fix(man.lua): cache pages until width changes #40607

Problem: :Man unloads hidden buffers, so reopening large pages reruns rendering
even when the width is unchanged.

Solution: keep regular man buffers loaded and refresh them only when the
effective width changes.

runtime/lua/man.lua

@@ -416,7 +416,7 @@ end
 local function set_options()
   vim.bo.swapfile = false
   vim.bo.buftype = 'nofile'
-  vim.bo.bufhidden = 'unload'
+  vim.bo.bufhidden = 'hide'
   vim.bo.modified = false
   vim.bo.readonly = true
   vim.bo.modifiable = false
@@ -427,10 +427,8 @@ end
 --- @type boolean?
 local localfile_arg
 
---- @param path string
---- @param silent boolean?
---- @return string
-local function get_page(path, silent)
+--- @return integer
+local function get_manwidth()
   -- Disable hard-wrap by using a big $MANWIDTH (max 1000 on some systems #9065).
   -- Soft-wrap: ftplugin/man.lua sets wrap/breakindent/….
   -- Hard-wrap: driven by `man`.
@@ -438,11 +436,20 @@ local function get_page(path, silent)
   if (vim.g.man_hardwrap or 1) ~= 1 then
     manwidth = 999
   elseif vim.env.MANWIDTH then
-    vim.env.MANWIDTH = vim._tointeger(vim.env.MANWIDTH) or 0
-    manwidth = math.min(vim.env.MANWIDTH, api.nvim_win_get_width(0) - vim.o.wrapmargin)
+    local env_manwidth = vim._tointeger(vim.env.MANWIDTH) or 0
+    manwidth = math.min(env_manwidth, api.nvim_win_get_width(0) - vim.o.wrapmargin)
   else
     manwidth = api.nvim_win_get_width(0) - vim.o.wrapmargin
   end
+  return manwidth
+end
+
+--- @param path string
+--- @param silent boolean?
+--- @param manwidth integer?
+--- @return string
+local function get_page(path, silent, manwidth)
+  manwidth = manwidth or get_manwidth()
 
   if localfile_arg == nil then
     local mpath = get_path('man')
@@ -690,6 +697,7 @@ function M.init_pager()
   end
 
   set_options()
+  vim.bo.bufhidden = 'unload'
 end
 
 --- Combine the name and sect into a manpage reference so that all
@@ -794,10 +802,12 @@ function M.read_page(ref)
     return 'no manual entry for ' .. name
   end
 
-  local _, sect1 = parse_path(path)
-  local page = get_page(path)
+  local _, page_sect = parse_path(path)
+  local manwidth = get_manwidth()
+  local page = get_page(path, nil, manwidth)
 
-  vim.b.man_sect = sect1
+  vim.b.manwidth = manwidth
+  vim.b.man_sect = page_sect
   vim.bo.modifiable = true
   vim.bo.readonly = false
   vim.bo.swapfile = false
@@ -822,6 +832,20 @@ function M.read_page(ref)
   set_options()
 end
 
+--- @return string? err
+function M.refresh_page()
+  if vim.bo.filetype ~= 'man' then
+    return
+  end
+
+  local ref = api.nvim_buf_get_name(0):match('man://(.*)')
+  if not ref or vim.b.manwidth == nil or vim.b.manwidth == get_manwidth() then
+    return
+  end
+
+  return M.read_page(ref)
+end
+
 function M.show_toc()
   local bufnr = api.nvim_get_current_buf()
   local bufname = api.nvim_buf_get_name(bufnr)