feat(server): introduce $NVIM
PROBLEM
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$NVIM_LISTEN_ADDRESS has conflicting purposes as both a parameter ("the
current process should listen on this address") and a descriptor ("the
current process is a child of this address").
This contradiction means the presence of NVIM_LISTEN_ADDRESS is
ambiguous, so child Nvim always tries to listen on its _parent's_
socket. This is the cause of lots of "Failed to start server" spam in
our test/CI logs:
WARN 2022-04-30… server_start:154: Failed to start server: address already in use: \\.\pipe\nvim-4480-0
WARN 2022-04-30… server_start:154: Failed to start server: address already in use: \\.\pipe\nvim-2168-0
SOLUTION
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1. Set $NVIM to the parent v:servername, *only* in child processes.
- Now the correct way to detect a "parent" Nvim is to check for $NVIM.
2. Do NOT set $NVIM_LISTEN_ADDRESS in child processes.
3. On startup if $NVIM_LISTEN_ADDRESS exists, unset it immediately after
server init.
4. Open a channel to parent automatically, expose it as v:parent.
Fixes#3118Fixes#6764Fixes#9336
Ref https://github.com/neovim/neovim/pull/8247#issuecomment-380275696
Ref #8696
(cherry picked from commit b9d97f5951)
Co-authored-by: Justin M. Keyes <justinkz@gmail.com>
fdd5178581