Parse return value of go functions

[geany-mirror.git] / doc / plugins.dox

/*
 * plugins.dox - this file is part of Geany, a fast and lightweight IDE
 *
 * Copyright 2008-2011 Enrico Tröger <enrico(dot)troeger(at)uvena(dot)de>
 * Copyright 2008-2011 Nick Treleaven <nick(dot)treleaven(at)btinternet(dot)com>
 * Copyright 2009-2012 Frank Lanitz <frank(at)frank(dot)uvena(dot)de>
 * Copyright 2014 Matthew Brush <matt(at)geany(dot)org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * This file contains additional plugin documentation like the signal system
 * and a small howto. It is best viewed when filetype is set to C or C++.
 */


/**

@mainpage Geany Plugin API Documentation

@author Enrico Tröger, Nick Treleaven, Frank Lanitz, Matthew Brush

@section Intro
This is the Geany API documentation. It should be considered work in progress.
We will try to document as many functions and structs as possible.

@warning Do not use any symbol not in the documentation - it may change.

@section pluginsupport Plugin Support
- @link howto Plugin HowTo @endlink - get started
- @link pluginsymbols.c Plugin Symbols @endlink
- @link plugindata.h Plugin Datatypes and Macros @endlink
- @link pluginsignals.c Plugin Signals @endlink
- @link pluginutils.h Plugin Utility Functions @endlink
- @link guidelines Plugin Writing Guidelines @endlink
- <b>plugins/demoplugin.c</b> - in Geany's source, bigger than the howto example

@section common Common API files
- @link dialogs.h @endlink
- @link document.h @endlink
- @link editor.h @endlink
- @link filetypes.h @endlink
- @link keybindings.h @endlink
- @link msgwindow.h @endlink
- @link project.h @endlink
- @link sciwrappers.h Scintilla Wrapper Functions @endlink
- @link stash.h Stash Pref/Setting Functions @endlink
- @link utils.h General Utility Functions @endlink
- @link ui_utils.h Widget Utility Functions @endlink

@section More
- All API functions and types - see <b>Files</b> link at the top
- Deprecated symbols - see <b>Related Pages</b> link at the top

@note See the HACKING file for information about developing the plugin API and
other useful notes.

@page guidelines Plugin Writing Guidelines

@section intro Introduction

The following hints and guidelines are only recommendations. Nobody is forced to follow
them at all.

@section general General notes

@subsection ideas Getting a plugin idea

If you want to write a plugin but don't know yet what it should do, have a look at
http://www.geany.org/Support/PluginWishlist to get an idea about what users wish.

@subsection code Managing the source code

For authors of plugins for Geany, we created a dedicated @a geany-plugins project
on Sourceforge and GitHub to ease development of plugins and help new authors.
All information about this project you can find at http://plugins.geany.org/

To add a new plugin to this project, get in touch with the people on the
geany-devel-mailing list and create a fork of the geany-plugins project
at https://github.com/geany/geany-plugins.
Beside of adding a new plugin, geany-devel-mailing list is also the place where
to discuss development related questions.
However, once you have done your fork of geany-plugins you can develop
your plugin until you think its the right time to publish it. At this point,
create a pull request for adding your patch set into the master branch of the main
geany-plugins repository.

Of course, you don't need to use GitHub - any Git is fine. But GitHub
is making it way easier for review, merging and get in touch with you for
comments.

If you don't want your plugin to be part of the geany-plugins project it is also fine.
Just skip the part about forking geany-plugins and sending a pull request.
In this case it is of course also a good idea to post some kind of announcement
to geany-devel and maybe to the main geany mailing list -- it's up to you.
You can also ask for your plugin to be listed on the http://plugins.geany.org/
website as a third party plugin, helping Geany user to know about your plugin.

At time of writing, there are some plugins already available in the
repositories. Feel free to use any of these plugins as a start for your own,
maybe by copying the directory structure and the autotools files
(Makefile.am, configure.in, ...). Most of the available plugins are also ready for
i18n support, just for reference.

We encourage authors using this service to only commit changes to their
own plugin and not to others' plugins. Instead just send patches to
geany-devel at uvena.de or the plugin author directly.

