patch 8.2.4684: cannot open a channel on a Unix domain socket

Problem:    Cannot open a channel on a Unix domain socket.
Solution:   Add Unix domain socket support. (closes #10062)
diff --git a/src/testdir/check.vim b/src/testdir/check.vim
index 55a64bd..aff0918 100644
--- a/src/testdir/check.vim
+++ b/src/testdir/check.vim
@@ -95,7 +95,7 @@
   endif
 endfunc
 
-" Command to check for running on Linix
+" Command to check for running on Linux
 command CheckLinux call CheckLinux()
 func CheckLinux()
   if !has('linux')
diff --git a/src/testdir/shared.vim b/src/testdir/shared.vim
index 01d741c..8e3dfc9 100644
--- a/src/testdir/shared.vim
+++ b/src/testdir/shared.vim
@@ -15,10 +15,16 @@
   if has('unix')
     " We also need the job feature or the pkill command to make sure the server
     " can be stopped.
-    if !(executable('python') && (has('job') || executable('pkill')))
+    if !(has('job') || executable('pkill'))
       return ''
     endif
-    let s:python = 'python'
+    if executable('python')
+      let s:python = 'python'
+    elseif executable('python3')
+      let s:python = 'python3'
+    else
+      return ''
+    end
   elseif has('win32')
     " Use Python Launcher for Windows (py.exe) if available.
     " NOTE: if you get a "Python was not found" error, disable the Python
diff --git a/src/testdir/test_channel.py b/src/testdir/test_channel.py
index 36aad2b..b0c3140 100644
--- a/src/testdir/test_channel.py
+++ b/src/testdir/test_channel.py
@@ -22,7 +22,8 @@
 class ThreadedTCPRequestHandler(socketserver.BaseRequestHandler):
 
     def setup(self):
-        self.request.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
+        if self.server.address_family != socket.AF_UNIX:
+            self.request.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
 
     def handle(self):
         print("=== socket opened ===")
diff --git a/src/testdir/test_channel.vim b/src/testdir/test_channel.vim
index 122bc57..6ad9dc0 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -23,6 +23,9 @@
   if g:testfunc =~ '_ipv6()$' 
     let s:localhost = '[::1]:'
     let s:testscript = 'test_channel_6.py'
+  elseif g:testfunc =~ '_unix()$'
+    let s:localhost = 'unix:Xtestsocket'
+    let s:testscript = 'test_channel_unix.py'
   else
     let s:localhost = 'localhost:'
     let s:testscript = 'test_channel.py'
@@ -39,6 +42,15 @@
   call RunServer(s:testscript, a:testfunc, a:000)
 endfunc
 
+" Returns the address of the test server.
+func s:address(port)
+  if s:localhost =~ '^unix:'
+    return s:localhost
+  else
+    return s:localhost . a:port
+  end
+endfunc
+
 " Return a list of open files.
 " Can be used to make sure no resources leaked.
 " Returns an empty list on systems where this is not supported.
@@ -65,7 +77,7 @@
   let s:chopt.drop = 'never'
   " Also add the noblock flag to try it out.
   let s:chopt.noblock = 1
-  let handle = ch_open(s:localhost . a:port, s:chopt)
+  let handle = ch_open(s:address(a:port), s:chopt)
   if ch_status(handle) == "fail"
     call assert_report("Can't open channel")
     return
@@ -77,7 +89,10 @@
   let dict = handle->ch_info()
   call assert_true(dict.id != 0)
   call assert_equal('open', dict.status)
-  call assert_equal(a:port, string(dict.port))
+  if has_key(dict, 'port')
+    " Channels using Unix sockets have no 'port' entry.
+    call assert_equal(a:port, string(dict.port))
+  end
   call assert_equal('open', dict.sock_status)
   call assert_equal('socket', dict.sock_io)
 
@@ -252,13 +267,19 @@
 
 func Test_communicate_ipv6()
   CheckIPv6
-
   call Test_communicate()
 endfunc
 
+func Test_communicate_unix()
+  CheckUnix
+  call Test_communicate()
+  call delete('Xtestsocket')
+endfunc
+
+
 " Test that we can open two channels.
 func Ch_two_channels(port)
-  let handle = ch_open(s:localhost . a:port, s:chopt)
+  let handle = ch_open(s:address(a:port), s:chopt)
   call assert_equal(v:t_channel, type(handle))
   if handle->ch_status() == "fail"
     call assert_report("Can't open channel")
@@ -267,7 +288,7 @@
 
   call assert_equal('got it', ch_evalexpr(handle, 'hello!'))
 
