diff --git a/changes/dead-code-after-drift-8980.internal.md b/changes/dead-code-after-drift-8980.internal.md
new file mode 100644
index 00000000000..0279fd3d60c
--- /dev/null
+++ b/changes/dead-code-after-drift-8980.internal.md
@@ -0,0 +1 @@
+- Remove dead code, stale comments and unused test inputs left by recent changes, including the unused `cmt_interface_digest` field of `.cmt` files.
diff --git a/compiler/bsc/rescript_compiler_main.mli b/compiler/bsc/rescript_compiler_main.mli
deleted file mode 100644
index 3999ce7f69e..00000000000
--- a/compiler/bsc/rescript_compiler_main.mli
+++ /dev/null
@@ -1,23 +0,0 @@
-(* Copyright (C) 2015-2016 Bloomberg Finance L.P.
- * 
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU Lesser General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * In addition to the permissions granted to you by the LGPL, you may combine
- * or link a "work that uses the Library" with a publicly distributed version
- * of this file to produce a combined library or application, then distribute
- * that combined work under the terms of your choosing, with no requirement
- * to comply with the obligations normally placed on you by section 4 of the
- * LGPL version 3 (or the corresponding section of a later version of the LGPL
- * should you choose to use a later version).
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU Lesser General Public License for more details.
- * 
- * You should have received a copy of the GNU Lesser General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. *)
diff --git a/compiler/ext/bsc_warnings.ml b/compiler/ext/bsc_warnings.ml
index 955f9da9be2..d2c2b3dc7f4 100644
--- a/compiler/ext/bsc_warnings.ml
+++ b/compiler/ext/bsc_warnings.ml
@@ -47,4 +47,3 @@
 let defaults_w = "+a-4-9-20-41-102"
 
 let defaults_warn_error = "-a+5+101+109"
-(*TODO: add +10*)
diff --git a/compiler/ext/config.ml b/compiler/ext/config.ml
index 1f2c26527d0..a3d5904c212 100644
--- a/compiler/ext/config.ml
+++ b/compiler/ext/config.ml
@@ -13,7 +13,7 @@ and ast0_impl_magic_number = "Caml1999M022"
 
 and ast0_intf_magic_number = "Caml1999N022"
 
-and cmt_magic_number = "Caml1999T047"
+and cmt_magic_number = "Caml1999T048"
 
 let get_load_path () = (Compiler_request_state.current ()).load_path
 let set_load_path path = (Compiler_request_state.current ()).load_path <- path
diff --git a/compiler/ext/ext_namespace.ml b/compiler/ext/ext_namespace.ml
index 619684cefd9..52253d3a094 100644
--- a/compiler/ext/ext_namespace.ml
+++ b/compiler/ext/ext_namespace.ml
@@ -33,13 +33,6 @@ let rec rindex_rec s i =
 let change_ext_ns_suffix name ext =
   let i = rindex_rec name (String.length name - 1) in
   if i < 0 then name ^ ext else String.sub name 0 i ^ ext
-(* FIXME: micro-optimizaiton*)
-
-let try_split_module_name name =
-  let len = String.length name in
-  let i = rindex_rec name (len - 1) in
-  if i < 0 then None
-  else Some (String.sub name (i + 1) (len - i - 1), String.sub name 0 i)
 
 let js_name_of_modulename s (case : Ext_js_file_kind.case) suffix : string =
   let s =
diff --git a/compiler/ext/ext_namespace.mli b/compiler/ext/ext_namespace.mli
index daba3f4a99e..bee1c678035 100644
--- a/compiler/ext/ext_namespace.mli
+++ b/compiler/ext/ext_namespace.mli
@@ -22,8 +22,6 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. *)
 
-val try_split_module_name : string -> (string * string) option
-
 (* Note  we have to output uncapitalized file Name,
    or at least be consistent, since by reading cmi file on Case insensitive OS, we don't really know it is `list.cmi` or `List.cmi`, so that `require (./list.js)` or `require(./List.js)`
    relevant issues: #1609, #913
diff --git a/compiler/jsoo/jsoo_playground_main.ml b/compiler/jsoo/jsoo_playground_main.ml
index 0b84139e32a..109b9ae619f 100644
--- a/compiler/jsoo/jsoo_playground_main.ml
+++ b/compiler/jsoo/jsoo_playground_main.ml
@@ -508,7 +508,6 @@ module Compile = struct
         cmt_source_digest = None;
         cmt_initial_env = env;
         cmt_imports = [];
-        cmt_interface_digest = None;
         cmt_use_summaries = false;
         cmt_extra_info = {Cmt_utils.deprecated_used = []};
       }
diff --git a/compiler/ml/ast_helper.ml b/compiler/ml/ast_helper.ml
index cf0bf224c1a..e89291e735d 100644
--- a/compiler/ml/ast_helper.ml
+++ b/compiler/ml/ast_helper.ml
@@ -360,8 +360,9 @@ module Jsx_component = struct
   (* The first [@react.component], or failing that the first
      [@react.componentWithProps]: the JSX transform has always given them
      this precedence. A later one, or one whose payload is not understood, is
-     left in the attributes for the JSX transform to reject, so that
-     formatting does not drop it. *)
+     left in the attributes, so that formatting does not drop it: the JSX
+     transform takes a payload on a lone [@react.componentWithProps] with a
+     deprecation warning and rejects the others. *)
   let take attrs =
     let take_first is_kind =
       let rec go seen = function
diff --git a/compiler/ml/ast_untagged_variants.ml b/compiler/ml/ast_untagged_variants.ml
index 37807fd4455..f4e99def1d8 100644
--- a/compiler/ml/ast_untagged_variants.ml
+++ b/compiler/ml/ast_untagged_variants.ml
@@ -88,12 +88,6 @@ let literal_tag_to_user_visible_string = function
 
 let untagged = "unboxed"
 
