debugmergestate: make templated Our IntelliJ team wants to be able to read the merge state in order to help the user resolve merge conflicts. They had so far been reading file contents from p1() and p2() and their merge base. That is not ideal for several reasons (merge base is not necessarily the "graft base", renames are not handled, commands like `hg update -m` is not handled). It will get especially bad as of my D7827. This patch makes the output s a templated. I haven't bothered to make it complete (e.g. merge driver states are not handled), but it's probably good enough as a start. I've done a web search for "debugmergestate" and I can't find any indication that any tools currently rely on its output. If it turns out that we get bug reports for it once this is released, I won't object to backing this patch out on the stable branch (and then perhaps replace it by a separate command, or put it behind a new flag). The changes in test-backout.t are interesting, in particular this: ``` - other path: foo (node not stored in v1 format) + other path: (node foo) ``` I wonder if that means that we actually read v1 format incorrectly. That seems to be an old format that was switched away from in 2014, so it doesn't matter now anyway. Differential Revision: https://phab.mercurial-scm.org/D8120

tests: add tests of debugmergestate with unresolved/resolved path conflicts I'm about to change `hg debugmergestate` and it broke on these "pu" and "pr" records on my first attempt (D8113), so let's add test coverage. Differential Revision: https://phab.mercurial-scm.org/D8119

mergestate: determine if active without looking for state files on disk I couldn't think of a reason that we need to check state files on disk to determine if a merge is active. I could imagine them being for there for detecting broken state files that would then be cleaned up by some later command, but we always delete the entire `.hg/merge/` tree, so that doesn't seem to be it. The checks were added in 4e932dc5c113 (resolve: abort when not applicable (BC), 2014-04-18). Perhaps there were needed for that and then made obsolete by 6062593d8b06 (resolve: don't abort resolve -l even when no merge is in progress, 2014-05-23). The reason I want to delete the checks is that I think `ms = mergestate.read(repo); ms.active() and ms.local` should be a valid pattern, but it crashes when the merge state file is an empty file if we consider mere presence of the file as "active". Differential Revision: https://phab.mercurial-scm.org/D8118