Functions not showing up in backtrace, even with calls to Sys.opaque

[EkanshdeepGupta]

Inserting calls to Sys.opaque is not working as expected. I made a branch, ppx_monad which you can checkout to see this issue: 6820184

The change is as follows: in the function Frontend.Typing.ProcessModule.process_module, the following tail:
let* x = y in z

was replaced by:
let __ret__ = (let* x = y in z ) |> Sys.opaque in Sys.opaque __ret__

However, even so, when running the following command:

git checkout origin/ppx_monad
dune build; dune exec -- raven test/bugs/interface_module_dep.rav --verbosity=debug

The backtrace I got was the following:

Raised at Util__Error.fail in file "lib/util/error.ml", line 31, characters 36-63
Called from Ast__SymbolTbl.add_symbol.add.(fun) in file "lib/ast/symbolTbl.ml", line 422, characters 52-102
Called from Base__List0.rev_map2_ok.rmap2_f in file "src/list0.ml", line 96, characters 39-46
Called from Base__List0.rev_map2_ok.(fun) in file "src/list0.ml" (inlined), line 99, characters 47-65
.
.
.
Called from Base__List.fold_map.(fun) in file "src/list.ml", line 524, characters 23-31
Called from Base__List.count_map in file "src/list.ml", line 494, characters 13-17
Called from Base__List.map in file "src/list.ml" (inlined), line 510, characters 15-31
Called from Base__List.fold_map in file "src/list.ml", line 523, characters 4-88
Called from Ast__Rewriter.Syntax.Let_syntax.map in file "lib/ast/rewriter.ml", line 31, characters 22-27
Called from Frontend__Typing.process_module.(fun) in file "lib/frontend/typing.ml", line 1875, characters 16-49
Called from Ast__Rewriter.eval in file "lib/ast/rewriter.ml", line 60, characters 18-23
Called from Frontend__Typing.process_module in file "lib/frontend/typing.ml", line 1873, characters 15-201
Called from Dune__exe__Raven.parse_and_check_cu in file "bin/raven.ml", line 28, characters 26-55
Called from Dune__exe__Raven.parse_and_check_all.(fun) in file "bin/raven.ml", line 66, characters 27-103
Called from Base__List0.fold in file "src/list0.ml", line 37, characters 27-37
Called from Dune__exe__Raven.parse_and_check_all in file "bin/raven.ml", line 61, characters 4-491
Called from Dune__exe__Raven.main in file "bin/raven.ml", line 124, characters 10-43

Note that there is a reference to Frontend__Typing.process_module (typing.ml: line 1875), but no Frontend__Typing.ProcessModule.process_module which is called from line 1875 (the names are confusing but there are two process_module functions). Somehow, even after this "rewrite", the function is still not showing up in the backtrace.

I'm using Ocaml 4.14.0