMMENT ON TRANSFORM FOR bool LANGUAGE plperl IS 'transform between bool and Perl';

contrib/bool_plperl/bool_plperl.c

+#include "postgres.h"
+
+#include "fmgr.h"
+#include "plperl.h"
+
+
+PG_MODULE_MAGIC;
+
+PG_FUNCTION_INFO_V1(bool_to_plperl);
+
+Datum
+bool_to_plperl(PG_FUNCTION_ARGS)
+{
+	dTHX;
+	bool		in = PG_GETARG_BOOL(0);
+
+	return PointerGetDatum(in ? &PL_sv_yes : &PL_sv_no);
+}
+
+
+PG_FUNCTION_INFO_V1(plperl_to_bool);
+
+Datum
+plperl_to_bool(PG_FUNCTION_ARGS)
+{
+	dTHX;
+	SV		   *in = (SV *) PG_GETARG_POINTER(0);
+
+	PG_RETURN_BOOL(SvTRUE(in));
+}

contrib/bool_plperl/bool_plperl.control

+# bool_plperl extension
+comment = 'transform between bool and plperl'
+default_version = '1.0'
+module_pathname = '$libdir/bool_plperl'
+relocatable = true
+trusted = true
+requires = 'plperl'

contrib/bool_plperl/bool_plperlu--1.0.sql

+/* contrib/bool_plperl/bool_plperlu--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION bool_plperlu" to load this file. \quit
+
+CREATE FUNCTION bool_to_plperlu(val internal) RETURNS internal
+LANGUAGE C STRICT IMMUTABLE
+AS 'MODULE_PATHNAME', 'bool_to_plperl';
+
+CREATE FUNCTION plperlu_to_bool(val internal) RETURNS bool
+LANGUAGE C STRICT IMMUTABLE
+AS 'MODULE_PATHNAME', 'plperl_to_bool';
+
+CREATE TRANSFORM FOR bool LANGUAGE plperlu (
+    FROM SQL WITH FUNCTION bool_to_plperlu(internal),
+    TO SQL WITH FUNCTION plperlu_to_bool(internal)
+);
+
+COMMENT ON TRANSFORM FOR bool LANGUAGE plperlu IS 'transform between bool and Perl';

contrib/bool_plperl/bool_plperlu.control

+# bool_plperlu extension
+comment = 'transform between bool and plperlu'
+default_version = '1.0'
+module_pathname = '$libdir/bool_plperl'
+relocatable = true
+requires = 'plperlu'

contrib/bool_plperl/expected/bool_plperl.out

+CREATE EXTENSION bool_plperl CASCADE;
+NOTICE:  installing required extension "plperl"
+--- test transforming from perl
+CREATE FUNCTION perl2int(int) RETURNS bool
+LANGUAGE plperl
+TRANSFORM FOR TYPE bool
+AS $$
+return shift;
+$$;
+CREATE FUNCTION perl2text(text) RETURNS bool
+LANGUAGE plperl
+TRANSFORM FOR TYPE bool
+AS $$
+return shift;
+$$;
+CREATE FUNCTION perl2undef() RETURNS bool
+LANGUAGE plperl
+TRANSFORM FOR TYPE bool
+AS $$
+return undef;
+$$;
+SELECT perl2int(1);
+ perl2int 
+----------
+ t
+(1 row)
+
+SELECT perl2int(0);
+ perl2int 
+----------
+ f
+(1 row)
+
+SELECT perl2text('foo');
+ perl2text 
+-----------
+ t
+(1 row)
+
+SELECT perl2text('');
+ perl2text 
+-----------
+ f
+(1 row)
+
+SELECT perl2undef() IS NULL AS p;
+ p 
+---
+ t
+(1 row)
+
+--- test transforming to perl
+CREATE FUNCTION bool2perl(bool, bool, bool) RETURNS void
+LANGUAGE plperl
+TRANSFORM FOR TYPE bool
+AS $$
+my ($x, $y, $z) = @_;
+
+die("NULL mistransformed") if (defined($z));
+die("TRUE mistransformed to UNDEF") if (!defined($x));
+die("FALSE mistransformed to UNDEF") if (!defined($y));
+die("TRUE mistransformed") if (!$x);
+die("FALSE mistransformed") if ($y);
+$$;
+SELECT bool2perl (true, false, NULL);
+ bool2perl 
+-----------
+ 
+(1 row)
+
+--- test selecting bool through SPI
+CREATE FUNCTION spi_test()  RETURNS void
+LANGUAGE plperl
+TRANSFORM FOR TYPE bool
+AS $$
+my $rv = spi_exec_query('SELECT true t, false f, NULL n')->{rows}->[0];
+
+die("TRUE mistransformed to UNDEF in SPI") if (!defined ($rv->{t}));
+die("FALSE mistransformed to UNDEF in SPI") if (!defined ($rv->{f}));
+die("NULL mistransformed in SPI") if (defined ($rv->{n}));
+die("TRUE mistransformed in SPI") if (!$rv->{t});
+die("FALSE mistransformed in SPI") if ($rv->{f});
+$$;
+SELECT spi_test();
+ spi_test 
+----------
+ 
+(1 row)
+
+DROP EXTENSION plperl CASCADE;
+NOTICE:  drop cascades to 6 other objects
+DETAIL:  drop cascades to function spi_test()
+drop cascades to extension bool_plperl
+drop cascades to function perl2int(integer)
+drop cascades to function perl2text(text)
+drop cascades to function perl2undef()
+drop cascades to function bool2perl(boolean,boolean,boolean)

