commands: use constants for merge things We have nice constants now. Let's use them to make the code easier to reason about. Differential Revision: https://phab.mercurial-scm.org/D2702

merge: use constants for actions We finish up establishing named constants in this file with actions. I remember scratching my head trying to figure out what this code was doing as part of addressing a recent security issue with subrepos. Having the named constants in place definitely makes things easier to read. I'm not convinced the new constants have the best names (I'm not an expert in this code). But they can be changed easily enough. Also, since these constants are internal only, we might want to change their values to something more human readable to facilitate debugging. Or maybe we could employ an enum type some day... Differential Revision: https://phab.mercurial-scm.org/D2701

merge: use constants for merge record state Named constants are easier to read than short string values. Differential Revision: https://phab.mercurial-scm.org/D2700

merge: use constants for merge driver state Named constants are superior to magic values. Differential Revision: https://phab.mercurial-scm.org/D2699

merge: use constants for merge state record types merge.py is using multiple discrete sets of 1 and 2 letter constants to define types and behavior. To the uninitiated, the code is very difficult to reason about. I didn't even realize there were multiple sets of constants in play initially! We begin our sanity injection with merge state records. The record types (which are serialized to disk) are now defined in RECORD_* constants. Differential Revision: https://phab.mercurial-scm.org/D2698

histedit: always define update results Before, we had a branch that could return None for the update stats. Let's just return an updateresult instance instead. Differential Revision: https://phab.mercurial-scm.org/D2693