Issue #2152211 by joelpittet, IshaDakota, rteijeiro, steveoliver, hussainweb, shanethehat, jenlampton, kpa, AnythonyR, EVIIILJ, kgoel, Cottser, dsdeiz, hanpersand: Convert theme_form() to Twig.

Issue #2152203 by joelpittet, InternetDevels, rteijeiro,  steveoliver, hussainweb, shanethehat, jenlampton, kpa, AnythonyR, EVIIILJ, kgoel, Cottser, dsdeiz, hanpersand: Convert theme_container() to Twig.

Issue #2152225 by longwave, JeroenT, steveoliver, joelpittet, hussainweb, shanethehat, jenlampton, kpa, AnythonyR, EVIIILJ, kgoel, Cottser, dsdeiz, hanpersand: Convert theme_select() to Twig

Revert "Issue #2210197 by sun, longwave: Remove public access to Extension::$type, ::$name, ::$filename." Broke 'drush en simpletest' on testbots

This reverts commit 2c51074d.

Issue #2192649 by sun, chakrapani, sidharthap: Remove drupal_set_title() from installation and update process.

Issue #2073621 by Cyberschorsch, m1n0: Remove unneeded variables from template_preprocess_maintenance_page().

Issue #2187717 by sun, dawehner: Remove code duplication in system_list() and ThemeHandler::rebuildThemeData().

This reverts commit ae8be3cc.

Issue #2070369 by herom, bdgreen, Mac_Weber, InternetDevels, sidharthap, JeroenT: Remove all calls to deprecated function language().

Issue #2045927 by herom, martin107, ianthomas_uk, Xano, michaellander, Sutharsan: Replace all drupal_alter() deprecated function calls.

Issue #1996238 by sun, nod_, damiankloip, Wim Leers, longwave, alexpott, Xano, mdrummond, Mark Carver, Jeff Burnz, highrockmedia, joelpittet, et al: Replace hook_library_info() by *.libraries.yml file.

Issue #2187735 by ianthomas_uk, Sutharsan, andypost: Add removal information to docblock of all @deprecated functions.

Issue #2173655 by Cottser, xjm, jessebeach, alexpott, rlmumford: Refactor theme() to _theme(); make it a private API to discourage module developers from circumventing the renderable build system.

Issue #2072647 by thedavidmeister, herom, jwilson3, Cottser, LinL: #theme 'maintenance_page' should support render arrays in #content.

Issue #1939064 by joelpittet, pwieck, farrington, mark.labrecque, Cottser, InternetDevels, mdrummond, drupalninja99, BarisW, jenlampton: Convert theme_links() to Twig.

Issue #2152207 by steveoliver, joelpittet, gnuget, idflood, hussainweb, shanethehat, jenlampton, kpa, AnythonyR, EVIIILJ, kgoel, Cottser, dsdeiz, hanpersand: Convert theme_details() to Twig

Issue #1939062 by steveoliver, mdrummond, jenlampton, hussainweb, Cottser, joelpittet, jerdavis, ekl1773, dale42, drupalninja99, gabesullice, c4rl: Convert theme_item_list() to Twig.

Issue #2152229 by steveoliver, rteijeiro, joelpittet, JeroenT, InternetDevels, michamilz, burgerboydaddy, hussainweb, shanethehat, jenlampton, kpa, AnythonyR, EVIIILJ, kgoel, Cottser, dsdeiz, hanpersand: Convert theme_textarea() to Twig

Issue #2152213 by steveoliver, joelpittet, hussainweb, shanethehat, jenlampton, kpa, AnythonyR, EVIIILJ, kgoel, Cottser, dsdeiz, hanpersand: Convert theme_form_element() to Twig

Issue #2168011 by xjm, jessebeach, Damien Tournoud, znerol, Xano: Remove all 7.x to 8.x update hooks and disallow updates from the previous major version.

Issue #2047633 by pwolanin, dawehner, kim.pepper, Xano, amateescu, tim.plunkett: Move definition of menu links to hook_menu_link_defaults(), decouple key name from path, and make 'parent' explicit.

Issue #2152231 by rteijeiro, steveoliver, joelpittet, hussainweb, shanethehat, jenlampton, kpa, AnythonyR, EVIIILJ, kgoel, Cottser, dsdeiz, hanpersand: Convert theme_vertical_tabs() to Twig

Revert "Issue #2047633 by dawehner, pwolanin, Xano, amateescu, tim.plunkett: Move definition of menu links to hook_menu_link_defaults(), decouple key name from path, and make 'parent' explicit."

This reverts commit 531fd593.

Issue #2047633 by dawehner, pwolanin, Xano, amateescu, tim.plunkett: Move definition of menu links to hook_menu_link_defaults(), decouple key name from path, and make 'parent' explicit.

Issue #1979468 by Wim Leers, nod_, pwolanin, longwave, thedavidmeister, jessebeach, larowlan | catch: .active from linkGenerator(), l() and theme_links() forces an upper limit of per-page caching for all content containing links.

Somehow this broke PHPUnit, so rolling back for now.

This reverts commit 91b465bd.

Issue #1862202 by plach, Berdir, katbailey, ParisLiakos, alexpott, chx, sun, larowlan, Gábor Hojtsy, cosmicdreams, vijaycs85, YesCT, penyaskito, andypost, Albert Volkman, joelpitett: Objectify the language system.

Issue #1649780 by effulgentsia, jibran, Wim Leers, nod_, hefox, joelpittet, kaare, BarisW, sun, rbayliss, Cottser, fubhy: Remove first/last/odd/even classes in favor of CSS3 pseudo selectors.

Issue #2168113 by penyaskito, jessebeach, catch: Add leading underscore and other discouragement to drupal_add_css() and drupal_add_js().

Revert "Issue #1979468 by Wim Leers, pwolanin, nod_, thedavidmeister, larowlan: .active from linkGenerator(), l() and theme_links() forces an upper limit of per-page caching for all content containing links."

This reverts commit 624296e7.