@section paths Installation paths

- The plugin binary (@c pluginname.so) should be installed in Geany's libdir. This is
  necessary so that Geany can find the plugin.
  An easy way to retrieve Geany's libdir is to use the pkg-config tool, e.g. @code
  `$PKG_CONFIG --variable=libdir geany`/ geany
  @endcode
- If your plugin creates other binary files like helper programs or helper libraries,
  they should go into @c $prefix/bin (for programs, ideally prefixed with @a geany),
  additional libraries should be installed in Geany's libdir, maybe in a subdirectory.
- Plugins should install their documentation files (README, NEWS, ChangeLog, licences and
  other documentation files) into the common documentation directory
  @c $prefix/share/doc/geany-plugins/$pluginname/
- Translation files should be installed normally into @c $prefix/share/locale. There is no
  need to use Geany's translation directory. To set up translation support properly and
  for additional information, see main_locale_init().
- Do @a never install anything into a user's home directory like installing
  the plugin binary in @c ~/.config/geany/plugins/.


@page howto Plugin HowTo

@section intro Introduction

Since Geany 0.12 there is a plugin interface to extend Geany's functionality and
add new features. This document gives a brief overview about how to add new
plugins by writing a simple "Hello World" plugin in C or C++.


@section buildenv Build environment

To be able to write plugins for Geany, you need the source code and some development
packages for GTK and its dependencies. The following will only describe the way to compile and
build plugins on Unix-like systems [1].
If you already have the Geany source code and compiled it from them, you can skip the
following.

First you need to have Geany installed. Then install the development files for GTK
and its dependencies. The easiest way to do this is to use your distribution's package
management system, e.g. on Debian and Ubuntu systems you can use
@code apt-get install libgtk2.0-dev intltool @endcode
This will install all necessary files to be able to compile plugins for Geany. On other
distributions, the package names and commands to use may differ.

Basically, you are done at this point and could continue with writing the plugin code.

[1] For Windows, it is basically the same but you might have some more work on setting up
the general build environment(compiler, GTK development files, ...). This is described on
Geany's website at http://www.geany.org/Support/BuildingOnWin32.

@section helloworld "Hello World"

When writing a plugin, you will find a couple of functions or macros which are mandatory
and some which are free to use for implementing some useful feature once your plugin
becomes more powerful like including a configuration or help dialog.

You should start your plugin with including some of the needed C header files and defining
some basic global variables which will help you to access all needed functions of the plugin
API in a more comfortable way.

Let's start with the very basic headers and add more later if necessary.
@code
#include <geanyplugin.h>
@endcode

@a geanyplugin.h includes all of the Geany API and also the necessary GTK header files,
so there is no need to include @a gtk/gtk.h yourself.

@note
@a plugindata.h contains the biggest part of the plugin API and provides some basic macros.

Then you should define two basic variables which will give access to data fields
provided by the plugin API.
@code
GeanyPlugin                     *geany_plugin;
GeanyData                       *geany_data;
@endcode

Now you can go on and write your first lines for your new plugin. As mentioned before,
you will need to implement and fill out a couple of functions/macros to make the plugin work.
So let's start with PLUGIN_VERSION_CHECK().

PLUGIN_VERSION_CHECK() is a convenient way to tell Geany which version of Geany's plugin API
is needed at minimum to run your plugin. The value is defined in
@a plugindata.h by @a GEANY_API_VERSION. In most cases this should be your minimum.
Nevertheless when setting this value, you should choose the lowest possible version here to
make the plugin compatible with a bigger number of versions of Geany.

For the next step, you will need to tell Geany some basic information about your plugin
which will be shown in the plugin manager dialog.

