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.

treemanifest: further optimize treemanifest.matches() The matches function was previously traversing all submanifests to look for matching files, even though it was possible to know if a submanifest won't contain any matches. This change adds a visitdir function on the match object to decide quickly if a directory should be visited when traversing. The function also decides if _all_ subdirectories should be traversed. Adding this logic as methods on the match object also makes the logic modifiable by extensions, such as largefiles. An example of a command this speeds up is running hg status --rev .^ python/ on the Mozilla repo with the treemanifest experiment enabled. It goes from 2.03s to 1.85s. More improvements to speed from this change will happen when treemanifests are lazily loaded. Because a flat manifest is still loaded and then converted into treemanifests, speed improvements are limited. This change has no negative effect on speed. For a worst-case example, this command is not negatively impacted: hg status --rev .^ 'relglob:*.js' on the Mozilla repo. It goes from 2.83s to 2.82s.

util: move dirs() and finddirs() from scmutil to util An upcoming commit requires that match.py be able to call scmutil.dirs(), but when match.py imports scmutil, a dependency cycle is created. This commit avoids the cycle by moving dirs() and its related finddirs() function from scmutil to util, which match.py already depends on.

parsers: remove unused dependency on util Parsers.py had a reference to util.sha1 which was unused. This commit removes this reference as well as the unused import of util to simplify the dependency graph. This is important for the next commit which actually relocates part of a module to eliminate a cycle.

changectx.walk: drop unnecessary call to match function If all the files in match.files() are in the context/manifest, we already know that the matcher will match each file.

merge with stable