--- a/mercurial/debugcommands.py	Mon Feb 13 16:35:49 2017 +0100
+++ b/mercurial/debugcommands.py	Wed Feb 01 17:31:05 2017 +0100
@@ -10,6 +10,8 @@
 import operator
 import os
 import random
+import sys
+import tempfile
 
 from .i18n import _
 from .node import (
@@ -26,6 +28,7 @@
     context,
     dagparser,
     dagutil,
+    encoding,
     error,
     exchange,
     extensions,
@@ -33,13 +36,16 @@
     hg,
     localrepo,
     lock as lockmod,
+    policy,
     pycompat,
     repair,
     revlog,
     scmutil,
     setdiscovery,
     simplemerge,
+    sslutil,
     streamclone,
+    templater,
     treediscovery,
     util,
 )
@@ -851,6 +857,172 @@
             ui.write("\t%d -> %d\n" % (r.rev(pp[1]), i))
     ui.write("}\n")
 
+@command('debuginstall', [] + commands.formatteropts, '', norepo=True)
+def debuginstall(ui, **opts):
+    '''test Mercurial installation
+
+    Returns 0 on success.
+    '''
+
+    def writetemp(contents):
+        (fd, name) = tempfile.mkstemp(prefix="hg-debuginstall-")
+        f = os.fdopen(fd, "wb")
+        f.write(contents)
+        f.close()
+        return name
+
+    problems = 0
+
+    fm = ui.formatter('debuginstall', opts)
+    fm.startitem()
+
+    # encoding
+    fm.write('encoding', _("checking encoding (%s)...\n"), encoding.encoding)
+    err = None
+    try:
+        encoding.fromlocal("test")
+    except error.Abort as inst:
+        err = inst
+        problems += 1
+    fm.condwrite(err, 'encodingerror', _(" %s\n"
+                 " (check that your locale is properly set)\n"), err)
+
+    # Python
+    fm.write('pythonexe', _("checking Python executable (%s)\n"),
+             pycompat.sysexecutable)
+    fm.write('pythonver', _("checking Python version (%s)\n"),
+             ("%d.%d.%d" % sys.version_info[:3]))
+    fm.write('pythonlib', _("checking Python lib (%s)...\n"),
+             os.path.dirname(pycompat.fsencode(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"),
+             hgver.split('+')[0])
+    fm.write('hgverextra', _("checking Mercurial custom build (%s)\n"),
+             '+'.join(hgver.split('+')[1:]))
+
+    # compiled modules
+    fm.write('hgmodulepolicy', _("checking module policy (%s)\n"),
+             policy.policy)
+    fm.write('hgmodules', _("checking installed modules (%s)...\n"),
+             os.path.dirname(__file__))
+
+    err = None
+    try:
+        from . import (
+            base85,
+            bdiff,
+            mpatch,
+            osutil,
+        )
+        dir(bdiff), dir(mpatch), dir(base85), dir(osutil) # quiet pyflakes
+    except Exception as inst:
+        err = inst
+        problems += 1
+    fm.condwrite(err, 'extensionserror', " %s\n", err)
+
+    compengines = util.compengines._engines.values()
+    fm.write('compengines', _('checking registered compression engines (%s)\n'),
+             fm.formatlist(sorted(e.name() for e in compengines),
+                           name='compengine', fmt='%s', sep=', '))
+    fm.write('compenginesavail', _('checking available compression engines '
+                                   '(%s)\n'),
+             fm.formatlist(sorted(e.name() for e in compengines
+                                  if e.available()),
+                           name='compengine', fmt='%s', sep=', '))
+    wirecompengines = util.compengines.supportedwireengines(util.SERVERROLE)
+    fm.write('compenginesserver', _('checking available compression engines '
+                                    'for wire protocol (%s)\n'),
+             fm.formatlist([e.name() for e in wirecompengines
+                            if e.wireprotosupport()],
+                           name='compengine', fmt='%s', sep=', '))
+
+    # templates
+    p = templater.templatepaths()
+    fm.write('templatedirs', 'checking templates (%s)...\n', ' '.join(p))
+    fm.condwrite(not p, '', _(" no template directories found\n"))
+    if p:
+        m = templater.templatepath("map-cmdline.default")
+        if m:
+            # template found, check if it is working
+            err = None
+            try:
+                templater.templater.frommapfile(m)
+            except Exception as inst:
+                err = inst
+                p = None
+            fm.condwrite(err, 'defaulttemplateerror', " %s\n", err)
+        else:
+            p = None
+        fm.condwrite(p, 'defaulttemplate',
+                     _("checking default template (%s)\n"), m)
+        fm.condwrite(not m, 'defaulttemplatenotfound',
+                     _(" template '%s' not found\n"), "default")
+    if not p:
+        problems += 1
+    fm.condwrite(not p, '',
+                 _(" (templates seem to have been installed incorrectly)\n"))
+
+    # editor
+    editor = ui.geteditor()
+    editor = util.expandpath(editor)
+    fm.write('editor', _("checking commit editor... (%s)\n"), editor)
+    cmdpath = util.findexe(pycompat.shlexsplit(editor)[0])
+    fm.condwrite(not cmdpath and editor == 'vi', 'vinotfound',
+                 _(" No commit editor set and can't find %s in PATH\n"
+                   " (specify a commit editor in your configuration"
+                   " file)\n"), not cmdpath and editor == 'vi' and editor)
+    fm.condwrite(not cmdpath and editor != 'vi', 'editornotfound',
+                 _(" Can't find editor '%s' in PATH\n"
+                   " (specify a commit editor in your configuration"
+                   " file)\n"), not cmdpath and editor)
+    if not cmdpath and editor != 'vi':
+        problems += 1
+
+    # check username
+    username = None
+    err = None
+    try:
+        username = ui.username()
+    except error.Abort as e:
+        err = e
+        problems += 1
+
+    fm.condwrite(username, 'username',  _("checking username (%s)\n"), username)
+    fm.condwrite(err, 'usernameerror', _("checking username...\n %s\n"
+        " (specify a username in your configuration file)\n"), err)
+
+    fm.condwrite(not problems, '',
+                 _("no problems detected\n"))
+    if not problems:
+        fm.data(problems=problems)
+    fm.condwrite(problems, 'problems',
+                 _("%d problems detected,"
+                   " please check your install!\n"), problems)
+    fm.end()
+
+    return problems
+
 @command('debugupgraderepo', [
     ('o', 'optimize', [], _('extra optimization to perform'), _('NAME')),
     ('', 'run', False, _('performs an upgrade')),