commands: print security protocol support in debuginstall

Over the past week I've had to instruct multiple people to run
Python code to query the ssl module to see what TLS protocol support
is present. I think it would be useful for `hg debuginstall` to print
this info to make it easier to access and debug why Mercurial is
complaining about using an insecure TLS 1.0 protocol.

Ideally we'd also print the path to the CA cert bundle. But the APIs
for querying that in sslutil can emit warnings, making it slightly
more difficult to integrate into `hg debuginstall`. That work will
have to wait for another day.

mercurial/commands.py

@@ -68,6 +68,7 b' from . import ('
     setdiscovery,
     simplemerge,
     sshserver,
+    sslutil,
     streamclone,
     templatekw,
     templater,
@@ -2703,6 +2704,25 b' def debuginstall(ui, **opts):'
     fm.write('pythonlib', _("checking Python lib (%s)...\n"),
              os.path.dirname(os.__file__))
 
+    security = set(sslutil.supportedprotocols)
+    if sslutil.hassni:
+        security.add('sni')
+
+    fm.write('pythonsecurity', _("checking Python security support (%s)\n"),
+             fm.formatlist(sorted(security), name='protocol',
+                           fmt='%s', sep=','))
+
+    # These are warnings, not errors. So don't increment problem count. This
+    # may change in the future.
+    if 'tls1.2' not in security:
+        fm.plain(_('  TLS 1.2 not supported by Python install; '
+                   'network connections lack modern security\n'))
+    if 'sni' not in security:
+        fm.plain(_('  SNI not supported by Python install; may have '
+                   'connectivity issues with some servers\n'))
+
+    # TODO print CA cert info
+
     # hg version
     hgver = util.version()
     fm.write('hgver', _("checking Mercurial version (%s)\n"),

tests/test-install.t

@@ -4,6 +4,9 b' hg debuginstall'
   checking Python executable (*) (glob)
   checking Python version (2.*) (glob)
   checking Python lib (*lib*)... (glob)
+  checking Python security support (*) (glob)
+    TLS 1.2 not supported by Python install; network connections lack modern security (?)
+    SNI not supported by Python install; may have connectivity issues with some servers (?)
   checking Mercurial version (*) (glob)
   checking Mercurial custom build (*) (glob)
   checking module policy (*) (glob)
@@ -33,6 +36,7 b' hg debuginstall JSON'
     "problems": 0,
     "pythonexe": "*", (glob)
     "pythonlib": "*", (glob)
+    "pythonsecurity": [*], (glob)
     "pythonver": "*.*.*", (glob)
     "templatedirs": "*mercurial?templates", (glob)
     "username": "test",
@@ -47,6 +51,9 b' hg debuginstall with no username'
   checking Python executable (*) (glob)
   checking Python version (2.*) (glob)
   checking Python lib (*lib*)... (glob)
+  checking Python security support (*) (glob)
+    TLS 1.2 not supported by Python install; network connections lack modern security (?)
+    SNI not supported by Python install; may have connectivity issues with some servers (?)
   checking Mercurial version (*) (glob)
   checking Mercurial custom build (*) (glob)
   checking module policy (*) (glob)
@@ -71,6 +78,9 b' path variables are expanded (~ is the sa'
   checking Python executable (*) (glob)
   checking Python version (*) (glob)
   checking Python lib (*lib*)... (glob)
+  checking Python security support (*) (glob)
+    TLS 1.2 not supported by Python install; network connections lack modern security (?)
+    SNI not supported by Python install; may have connectivity issues with some servers (?)
   checking Mercurial version (*) (glob)
   checking Mercurial custom build (*) (glob)
   checking module policy (*) (glob)