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 d87296af0863318b74712261dc296cfd68b463da..bf982101a57eecc4b691c105fd97544532a2a8ed 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();
@@ -855,20 +855,24 @@ 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;
@@ -913,7 +917,7 @@ 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 cc6edfb3838a338b53273d0482f55ab70857d823..c61c3f5e9423920249b4e7db58117dd469e2eea4 100644 (file)
--- a/src/test/perl/README
+++ b/src/test/perl/README
@@ -48,7 +48,7 @@ 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;