worker: don't expose readinto() on _blockingreader since pickle is picky The `pickle` module expects the input to be buffered and a whole object to be available when `pickle.load()` is called, which is not necessarily true when we send data from workers back to the parent process (i.e., it seems like a bad assumption for the `pickle` module to make). We added a workaround for that in https://phab.mercurial-scm.org/D8076, which made `read()` continue until all the requested bytes have been read. As we found out at work after a lot of investigation (I've spent the last two days on this), the native version of `pickle.load()` has started calling `readinto()` on the input since Python 3.8. That started being called in https://github.com/python/cpython/commit/91f4380cedbae32b49adbea2518014a5624c6523 (and only by the C version of `pickle.load()`)). Before that, it was only `read()` and `readline()` that were called. The problem with that was that `readinto()` on our `_blockingreader` was simply delegating to the underlying, *unbuffered* object. The symptom we saw was that `hg fix` started failing sometimes on Python 3.8 on Mac. It failed very relyable in some cases. I still haven't figured out under what circumstances it fails and I've been unable to reproduce it in test cases (I've tried writing larger amounts of data, using different numbers of workers, and making the formatters sleep). I have, however, been able to reproduce it 3-4 times on Linux, but then it stopped reproducing on the following few hundred attempts. To fix the problem, we can simply remove the implementation of `readinto()`, since the unpickler will then fall back to calling `read()`. The fallback was added a bit later, in https://github.com/python/cpython/commit/b19f7ecfa3adc6ba1544225317b9473649815b38. However, that commit also added checking that what `read()` returns is a `bytes`, so we also need to convert the `bytearray` we use into that. I was able to add a test for that failure at least. Differential Revision: https://phab.mercurial-scm.org/D8928

commit: clear mergestate also with --amend (issue6304) The `hg commit --amend` uses the in-memory code, which naturally doesn't touch the merge state (well, it shouldn't anyway; I think I've fixed bugs in that area recently). We therefore need to clear the mergestate after calling `repo.commitctx()` since we expect that from `hg commit --amend`. Differential Revision: https://phab.mercurial-scm.org/D8932

tests: add test showing that merge state is not cleared by amend This is slightly modified version of the test case I provided in issue6304. Differential Revision: https://phab.mercurial-scm.org/D8931

requirements: introduce constants for `shared` and `relshared` requirements We add them to `WORKING_DIR_REQUIREMENTS` too as they should be stored in `.hg/requires` and have information about the type of working copy. Differential Revision: https://phab.mercurial-scm.org/D8926

mergestate: replace `addmergedother()` with generic `addcommitinfo()` (API) Storing that a file is resolved for the other parent while merging is just one case of things we will like to store in the mergestate. There are more which we will like to store. This patch replaces `addmergedother()` with a much more generic `addcommitinfo()`. Doing this, we also blinding stores the same key value pair generated by the merge code instead of touching them. Differential Revision: https://phab.mercurial-scm.org/D8923

merge: introduce `addcommitinfo()` on mergeresult object This makes code little bit nicer as we directly update information in the mergeresult object instead of building up a dict first and then setting it. Differential Revision: https://phab.mercurial-scm.org/D8922

merge: use collections.defaultdict() for mergeresult.commitinfo We will be storing info from mergeresult.commitinfo to mergestate._stateextras in upcoming patches, let's make them use same structure so that we don't have to make much efforts in transferring info from one to other. Differential Revision: https://phab.mercurial-scm.org/D8921

mergestate: use _stateextras instead of merge records for commit related info There is a set of information related to a merge which is needed on commit. We want to store such information in the mergestate so that we can read it while committing. For this purpose, we are using merge records and introduced a merge entry state for that. However this won't scale and is not clean way to implement this. This patch reworks the existing logic related to this to use _stateextras and read from it. Right now the information stored is not very descriptive but it will be in next patch. Using _stateextras also makes MERGE_RECORD_MERGED_OTHER useless and only to be kept for BC. Differential Revision: https://phab.mercurial-scm.org/D8920