lfs: add a switch to `hg verify` to ignore the content of blobs

Trying to validate the fulltext of an external revision causes missing blobs to
be downloaded and cached.  Since the downloads aren't batch prefetched[1] and
aren't compressed, this can be expensive both in terms of time and space.

I made this a tri-state instead of a simple bool because there's an existing
(undocumented) config to handle this, and it would be weird if `hg verify` were
to suddenly start ignoring that config but an `hg recover` initiated verify
honors it.  Since this uses the same config setting, it too will skip
rename verification (which requires fulltext, but not for LFS).

[1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2018-April/116118.html

Differential Revision: https://phab.mercurial-scm.org/D7708

hgext/lfs/__init__.py

@@ -402,3 +402,24 b' def debuglfsupload(ui, repo, **opts):'
     revs = opts.get('rev', [])
     pointers = wrapper.extractpointers(repo, scmutil.revrange(repo, revs))
     wrapper.uploadblobs(repo, pointers)
+
+
[e-mail](
+    b'verify', opts=[(b'', b'no-lfs', None, _(b'skip all lfs blob content'))]
+)
+def verify(orig, ui, repo, **opts):
+    skipflags = repo.ui.configint(b'verify', b'skipflags')
+    no_lfs = opts.pop('no_lfs')
+
+    if skipflags:
+        # --lfs overrides the config bit, if set.
+        if no_lfs is False:
+            skipflags &= ~repository.REVISION_FLAG_EXTSTORED
+    else:
+        skipflags = 0
+
+    if no_lfs is True:
+        skipflags |= repository.REVISION_FLAG_EXTSTORED
+
+    with ui.configoverride({(b'verify', b'skipflags'): skipflags}):
+        return orig(ui, repo, **opts)

tests/test-lfs.t

@@ -796,6 +796,27 b" because they aren't accessed."
   $ test -f fromcorrupt/.hg/store/lfs/objects/66/100b384bf761271b407d79fc30cdd0554f3b2c5d944836e936d584b88ce88e
   [1]
 
+Verify will not try to download lfs blobs, if told not to process lfs content
+
+  $ hg -R fromcorrupt --config lfs.usercache=emptycache verify -v --no-lfs
+  repository uses revlog format 1
+  checking changesets
+  checking manifests
+  crosschecking files in changesets and manifests
+  checking files
+  checked 5 changesets with 10 changes to 4 files
+
+Verify will not try to download lfs blobs, if told not to by the config option
+
+  $ hg -R fromcorrupt --config lfs.usercache=emptycache verify -v \
+  >                   --config verify.skipflags=8192
+  repository uses revlog format 1
+  checking changesets
+  checking manifests
+  crosschecking files in changesets and manifests
+  checking files
+  checked 5 changesets with 10 changes to 4 files
+
 Verify will copy/link all lfs objects into the local store that aren't already
 present.  Bypass the corrupted usercache to show that verify works when fed by
 the (uncorrupted) remote store.