Signed-off-by: Koichi Shiraishi <zchee.io@gmail.com>

Now remove the addition of "start/*" packages in 'packpath' as
explicit items in 'runtimepath'. This avoids 'runtimepath' from becoming
very long when using a lot of plugins as packages.

To get the effective search path as a list, use |nvim_list_runtime_paths()|

fixes #12410

fix #9799
regression of #7081
Helped-by: Björn Linse <bjorn.linse@gmail.com>

Problem: :UpdateRemotePlugins (which calls rpcstop()) sometimes crashes:

    remote/host: python3 host registered plugins []
    nvim: ../src/nvim/event/wstream.c:78:
      _Bool wstream_write(Stream *, WBuffer *): Assertion `!stream->closed' failed.
    Aborted (core dumped)

  Order of events (channel 163, see logs below):

    1. Channel's in-stream (0x2ba86c0) is **closed** by `f_rpcstop`..`process_stop`.
    2. `receive_msgpack` parses the channel out-stream (0x2ba8860)
    3. Invokes "nvim_command_output" API method.
    4. Writes result to the **closed** in-stream  => **abort**

  - af993da4351d (`receive_msgpack`) tried to hack around same/similar issue.
  - Hack was removed in 5215e3205a07.

Solution: in jobstop(), close the channel before process_stop().

Log:

