[mini.sessions] preserve buffer-local variables across sessions

[ivomac]

mksession does not save user-defined b: variables. Plugins that store per-buffer metadata lose it when a session is restored.

I use a custom session config that appends buffer-variable restore commands to the session file after mksession:

local function encode_varval(buf, varname, varval)
  -- handles multiline strings, quotes, unnamed buffers, etc.
  -- returns a Lua expression equal to the original value
end

local tmpl = "lua pcall(vim.api.nvim_buf_set_var, vim.fn.bufnr('%s'), '%s', %s)"

local f = io.open(session_path, "a")
if f then
  for _, buf in ipairs(vim.fn.getbufinfo({ buflisted = 1 })) do
    for varname, varval in pairs(buf.variables) do
      local t = type(varval)
      local upper = varname:sub(1, 1):match("%u")
      local ok = vim.tbl_contains({"string", "number"}, t)
      if upper and ok then
        f:write("\n" .. string.format(
          tmpl, buf.name, varname, encode_varval(buf, varname, varval))
      )
      end
    end
  end
  f:close()
end

Only uppercase string/number variables are preserved (these are internal plugin vars by convention).

Table support is feasible with vim.inspect but not essential.

Proposal: save_buffer_variables option in config (default false). When enabled, write() appends the restore commands to the session file. No changes to read() needed.

Happy to implement it myself!

[echasnovski]

Thanks for sharing and the suggestion!

The overall design of 'mini.sessions' is to serve as a thin layer between :mksession and its side effects (session files, etc.). Anything related to the session file content is delegated to :mksession. For anything else there are pre and post hooks in 'mini.sessions'.

So I think rewriting this as a hooks might be a better fit for 'mini.sessions'.