-  let newhandle = ch_open(s:localhost . a:port, s:chopt)
+  let newhandle = ch_open(s:address(a:port), s:chopt)
   if ch_status(newhandle) == "fail"
     call assert_report("Can't open second channel")
     return
@@ -292,9 +313,15 @@
   call Test_two_channels()
 endfunc
 
+func Test_two_channels_unix()
+  CheckUnix
+  call Test_two_channels()
+  call delete('Xtestsocket')
+endfunc
+
 " Test that a server crash is handled gracefully.
 func Ch_server_crash(port)
-  let handle = ch_open(s:localhost . a:port, s:chopt)
+  let handle = ch_open(s:address(a:port), s:chopt)
   if ch_status(handle) == "fail"
     call assert_report("Can't open channel")
     return
@@ -314,6 +341,12 @@
   call Test_server_crash()
 endfunc
 
+func Test_server_crash_unix()
+  CheckUnix
+  call Test_server_crash()
+  call delete('Xtestsocket')
+endfunc
+
 """""""""
 
 func Ch_handler(chan, msg)
@@ -323,7 +356,7 @@
 endfunc
 
 func Ch_channel_handler(port)
-  let handle = ch_open(s:localhost . a:port, s:chopt)
+  let handle = ch_open(s:address(a:port), s:chopt)
   if ch_status(handle) == "fail"
     call assert_report("Can't open channel")
     return
@@ -352,6 +385,12 @@
   call Test_channel_handler()
 endfunc
 
+func Test_channel_handler_unix()
+  CheckUnix
+  call Test_channel_handler()
+  call delete('Xtestsocket')
+endfunc
+
 """""""""
 
 let g:Ch_reply = ''
@@ -367,7 +406,7 @@
 endfunc
 
 func Ch_channel_zero(port)
-  let handle = (s:localhost .. a:port)->ch_open(s:chopt)
+  let handle = (s:address(a:port))->ch_open(s:chopt)
   if ch_status(handle) == "fail"
     call assert_report("Can't open channel")
     return
@@ -415,6 +454,13 @@
   call Test_zero_reply()
 endfunc
 
+func Test_zero_reply_unix()
+  CheckUnix
+  call Test_zero_reply()
+  call delete('Xtestsocket')
+endfunc
+
+
 """""""""
 
 let g:Ch_reply1 = ""
@@ -436,7 +482,7 @@
 endfunc
 
 func Ch_raw_one_time_callback(port)
-  let handle = ch_open(s:localhost . a:port, s:chopt)
+  let handle = ch_open(s:address(a:port), s:chopt)
   if ch_status(handle) == "fail"
     call assert_report("Can't open channel")
     return
@@ -462,6 +508,12 @@
   call Test_raw_one_time_callback()
 endfunc
 
+func Test_raw_one_time_callback_unix()
+  CheckUnix
+  call Test_raw_one_time_callback()
+  call delete('Xtestsocket')
+endfunc
+
 """""""""
 
 " Test that trying to connect to a non-existing port fails quickly.
@@ -1398,7 +1450,7 @@
 
 " Test that "unlet handle" in a handler doesn't crash Vim.
 func Ch_unlet_handle(port)
-  let s:channelfd = ch_open(s:localhost . a:port, s:chopt)
+  let s:channelfd = ch_open(s:address(a:port), s:chopt)
   eval s:channelfd->ch_sendexpr("test", {'callback': function('s:UnletHandler')})
   call WaitForAssert({-> assert_equal('what?', g:Ch_unletResponse)})
 endfunc
@@ -1422,7 +1474,7 @@
 
 " Test that "unlet handle" in a handler doesn't crash Vim.
 func Ch_close_handle(port)
-  let s:channelfd = ch_open(s:localhost . a:port, s:chopt)
+  let s:channelfd = ch_open(s:address(a:port), s:chopt)
   call ch_sendexpr(s:channelfd, "test", {'callback': function('Ch_CloseHandler')})
   call WaitForAssert({-> assert_equal('what?', g:Ch_unletResponse)})
 endfunc
@@ -1439,7 +1491,7 @@
 """"""""""
 
 func Ch_open_ipv6(port)
-  let handle = ch_open('[::1]:' .. a:port, s:chopt)
+  let handle = ch_open(s:address(a:port), s:chopt)
   call assert_notequal('fail', ch_status(handle))
 endfunc
 
@@ -1479,7 +1531,7 @@
 func Ch_open_delay(port)
   " Wait up to a second for the port to open.
   let s:chopt.waittime = 1000
-  let channel = ch_open(s:localhost . a:port, s:chopt)
+  let channel = ch_open(s:address(a:port), s:chopt)
   if ch_status(channel) == "fail"
     call assert_report("Can't open channel")
     return
@@ -1505,7 +1557,7 @@
 endfunc
 
 function Ch_test_call(port)
-  let handle = ch_open(s:localhost . a:port, s:chopt)
+  let handle = ch_open(s:address(a:port), s:chopt)
   if ch_status(handle) == "fail"
     call assert_report("Can't open channel")
     return
@@ -1529,6 +1581,12 @@
   call Test_call()
 endfunc
 