    DEBUG 2019-07-16T20:54:12.191 25159 stream_close:96: closing Stream: 0x2b01a90
    DEBUG 2019-07-16T20:54:12.210 25159 process_spawn:124: new: pid=28407 argv=[/usr/bin/python3]
    DEBUG 2019-07-16T20:54:12.210 25159 rpc_start:72: rpc ch 163 in-stream=0x2ba86c0 out-stream=0x2ba8860
    INFO  2019-07-16T20:54:12.210 25159 channel_create_event:199: new channel 163 (function <SNR>61_on_exit[4]..<SNR>60_job_exit_cb[101]..<SNR>60_decrement_job_count[8]..remote#host#UpdateRemotePlugins[6]..<SNR>31_RegistrationCommands[15]..remote#host#Require[10]..provider#pythonx#Require[13]..provider#Poll:3) : {"id": 163, "client": {}, "mode": "rpc", "stream": "job"}
    DEBUG 2019-07-16T20:54:12.211 25159 log_server_msg:729: RPC ->ch 163: [request]  [0, 1, "poll", []]
    DEBUG 2019-07-16T20:54:12.355 25159 receive_msgpack:227: ch 163: parsing 21 bytes from msgpack Stream: 0x2ba8860
    DEBUG 2019-07-16T20:54:12.355 25159 log_client_msg:766: RPC <-ch 163: [request]  [0, 1, "vim_get_api_info", []]
    DEBUG 2019-07-16T20:54:12.355 25159 RPC: <-ch 163: invoke nvim_get_api_info
    DEBUG 2019-07-16T20:54:12.357 25159 log_server_msg:729: RPC ->ch 163: [response] [1, 1, nil, [163, {"version"=>{"major"=>0, "minor"=>4, }, ...
    DEBUG 2019-07-16T20:54:12.377 25159 receive_msgpack:227: ch 163: parsing 85 bytes from msgpack Stream: 0x2ba8860
    DEBUG 2019-07-16T20:54:12.377 25159 log_client_msg:766: RPC <-ch 163: [request]  [0, 2, "nvim_eval", ["((&number||&relativenumber) ? &numberwidth : 0) + &foldcolumn"]]
    DEBUG 2019-07-16T20:54:12.377 25159 handle_request:359: RPC: scheduled nvim_eval
    DEBUG 2019-07-16T20:54:12.377 25159 log_client_msg:766: RPC <-ch 163: [response] [1, 1, nil, "ok"]
    DEBUG 2019-07-16T20:54:12.378 25159 log_server_msg:729: RPC ->ch 163: [request]  [0, 2, "specs", ["/home/vagrant/.config/nvim/rplugin/python3/__pycache__"]]
    DEBUG 2019-07-16T20:54:12.378 25159 RPC: <-ch 163: invoke nvim_eval
    DEBUG 2019-07-16T20:54:12.379 25159 log_server_msg:729: RPC ->ch 163: [response] [1, 2, nil, 0]
    DEBUG 2019-07-16T20:54:12.379 25159 receive_msgpack:227: ch 163: parsing 5 bytes from msgpack Stream: 0x2ba8860
    DEBUG 2019-07-16T20:54:12.379 25159 log_client_msg:766: RPC <-ch 163: [response] [1, 2, nil, 0]
    DEBUG 2019-07-16T20:54:12.380 25159 log_server_msg:729: RPC ->ch 163: [request]  [0, 3, "specs", ["/home/vagrant/.config/nvim/rplugin/python3/foo.py"]]
    DEBUG 2019-07-16T20:54:12.380 25159 receive_msgpack:227: ch 163: parsing 79 bytes from msgpack Stream: 0x2ba8860
    DEBUG 2019-07-16T20:54:12.380 25159 log_client_msg:766: RPC <-ch 163: [request]  [0, 3, "nvim_command", ["redir =>a |exe "sil sign place buffer=".bufnr('')|redir end"]]
    DEBUG 2019-07-16T20:54:12.381 25159 handle_request:359: RPC: scheduled nvim_command
    DEBUG 2019-07-16T20:54:12.381 25159 RPC: <-ch 163: invoke nvim_command
    DEBUG 2019-07-16T20:54:12.381 25159 log_server_msg:729: RPC ->ch 163: [response] [1, 3, nil, nil]
    DEBUG 2019-07-16T20:54:12.381 25159 receive_msgpack:227: ch 163: parsing 5 bytes from msgpack Stream: 0x2ba8860
    DEBUG 2019-07-16T20:54:12.381 25159 log_client_msg:766: RPC <-ch 163: [response] [1, 3, nil, 0]
    DEBUG 2019-07-16T20:54:12.382 25159 stream_close:95: trace:
      log_callstack at /home/vagrant/neovim/build/../src/nvim/log.c:256
      stream_close at /home/vagrant/neovim/build/../src/nvim/event/stream.c:95
      stream_may_close at /home/vagrant/neovim/build/../src/nvim/event/stream.c:111
      process_stop at /home/vagrant/neovim/build/../src/nvim/event/process.c:230
      f_jobstop at /home/vagrant/neovim/build/../src/nvim/eval.c:12231
      f_rpcstop at /home/vagrant/neovim/build/../src/nvim/eval.c:14533
      call_func at /home/vagrant/neovim/build/../src/nvim/eval.c:6564
      get_func_tv at /home/vagrant/neovim/build/../src/nvim/eval.c:6304
      ex_call at /home/vagrant/neovim/build/../src/nvim/eval.c:2903
      do_one_cmd at /home/vagrant/neovim/build/../src/nvim/ex_docmd.c:2249
      do_cmdline at /home/vagrant/neovim/build/../src/nvim/ex_docmd.c:593
      call_user_func at /home/vagrant/neovim/build/../src/nvim/eval.c:22666
      call_func at /home/vagrant/neovim/build/../src/nvim/eval.c:6550
      get_func_tv at /home/vagrant/neovim/build/../src/nvim/eval.c:6304
      eval7 at /home/vagrant/neovim/build/../src/nvim/eval.c:4407
      eval6 at /home/vagrant/neovim/build/../src/nvim/eval.c:4104
      eval5 at /home/vagrant/neovim/build/../src/nvim/eval.c:3985
      eval4 at /home/vagrant/neovim/build/../src/nvim/eval.c:3688
      eval3 at /home/vagrant/neovim/build/../src/nvim/eval.c:3606
      eval2 at /home/vagrant/neovim/build/../src/nvim/eval.c:3537
      eval1 at /home/vagrant/neovim/build/../src/nvim/eval.c:3464
      eval0 at /home/vagrant/neovim/build/../src/nvim/eval.c:3424
      ex_let_const at /home/vagrant/neovim/build/../src/nvim/eval.c:1604
      ex_let at /home/vagrant/neovim/build/../src/nvim/eval.c:1546
      do_one_cmd at /home/vagrant/neovim/build/../src/nvim/ex_docmd.c:2249
      do_cmdline at /home/vagrant/neovim/build/../src/nvim/ex_docmd.c:593
      call_user_func at /home/vagrant/neovim/build/../src/nvim/eval.c:22666
