Handle Neovim LSP diagnostics via ALE's functions

autoload/ale/lsp_linter.vim

@@ -488,12 +488,6 @@ function! ale#lsp_linter#StartLSP(buffer, linter, Callback) abort
 endfunction
 
 function! s:CheckWithLSP(linter, details) abort
-    if g:ale_use_neovim_lsp_api && a:linter.lsp isnot# 'tsserver'
-        " If running an LSP client via Neovim's API then Neovim will
-        " internally track buffers for changes for us, and we can stop here.
-        return
-    endif
-
     let l:buffer = a:details.buffer
     let l:info = get(g:ale_buffer_info, l:buffer)
 
@@ -503,13 +497,19 @@ function! s:CheckWithLSP(linter, details) abort
 
     let l:id = a:details.connection_id
 
+    " Remember the linter this connection is for.
+    let s:lsp_linter_map[l:id] = a:linter
+
+    if g:ale_use_neovim_lsp_api && a:linter.lsp isnot# 'tsserver'
+        " If running an LSP client via Neovim's API then Neovim will
+        " internally track buffers for changes for us, and we can stop here.
+        return
+    endif
+
     " Register a callback now for handling errors now.
     let l:Callback = function('ale#lsp_linter#HandleLSPResponse')
     call ale#lsp#RegisterCallback(l:id, l:Callback)
 
-    " Remember the linter this connection is for.
-    let s:lsp_linter_map[l:id] = a:linter
-
     if a:linter.lsp is# 'tsserver'
         let l:message = ale#lsp#tsserver_message#Geterr(l:buffer)
         let l:notified = ale#lsp#Send(l:id, l:message) != 0

lua/ale/lsp.lua

@@ -8,7 +8,26 @@ module.start = function(config)
         config.init_options[true] = nil
     end
 
+    config.handlers = {
+        -- Override Neovim's handling of diagnostics to run through ALE's
+        -- functions so all of the functionality in ALE works.
+        ["textDocument/publishDiagnostics"] = function(err, result, _, _)
+            if err == nil then
+                vim.fn["ale#lsp_linter#HandleLSPResponse"](config.name, {
+                    jsonrpc = "2.0",
+                    method = "textDocument/publishDiagnostics",
+                    params = result
+                })
+            end
+        end
+    }
+
     config.on_init = function(_, _)
+        -- Neovim calls `on_init` before marking a client as active, meaning
+        -- we can't get a client via get_client_by_id until after `on_init` is
+        -- called. By deferring execution of calling the init callbacks we
+        -- can only call them after the client becomes available, which
+        -- will make notifications for configuration changes work, etc.
         vim.defer_fn(function()
             vim.fn["ale#lsp#CallInitCallbacks"](config.name)
         end, 0)