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

Issue #2185831 by tim.plunkett: Split up ParamConverterManager and stop throwing NotFoundHttpException.

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 #2167109 by Berdir, sun, alexpott, ACF, acrollet, adamdicarlo, Albert Volkman, andreiashu, andyceo, andypost, anenkov, aspilicious, barbun, beejeebus, boombatower, cam8001, chriscalip, chx, cosmicdreams, dagmar, damiankloip, dawehner, deviance, disasm, dixon_, dstol, ebrowet, Gábor Hojtsy, heyrocker, Hydra, ianthomas_uk, japicoder, jcisio, jibran, julien, justafish, jvns, KarenS, kbasarab, kim.pepper, larowlan, Lars Toomre, leschekfm, Letharion, LinL, lirantal, Lukas von Blarer, marcingy, Mike Wacker, mrf, mtift, mtunay, n3or, nadavoid, nick_schuch, Niklas Fiekas, ParisLiakos, pcambra, penyaskito, pfrenssen, plopesc, Pol, Rok Žlender, rvilar, swentel, tim.plunkett, tobiasb, tsvenson, typhonius, vasi1186, vijaycs85, wamilton, webchick, webflo, wizonesolutions, xjm, yched, YesCT, znerol: Remove Variable subsystem.

This reverts commit f2769f4d.

Issue #2164367 by alexpott, tim.plunkett, dawehner: Rebuild router as few times as possible per request.

Issue #2169447 by damiankloip, sun, longwave: DX: Supply CacheBackendInterface::CACHE_PERMANENT as Cache::PERMANENT.

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.

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 #2098119 by beejeebus, alexpott, chx: Replace config context system with baked-in locale support and single-event based overrides.

Issue #2042807 by tim.plunkett, pwolanin, ianthomas_uk, jhodgdon: Convert search plugins to use a ConfigEntity and a PluginBag.

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.

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.

Issue #2001206 by andypost, penyaskito, herom, Crell, ebeyrent, DmitryDrozdik: Replace drupal_container() with Drupal::service().

Issue #1954892 by dawehner, David_Rothstein, tim.plunkett: Replace 'theme callback' and hook_custom_theme() with a clean theme negotiation system.

Issue #2115025 by Gábor Hojtsy, pfrenssen, dawehner: Content admin views title saved localized to the menu table.

Issue #2081133 by mrsinguyen, dsdeiz, janstoeckler: Remove Unused local variable from /core/includes/menu.inc.

Revert "Issue #1954892 by dawehner, tim.plunkett, David_Rothstein, effulgentsia: Replace 'theme callback' and hook_custom_theme() with a clean theme negotiation system."

This reverts commit fc04601c.

Issue #1954892 by dawehner, tim.plunkett, David_Rothstein, effulgentsia: Replace 'theme callback' and hook_custom_theme() with a clean theme negotiation system.

Issue #2084463 by dawehner, pwolanin, David_Rothstein, tim.plunkett, Xano: Convert contextual links to a plugin system similar to local tasks/actions.

Issue #2048223 by dawehner, ParisLiakos, herom, fubhy, damiankloip, vijaycs85, joelpittet, tim.plunkett: Add $account argument to AccessCheckInterface::access() method and use the current_user() service.

Issue #2046367 by jhodgdon, amateescu, larowlan, juanolalla: Menu routing docs do not match what the code is doing.

Issue #2045931 by PerthSam152, LinL, adsw12, joelpittet: Replace all module_exists() deprecated function calls.

This reverts commit cc84f390 - bad
commit message.

Issue #2105167 by tim.plunkett: Fixed Legacy local actions are added alongside modern local actions.

Issue #2089351 by thedavidmeister, meba: Convert all calls to check_plain() in core to Drupal\Component\Utility\String::checkPlain() in core/includes.

Issue #2077473 by dawehner, damiankloip, pwolanin: Replace local action plugin discovery with YamlDiscovery and handle routes with parameters.

Issue #2100753 by Berdir: Fixed route_parameters break lazy-save logic in MenuLinkStorageController::save().

Issue #2070651 by pwolanin, dawehner, larowlan, tim.plunkett, ParisLiakos: Introduce a path-based breadcrumb builder, remove the one that's based on {menu_links()}.

Issue #1831846 by katbailey, maciej.zgadzaj, dawehner, RobLoach, moe4715, Hydra, larowlan, andypost: Fixed Help block is broken with language path prefixes.