util: add a simple poll utility We'll use it to detect when a sshpeer have server output to be displayed. The implementation is super basic because all case support is not the focus of this series.

crecord: fix blue artifact bug coming back from help screen Before this patch, with record's curses interface: - When one pressed the ? key to see the help menu and then leaves the help menu - Then, blue artifacts would remain on the screen This patch forces a screen clear / refresh after coming back from the help menu. Since we don't have UI test for crecord I checked on my machine that the bug does not reproduce.

scmutil: consistently return subrepos relative to ctx1 from itersubrepos() Previously, if a subrepo was added in ctx2 and then compared to another without it (ctx1), the subrepo for ctx2 was returned amongst all of the ctx1 based subrepos, since no subrepo exists in ctx1 to replace it in the 'subpaths' dict. The two callers of this, basectx.status() and cmdutil.diffordiffstat(), both compare the yielded subrepo against ctx2, and thus saw no changes when ctx2's subrepo was returned. The tests here previously didn't mention 's/a' for the 'p1()' case. This appears to have been a known issue, because some diffordiffstat() comments mention that the subpath disappeared, and "the best we can do is ignore it". I originally ran into the issue with some custom convert code to flatten a tree of subrepos causing hg.putcommit() to abort, but this new behavior seems like the correct status and diff behavior regardless. (The abort in convert isn't something users will see, because convert doesn't currently support subrepos in the official repo.)

context: introduce the nullsub() method Ultimately, this will be used by scmutil. The subrepo module already imports it, so it can't import the subrepo module to access the underlying method.