feat(lsp): add logging level "OFF" (#18379)

runtime/doc/lsp.txt

@@ -750,7 +750,9 @@ omnifunc({findstart}, {base})                             *vim.lsp.omnifunc()*
 set_log_level({level})                               *vim.lsp.set_log_level()*
                 Sets the global log level for LSP logging.
 
-                Levels by name: "TRACE", "DEBUG", "INFO", "WARN", "ERROR"
+                Levels by name: "TRACE", "DEBUG", "INFO", "WARN", "ERROR",
+                "OFF"
+
                 Level numbers begin with "TRACE" at 0
 
                 Use `lsp.log_levels` for reverse lookup.

runtime/doc/lua.txt

@@ -1012,6 +1012,7 @@ Log levels are one of the values defined in `vim.log.levels`:
         vim.log.levels.INFO
         vim.log.levels.TRACE
         vim.log.levels.WARN
+        vim.log.levels.OFF
 
 ------------------------------------------------------------------------------
 LUA-VIMSCRIPT BRIDGE                                    *lua-vimscript*

runtime/lua/vim/_editor.lua

@@ -58,6 +58,7 @@ vim.log = {
     INFO  = 2;
     WARN  = 3;
     ERROR = 4;
+    OFF   = 5;
   }
 }
 

runtime/lua/vim/lsp.lua

@@ -1790,13 +1790,14 @@ end
 --
 -- Can be used to lookup the number from the name or the
 -- name from the number.
--- Levels by name: "TRACE", "DEBUG", "INFO", "WARN", "ERROR"
+-- Levels by name: "TRACE", "DEBUG", "INFO", "WARN", "ERROR", "OFF"
 -- Level numbers begin with "TRACE" at 0
 lsp.log_levels = log.levels
 
 --- Sets the global log level for LSP logging.
 ---
---- Levels by name: "TRACE", "DEBUG", "INFO", "WARN", "ERROR"
+--- Levels by name: "TRACE", "DEBUG", "INFO", "WARN", "ERROR", "OFF"
+---
 --- Level numbers begin with "TRACE" at 0
 ---
 --- Use `lsp.log_levels` for reverse lookup.

runtime/lua/vim/lsp/log.lua

@@ -8,7 +8,7 @@ local log = {}
 -- Log level dictionary with reverse lookup as well.
 --
 -- Can be used to lookup the number from the name or the name from the number.
--- Levels by name: "TRACE", "DEBUG", "INFO", "WARN", "ERROR"
+-- Levels by name: "TRACE", "DEBUG", "INFO", "WARN", "ERROR", "OFF"
 -- Level numbers begin with "TRACE" at 0
 log.levels = vim.deepcopy(vim.log.levels)
 
@@ -25,14 +25,31 @@ do
   end
   local logfilename = path_join(vim.fn.stdpath('cache'), 'lsp.log')
 
+  -- TODO: Ideally the directory should be created in open_logfile(), right
+  -- before opening the log file, but open_logfile() can be called from libuv
+  -- callbacks, where using fn.mkdir() is not allowed.
+  vim.fn.mkdir(vim.fn.stdpath('cache'), "p")
+
   --- Returns the log filename.
   ---@returns (string) log filename
   function log.get_filename()
     return logfilename
   end
 
-  vim.fn.mkdir(vim.fn.stdpath('cache'), "p")
+  local logfile, openerr
-  local logfile = assert(io.open(logfilename, "a+"))
+  ---@private
+  --- Opens log file. Returns true if file is open, false on error
+  local function open_logfile()
+    -- Try to open file only once
+    if logfile then return true end
+    if openerr then return false end
+
+    logfile, openerr = io.open(logfilename, "a+")
+    if not logfile then
+      local err_msg = string.format("Failed to open LSP client log file: %s", openerr)
+      vim.notify(err_msg, vim.log.levels.ERROR)
+      return false
+    end
 
     local log_info = vim.loop.fs_stat(logfilename)
     if log_info and log_info.size > 1e9 then
@@ -46,6 +63,9 @@ do
 
     -- Start message for logging
     logfile:write(string.format("[START][%s] LSP logging initiated\n", os.date(log_date_format)))
+    return true
+  end
+
   for level, levelnr in pairs(log.levels) do
     -- Also export the log level on the root object.
     log[level] = levelnr
@@ -63,10 +83,12 @@ do
     -- ```
     --
     -- This way you can avoid string allocations if the log level isn't high enough.
+    if level ~= "OFF" then
       log[level:lower()] = function(...)
         local argc = select("#", ...)
         if levelnr < current_log_level then return false end
         if argc == 0 then return true end
+        if not open_logfile() then return false end
         local info = debug.getinfo(2, "Sl")
         local header = string.format("[%s][%s] ...%s:%s", level, os.date(log_date_format), string.sub(info.short_src, #info.short_src - 15), info.currentline)
         local parts = { header }
@@ -82,6 +104,7 @@ do
         logfile:flush()
       end
     end
+  end
 end
 
 -- This is put here on purpose after the loop above so that it doesn't