+func Test_call_unix()
+  CheckUnix
+  call Test_call()
+  call delete('Xtestsocket')
+endfunc
+
 """""""""
 
 let g:Ch_job_exit_ret = 'not yet'
@@ -1605,7 +1663,7 @@
 endfunc
 
 function Ch_test_close_callback(port)
-  let handle = ch_open(s:localhost . a:port, s:chopt)
+  let handle = ch_open(s:address(a:port), s:chopt)
   if ch_status(handle) == "fail"
     call assert_report("Can't open channel")
     return
@@ -1625,8 +1683,14 @@
   call Test_close_callback()
 endfunc
 
+func Test_close_callback_unix()
+  CheckUnix
+  call Test_close_callback()
+  call delete('Xtestsocket')
+endfunc
+
 function Ch_test_close_partial(port)
-  let handle = ch_open(s:localhost . a:port, s:chopt)
+  let handle = ch_open(s:address(a:port), s:chopt)
   if ch_status(handle) == "fail"
     call assert_report("Can't open channel")
     return
@@ -1651,6 +1715,12 @@
   call Test_close_partial()
 endfunc
 
+func Test_close_partial_unix()
+  CheckUnix
+  call Test_close_partial()
+  call delete('Xtestsocket')
+endfunc
+
 func Test_job_start_fails()
   " this was leaking memory
   call assert_fails("call job_start([''])", "E474:")
@@ -1920,7 +1990,7 @@
 endfunc
 
 function Ch_test_close_lambda(port)
-  let handle = ch_open(s:localhost . a:port, s:chopt)
+  let handle = ch_open(s:address(a:port), s:chopt)
   if ch_status(handle) == "fail"
     call assert_report("Can't open channel")
     return
@@ -1942,6 +2012,12 @@
   call Test_close_lambda()
 endfunc
 
+func Test_close_lambda_unix()
+  CheckUnix
+  call Test_close_lambda()
+  call delete('Xtestsocket')
+endfunc
+
 func s:test_list_args(cmd, out, remove_lf)
   try
     let g:out = ''
@@ -2243,6 +2319,8 @@
   let job = job_start("cat ", #{in_io: 'null'})
   call WaitForAssert({-> assert_equal("dead", job_status(job))})
   call assert_equal(0, job_info(job).exitval)
+
+  call delete('Xtestsocket')
 endfunc
 
 func Test_ch_getbufnr()
diff --git a/src/testdir/test_channel_unix.py b/src/testdir/test_channel_unix.py
new file mode 100644
index 0000000..4836e26
--- /dev/null
+++ b/src/testdir/test_channel_unix.py
@@ -0,0 +1,50 @@
+#!/usr/bin/env python
+#
+# Server that will accept connections from a Vim channel.
+# Used by test_channel.vim.
+#
+# This requires Python 2.6 or later.
+
+from __future__ import print_function
+from test_channel import ThreadedTCPServer, ThreadedTCPRequestHandler, \
+    writePortInFile
+import socket
+import threading
+import os
+
+try:
+    FileNotFoundError
+except NameError:
+    # Python 2
+    FileNotFoundError = (IOError, OSError)
+
+class ThreadedUnixServer(ThreadedTCPServer):
+    address_family = socket.AF_UNIX
+
+def main(path):
+    server = ThreadedUnixServer(path, ThreadedTCPRequestHandler)
+
+    # Start a thread with the server.  That thread will then start a new thread
+    # for each connection.
+    server_thread = threading.Thread(target=server.serve_forever)
+    server_thread.start()
+
+    # Signal the test harness we're ready, the port value has no meaning.
+    writePortInFile(1234)
+
+    print("Listening on {0}".format(server.server_address))
+
+    # Main thread terminates, but the server continues running
+    # until server.shutdown() is called.
+    try:
+        while server_thread.is_alive():
+            server_thread.join(1)
+    except (KeyboardInterrupt, SystemExit):
+        server.shutdown()
+
+if __name__ == "__main__":
+    try:
+        os.remove("Xtestsocket")
+    except FileNotFoundError:
+        pass
+    main("Xtestsocket")
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index e38a569..8034bdb 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -620,8 +620,8 @@
         \ ':5s':        'substitute',
         \ "'<,'>s":     'substitute',
         \ ":'<,'>s":    'substitute',
-        \ 'CheckUni':   'CheckUnix',
-        \ 'CheckUnix':  'CheckUnix',
+        \ 'CheckLin':   'CheckLinux',
+        \ 'CheckLinux': 'CheckLinux',
   \ }
 
   for [in, want] in items(tests)