hg-core: minor code style change (D8958#inline-14993 followup) Differential Revision: https://phab.mercurial-scm.org/D9083

changing-files: move default constructor value to None According to Augie Fackler, using tuple as default value confuse PyType when actual values are passed at init time. Differential Revision: https://phab.mercurial-scm.org/D9086

rust: format with rustfmt I suppose I ran the formatter on the tip but not on every patch. Differential Revision: https://phab.mercurial-scm.org/D9093

merge: store cases when a file is absent post merge in commitinfo Some merges can result in file being absent form working directory. This can be one of file was kept deleted or file was removed by merge code. User might revert the file back before committing. In such cases we will like to have better handling and create new filenodes. We store this info in mergestate as commitinfo so that we can use it while committing to create new filenode if required. Differential Revision: https://phab.mercurial-scm.org/D9003

tests: add some more debugmergestate calls in `test-merge-criss-cross.t` Differential Revision: https://phab.mercurial-scm.org/D9029

commit: force create a new filenode if it was set in mergestate by merge For reasons mentioned in previous commits, we will like to forcefully create a new filenode sometimes. Combination of this patch and previous one, we fixed a case in `test-merge-combination.t`. This does not yet results in conflict where it should, I need to investigate more about what's happening as it should be a change-delete conflict now. Differential Revision: https://phab.mercurial-scm.org/D8989

merge: store commitinfo if these is a dc or cd conflict delete-changed or changed-delete conflicts can either be resolved by mergetool, if some tool is passed and using or by user choose something on prompt or user doing some `hg revert` after choosing the file to remain conflicted. If the user decides to keep the changed side, on commit we just reuse the parent filenode. This is mostly fine unless we are in a distributed environment and people are doing criss-cross merges. Since, we don't have recursive merges or any other way of describing the end result of the merge was an explicit choice and it should be differentiated from it's ancestors, merge algo during criss-cross merges fails to take in account the explicit choice made by user and end up with a what-can-be-said-wrong-merge. The solution which we are trying to fix this is by creating a filenode on commit instead of reusing the parent filenode. This helps differentiate between pre-merged filenode and post-merge filenode and kind of tells about the choice user made. To implement creating new filenode functionality, we store info about these files in mergestate so that we can read them on commit and force create a new filenode. Differential Revision: https://phab.mercurial-scm.org/D8988

mergestate: update _stateextras instead of reassinging `merge.applyupdates()` can store extras for a file and _stateextras may not be empty always. Hence reassigning loses the old values. We can directly update like this because we switched to using `collections.defaultdict` for `_stateextras` sometime ago.