merge: cache unknown dir checks (issue5716) As mentioned in D1222, the recent pathconflicts change regresses update performance in large repositories when many files are being updated. To mitigate this, we introduce two caches of directories that have already found to be either: - unknown directories, but which are not aliased by files and so don't need to be checked if they are files again; and - missing directores, which cannot cause path conflicts, and cannot contain a file that causes a path conflict. When checking the paths of a file, testing against this caches means we can skip tests that involve touching the filesystem. Differential Revision: https://phab.mercurial-scm.org/D1224

dispatch: add HGPLAIN=+strictflags to restrict early parsing of global options If this feature is enabled, early options are parsed using the global options table. As the parser stops processing options when non/unknown option is encountered, it won't mistakenly take an option value as a new early option. Still "--" can be injected to terminate the parsing (e.g. "hg -R -- log"), I think it's unlikely to lead to an RCE. To minimize a risk of this change, new fancyopts.earlygetopt() path is enabled only when +strictflags is set. Also the strict parser doesn't support '--repo', a short for '--repository' yet. This limitation will be removed later. As this feature is backward incompatible, I decided to add a new opt-in mechanism to HGPLAIN. I'm not pretty sure if this is the right choice, but I'm thinking of adding +feature/-feature syntax to HGPLAIN. Alternatively, we could add a new environment variable. Any bikeshedding is welcome. Note that HGPLAIN=+strictflags doesn't work correctly in chg session since command arguments are pre-processed in C. This wouldn't be easily fixed.