build(docs): sort/lint class fields and keysets

Problem:
Fields (key names) in classes, keysets, and quasi-keysets are ordered
randomly, which adds friction when reading docs.

Solution:
- Sort class fields and keysets when generating docs.
- Add a lint check for quasi-keysets (keysets defined as unstructured
  markdown lists within a docstring).

src/gen/gen_eval_files.lua

@@ -328,6 +328,7 @@ local function get_api_keysets_meta()
   lint.lint_names('src/nvim/api/keysets_defs.h', nil, keysets)
 
   for _, k in ipairs(keysets) do
+    util.sort_by_key(k.keys)
     local params = {}
     for _, key in ipairs(k.keys) do
       local pty = k.types[key] or 'any'

src/gen/gen_vimdoc.lua

@@ -610,6 +610,8 @@ local function inline_type(obj, classes)
     end
   end
 
+  util.sort_by_key(cls.fields, 'name')
+
   local desc_append = {}
   for _, f in ipairs(cls.fields) do
     if not f.access then
@@ -715,6 +717,8 @@ local function render_class(class, classes, hidden_fields, cfg)
     end, fields)
   end
 
+  util.sort_by_key(fields, 'name')
+
   local fields_txt = render_fields_or_params(fields, nil, classes, cfg)
   if not fields_txt:match('^%s*$') then
     table.insert(ret, '\n    Fields: ~\n')
@@ -1145,6 +1149,7 @@ local function gen_target(cfg)
 
     if not f:find('ui_events%.in%.h$') then -- TODO(justinmk): also lint UI events.
       lint.lint_names(f, funs, nil, classes)
+      lint.lint_quasi_keysets(f, funs)
     end
 
     local mod_cls_nm = find_module_class(classes, 'M')

src/gen/lint.lua

@@ -226,4 +226,46 @@ function M.lint_names(source, api_funs, keysets, classes)
   end
 end
 
+--- Checks that markdown list items (`- name :` or `- {name}`) in parameter/field
+--- descriptions are in sorted order.
+---
+--- This is for "quasi-keysets" defined as markdown lists in docstrings. Ideally they would be
+--- defined as a luals `@class` or a API keyset, but sometimes that isn't possible.
+---
+--- @param source string Source filename.
+--- @param funs {name:string, params:{name:string, desc?:string}[]}[]
+function M.lint_quasi_keysets(source, funs)
+  local errors = {} --- @type string[]
+
+  for _, fun in ipairs(funs) do
+    for _, p in ipairs(fun.params or {}) do
+      if p.desc then
+        local prev = nil --- @type string?
+        for name in p.desc:gmatch('\n%- ([%w_]+)') do
+          -- Sort underscore-prefixed keys (e.g. "_cmdline_offset") at the end.
+          local prev_key = prev and prev:gsub('^_', '~') or nil
+          local name_key = name:gsub('^_', '~')
+          if prev_key and name_key < prev_key then
+            errors[#errors + 1] = fmt(
+              '%s: %s(): param "%s": key "%s" should come before "%s" (sort alphabetically)',
+              source,
+              fun.name,
+              p.name,
+              name,
+              prev
+            )
+          end
+          prev = name
+        end
+      end
+    end
+  end
+
+  if #errors > 0 then
+    error(
+      'lint_quasi_keysets(): unsorted keys in doc comments:\n  ' .. table.concat(errors, '\n  ')
+    )
+  end
+end
+
 return M

src/gen/util.lua

@@ -404,4 +404,17 @@ function M.md_to_vimdoc(text, start_indent, indent, text_width, is_list)
   return s
 end
 
+--- Sorts a list in-place, with underscore-prefixed names last (e.g. "_cmdline_offset").
+--- If `key` is given, sorts by `item[key]`; otherwise sorts by value.
+---
+--- @param t any[]
+--- @param key? string
+function M.sort_by_key(t, key)
+  table.sort(t, function(a, b)
+    local a_val = key and a[key] or a
+    local b_val = key and b[key] or b
+    return a_val:gsub('^_', '~') < b_val:gsub('^_', '~')
+  end)
+end
+
 return M