build: make generated source files reproducible #21586

Problem:
Build is not reproducible, because generated source files (.c/.h/) are not
deterministic, mostly because Lua pairs() is unordered by design (for security).

https://github.com/LuaJIT/LuaJIT/issues/626#issuecomment-707005671
https://www.lua.org/manual/5.1/manual.html#pdf-next
> The order in which the indices are enumerated is not specified [...]
>
>> The hardening of the VM deliberately randomizes string hashes. This in
>> turn randomizes the iteration order of tables with string keys.

Solution:
- Update the code generation scripts to be deterministic.
    - That is only a partial solution: the exported function
      (funcs_metadata.generated.h) and ui event
      (ui_events_metadata.generated.h) metadata have some mpack'ed
      tables, which are not serialized deterministically.
    - As a workaround, introduce `PRG_GEN_LUA` cmake setting, so you can
      inject a modified build of luajit (with LUAJIT_SECURITY_PRN=0)
      that preserves table order.
    - Longer-term we should change the mpack'ed data structure so it no
      longer uses tables keyed by strings.

Closes #20124

Co-Authored-By: dundargoc <gocdundar@gmail.com>
Co-Authored-By: Arnout Engelen <arnout@bzzt.net>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/nvim/generators/gen_options.lua b/src/nvim/generators/gen_options.lua
index af21d44eaf..edb7dae159 100644
--- a/src/nvim/generators/gen_options.lua
+++ b/src/nvim/generators/gen_options.lua
@@ -159,7 +159,7 @@ local dump_option = function(i, o)
     if #o.scope == 2 then
       pv_name = 'OPT_BOTH(' .. pv_name .. ')'
     end
-    defines['PV_' .. varname:sub(3):upper()] = pv_name
+    table.insert(defines,  { 'PV_' .. varname:sub(3):upper() , pv_name})
     w('    .indir=' .. pv_name)
   end
   if o.enable_if then
@@ -192,7 +192,7 @@ w('  [' .. ('%u'):format(#options.options) .. ']={.fullname=NULL}')
 w('};')
 w('')
 
-for k, v in pairs(defines) do
-  w('#define ' .. k .. ' ' .. v)
+for _, v in ipairs(defines) do
+  w('#define ' .. v[1] .. ' ' .. v[2])
 end
 opt_fd:close()