      call_func at /home/vagrant/neovim/build/../src/nvim/eval.c:6550
      get_func_tv at /home/vagrant/neovim/build/../src/nvim/eval.c:6304
      ex_call at /home/vagrant/neovim/build/../src/nvim/eval.c:2903
      do_one_cmd at /home/vagrant/neovim/build/../src/nvim/ex_docmd.c:2249
      do_cmdline at /home/vagrant/neovim/build/../src/nvim/ex_docmd.c:593
      do_ucmd at /home/vagrant/neovim/build/../src/nvim/ex_docmd.c:5803
      do_one_cmd at /home/vagrant/neovim/build/../src/nvim/ex_docmd.c:2243
      do_cmdline at /home/vagrant/neovim/build/../src/nvim/ex_docmd.c:593
      call_user_func at /home/vagrant/neovim/build/../src/nvim/eval.c:22666
      call_func at /home/vagrant/neovim/build/../src/nvim/eval.c:6550
      get_func_tv at /home/vagrant/neovim/build/../src/nvim/eval.c:6304
      ex_call at /home/vagrant/neovim/build/../src/nvim/eval.c:2903
      do_one_cmd at /home/vagrant/neovim/build/../src/nvim/ex_docmd.c:2249
      do_cmdline at /home/vagrant/neovim/build/../src/nvim/ex_docmd.c:593
      call_user_func at /home/vagrant/neovim/build/../src/nvim/eval.c:22666
      call_func at /home/vagrant/neovim/build/../src/nvim/eval.c:6550
      get_func_tv at /home/vagrant/neovim/build/../src/nvim/eval.c:6304
      ex_call at /home/vagrant/neovim/build/../src/nvim/eval.c:2903
      do_one_cmd at /home/vagrant/neovim/build/../src/nvim/ex_docmd.c:2249
      do_cmdline at /home/vagrant/neovim/build/../src/nvim/ex_docmd.c:593
      call_user_func at /home/vagrant/neovim/build/../src/nvim/eval.c:22666
      call_func at /home/vagrant/neovim/build/../src/nvim/eval.c:6550
      callback_call at /home/vagrant/neovim/build/../src/nvim/eval.c:17917
      channel_callback_call at /home/vagrant/neovim/build/../src/nvim/channel.c:675
      on_channel_event at /home/vagrant/neovim/build/../src/nvim/channel.c:581
      multiqueue_process_events at /home/vagrant/neovim/build/../src/nvim/event/multiqueue.c:147
      nv_event at /home/vagrant/neovim/build/../src/nvim/normal.c:7987
      normal_execute at /home/vagrant/neovim/build/../src/nvim/normal.c:1133
      state_enter at /home/vagrant/neovim/build/../src/nvim/state.c:73
      normal_enter at /home/vagrant/neovim/build/../src/nvim/normal.c:462
      main at /home/vagrant/neovim/build/../src/nvim/main.c:570
      ?? ??:0
      _start at ??:?
    DEBUG 2019-07-16T20:54:12.417 25159 stream_close:96: closing Stream: 0x2ba86c0
    INFO  2019-07-16T20:54:12.417 25159 os_proc_tree_kill:96: sending SIGTERM to process group: -28407
    DEBUG 2019-07-16T20:54:12.417 25159 receive_msgpack:227: ch 163: parsing 31 bytes from msgpack Stream: 0x2ba8860
    DEBUG 2019-07-16T20:54:12.417 25159 log_client_msg:766: RPC <-ch 163: [request]  [0, 4, "nvim_command_output", ["echo a"]]
    DEBUG 2019-07-16T20:54:12.417 25159 handle_request:359: RPC: scheduled nvim_command_output
    DEBUG 2019-07-16T20:54:12.424 25159 RPC: <-ch 163: invoke nvim_command_output
    DEBUG 2019-07-16T20:54:12.424 25159 log_server_msg:729: RPC ->ch 163: [response] [1, 4, [0, "Vim(echo):E121: Undefined variable: a"], nil]
    ERROR 2019-07-16T20:54:12.424 25159 wstream_write:78: xxx stream=0x2ba86c0
    DEBUG 2019-07-16T20:54:12.425 25159 wstream_write:79: trace:
      log_callstack at /home/vagrant/neovim/build/../src/nvim/log.c:256
      wstream_write at /home/vagrant/neovim/build/../src/nvim/event/wstream.c:82
      channel_write at /home/vagrant/neovim/build/../src/nvim/msgpack_rpc/channel.c:407
      request_event at /home/vagrant/neovim/build/../src/nvim/msgpack_rpc/channel.c:383
      multiqueue_process_events at /home/vagrant/neovim/build/../src/nvim/event/multiqueue.c:147
      nv_event at /home/vagrant/neovim/build/../src/nvim/normal.c:7987
      normal_execute at /home/vagrant/neovim/build/../src/nvim/normal.c:1133
      state_enter at /home/vagrant/neovim/build/../src/nvim/state.c:73
      normal_enter at /home/vagrant/neovim/build/../src/nvim/normal.c:462
      main at /home/vagrant/neovim/build/../src/nvim/main.c:570
      ?? ??:0
      _start at ??:?

With the old behavior, if a GUI makes a blocking request that requires user
interaction (like nvim_input()), it would not get any screen updates.

The client, not nvim, should decide how to handle notifications during a
pending request. If an rplugin wants to avoid async calls while a sync call is
busy, it likely wants to avoid processing async calls while another async call
also is handled as well.

This may break the expectation of some existing rplugins. For compatibility,
remote/define.vim reimplements the old behavior. Clients can opt-out by
specifying `sync=urgent`.

- Legacy hosts should be updated to use `sync=urgent`. They could add a flag
  indicating which async methods are always safe to call and which must wait
  until the main loop returns.
- New hosts can expose the full asyncness, they don't need to offer both
  behaviors.

ref #6532
ref #1398 d83868fe9071af1b4866594eac12f7aa0fa71b53

Fixes #7046
Fixes autozimu/LanguageClient-neovim#77

Dispense with the FuncUndefined/CmdUndefined quasi-optimization.
If there are no rplugins, plugin/rplugin.vim takes less than 1ms.

Closes #5821
Closes #6250

Helped-by: Qiming zhao <chemzqm@gmail.com>