Talk about the problems of child themes in WordPress (incl. solution per plugin) from WordCamp Milano 20156 (updated version)

1. The
Child Theme Dilemma
WordCamp Milano 2016
Torsten Landsiedel

2. Hello!
Torsten Landsiedel
WordPress- Freelancer
Moderator German Supportforum
Editor Team de.w.org
Translation Contributor and Editor
Co-Organisator WP Meetup Hamburg
Co-Organisator WordCamp Hamburg
@zodiac1978

3. Child Theme Usage
Who has used Child Themes?

4. Child Theme Usage
Why?

5. Child Theme Problems
Security
Extensibility
Performance

6. Security Problems
Parent Theme
search.php (with
vulnerability)
Child Theme
search.php (with
vulnerability)
Parent Theme
search.php (without
vulnerability)
Child Theme
search.php (with
vulnerability)
update
overwrites
no update!overwrites

7. Child Themes aren’t safe?
Why nobody told us?

8. Extensibility
Pluggable Functions:
if ( ! function_exists( 'theme_special_nav' ) ) {
function theme_special_nav() {
// Do something.
}
}
Attention:
Now you have to maintain the code!

9. Missing extensibilities
Framework Theme + Premium Child Theme?
WordPress.org Theme + Child Theme?
Where to put the customizations?
There are no Grandchild Themes :(

10. Missing extensibilities
Why shouldn’t there be Grandchild Themes?

11. Missing extensibilities
This idea of releasing advanced child themes just creates
the same problem child themes were meant to solve:
upgradability.
– Justin Tadlock
http://justintadlock.com/archives/2010/08/16/frameworks-parent-child-an
d-grandchild-themes

12. Update of Parent Theme
Without any problems?
It depends …
filter/actions removed?
CSS classes changed?
Markup changed?
Paths changed?

13. Performance problems
Many Child Themes are using @import
@import url(../parent-theme/style.css);
But @import stops parallel loading
in all browsers.
http://www.stevesouders.com/blog/2009/04/09/dont-use-import/

14. Solution:
De-register styles und re-register/re-enqeue parent and
child styles
function twentytwelve_child_scripts() {
wp_deregister_style( 'twentytwelve-style' );
wp_register_style( 'twentytwelve-style',
get_template_directory_uri() . '/style.css' );
wp_enqueue_style( 'twentytwelve-child-style',
get_stylesheet_uri(), array( 'twentytwelve-style' ) );
}
add_action( 'wp_enqueue_scripts', 'twentytwelve_child_scripts', 11 );
Performance problems

15. Even simpler:
Enqueue parent styles. Done! Just works if
get_stylesheet is used (and just this) in the parent
theme.
// Faster than @import
add_action( 'wp_enqueue_scripts', 'my_child_theme_scripts' );
function my_child_theme_scripts() {
wp_enqueue_style( 'parent-theme-css', get_template_directory_uri() .
'/style.css' );
}
Performance problems

16. New problem:
Many themes are not build that way.
Hardcoded stylesheets in the header.php for example:
<link rel="stylesheet" type="text/css" media="all"
href="<?php bloginfo( 'stylesheet_url' ); ?>" />
Performance problems

17. Performance problems
Or the theme is not compatible with using a child
theme.
Or you have to de-register everything to preserve the
correct order.
wp_enqueue_style( 'base_styles',
get_template_directory_uri() . '/css/base.css' );
wp_enqueue_style( 'responsive_styles',
get_template_directory_uri() . '/css/mobile.css' );
wp_enqueue_style( 'ie_styles',
get_template_directory_uri() . '/css/ie.css' );

18. Performance problems
Can be very complicated for beginners ...

19. Performance problems
Justin Tadlocks brilliant solution for the parent theme:
function my_enqueue_styles() {
/* If using a child theme, auto-load the parent theme style. */
if ( is_child_theme() ) {
wp_enqueue_style( 'parent-style',
trailingslashit( get_template_directory_uri() ) . 'style.css' );
}
/* Always load active theme's style.css. */
wp_enqueue_style( 'style', get_stylesheet_uri() );
}
add_action( 'wp_enqueue_scripts', 'my_enqueue_styles' );
http://justintadlock.com/archives/2014/11/03/loading-parent-styles-for-child-themes

20. Hey Torsten!
Grab some water.
Don’t speak too fast.
:)

21. Child Theme Problems
Security
Extensibilities
Performance ✓

22. Idea 1: Child Theme Lite
“Child themes from theme developers should be nothing
more than a stylesheet and a few functions.”
– Justin Tadlock
http://justintadlock.com/archives/2010/08/16/frameworks-parent-child-and-grandchild-themes

23. Idea 1: Child Theme Lite
Child Theme just contains functions.php
and style.css.
All changes should just be made with hooks
and filters.
This would be made within a plugin.
Child Theme remains update-ability.

24. Idea 1: Child Theme Lite
Problem:
How many themes do something like that?

25. Idea 2: Child Theme Check
Every template file in the theme is getting a version
number in the file header.
@version 1.0.0
Check of the version number via plugin
(or even better via WordPress core).
Differences between files can be shown via
wp_text_diff().

26. Idea 2: Child Theme Check
DEMO!

27. Child Theme Check
Voilá!

28. Child Theme Check

29. Child Theme Check
http://de.wordpress.org/plugins/child-theme-check/
https://github.com/Zodiac1978/tl-template-checker
- This is a Twitter opportunity! -

30. Child Theme Problems
Security ✓
Extensibilities (✓)
Performance ✓

31. Spread the word!
The new default theme is using it, too!
https://github.com/WordPress/twentyseventeen/issues/72

32. ● Italian Translation is waiting for you!
https://translate.wordpress.org/locale/it/default/wp-plugins/chi
ld-theme-check
● Found a bug? Just open an issue on Github:
https://github.com/Zodiac1978/tl-template-checker/issues
● Help me to get this as a recommendation in the Theme Check Plugin
(https://de.wordpress.org/plugins/theme-check/):
https://github.com/WordPress/theme-check/issues/115
Conribute? Great!

33. Discussion!
Questions? Contradiction? Alternative solutions?
Theme Shop/Theme Developer: Interested?
Let’s speak about it!
@zodiac1978
http://torstenlandsiedel.de/kontakt

34. Thank you for your time!
Have a great coffee break.
Don’t miss the talk about
Child Plugins from Bernhard Kau
(Track 1 - 17:10 h)