Rewrite rules should be flushed when you switch themes

[jorbin]

@nacin said so at WCMA, so here's a patch to do it.

[greenshady]

Why should rewrite rules be flushed when switching themes?

[filosofo]

I suppose in case a theme is using custom post types. But it seems that, like plugins, themes that need flushed rules should handle it themselves.

[nacin]

Replying to filosofo:

But it seems that, like plugins, themes that need flushed rules should handle it themselves.

Unfortunately, there's no activation hook for them to do so. (For example P2 uses an option to store whether rules have been flushed.) I suggested this in response to a question for how to handle things that add rewrite rules...

I don't think this patch will work, though, because the new theme isn't included on that pageload so the old rules will still be regenerated. Sounds to me that to do an activation hook for themes, we need to add an autoloaded option to keep track.

[greenshady]

Adding an activation hook sounds like the best solution for this. We have switch_theme, which works on deactivation. Themes that add custom post types and taxonomies should be flushing the rewrite rules themselves.

[hakre]

+1 for theme activation hook.

[dd32]

resetting keywords since the attached patch will not work as intended.

[jane]

If anyone would like to get this in for 3.1, there are a few days left to submit patches for enhancements before freeze.

[nacin]

This is done in 3.1 on wp-admin/themes.php. We should do this better, in conjunction with a real theme activation hook, in the future.

[nacin]

FYI, the jank was removed in 3.1. [17241]. Need to do this properly in 3.2.

[scribu]

Related: #7795

[chriscct7]

Can't themes who want to do this simply hook into after_switch_theme and do this?

[jorbin]

r18655 in 3.3 introduced after_switch_theme which can be used for this. Core shouldn't encourage themes to include there own custom rewrite rules.

Also, bad on me for such a bad description.

[jorbin]

I didn't consider the use case of needing to get rid of old rewrites from the last theme. Dion pointed it out. Let's fix this in 4.4

[jorbin]

I can't figure out a good way to unit test this since:

1) None of the default themes that we use for testing have custom rewrite rules.
2) flush_rewrite_rules relies upon saving the in memory rules. As the tests all run in a single memory session, there isn't a good way to fake this that would produce reliable test results.

This is the test code I was playing around with before coming to this conclusion.

class Tests_Flush_On_Theme_Change extends WP_UnitTestCase {
    private $original_rewrite_rules;
    private $current_theme;

    function setUp() {
        global $wp_rewrite;
        parent::setUp();

        // Need rewrite rules in place to use url_to_postid
        $wp_rewrite->init();
        $wp_rewrite->set_permalink_structure( '/%year%/%monthnum%/%day%/%postname%/' );

        create_initial_taxonomies();

        $wp_rewrite->flush_rules();

        $this->original_rewrite_rules = get_option( 'rewrite_rules' );

        $this->current_theme = wp_get_theme();

    }

    function tearDown() {
        global $wp_rewrite;
        $wp_rewrite->init();

        $theme = $this->current_theme;

        switch_theme( $theme->Stylesheet );
        parent::tearDown();
    }

    /**
     * @ticket 14849
     */
    function test_switch_theme_rewrite_flush() {
        $themes = wp_get_themes();

        flush_rewrite_rules();

        add_rewrite_rule('^test/([0-9]+)/?', 'index.php?page_id=$matches[1]', 'top');

        flush_rewrite_rules();

        $updated_rewrite_rules =  get_option( 'rewrite_rules' );
        $this->assertNotEquals( $this->original_rewrite_rules , $updated_rewrite_rules );

        foreach ( $themes as $theme ) {
            switch_theme( $theme->Template, $theme->Stylesheet );
            $updated_rewrite_rules =  get_option( 'rewrite_rules' );
            $this->assertEquals( $this->original_rewrite_rules , $updated_rewrite_rules );
        }

    }


}

[jorbin]

In 34028:

Flush rewrite rules upon theme switch

Themes can ( and do ) but shouldn't include custom rewrite rules.This can lead to hard to debug issues for theme authors. Theme changes are not a ultra common conclusion. Flushing the rewrite rules on theme switch will lead to a clean slate for each theme which helps make debugging easier.

And @nacin said we should do this 5 years ago at WordCamp Mid Atlantic.

Fixes #14849