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, 4 insertions, 5 deletions

diff --git a/src/nvim/generators/gen_eval.lua b/src/nvim/generators/gen_eval.lua
index a50e058e00..baed6a74c2 100644
--- a/src/nvim/generators/gen_eval.lua
+++ b/src/nvim/generators/gen_eval.lua
@@ -73,14 +73,13 @@ for _,fun in ipairs(metadata) do
   end
 end
 
+local func_names = vim.tbl_keys(funcs)
+table.sort(func_names)
 local funcsdata = io.open(funcs_file, 'w')
-funcsdata:write(mpack.pack(funcs))
+funcsdata:write(mpack.pack(func_names))
 funcsdata:close()
 
-
-local names = vim.tbl_keys(funcs)
-
-local neworder, hashfun = hashy.hashy_hash("find_internal_func", names, function (idx)
+local neworder, hashfun = hashy.hashy_hash("find_internal_func", func_names, function (idx)
   return "functions["..idx.."].name"
 end)
 hashpipe:write("static const EvalFuncDef functions[] = {\n")