AFAICT, there's no D8 equivalent of the 'theme callback' property of hook_menu() items on D7.
But... there is, it's CustomThemeNegotiator. But it's in a test module, theme_test.
It provides a '_custom_theme' property to routes, which lets you specify the theme:
theme_test.function_template_override:
path: '/theme-test/function-template-overridden'
options:
_custom_theme: 'test_theme'
defaults:
_controller: '\Drupal\theme_test\ThemeTestController::functionTemplateOverridden'
requirements:
_access: 'TRUE'
It would be useful to move this into system module, so it can be used.
Postponed: needs info
11.0 🔥
system.module
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Is this still relevant, given the lack of interest in the past 9 years? As @dawehner pointed out, you can just write your own ThemeNegotiator.
It's much simpler to add one line to a route than to write a whole theme negotiator class, and the code is already right there.
Is there much of a use case for this in core? Maybe it's better to use contrib such as https://www.drupal.org/project/theme_switcher →