py3: fix stringmatcher() to byte-stringify exception message Spotted while writing regexp variant of stringmatcher().

stringutil: extract helper function that splits stringmatcher() pattern

grep: extract main search loop as searcher method Still displayer part is in commands.grep(), the core grep logic is now reusable. I'll revisit the displayer stuff later since it will be another long series.

scmutil: move walkchangerevs() from cmdutil It's no longer a command-level function, but a pure helper to walk revisions in a windowed way. This change will help eliminate reverse dependency of revset.py -> grep.py -> cmdutil.py in future patches.

grep: extract public function to register file to be skipped The main grep loop will be extracted to a searcher method, but this skipping condition depends on the result of display() function.

posix: avoid a leaked file descriptor in a unix domain socket exception case Differential Revision: https://phab.mercurial-scm.org/D9206

posix: use context managers in a couple of places Differential Revision: https://phab.mercurial-scm.org/D9205

record: when backing up, avoid generating very long filenames If the original file's path is longer than the individual filename maximum length (256 on Linux, I believe?), then this mechanism of "replace slashes with underscores" causes an error. Now, we'll produce just the "basename" of the file, plus some stuff to ensure it's unique. This can be potentially confusing for users if there's a file with the same name in multiple directories, but I suspect that this is better than just breaking. Example: `<reporoot>/a/long/path/to/somefile.txt` used to be backed up as `<reporoot>/.hg/record-backups/a_long_path_to_somefile.txt.abcdefgh`, it will now be backed up as `<reporoot>/.hg/record-backups/somefile.txt.abcdefgh` We could do the naive thing (what we were doing before) and have it to doing something with either subdirectories (`<backuproot>/a/long/path/to/somefile.txt.abcdefgh` or minimize #dirs with `<backuproot>/a_long_path/to_somefile.txt.abcdefgh`), prefix-truncated paths (such as `<backuproot>/__ath_to_somefile.txt.abcdefgh`, where that `__` elides enough to get us under 255 chars (counting the +9 we need to add!)), or hash-of-dirname (`<backuproot>/<sha1sum_of_dirname>/somefile.txt.abcdefgh`), but ultimately every option felt over engineered and that it would be more likely to cause problems than it would be to solve any, especially if it was conditional on directory length. Differential Revision: https://phab.mercurial-scm.org/D9207

mergestate: add `allextras()` to get all extras `extras()` can only be used for getting extra for a file. However at couple of places in code, we wanted to iterate over all the extras stored with the mergestate and they were accessing the private `_stateextras`. We add a new function for this. Differential Revision: https://phab.mercurial-scm.org/D9190

mergestate: document `o` merge record state in _mergestate_base docs _mergestate_base documentation serves as a nice documentation for mergestate. This also documents known merge records and known merge record states. I missed adding `o` state to it when I introduced it. Let's add it now. Differential Revision: https://phab.mercurial-scm.org/D9156