add support to show diagnostics count in statusline (#11641)

* add support to show diagnostics count in statusline
* documentation

runtime/doc/lsp.txt

@@ -294,6 +294,12 @@ The example will:
 <
 
 
+==============================================================================
+AUTOCOMMANDS                                                *lsp-autocommands*
+
+                                                       *LspDiagnosticsChanged*
+LspDiagnosticsChanged           After receiving publishDiagnostics server response
+
 
 ==============================================================================
 Lua module: vim.lsp                                                 *lsp-core*
@@ -337,7 +343,7 @@ buf_notify({bufnr}, {method}, {params})                 *vim.lsp.buf_notify()*
                     {params}  (string) Parameters to send to the server
 
                 Return: ~
-                    nil
+                    true if any client returns true; false otherwise
 
                                                        *vim.lsp.buf_request()*
 buf_request({bufnr}, {method}, {params}, {callback})
@@ -758,6 +764,10 @@ rename({new_name})                                      *vim.lsp.buf.rename()*
 request({method}, {params}, {callback})                *vim.lsp.buf.request()*
                 TODO: Documentation
 
+server_ready()                                    *vim.lsp.buf.server_ready()*
+                Sends a notification through all clients associated with current
+                buffer and returns `true` if server responds.
+
 signature_help()                                *vim.lsp.buf.signature_help()*
                 TODO: Documentation
 
@@ -903,6 +913,30 @@ apply_workspace_edit({workspace_edit})
 
 buf_clear_diagnostics({bufnr})          *vim.lsp.util.buf_clear_diagnostics()*
                 TODO: Documentation
+ 
+                                        *vim.lsp.util.buf_diagnostics_count()*
+buf_diagnostics_count({kind})
+                Returns the number of diagnostics of given kind for current buffer.
+                Useful for showing diagnostics counts in statusline. eg:
+
+>
+    function! LspStatus() abort
+        let sl = ''
+        if luaeval('vim.lsp.buf.server_ready()')
+            let sl.='%#MyStatuslineLSP#E:'
+            let sl.='%#MyStatuslineLSPErrors#%{luaeval("vim.lsp.util.buf_diagnostics_count(\"Error\")")}'
+            let sl.='%#MyStatuslineLSP# W:'
+            let sl.='%#MyStatuslineLSPWarnings#%{luaeval("vim.lsp.util.buf_diagnostics_count(\"Warning\")")}'
+        else
+            let sl.='%#MyStatuslineLSPErrors#off'
+        endif
+        return sl
+    endfunction
+    let &l:statusline = '%#MyStatuslineLSP#LSP '.LspStatus() 
+<
+
+                Parameters: ~
+                    {kind}       Diagnostic severity kind: Error, Warning, Information or Hint.
 
 buf_clear_references({bufnr})            *vim.lsp.util.buf_clear_references()*
                 TODO: Documentation

runtime/lua/vim/lsp.lua

@@ -893,21 +893,22 @@ function lsp.buf_request_sync(bufnr, method, params, timeout_ms)
   return request_results
 end
 
---- Sends a notification to all servers attached to the buffer.
+--- Send a notification to a server
----
+-- @param bufnr [number] (optional): The number of the buffer
---@param bufnr (optional, number) Buffer handle, or 0 for current
+-- @param method [string]: Name of the request method
---@param method (string) LSP method name
+-- @param params [string]: Arguments to send to the server
---@param params (string) Parameters to send to the server
+--
----
+-- @returns true if any client returns true; false otherwise
---@returns nil
 function lsp.buf_notify(bufnr, method, params)
   validate {
     bufnr    = { bufnr, 'n', true };
     method   = { method, 's' };
   }
+  local resp = false
   for_each_buffer_client(bufnr, function(client, _client_id)
-    client.rpc.notify(method, params)
+    if client.rpc.notify(method, params) then resp = true end
   end)
+  return resp
 end
 
 --- Implements 'omnifunc' compatible LSP completion.

runtime/lua/vim/lsp/buf.lua

@@ -23,6 +23,10 @@ local function request(method, params, callback)
   return vim.lsp.buf_request(0, method, params, callback)
 end
 
+function M.server_ready()
+  return not not vim.lsp.buf_notify(0, "window/progress", {})
+end
+
 function M.hover()
   local params = util.make_position_params()
   request('textDocument/hover', params)

runtime/lua/vim/lsp/callbacks.lua

@@ -33,6 +33,7 @@ M['textDocument/publishDiagnostics'] = function(_, _, result)
   util.buf_diagnostics_underline(bufnr, result.diagnostics)
   util.buf_diagnostics_virtual_text(bufnr, result.diagnostics)
   -- util.set_loclist(result.diagnostics)
+  vim.api.nvim_command("doautocmd User LspDiagnosticsChanged")
 end
 
 M['textDocument/references'] = function(_, _, result)

runtime/lua/vim/lsp/util.lua

@@ -743,6 +743,18 @@ do
       api.nvim_buf_set_virtual_text(bufnr, diagnostic_ns, line, virt_texts, {})
     end
   end
+  function M.buf_diagnostics_count(kind)
+    local bufnr = vim.api.nvim_get_current_buf()
+    local buffer_line_diagnostics = all_buffer_diagnostics[bufnr]
+    if not buffer_line_diagnostics then return end
+    local count = 0
+    for _, line_diags in pairs(buffer_line_diagnostics) do
+      for _, diag in ipairs(line_diags) do
+        if protocol.DiagnosticSeverity[kind] == diag.severity then count = count + 1 end
+      end
+    end
+    return count
+  end
 end
 
 local position_sort = sort_by_key(function(v)