To do this you should use the PLUGIN_SET_INFO() macro, which expects 4 parameters:
- Plugin name
- Short description
- Version
- Author

Based on this, the line could look like:
@code
PLUGIN_SET_INFO("HelloWorld", "Just another tool to say hello world",
                                "1.0", "John Doe <john.doe@example.org>");
@endcode

Once this is done, you will need to implement the function which will be executed when the
plugin is loaded. Part of that function could be adding and removing of an item to
Geany's Tools menu, setting up keybindings or registering some callbacks. Also you will
need to implement the function that is called when your plugin is unloaded.
These functions are called plugin_init() and plugin_cleanup(). Let's see what this
looks like:
@code
PLUGIN_VERSION_CHECK(211)

PLUGIN_SET_INFO("HelloWorld", "Just another tool to say hello world",
                                "1.0", "Joe Doe <joe.doe@example.org>");

void plugin_init(GeanyData *data)
{
}

void plugin_cleanup(void)
{
}
@endcode

If you think this plugin seems not to implement any functionality right now and only wastes
some memory, you are right. But it should compile and load/unload in Geany nicely.
Now you have the very basic layout of a new plugin. Great, isn't it?

@note

If you would rather write the plugin in C++, you can do that by marking the
plugin functions that it implements as @c extern @c "C", for example:

@code

extern "C" void plugin_init(GeanyData *data)
{
}

extern "C" void plugin_cleanup(void)
{
}
@endcode

@section building Building

First make plugin.o:

@code gcc -c plugin.c -fPIC `pkg-config --cflags geany` @endcode

Then make the plugin library plugin.so (or plugin.dll on Windows):

@code gcc plugin.o -o plugin.so -shared `pkg-config --libs geany` @endcode

If all went OK, put the library into one of the paths Geany looks for plugins,
e.g. $prefix/lib/geany. See @ref paths "Installation paths" for details.

@note

If you are writing the plugin in C++, then you will need to use your C++
compiler here, for example @c g++.

@section realfunc Adding functionality

Let's go on and implement some real functionality.

As mentioned before, plugin_init() will be called when the plugin is loaded in Geany.
So it should implement everything that needs to be done during startup. In this case,
we'd like to add a menu item to Geany's Tools menu which runs a dialog printing "Hello World".
@code
void plugin_init(GeanyData *data)
{
        GtkWidget *main_menu_item;

        // Create a new menu item and show it
        main_menu_item = gtk_menu_item_new_with_mnemonic("Hello World");
        gtk_widget_show(main_menu_item);

        // Attach the new menu item to the Tools menu
        gtk_container_add(GTK_CONTAINER(geany->main_widgets->tools_menu),
                main_menu_item);

        // Connect the menu item with a callback function
        // which is called when the item is clicked
        g_signal_connect(main_menu_item, "activate",
                G_CALLBACK(item_activate_cb), NULL);
}
@endcode

This will add an item to the Tools menu and connect this item to a function which implements
what should be done when the menu item is activated by the user.
This is done by g_signal_connect(). The Tools menu can be accessed with
geany->main_widgets->tools_menu. The structure @a main_widgets contains pointers to the
main GUI elements in Geany.

Geany has a simple API for showing message dialogs. So our function contains
only a few lines:
@code
void item_activate_cb(GtkMenuItem *menuitem, gpointer user_data)
{
        dialogs_show_msgbox(GTK_MESSAGE_INFO, "Hello World");
}
@endcode

For the moment you don't need to worry about the parameters of that function.

Now we need to clean up properly when the plugin is unloaded.

To remove the menu item from the Tools menu, you can use gtk_widget_destroy().
gtk_widget_destroy() expects a pointer to a GtkWidget object.

First you should add gtk_widget_destroy() to your plugin_cleanup() function.
The argument for gtk_widget_destroy() is the widget object you created earlier in
plugin_init(). To be able to access this pointer in plugin_cleanup(), you need to move
its definition from plugin_init() into the global context so its visibility will increase
and it can be accessed in all functions.
@code
static GtkWidget *main_menu_item = NULL;

// ...
void plugin_init(GeanyData *data)
{
        main_menu_item = gtk_menu_item_new_with_mnemonic("Hello World");
        gtk_widget_show(main_menu_item);
// ...
}

void plugin_cleanup(void)
{
        gtk_widget_destroy(main_menu_item);
}
@endcode

This will ensure your menu item is removed from the Tools menu as well as from
memory once your plugin is unloaded, so you don't leave any memory leaks.
Once this is done, your first plugin is ready. Congratulations!

