tests: add a (very slow) test that executes pytype

tests: add a (very slow) test that executes pytype

This is an updated form of D7295, and completes successfully with pytype
2021.03.22.  The 5 or so crashes that were mostly in the hgweb files seems to
have been fixed in 2021.03.10.

Differential Revision: https://phab.mercurial-scm.org/D10237

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-check-pytype.t	Fri Mar 19 00:36:26 2021 -0400
@@ -0,0 +1,105 @@
+#require pytype py3 slow
+
+  $ cd $RUNTESTDIR/..
+
+Many of the individual files that are excluded here confuse pytype
+because they do a mix of Python 2 and Python 3 things
+conditionally. There's no good way to help it out with that as far as
+I can tell, so let's just hide those files from it for now. We should
+endeavor to empty this list out over time, as some of these are
+probably hiding real problems.
+
+mercurial/bundlerepo.py       # no vfs and ui attrs on bundlerepo
+mercurial/changegroup.py      # mysterious incorrect type detection
+mercurial/chgserver.py        # [attribute-error]
+mercurial/cmdutil.py          # No attribute 'markcopied' on mercurial.context.filectx [attribute-error]
+mercurial/context.py          # many [attribute-error]
+mercurial/copies.py           # No attribute 'items' on None [attribute-error]
+mercurial/crecord.py          # tons of [attribute-error], [module-attr]
+mercurial/debugcommands.py    # [wrong-arg-types]
+mercurial/dispatch.py         # initstdio: No attribute ... on TextIO [attribute-error]
+mercurial/exchange.py         # [attribute-error]
+mercurial/hgweb/hgweb_mod.py  # [attribute-error], [name-error], [wrong-arg-types]
+mercurial/hgweb/server.py     # [attribute-error], [name-error], [module-attr]
+mercurial/hgweb/webcommands.py  # [missing-parameter]
+mercurial/hgweb/wsgicgi.py    # confused values in os.environ
+mercurial/httppeer.py         # [attribute-error], [wrong-arg-types]
+mercurial/interfaces          # No attribute 'capabilities' on peer [attribute-error]
+mercurial/keepalive.py        # [attribute-error]
+mercurial/localrepo.py        # [attribute-error]
+mercurial/lsprof.py           # unguarded import
+mercurial/manifest.py         # [unsupported-operands], [wrong-arg-types]
+mercurial/minirst.py          # [unsupported-operands], [attribute-error]
+mercurial/patch.py            # [wrong-arg-types]
+mercurial/pure/osutil.py      # [invalid-typevar], [not-callable]
+mercurial/pure/parsers.py     # [attribute-error]
+mercurial/pycompat.py         # bytes vs str issues
+mercurial/repoview.py         # [attribute-error]
+mercurial/sslutil.py          # [attribute-error]
+mercurial/statprof.py         # bytes vs str on TextIO.write() [wrong-arg-types]
+mercurial/testing/storage.py  # tons of [attribute-error]
+mercurial/ui.py               # [attribute-error], [wrong-arg-types]
+mercurial/unionrepo.py        # ui, svfs, unfiltered [attribute-error]
+mercurial/upgrade.py          # line 84, in upgraderepo: No attribute 'discard' on Dict[nothing, nothing] [attribute-error]
+mercurial/util.py             # [attribute-error], [wrong-arg-count]
+mercurial/utils/procutil.py   # [attribute-error], [module-attr], [bad-return-type]
+mercurial/utils/stringutil.py # [module-attr], [wrong-arg-count]
+mercurial/utils/memorytop.py  # not 3.6 compatible
+mercurial/win32.py            # [not-callable]
+mercurial/wireprotoframing.py # [unsupported-operands], [attribute-error], [import-error]
+mercurial/wireprotoserver.py  # line 253, in _availableapis: No attribute '__iter__' on Callable[[Any, Any], Any] [attribute-error]
+mercurial/wireprotov1peer.py  # [attribute-error]
+mercurial/wireprotov1server.py  # BUG?: BundleValueError handler accesses subclass's attrs
+mercurial/wireprotov2server.py  # [unsupported-operands], [attribute-error]
+
+TODO: use --no-cache on test server?  Caching the files locally helps during
+development, but may be a hinderance for CI testing.
+
+  $ pytype -V 3.6 --keep-going --jobs auto mercurial \
+  >    -x mercurial/bundlerepo.py \
+  >    -x mercurial/changegroup.py \
+  >    -x mercurial/chgserver.py \
+  >    -x mercurial/cmdutil.py \
+  >    -x mercurial/context.py \
+  >    -x mercurial/copies.py \
+  >    -x mercurial/crecord.py \
+  >    -x mercurial/debugcommands.py \
+  >    -x mercurial/dispatch.py \
+  >    -x mercurial/exchange.py \
+  >    -x mercurial/hgweb/hgweb_mod.py \
+  >    -x mercurial/hgweb/server.py \
+  >    -x mercurial/hgweb/webcommands.py \
+  >    -x mercurial/hgweb/wsgicgi.py \
+  >    -x mercurial/httppeer.py \
+  >    -x mercurial/interfaces \
+  >    -x mercurial/keepalive.py \
+  >    -x mercurial/localrepo.py \
+  >    -x mercurial/lsprof.py \
+  >    -x mercurial/manifest.py \
+  >    -x mercurial/minirst.py \
+  >    -x mercurial/patch.py \
+  >    -x mercurial/pure/osutil.py \
+  >    -x mercurial/pure/parsers.py \
+  >    -x mercurial/pycompat.py \
+  >    -x mercurial/repoview.py \
+  >    -x mercurial/sslutil.py \
+  >    -x mercurial/statprof.py \
+  >    -x mercurial/testing/storage.py \
+  >    -x mercurial/thirdparty \
+  >    -x mercurial/ui.py \
+  >    -x mercurial/unionrepo.py \
+  >    -x mercurial/upgrade.py \
+  >    -x mercurial/util.py \
+  >    -x mercurial/utils/procutil.py \
+  >    -x mercurial/utils/stringutil.py \
+  >    -x mercurial/utils/memorytop.py \
+  >    -x mercurial/win32.py \
+  >    -x mercurial/wireprotoframing.py \
+  >    -x mercurial/wireprotoserver.py \
+  >    -x mercurial/wireprotov1peer.py \
+  >    -x mercurial/wireprotov1server.py \
+  >    -x mercurial/wireprotov2server.py \
+  >  > $TESTTMP/pytype-output.txt || cat $TESTTMP/pytype-output.txt
+
+Only show the results on a failure, because the output on success is also
+voluminous and variable.