(mini.statusline) Improve performance of section_diagnostics().

Details:
- And overall 'mini.statusline' startup footprint by avoiding usage of
  `vim.diagnostic` during module load.

Author: echasnovski

lua/mini/statusline.lua

@@ -299,10 +299,11 @@ MiniStatusline.section_diagnostics = function(args)
   local dont_show_lsp = MiniStatusline.is_truncated(args.trunc_width) or H.isnt_normal_buffer() or hasnt_attached_client
   if dont_show_lsp then return '' end
 
-  -- Construct diagnostic info using predefined order
-  local t = {}
+  -- Construct string parts
+  local counts = H.get_diagnostic_count()
+  local severity, t = vim.diagnostic.severity, {}
   for _, level in ipairs(H.diagnostic_levels) do
-    local n = H.get_diagnostic_count(level.id)
+    local n = counts[severity[level.name]] or 0
     -- Add level info only if diagnostic is present
     if n > 0 then table.insert(t, string.format(' %s%s', level.sign, n)) end
   end
@@ -419,10 +420,10 @@ H.default_config = vim.deepcopy(MiniStatusline.config)
 
 -- Showed diagnostic levels
 H.diagnostic_levels = {
-  { id = vim.diagnostic.severity.ERROR, sign = 'E' },
-  { id = vim.diagnostic.severity.WARN, sign = 'W' },
-  { id = vim.diagnostic.severity.INFO, sign = 'I' },
-  { id = vim.diagnostic.severity.HINT, sign = 'H' },
+  { name = 'ERROR', sign = 'E' },
+  { name = 'WARN', sign = 'W' },
+  { name = 'INFO', sign = 'I' },
+  { name = 'HINT', sign = 'H' },
 }
 
 -- Helper functionality =======================================================
@@ -582,6 +583,14 @@ H.get_filetype_icon = function()
   return devicons.get_icon(file_name, file_ext, { default = true })
 end
 
-H.get_diagnostic_count = function(id) return #vim.diagnostic.get(0, { severity = id }) end
+H.get_diagnostic_count = function()
+  local res = {}
+  for _, d in ipairs(vim.diagnostic.get(0)) do
+    res[d.severity] = (res[d.severity] or 0) + 1
+  end
+  return res
+end
+
+if vim.fn.has('nvim-0.10') == 1 then H.get_diagnostic_count = function() return vim.diagnostic.count(0) end end
 
 return MiniStatusline

tests/dir-statusline/mock-diagnostics.lua

@@ -1,9 +1,24 @@
 vim.lsp.buf_get_clients = function() return { 'mock client' } end
 
-vim.diagnostic.get = function(buf_id, opts)
-  local severity = vim.diagnostic.severity
-  local n = ({ [severity.ERROR] = 4, [severity.WARN] = 3, [severity.INFO] = 2, [severity.HINT] = 1 })[opts.severity]
+vim.diagnostic.get = function(_, _)
+  local s = vim.diagnostic.severity
+  return {
+    { severity = s.ERROR },
+    { severity = s.WARN },
+    { severity = s.INFO },
+    { severity = s.HINT },
+    { severity = s.ERROR },
+    { severity = s.WARN },
+    { severity = s.INFO },
+    { severity = s.ERROR },
+    { severity = s.WARN },
+    { severity = s.ERROR },
+  }
+end
 
-  -- Original returns array with one entry per diagnostic element
-  return (vim.split(string.rep('a', n), ''))
+if vim.fn.has('nvim-0.10') == 1 then
+  vim.diagnostic.count = function(_, _)
+    local s = vim.diagnostic.severity
+    return { [s.ERROR] = 4, [s.WARN] = 3, [s.INFO] = 2, [s.HINT] = 1 }
+  end
 end

tests/test_statusline.lua

@@ -260,7 +260,8 @@ T['section_diagnostics()']['works'] = function()
   eq(child.lua_get('MiniStatusline.section_diagnostics({})'), ' E4 W3 I2 H1')
 
   -- Should return predefined string if no diagnostic output
-  child.lua('vim.lsp.diagnostic.get_count = function(...) return 0 end')
+  child.lua('vim.diagnostic.get = function(...) return {} end')
+  child.lua('vim.diagnostic.count = function(...) return {} end')
   child.lua('vim.diagnostic.get = function(...) return {} end')
   eq(child.lua_get('MiniStatusline.section_diagnostics({})'), ' -')