mergestate: extract a base class to be shared by future memmergestate This extracts a new base class from `mergestate` and leaves all the vfs-touching code in `mergestate`. Differential Revision: https://phab.mercurial-scm.org/D9039

mergestate: extract overridable methods for making/restoring file backups In-memory merge currently still uses on-disk mergestate. That's mostly harmless (I don't think I've seen any problem it's actually caused). It's still a little weird. I'm planning to add an in-memory mergestate, which will be used with `overlayworkingctx`. This patch prepares for that by extracting that logic, so it's easier to change per subclass. Differential Revision: https://phab.mercurial-scm.org/D9038

mergestate: initialize all properties in __init__() This is hopefully not very controverial. I found the initialization before this patch unorthodox. It wasn't clear which properties the object was supposed to have. Differential Revision: https://phab.mercurial-scm.org/D9037

mergestate: remove unnecessary clearing of `localctx` and `otherctx` As noted in the previous commit, there are no callers that (re-)use the instance after calling `reset()`. There are also no callers that call `_read()` after doing anything with the instance (it's only called right after an instance is created). If reviewers feel that this is too risky, I can extract and reuse the poisoning code that indygreg once added for poisining repo instances. Differential Revision: https://phab.mercurial-scm.org/D9036

mergestate: move most of of reset() into start() `ms.reset()` has somehow become a combination of two different things: 1. A constructor-like function creating an empty instance 2. A call to `shutil.rmtree()` to clear the mergestate. It seems that all callers now care only about the latter (since we changed one caller to use the new `ms.start()` method instead). Let's move the code for the former into `start()`, since that's the only place it's needed. Differential Revision: https://phab.mercurial-scm.org/D9035

mergestate: make clean() only be about creating a clean mergestate This is similar to the previous patch, but moves the separation one step further out, to `merge.py`. Differential Revision: https://phab.mercurial-scm.org/D9034

mergestate: split up reset() for its two use cases We only have one place that calls `ms.reset()` with any arguments. That place is `mergestate.clean()`. The callers that call the function with no arguments seem to all just want delete the mergestate -- none of them look at the instance after calling `reset()`. Let's separate out the two different use cases to make the code clearer. I'll clean up further soon. Differential Revision: https://phab.mercurial-scm.org/D9033

mergestate: simplify reset(), knowing that `other` and `node` go together There's only one caller of `reset()` that passes any arguments at all, and that originates from `merge.py:1371`. That code always passes values for both `node` and `other`. Differential Revision: https://phab.mercurial-scm.org/D9032

mergestate: make some callers not pass pointless node argument The node argument is set on the created `mergestate` instance, but these callers don't even look at that instance. Differential Revision: https://phab.mercurial-scm.org/D9031

py3: don't risk passing a None value to error.ManifestLookupError() This makes the test case added in 20dd2a259b0f (test-grep: add tests for --follow with/without --diff and/or paths, 2020-09-11) pass on Python 3. Differential Revision: https://phab.mercurial-scm.org/D9030

merge: move initial handling of mergeactions near to later one We build `mergeactions` in the beginning and use it in end. Let's build it just before where it will be used. Helps making code much easier to understand. Differential Revision: https://phab.mercurial-scm.org/D8983

upgrade: support running upgrade if repository has share-safe requirement This helps us in testing changing requirements of source repository and checking that the shared repository works. Differential Revision: https://phab.mercurial-scm.org/D8660

config: add `--shared` flag to edit config file of shared source With `format.exp-share-safe` enabled, we now read the `.hg/hgrc` of the shared source also. This patch adds `--shared` flag to `hg config` command which can be used to edit that shared source config file. It only works if the repository is shared one and is shared using the safe method. Differential Revision: https://phab.mercurial-scm.org/D8659

localrepo: load the share source .hg/hgrc also in share-safe mode (API) The second part of the Share Safe Plan is to share source repo config also. This patch adds logic to load the source repo .hg/hgrc if we are in share safe mode. On unshare, we copy and prepend source config to current repo so that config which was shared is persisted. A test is added to show that now if we enable a hook on the source repo, that also runs on the shared repositories. API change as a new optional argument sharedvfs added to localrepo.loadhgrc() Differential Revision: https://phab.mercurial-scm.org/D8656

helptext: document exp-sharesafe in internals/requirements.txt `exp-sharesafe` is a new requirement and we should document it. Differential Revision: https://phab.mercurial-scm.org/D8914

share: introduce config option to store requires in .hg/store This introduces a config option which enabled stores the requirements on a repository in store instead. When enabled, `.hg/requires` will contain the `share-safe` requirement which marks that the requirements are present in the store. This is done so that repository requirements can be shared with shares made using `hg share` command. After this patch, `hg share` checks whether the source repository has share-safe requirement, if yes, it does not copy the requirements. Test for the new functionality is added and a test case in exitsing share tests is also added. Differential Revision: https://phab.mercurial-scm.org/D8633