@section listing Complete listing (without comments)

@code
#include <geanyplugin.h>

GeanyPlugin             *geany_plugin;
GeanyData               *geany_data;

PLUGIN_VERSION_CHECK(211)

PLUGIN_SET_INFO("HelloWorld", "Just another tool to say hello world",
                                "1.0", "John Doe <john.doe@example.org>");


static GtkWidget *main_menu_item = NULL;

static void item_activate_cb(GtkMenuItem *menuitem, gpointer gdata)
{
        dialogs_show_msgbox(GTK_MESSAGE_INFO, "Hello World");
}

void plugin_init(GeanyData *data)
{
        main_menu_item = gtk_menu_item_new_with_mnemonic("Hello World");
        gtk_widget_show(main_menu_item);
        gtk_container_add(GTK_CONTAINER(geany->main_widgets->tools_menu),
                main_menu_item);
        g_signal_connect(main_menu_item, "activate",
                G_CALLBACK(item_activate_cb), NULL);
}

void plugin_cleanup(void)
{
        gtk_widget_destroy(main_menu_item);
}
 @endcode


Now you might like to look at Geany's source code for core plugins such as
@a plugins/demoplugin.c.

@section furtherimprovements Furter Improvements and next steps
@subsection translatable_plugin_information Translatable plugin information

After having written our first plugin, there is still room for improvement.

By default, PLUGIN_SET_INFO() does not allow translation of the basic plugin
information for plugins which are not shipped with Geany's core distribution.
Since most plugins are not shipped with Geany's core, it makes sense to
enable translation when the plugin is loaded so that it gets translated
inside Geany's Plugin Manager.  As of Geany 0.19, the plugin API contains
the PLUGIN_SET_TRANSLATABLE_INFO() macro which enables translation of the
basic plugin details passed to PLUGIN_SET_INFO() when the plugin is loaded.

PLUGIN_SET_TRANSLATABLE_INFO() takes two more parameters than PLUGIN_SET_INFO(),
for a total of six parameters.

 - Localedir
 - Gettextpackage
 - Plugin name
 - Short description
 - Version
 - Author

The @a Localdir and the @a Gettextpackage parameters are usually set inside
the build system.  If this has been done, the call for example HelloWorld
plugin could look like:

@code
PLUGIN_SET_TRANSLATABLE_INFO(
        LOCALEDIR, GETTEXT_PACKAGE, _("Hello World"),
        _("Just another tool to say hello world"),
        "1.0", "John Doe <john.doe@example.org>");
@endcode

When using this macro, you should use the gettext macro @a _() to mark
the strings like name and the short description as translatable as well. You
can see how this is done in the above example.

As you can see the author's information is not marked as translatable in
this example.  The community has agreed that the best practice here is to
use, if possible, the latin version of the author's name followed by the
native spelling inside parenthesis, where applicable.

@subsection plugin_i18n Using i18n/l10n inside Plugin


You can (and should) also mark other strings beside the plugin's meta
information as translatable.  Strings used in menu entries, information
boxes or configuration dialogs should also be translatable as well.  Geany
offers a way to enable this in the plugin's code using the main_locale_init()
function provided by the plugin API. This function takes the same two
parameters discussed in the previous section; @a GETTEXT_PACKAGE and
@a LOCALEDIR.

The main_locale_init() function is best called during initialization in the
plugin's plugin_init() function.  Adding this to the HelloWorld example could
look like:
@code
void plugin_init(GeanyData *data)
{
        main_locale_init(LOCALEDIR, GETTEXT_PACKAGE);
        main_menu_item = gtk_menu_item_new_with_mnemonic("Hello World");
        gtk_widget_show(main_menu_item);
        gtk_container_add(GTK_CONTAINER(geany->main_widgets->tools_menu),
                main_menu_item);
        g_signal_connect(main_menu_item, "activate",
                G_CALLBACK(item_activate_cb), NULL);
}
@endcode

@note If you've previously called the PLUGIN_SET_TRANSLATABLE_INFO() you do not
need to call main_locale_init() yourself, as this has been already been
done for you.

*/