perf: use getbufinfo() over nvim_list_bufs()

The former is faster at filtering buffers than using the latter while
filtering manually (in Lua). The former is faster both cold (first
call), and after warmup, and overall is at least 10% quicker in this
situation.

This change improves the performance of the timer callback which goes
through all buffers and saves those that are modified and meet the other
criteria.

lua/sos/impl.lua

@@ -80,62 +80,76 @@ local function write_buf(buf)
 end
 
 ---@param buf integer
+---@return boolean success
+---@return string? errmsg
 ---@nodiscard
----@return boolean, string?
 function M.write_buf_if_needed(buf)
-  -- TODO: bufloaded, modifiable, acwrite pattern
+  -- TODO: bufloaded, ignore nomodifiable, acwrite pattern
+
+  -- TODO: consider the case where it's not allowed to modify file but is
+  -- allowed to create a file/dirent?
+
+  -- Using values directly from `getbufinfo()` table (from caller) might be a
+  -- little bit faster here, but those values potentially become outdated due to
+  -- `BufWrite` autocmds? So, we'll just check everything again below and not
+  -- assume anything.
+  local bufinfo = vim.fn.getbufinfo(buf)[1]
+
+  -- Invalid buf (wiped by autocmd?)
+  if not bufinfo then return true end
+  local name = bufinfo.name
+
   if
-    vim.bo[buf].mod
-    and vim.o.write
-    and not vim.bo[buf].ro
-    and api.nvim_buf_is_loaded(buf)
-    and wanted_buftype(buf)
-    and not vim.b[buf].sos_ignore
+    bufinfo.changed == 0
+    or not vim.o.write
+    or vim.bo[buf].ro
+    or bufinfo.loaded == 0
+    or not wanted_buftype(buf)
+    or bufinfo.variables.sos_ignore
+    or #name == 0
   then
-    local name = api.nvim_buf_get_name(buf)
-    -- Cannot write to an empty filename
-    if name == '' then return true end
-    local buftype = vim.bo[buf].bt
-
-    if buftype == 'acwrite' then
-      return write_buf(buf)
-    elseif buftype == '' then
-      local stat, _errmsg, errname = uv.fs_stat(name)
-
-      if stat then
-        -- File exists: only write if it's writeable and not a dir.
-        if vim.fn.filewritable(name) == 1 and not stat.type:find '^dir' then
-          return write_buf(buf)
-        end
+    return true
+  end
 
-        return true
-      elseif errname == 'ENOENT' then
-        -- TODO: Try stat again on error (or certain errors, like if
-        -- EINTR is possible to observe in lua)?
-        if name:find '[\\/]$' then
-          -- Unsure what the user would want here, so just return
-          -- success and don't write anything.
-          return true
-        end
+  local buftype = vim.bo[buf].bt
+
+  if buftype == 'acwrite' then
+    return write_buf(buf)
+  elseif buftype == '' then
+    local stat, _errmsg, errname = uv.fs_stat(name)
 
-        local dir = vim.fn.fnamemodify(name, ':h')
-        local dir_stat, _dir_errmsg, dir_errname = uv.fs_stat(dir)
+    if stat then
+      -- File exists: only write if it's writeable and not a dir.
+      if vim.fn.filewritable(name) == 1 and not stat.type:find '^dir' then
+        return write_buf(buf)
+      end
 
-        if dir_stat then
-          if vim.fn.filewritable(dir) == 2 then
-            -- Parent is writeable dir
-            return write_buf(buf)
-          end
+      return true
+    elseif errname == 'ENOENT' then
+      -- TODO: Try stat again on error (or certain errors, like if
+      -- EINTR is possible to observe in lua)?
+      if name:find '[\\/]$' then
+        -- Unsure what the user would want here, so just return
+        -- success and don't write anything.
+        return true
+      end
 
-          -- Parent dir exists but isn't writeable.
-          return true
-        elseif dir_errname == 'ENOENT' then
-          if util.to_bool(vim.fn.mkdir(dir, 'p')) then return write_buf(buf) end
+      local dir = vim.fn.fnamemodify(name, ':h')
+      local dir_stat, _dir_errmsg, dir_errname = uv.fs_stat(dir)
 
-          -- Parent dir doesn't exist, failed to create it (e.g.
-          -- perms).
-          return true
+      if dir_stat then
+        if vim.fn.filewritable(dir) == 2 then
+          -- Parent is writeable dir
+          return write_buf(buf)
         end
+
+        -- Parent dir exists, but isn't writeable.
+        return true
+      elseif dir_errname == 'ENOENT' then
+        if util.to_bool(vim.fn.mkdir(dir, 'p')) then return write_buf(buf) end
+
+        -- Parent dir doesn't exist, failed to create it (e.g. perms).
+        return true
       end
     end
   end
@@ -158,7 +172,8 @@ end
 function M.on_timer()
   local errs = {}
 
-  for _, buf in ipairs(api.nvim_list_bufs()) do
+  for _, bufinfo in ipairs(vim.fn.getbufinfo { bufloaded = 1, bufmodified = 1 }) do
+    local buf = bufinfo.bufnr
     local ok, res = M.write_buf_if_needed(buf)
 
     if not ok then

lua/sos/observer.lua

@@ -212,6 +212,7 @@ function MultiBufObserver:new()
       }),
     })
 
+    -- TODO: Use getbufinfo() here for performance?
     for _, bufnr in ipairs(api.nvim_list_bufs()) do
       self:process_buf(bufnr)
     end