contrib/bool_plperl/expected/bool_plperlu.out

+CREATE EXTENSION bool_plperlu CASCADE;
+NOTICE:  installing required extension "plperlu"
+--- test transforming from perl
+CREATE FUNCTION perl2int(int) RETURNS bool
+LANGUAGE plperlu
+TRANSFORM FOR TYPE bool
+AS $$
+return shift;
+$$;
+CREATE FUNCTION perl2text(text) RETURNS bool
+LANGUAGE plperlu
+TRANSFORM FOR TYPE bool
+AS $$
+return shift;
+$$;
+CREATE FUNCTION perl2undef() RETURNS bool
+LANGUAGE plperlu
+TRANSFORM FOR TYPE bool
+AS $$
+return undef;
+$$;
+SELECT perl2int(1);
+ perl2int 
+----------
+ t
+(1 row)
+
+SELECT perl2int(0);
+ perl2int 
+----------
+ f
+(1 row)
+
+SELECT perl2text('foo');
+ perl2text 
+-----------
+ t
+(1 row)
+
+SELECT perl2text('');
+ perl2text 
+-----------
+ f
+(1 row)
+
+SELECT perl2undef() IS NULL AS p;
+ p 
+---
+ t
+(1 row)
+
+--- test transforming to perl
+CREATE FUNCTION bool2perl(bool, bool, bool) RETURNS void
+LANGUAGE plperlu
+TRANSFORM FOR TYPE bool
+AS $$
+my ($x, $y, $z) = @_;
+
+die("NULL mistransformed") if (defined($z));
+die("TRUE mistransformed to UNDEF") if (!defined($x));
+die("FALSE mistransformed to UNDEF") if (!defined($y));
+die("TRUE mistransformed") if (!$x);
+die("FALSE mistransformed") if ($y);
+$$;
+SELECT bool2perl (true, false, NULL);
+ bool2perl 
+-----------
+ 
+(1 row)
+
+--- test selecting bool through SPI
+CREATE FUNCTION spi_test()  RETURNS void
+LANGUAGE plperlu
+TRANSFORM FOR TYPE bool
+AS $$
+my $rv = spi_exec_query('SELECT true t, false f, NULL n')->{rows}->[0];
+
+die("TRUE mistransformed to UNDEF in SPI") if (!defined ($rv->{t}));
+die("FALSE mistransformed to UNDEF in SPI") if (!defined ($rv->{f}));
+die("NULL mistransformed in SPI") if (defined ($rv->{n}));
+die("TRUE mistransformed in SPI") if (!$rv->{t});
+die("FALSE mistransformed in SPI") if ($rv->{f});
+$$;
+SELECT spi_test();
+ spi_test 
+----------
+ 
+(1 row)
+
+DROP EXTENSION plperlu CASCADE;
+NOTICE:  drop cascades to 6 other objects
+DETAIL:  drop cascades to function spi_test()
+drop cascades to extension bool_plperlu
+drop cascades to function perl2int(integer)
+drop cascades to function perl2text(text)
+drop cascades to function perl2undef()
+drop cascades to function bool2perl(boolean,boolean,boolean)

