tests: update narrowspec when narrowspec, not dirstate, is accessed test-narrow-expanddirstate.t mimics a Google-internal extension that updates the narrowspec whenever the dirstate is accessed. Since 1d09ba0d2ed3 (narrow: move remaining narrow-limited dirstate walks to core, 2018-10-01) and a few commits before it, we no longer restrict repo.dirstate.walk() to the narrowspec. It is instead done at a higher level (e.g. context.status()). We were running into problems with the Google-internal extension when importing those commits. The issue was that the narrowspec was read before the first dirstate access. I believe the right fix is to instead update the narrowspec when trying to read it (not when reading the dirstate), so that's what this patch does. Differential Revision: https://phab.mercurial-scm.org/D5275

merge: extract helper for creating empty "actions" dict Replicating the set of actions in multiple places is bad. Differential Revision: https://phab.mercurial-scm.org/D5472

manifest: accept narrowmatch into constructor instead of getting from repo The manifest should ideally not know at all about the repo, so this is just a little step towards cleaning that up. Differential Revision: https://phab.mercurial-scm.org/D5469

py3: byteify one more sys.argv in gendoc.py

test: introduce a new flag to display env variable line per line It's easier to conditionalize some of the environment variables per Mercurial version once there is only one value per line. Differential Revision: https://phab.mercurial-scm.org/D5453

revlog: add an explicit test for `issnapshot` We test the method on a real revlog containing "real" data.

revlog: add some direct testing of the slicing logic This test check slicing backed by an actual revlog. It will test the C version of slicing (if the test are run with the C extensions).