Add test of various escape functions

As highlighted by the prior commit, writing correct escape functions is less
trivial than one might hope.

This test module tries to verify that different escaping functions behave
reasonably. It e.g. tests:

- Invalidly encoded input to an escape function leads to invalidly encoded
  output

- Trailing incomplete multi-byte characters are handled sensibly

- Escaped strings are parsed as single statement by psql's parser (which
  derives from the backend parser)

There are further tests that would be good to add. But even in the current
state it was rather useful for writing the fix in the prior commit.

Reviewed-by: Noah Misch <noah@leadboat.com>
Backpatch-through: 13
Security: CVE-2025-1094
(cherry picked from commit de4b92f)

Author: anarazel

src/test/modules/Makefile

@@ -16,6 +16,7 @@ SUBDIRS = \
 		  spgist_name_ops \
 		  test_bloomfilter \
 		  test_ddl_deparse \
+		  test_escape \
 		  test_extensions \
 		  test_ginpostinglist \
 		  test_integerset \

src/test/modules/test_escape/.gitignore

@@ -0,0 +1,2 @@
+/tmp_check/
+/test_escape

src/test/modules/test_escape/Makefile

@@ -0,0 +1,27 @@
+# src/test/modules/test_escape/Makefile
+
+PGFILEDESC = "test escape program"
+PGAPPICON = win32
+
+PROGRAM = test_escape
+OBJS = $(WIN32RES) test_escape.o
+
+PG_CPPFLAGS = -I$(libpq_srcdir)
+PG_LIBS_INTERNAL += -L$(top_builddir)/src/fe_utils -lpgfeutils $(libpq_pgport)
+
+NO_INSTALL = 1
+TAP_TESTS = 1
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = src/test/modules/test_escape
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
+
+test_escape$(X): | submake-libpgfeutils
+check: test_escape$(X)

src/test/modules/test_escape/t/001_test_escape.pl

@@ -0,0 +1,53 @@
+# Copyright (c) 2023-2025, PostgreSQL Global Development Group
+use strict;
+use warnings FATAL => 'all';
+use Config;
+use PostgreSQL::Test::Utils;
+use PostgreSQL::Test::Cluster;
+use Test::More;
+
+my $node = PostgreSQL::Test::Cluster->new('node');
+
+$node->init();
+$node->start();
+
+$node->safe_psql('postgres',
+	q(CREATE DATABASE db_sql_ascii ENCODING "sql_ascii" TEMPLATE template0;));
+
+my $cmd =
+  [ 'test_escape', '--conninfo', $node->connstr . " dbname=db_sql_ascii" ];
+
+# There currently is no good other way to transport test results from a C
+# program that requires just the node being set-up...
+my ($stderr, $stdout);
+my $result = IPC::Run::run $cmd, '>', \$stdout, '2>', \$stderr;
+
+is($result, 1, "test_escape returns 0");
+is($stderr, '', "test_escape stderr is empty");
+
+foreach my $line (split('\n', $stdout))
+{
+	if ($line =~ m/^ok \d+ ?(.*)/)
+	{
+		ok(1, $1);
+	}
+
+	elsif ($line =~ m/^not ok \d+ ?(.*)/)
+	{
+		ok(0, $1);
+	}
+
+	elsif ($line =~ m/^# ?(.*)/)
+	{
+		note $1;
+	}
+	elsif ($line =~ m/^\d+..\d+$/)
+	{
+	}
+	else
+	{
+		BAIL_OUT("no unmapped lines, got $line");
+	}
+}
+
+done_testing();