contrib/bool_plperl/sql/bool_plperl.sql

+CREATE EXTENSION bool_plperl CASCADE;
+
+--- test transforming from perl
+
+CREATE FUNCTION perl2int(int) RETURNS bool
+LANGUAGE plperl
+TRANSFORM FOR TYPE bool
+AS $$
+return shift;
+$$;
+
+CREATE FUNCTION perl2text(text) RETURNS bool
+LANGUAGE plperl
+TRANSFORM FOR TYPE bool
+AS $$
+return shift;
+$$;
+
+CREATE FUNCTION perl2undef() RETURNS bool
+LANGUAGE plperl
+TRANSFORM FOR TYPE bool
+AS $$
+return undef;
+$$;
+
+SELECT perl2int(1);
+SELECT perl2int(0);
+SELECT perl2text('foo');
+SELECT perl2text('');
+SELECT perl2undef() IS NULL AS p;
+
+--- test transforming to perl
+
+CREATE FUNCTION bool2perl(bool, bool, bool) RETURNS void
+LANGUAGE plperl
+TRANSFORM FOR TYPE bool
+AS $$
+my ($x, $y, $z) = @_;
+
+die("NULL mistransformed") if (defined($z));
+die("TRUE mistransformed to UNDEF") if (!defined($x));
+die("FALSE mistransformed to UNDEF") if (!defined($y));
+die("TRUE mistransformed") if (!$x);
+die("FALSE mistransformed") if ($y);
+$$;
+
+SELECT bool2perl (true, false, NULL);
+
+--- test selecting bool through SPI
+
+CREATE FUNCTION spi_test()  RETURNS void
+LANGUAGE plperl
+TRANSFORM FOR TYPE bool
+AS $$
+my $rv = spi_exec_query('SELECT true t, false f, NULL n')->{rows}->[0];
+
+die("TRUE mistransformed to UNDEF in SPI") if (!defined ($rv->{t}));
+die("FALSE mistransformed to UNDEF in SPI") if (!defined ($rv->{f}));
+die("NULL mistransformed in SPI") if (defined ($rv->{n}));
+die("TRUE mistransformed in SPI") if (!$rv->{t});
+die("FALSE mistransformed in SPI") if ($rv->{f});
+$$;
+
+SELECT spi_test();
+
+DROP EXTENSION plperl CASCADE;

contrib/bool_plperl/sql/bool_plperlu.sql

+CREATE EXTENSION bool_plperlu CASCADE;
+
+--- test transforming from perl
+
+CREATE FUNCTION perl2int(int) RETURNS bool
+LANGUAGE plperlu
+TRANSFORM FOR TYPE bool
+AS $$
+return shift;
+$$;
+
+CREATE FUNCTION perl2text(text) RETURNS bool
+LANGUAGE plperlu
+TRANSFORM FOR TYPE bool
+AS $$
+return shift;
+$$;
+
+CREATE FUNCTION perl2undef() RETURNS bool
+LANGUAGE plperlu
+TRANSFORM FOR TYPE bool
+AS $$
+return undef;
+$$;
+
+SELECT perl2int(1);
+SELECT perl2int(0);
+SELECT perl2text('foo');
+SELECT perl2text('');
+SELECT perl2undef() IS NULL AS p;
+
+--- test transforming to perl
+
+CREATE FUNCTION bool2perl(bool, bool, bool) RETURNS void
+LANGUAGE plperlu
+TRANSFORM FOR TYPE bool
+AS $$
+my ($x, $y, $z) = @_;
+
+die("NULL mistransformed") if (defined($z));
+die("TRUE mistransformed to UNDEF") if (!defined($x));
+die("FALSE mistransformed to UNDEF") if (!defined($y));
+die("TRUE mistransformed") if (!$x);
+die("FALSE mistransformed") if ($y);
+$$;
+
+SELECT bool2perl (true, false, NULL);
+
+--- test selecting bool through SPI
+
+CREATE FUNCTION spi_test()  RETURNS void
+LANGUAGE plperlu
+TRANSFORM FOR TYPE bool
+AS $$
+my $rv = spi_exec_query('SELECT true t, false f, NULL n')->{rows}->[0];
+
+die("TRUE mistransformed to UNDEF in SPI") if (!defined ($rv->{t}));
+die("FALSE mistransformed to UNDEF in SPI") if (!defined ($rv->{f}));
+die("NULL mistransformed in SPI") if (defined ($rv->{n}));
+die("TRUE mistransformed in SPI") if (!$rv->{t});
+die("FALSE mistransformed in SPI") if ($rv->{f});
+$$;
+
+SELECT spi_test();
+
+DROP EXTENSION plperlu CASCADE;

doc/src/sgml/plperl.sgml

@@ -55,8 +55,11 @@
    syntax:
 
