= InterTrac and InterWiki Extension for TracLinks =

''This is a proposal for implementing #234, #40 and #1414''
''I think it's now ready for testing (see r1912)''

== Definitions ==

=== InterTrac ===
An InterTrac link is used for referring to a Trac object 
(Wiki page, changeset, ticket, ...) located in another
Trac environment.

=== InterWiki ===
An InterWiki link can be used for referring to a Wiki page
located in another Wiki system, and by extension, to any object
located in any other Web application, provided a simple URL 
mapping can be done.

== Link Syntax ==

=== InterTrac ===
{{{
<target_environment>:<TracLinks>
}}}

The link is composed by the target environment name, 
followed by a colon (e.g. {{{trac:}}}),
followed by a regular TracLinks, of any flavor.

That target environment name is either the real name of the 
environment, or an alias for it. 
The aliases are defined in {{{trac.ini}}} (see below).
The prefix is case insensitive.

For convenience, there's also an alternative short-hand form, 
where one can use an alias as an immediate prefix 
for the identifier of a ticket, changeset or report:
(e.g. {{{#T234}}}, {{{[T1508]}}}...)
That alias must be at most 3 letters long.

=== InterWiki ===
{{{
<target_wiki>(:<identifier>)+
}}}

The link is composed by the targeted Wiki (or system) name,
followed by a column (e.g. {{{MeatBall:}}}),
followed by a page specification in the target.

The target Wiki URL is looked up in a the InterMapTxt wiki page, 
modelled after
[http://www.usemod.com/cgi-bin/mb.pl?InterMapTxt MeatBall:InterMapTxt].

An addition to traditional InterWiki links, where the target
is simply ''appended'' to the URL, 
Trac supports parametric InterWiki URLs:
identifiers {{{$1}}}, {{{$2}}}, ... in the URL
will be replaced by corresponding arguments from a list
made up from the page specification split by the ':' token.

== Examples ==

=== InterTrac ===
Besides the other environments run by the same server process
(called ''sibling'' environments), which are automatically detected,
(''Note: currently only in {{{tracd}}}''),
it is necessary to setup a configuration for the InterTrac facility:
 * in order to refer to a remote Trac
 * for defining environment aliases

This is done quite simply in an {{{[intertrac]}}} section
within the {{{trac.ini}}} file.

Example configuration:
{{{
...
[intertrac]
## -- Example of setting up an alias:
t.key = trac

## -- Link to an external Trac:
trac.title = Edgewall's Trac for Trac
trac.url = http://projects.edgewall.com/trac

#trac.svn = http://repos.edgewall.com/projects/trac 
# Hint: .svn information could be used in the future to support svn:externals...
}}}

Now, given this configuration, one could create the following links:
 * to the current InterTrac page:
   * {{{trac:wiki:InterTrac}}} ->
     [http://projects.edgewall.com/trac/wiki/InterTrac trac:wiki:InterTrac]
   * {{{t:wiki:InterTrac}}} ->
     [http://projects.edgewall.com/trac/wiki/InterTrac t:wiki:InterTrac]
   * Keys are case insensitive: {{{T:wiki:InterTrac}}} -> 
     [http://projects.edgewall.com/trac/wiki/InterTrac T:wiki:InterTrac]
 * to the ticket #234:
   * {{{trac:ticket:234}}} ->
     [http://projects.edgewall.com/trac/ticket/234 trac:ticket:234]
   * {{{trac:#234}}} ->
     [http://projects.edgewall.com/trac/search?q=#234 trac:#234]
   * {{{#T234}}} ->
     [http://projects.edgewall.com/trac/ticket/234 #T234]
 * to the changeset [1912]:
   * {{{trac:changeset:1912}}} ->
     [http://projects.edgewall.com/trac/changset/1912 trac:changeset:1912]
   * {{{trac:[1912]}}} 
     [http://projects.edgewall.com/trac/search?q=[1912] trac:[1912]]
   * {{{[T1912]}}} ->
     [http://projects.edgewall.com/trac/changeset/1912 [T1508]]

=== InterWiki ===

The following would be an excerpt of the InterMapTxt page:

{{{
= InterWiki Map =

This is the InterMapTxt wiki page,
modelled after the MeatBall:InterMapTxt page.
----
{{{
...
LiveJournal http://livejournal.com/users/
Login http://www.usemod.com/cgi-bin/mb.pl?action=login&p_userid=
MbTest http://www.usemod.com/cgi-bin/mbtest.pl?
MeatBall http://www.usemod.com/cgi-bin/mb.pl?
MetaWiki http://sunir.org/apps/meta.pl?
MetaWikiPedia http://meta.wikipedia.org/wiki/
Mineralienatlas http://www.mineralienatlas.de/lexikon/index.php/
MoinMoin http://moinmoin.wikiwikiweb.de/
...
}}}
}}}

== Implementation Notes ==

Currently, the {{{[intertrac]}}} configuration has to be repeated 
for each Trac environment, but there's work in progress concerning a 
[ticket:1051 centralized trac.ini], which would help greatly here.

This idea was first proposed as a patch for #234, and 
has been implemented in the following branch: 
source:branches/cboos-dev/intertrac-branch

In particular, [1912] should implement the behavior described 
in version 9 of this page.


The general idea is that any {{{[a-zA-Z][a-zA-Z0-9]*:}}} prefix, 
followed by anything which is not a space, has to be interpreted as:
 1. maybe an alias to something else; it yes, it is dereferenced
    before going on
 1. either a link prefix given by an IWikiSyntaxProvider component 
 1. if not found, an environment name (!InterTrac link)
 1. if not found, an external system name (!InterWiki link)
 1. if not found, it is left unchanged

This order enables one to configure Trac for using another
ticket system: first disable the {{{[ticket]}}} component 
and setup a {{{ticket}}} !InterWiki link pointing to the other 
BugTrackingSystem.