Make PostgresNode easily subclassable

This module becomes much more useful if we allow it to be used as base
class for external projects.  To achieve this, change the exported
get_new_node function into a class method instead, and use the standard
Perl idiom of accepting the class as first argument.  This method works
as expected for subclasses.  The standalone function is kept for
backwards compatibility, though it could be removed in pg11.

Author: Chap Flackman, based on an earlier patch from Craig Ringer
Discussion: https://postgr.es/m/CAMsr+YF8kO+4+K-_U4PtN==2FndJ+5Bn6A19XHhMiBykEwv0wA@mail.gmail.com

diff --git a/src/test/perl/PostgresNode.pm b/src/test/perl/PostgresNode.pm
index 711d0deae8f87a1f11f073b93b1413c3736c70e2..8ec843edeaa9fd80aac6e8d3465842259a256c33 100644 (file)
--- a/src/test/perl/PostgresNode.pm
+++ b/src/test/perl/PostgresNode.pm
@@ -9,7 +9,7 @@ PostgresNode - class representing PostgreSQL server instance
 
   use PostgresNode;
 
-  my $node = get_new_node('mynode');
+  my $node = PostgresNode->get_new_node('mynode');
 
   # Create a data directory with initdb
   $node->init();
@@ -845,20 +845,24 @@ sub _update_pid
 
 =pod
 
-=item get_new_node(node_name)
+=item PostgresNode->get_new_node(node_name)
 
-Build a new PostgresNode object, assigning a free port number. Standalone
-function that's automatically imported.
+Build a new object of class C<PostgresNode> (or of a subclass, if you have
+one), assigning a free port number.  Remembers the node, to prevent its port
+number from being reused for another node, and to ensure that it gets
+shut down when the test script exits.
 
-Remembers the node, to prevent its port number from being reused for another
-node, and to ensure that it gets shut down when the test script exits.
+You should generally use this instead of C<PostgresNode::new(...)>.
 
-You should generally use this instead of PostgresNode::new(...).
+For backwards compatibility, it is also exported as a standalone function,
+which can only create objects of class C<PostgresNode>.
 
 =cut
 
 sub get_new_node
 {
+       my $class = 'PostgresNode';
+       $class = shift if 1 < scalar @_;
        my $name  = shift;
        my $found = 0;
        my $port  = $last_port_assigned;
@@ -903,7 +907,7 @@ sub get_new_node
        print "# Found free port $port\n";
 
        # Lock port number found by creating a new node
-       my $node = new PostgresNode($name, $test_pghost, $port);
+       my $node = $class->new($name, $test_pghost, $port);
 
        # Add node to list of nodes
        push(@all_nodes, $node);

diff --git a/src/test/perl/README b/src/test/perl/README
index 4279d316c4d113a09e627734b0c1e099321ef0d8..cbee418e14bedde54400ff0abdb3626d74d8913f 100644 (file)
--- a/src/test/perl/README
+++ b/src/test/perl/README
@@ -42,7 +42,7 @@ Each test script should begin with:
 then it will generally need to set up one or more nodes, run commands
 against them and evaluate the results. For example:
 
-    my $node = get_new_node('master');
+    my $node = PostgresNode->get_new_node('master');
     $node->init;
     $node->start;