 <programlisting>
-CREATE FUNCTION <replaceable>funcname</replaceable> (<replaceable>argument-types</replaceable>) RETURNS <replaceable>return-type</replaceable> AS $$
-    # PL/Perl function body
+CREATE FUNCTION <replaceable>funcname</replaceable> (<replaceable>argument-types</replaceable>)
+RETURNS <replaceable>return-type</replaceable>
+-- function attributes can go here
+AS $$
+    # PL/Perl function body goes here
 $$ LANGUAGE plperl;
 </programlisting>
 
@@ -188,6 +191,39 @@ $$ LANGUAGE plperl;
    escape binary data for a return value of type <type>bytea</type>.
   </para>
 
+  <para>
+   One case that is particularly important is boolean values.  As just
+   stated, the default behavior for <type>bool</type> values is that they
+   are passed to Perl as text, thus either <literal>'t'</literal>
+   or <literal>'f'</literal>.  This is problematic, since Perl will not
+   treat <literal>'f'</literal> as false!  It is possible to improve matters
+   by using a <quote>transform</quote> (see
+   <xref linkend="sql-createtransform"/>).  Suitable transforms are provided
+   by the <filename>bool_plperl</filename> extension.  To use it, install
+   the extension:
+<programlisting>
+CREATE EXTENSION bool_plperl;  -- or bool_plperlu for PL/PerlU
+</programlisting>
+   Then use the <literal>TRANSFORM</literal> function attribute for a
+   PL/Perl function that takes or returns <type>bool</type>, for example:
+<programlisting>
+CREATE FUNCTION perl_and(bool, bool) RETURNS bool
+TRANSFORM FOR TYPE bool
+AS $$
+  my ($a, $b) = @_;
+  return $a &amp;&amp; $b;
+$$ LANGUAGE plperl;
+</programlisting>
+   When this transform is applied, <type>bool</type> arguments will be seen
+   by Perl as being <literal>1</literal> or empty, thus properly true or
+   false.  If the function result is type <type>bool</type>, it will be true
+   or false according to whether Perl would evaluate the returned value as
+   true.
+   Similar transformations are also performed for boolean query arguments
+   and results of SPI queries performed inside the function
+   (<xref linkend="plperl-database"/>).
+  </para>
+
   <para>
    Perl can return <productname>PostgreSQL</productname> arrays as
    references to Perl arrays.  Here is an example:
@@ -382,6 +418,13 @@ use strict;
    commands will accept any string that is acceptable input format
    for the function's declared return type.
   </para>
+
+  <para>
+   If this behavior is inconvenient for a particular case, it can be
+   improved by using a transform, as already illustrated
+   for <type>bool</type> values.  Several examples of transform modules
+   are included in the <productname>PostgreSQL</productname> distribution.
+  </para>
  </sect1>
 
  <sect1 id="plperl-builtins">

src/tools/msvc/Mkvcbuild.pm

@@ -43,6 +43,7 @@ my $contrib_extrasource = {
 	'seg'  => [ 'contrib/seg/segscan.l',   'contrib/seg/segparse.y' ],
 };
 my @contrib_excludes = (
+	'bool_plperl',
 	'commit_ts',        'hstore_plperl',
 	'hstore_plpython',  'intagg',
 	'jsonb_plperl',     'jsonb_plpython',
@@ -763,6 +764,9 @@ sub mkvcbuild
 		}
 
 		# Add transform modules dependent on plperl
+		my $bool_plperl = AddTransformModule(
+			'bool_plperl',  'contrib/bool_plperl',
+			'plperl',       'src/pl/plperl');
 		my $hstore_plperl = AddTransformModule(
 			'hstore_plperl', 'contrib/hstore_plperl',
 			'plperl',        'src/pl/plperl',
@@ -773,6 +777,7 @@ sub mkvcbuild
 
 		foreach my $f (@perl_embed_ccflags)
 		{
+			$bool_plperl->AddDefine($f);
 			$hstore_plperl->AddDefine($f);
 			$jsonb_plperl->AddDefine($f);
 		}