Add Neovim TCP connections to language servers

Support TCP connections to language servers through Neovim's built in
client. In all but what is currently the nightly builds of Neovim
connections via a hostname will fail, but connections via an IP address
should function. We will still enable the built in Neovim client by
default anyway, as LSP clients very rarely connect over TCP.

autoload/ale/lsp.vim

@@ -569,6 +569,21 @@ function! ale#lsp#StartProgram(conn_id, executable, command) abort
     return l:job_id > 0
 endfunction
 
+" Split an address into [host, port].
+" The port will either be a number or v:null.
+function! ale#lsp#SplitAddress(address) abort
+    let l:port_match = matchlist(a:address, '\v:(\d+)$')
+
+    if !empty(l:port_match)
+        let l:host = a:address[:-len(l:port_match[1]) - 2]
+        let l:port = l:port_match[1] + 0
+
+        return [l:host, l:port ? l:port : v:null]
+    endif
+
+    return [a:address, v:null]
+endfunction
+
 " Connect to an LSP server via TCP.
 "
 " 1 will be returned if the connection is running, or 0 if the connection could
@@ -577,8 +592,23 @@ function! ale#lsp#ConnectToAddress(conn_id, address) abort
     let l:conn = s:connections[a:conn_id]
     let l:started = 0
 
-    " TODO: Start Neovim client here.
-    if !has_key(l:conn, 'channel_id') || !ale#socket#IsOpen(l:conn.channel_id)
+    if g:ale_use_neovim_lsp_api && !l:conn.is_tsserver
+        let [l:host, l:port] = ale#lsp#SplitAddress(a:address)
+
+        let l:client_id = luaeval('require("ale.lsp").start(_A)', {
+        \   'name': a:conn_id,
+        \   'host': l:host,
+        \   'port': l:port,
+        \   'root_dir': l:conn.root,
+        \   'init_options': l:conn.init_options,
+        \})
+
+        if l:client_id > 0
+            let l:conn.client_id = l:client_id
+        endif
+
+        return l:client_id > 0
+    elseif !has_key(l:conn, 'channel_id') || !ale#socket#IsOpen(l:conn.channel_id)
         let l:channel_id = ale#socket#Open(a:address, {
         \   'callback': {_, mess -> ale#lsp#HandleMessage(a:conn_id, mess)},
         \})

doc/ale.txt

@@ -476,6 +476,11 @@ functionality for Neovim's LSP client should work as expected, and this
 ensures ALE integrates well with other plugins that rely on Neovim's LSP
 client.
 
+NOTE: Neovim versions below `0.11.0` do not support socket connections to
+language servers when the `address` defined in ALE uses a hostname instead of
+an IP address. To work around this, configure language clients with an IP
+address instead of a hostname, or revert back to ALE's custom LSP client.
+
 See |lsp| for information on Neovim's built in LSP client.
 
 For diagnostics, for computing problems to show via ALE, ALE overrides the

lua/ale/lsp.lua

@@ -6,6 +6,31 @@ module.start = function(config)
         config.init_options[true] = nil
     end
 
+    -- If configuring LSP via a socket connection, then generate the cmd
+    -- using vim.lsp.rpc.connect(), as defined in Neovim documentation.
+    if config.host then
+        local cmd_func = vim.lsp.rpc.connect(config.host, config.port)
+        config.host = nil
+        config.port = nil
+
+        -- Wrap the cmd function so we don't throw errors back to the user
+        -- if the connection to an address fails to start.
+        --
+        -- We will separately log in ALE that we failed to start a connection.
+        --
+        -- In older Neovim versions TCP connections do not function if supplied
+        -- a hostname instead of an address.
+        config.cmd = function(dispatch)
+            local success, result = pcall(cmd_func, dispatch)
+
+            if success then
+                return result
+            end
+
+            return nil
+        end
+    end
+
     config.handlers = {
         -- Override Neovim's handling of diagnostics to run through ALE's
         -- functions so all of the functionality in ALE works.

test/lsp/test_lsp_address_split.vader

@@ -0,0 +1,9 @@
+Execute(Address splitting should function as intended):
+  AssertEqual ['foo', v:null], ale#lsp#SplitAddress('foo')
+  AssertEqual ['foo:', v:null], ale#lsp#SplitAddress('foo:')
+  AssertEqual ['foo', v:null], ale#lsp#SplitAddress('foo:0')
+  AssertEqual ['foo', 123], ale#lsp#SplitAddress('foo:123')
+  AssertEqual ['protocol:/foo:', v:null], ale#lsp#SplitAddress('protocol:/foo:')
+  AssertEqual ['protocol:/foo', v:null], ale#lsp#SplitAddress('protocol:/foo:0')
+  AssertEqual ['protocol:/foo', 123], ale#lsp#SplitAddress('protocol:/foo:123')
+  AssertEqual ['protocol:foo', v:null], ale#lsp#SplitAddress('protocol:foo')