graft: allow creating sibling grafts Previously it was impossible to graft a commit onto it's own parent (i.e. create a copy of the commit). This is useful when wanting to create a backup of the commit before continuing to amend it. This patch enables that behavior. The change to the histedit test is because histedit uses graft to apply commits. The test in question moves a commit backwards onto an ancestor. Since the graft logic now more explicitly supports this, it knows to simply accept the incoming changes (since they are more recent), instead of prompting.

unbundle20: move header parsing into the 'getunbundler' function The dispatching will be based on the header content, so we need to move this logic into the factory function.

unbundle20: retrieve unbundler instances through a factory function To support multiple bundle2 formats, we will need a function returning the proper unbundler according to the header. We introduce such aa function and change the usage in the code base. The function will get smarter in later changesets. This is somewhat similar to the dispatching we do for 'HG10' and 'HG11'. The main target is to allow HG2Y support in an extension to ease transition of companies using the experimental protocol in production (yeah...) But I've no doubt this will be useful when playing with a future HG21.

bundle20: move magic string into the class This makes it easy to create a new bundler class that inherits from the core one. This matches the way 'changegroup' packers work. The main target is to allow HG2Y support in an extension to ease transition of companies using the experimental protocol in production (yeah...) But I've no doubt this will be useful when playing with a future HG21.

localrepo.getbundle: drop unused 'format' argument The 'format' argument was not used even when it was added in 60ad2ea5b106 (getbundle: pass arbitrary arguments all along the call chain, 2014-04-17). Note that by removing the argument, if any caller did pass a named 'format' argument, we will now pass that along to exchange.getbundle() via the kwargs. If the idea was to remove such a key, that should have been done explicitly.

exchange: remove check for 'format' key When the 'kwargs' variable was added in 12f161f08d74 (bundle2: allow pulling changegroups using bundle2, 2014-04-01), it could contain only 'bundlecaps', 'common' and 'heads', so the check for 'format' would always be false. Since then, _pullbundle2extraprepare() has been added for hooks, but it seems unlikely that they would a 'format' key.

templates-default: do not show description or summary if empty changeset_printer shows description only if ctx.description().strip() is not empty. The default template should do the same way.