Make PostgresNode version aware

A new PostgresVersion object type is created and this is used in
PostgresNode using the output of `pg_config --version` and the result
stored in the PostgresNode object.  This object can be compared to other
PostgresVersion objects, or to a number or string.

PostgresNode is currently believed to be compatible with versions down
to release 12, so PostgresNode will issue a warning if used with a
version prior to that.

No attempt has been made to deal with incompatibilities in older
versions - that remains work to be undertaken in a subsequent
development cycle.

Based on code from Mark Dilger and Jehan-Guillaume de Rorthais.

Discussion: https://postgr.es/m/a80421c0-3d7e-def1-bcfe-24777f15e344@dunslane.net

1 files changed, 137 insertions, 0 deletions

diff --git a/src/test/perl/PostgresVersion.pm b/src/test/perl/PostgresVersion.pm
new file mode 100644
index 00000000000..14750365acf
--- /dev/null
+++ b/src/test/perl/PostgresVersion.pm
@@ -0,0 +1,137 @@
+############################################################################
+#
+# PostgresVersion.pm
+#
+# Module encapsulating Postgres Version numbers
+#
+# Copyright (c) 2021, PostgreSQL Global Development Group
+#
+############################################################################
+
+=pod
+
+=head1 NAME
+
+PostgresVersion - class representing PostgreSQL version numbers
+
+=head1 SYNOPSIS
+
+  use PostgresVersion;
+
+  my $version = PostgresVersion->new($version_arg);
+
+  # compare two versions
+  my $bool = $version1 <= $version2;
+
+  # or compare with a number
+  $bool = $version < 12;
+
+  # or with a string
+  $bool = $version lt "13.1";
+
+  # interpolate in a string
+  my $stringyval = "version: $version";
+
+=head1 DESCRIPTION
+
+PostgresVersion encapsulated Postgres version numbers, providing parsing
+of common version formats and comparison operations.
+
+=cut
+
+package PostgresVersion;
+
+use strict;
+use warnings;
+
+use Scalar::Util qw(blessed);
+
+use overload
+  '<=>' => \&_version_cmp,
+  'cmp' => \&_version_cmp,
+  '""'  => \&_stringify;
+
+=pod
+
+=head1 METHODS
+
+=over
+
+=item PostgresVersion->new($version)
+
+Create a new PostgresVersion instance.
+
+The argument can be a number like 12, or a string like '12.2' or the output
+of a Postgres command like `psql --version` or `pg_config --version`;
+
+=back
+
+=cut
+
+sub new
+{
+	my $class = shift;
+	my $arg   = shift;
+
+	# Accept standard formats, in case caller has handed us the output of a
+	# postgres command line tool
+	$arg = $1
+	  if ($arg =~ m/\(?PostgreSQL\)? (\d+(?:\.\d+)*(?:devel)?)/);
+
+	# Split into an array
+	my @result = split(/\./, $arg);
+
+	# Treat development versions as having a minor/micro version one less than
+	# the first released version of that branch.
+	if ($result[$#result] =~ m/^(\d+)devel$/)
+	{
+		pop(@result);
+		push(@result, $1, -1);
+	}
+
+	my $res = [@result];
+	bless $res, $class;
+	return $res;
+}
+
+
+# Routine which compares the _pg_version_array obtained for the two
+# arguments and returns -1, 0, or 1, allowing comparison between two
+# PostgresVersion objects or a PostgresVersion and a version string or number.
+#
+# If the second argument is not a blessed object we call the constructor
+# to make one.
+#
+# Because we're overloading '<=>' and 'cmp' this function supplies us with
+# all the comparison operators ('<' and friends, 'gt' and friends)
+#
+sub _version_cmp
+{
+	my ($a, $b) = @_;
+
+	$b = __PACKAGE__->new($b) unless blessed($b);
+
+	for (my $idx = 0;; $idx++)
+	{
+		return 0 unless (defined $a->[$idx] && defined $b->[$idx]);
+		return $a->[$idx] <=> $b->[$idx]
+		  if ($a->[$idx] <=> $b->[$idx]);
+	}
+}
+
+# Render the version number in the standard "joined by dots" notation if
+# interpolated into a string. Put back 'devel' if we previously turned it
+# into a -1.
+sub _stringify
+{
+	my $self     = shift;
+	my @sections = @$self;
+	if ($sections[-1] == -1)
+	{
+		pop @sections;
+		$sections[-1] = "$sections[-1]devel";
+	}
+	return join('.', @sections);
+}
+
+1;