-let block_type_can_be_undefined = function
-  | IntType | StringType | FloatType | BigintType | BooleanType | InstanceType _
-  | FunctionType | ObjectType ->
-    false
-  | UnknownType -> true
-
 let has_untagged (attrs : Parsetree.attributes) =
   Ext_list.exists attrs (function {txt}, _ -> txt = untagged)
 
diff --git a/compiler/ml/cmi_format.ml b/compiler/ml/cmi_format.ml
index 92a71bd5989..46a4a0594f6 100644
--- a/compiler/ml/cmi_format.ml
+++ b/compiler/ml/cmi_format.ml
@@ -61,20 +61,8 @@ let read_cmi filename =
     (fun () -> read_cmi_channel filename ic)
     ~finally:(fun () -> close_in_noerr ic)
 
-let output_cmi filename oc cmi =
-  (* beware: the provided signature must have been substituted for saving *)
-  output_string oc Config.cmi_magic_number;
-  output_value oc (cmi.cmi_name, cmi.cmi_sign);
-  flush oc;
-  let crc = Digest.file (Compiler_request_state.resolve_path filename) in
-  let crcs = (cmi.cmi_name, Some crc) :: cmi.cmi_crcs in
-  output_value oc crcs;
-  output_value oc cmi.cmi_flags;
-  crc
-
-(* This function is also called by [save_cmt] as cmi_format is subset of
-       cmt_format, so dont close the channel yet
-*)
+(* Writes the .cmi file, keeping an existing one with the same contents
+   when [check_exists] is given *)
 let create_cmi ?check_exists filename (cmi : cmi_infos) =
   (* beware: the provided signature must have been substituted for saving *)
   let content =
diff --git a/compiler/ml/cmi_format.mli b/compiler/ml/cmi_format.mli
index 15273591efc..8f21bc6df6c 100644
--- a/compiler/ml/cmi_format.mli
+++ b/compiler/ml/cmi_format.mli
@@ -22,9 +22,6 @@ type cmi_infos = {
   cmi_flags: pers_flags list;
 }
 
-(* write the magic + the cmi information *)
-val output_cmi : string -> out_channel -> cmi_infos -> Digest.t
-
 val create_cmi : ?check_exists:unit -> string -> cmi_infos -> Digest.t
 
 (* read the cmi information (the magic is supposed to have already been read) *)
diff --git a/compiler/ml/cmt_format.mli b/compiler/ml/cmt_format.mli
index 75953e14641..fccae7f2225 100644
--- a/compiler/ml/cmt_format.mli
+++ b/compiler/ml/cmt_format.mli
@@ -15,16 +15,11 @@
 
 (** cmt and cmti files format. *)
 
-(** The layout of a cmt or cmti file is as follows:
-      <cmt> := \{<cmi>\} <cmt magic> \{cmt infos\}
-    where <cmi> is the cmi file format:
-      <cmi> := <cmi magic> <cmi info>.
-    The compiler no longer writes the optional <cmi> part: the signature is
-    read from the .cmi file. Files written by older compilers have it in a
-    cmti, and in the cmt of a module without an interface.
+(** A cmt or cmti file is <cmt magic> <cmt infos>; the signature is read
+    from the .cmi file.
 
-    [read] accepts cmi, cmt and cmti files, with or without the <cmi> part,
-    and returns an option for the cmi info and the cmt info. *)
+    [read] accepts cmi, cmt and cmti files and returns the cmi info of a cmi
+    file and the cmt info of a cmt or cmti file. *)
 
 open Typedtree
 
@@ -56,7 +51,6 @@ type cmt_infos = {
   cmt_source_digest: Digest.t option;
   cmt_initial_env: Env.t;
   cmt_imports: (string * Digest.t option) list;
-  cmt_interface_digest: Digest.t option;
   cmt_use_summaries: bool;
   cmt_extra_info: Cmt_utils.cmt_extra_info;
 }
diff --git a/compiler/ml/cmt_format_common.ml b/compiler/ml/cmt_format_common.ml
index 9ad18767174..9a7b25a222a 100644
--- a/compiler/ml/cmt_format_common.ml
+++ b/compiler/ml/cmt_format_common.ml
@@ -48,7 +48,6 @@ type cmt_infos = {
   cmt_source_digest: Digest.t option;
   cmt_initial_env: Env.t;
   cmt_imports: (string * Digest.t option) list;
-  cmt_interface_digest: Digest.t option;
   cmt_use_summaries: bool;
   cmt_extra_info: Cmt_utils.cmt_extra_info;
 }
@@ -103,13 +102,8 @@ exception Error of error
 
 let input_cmt ic = (input_value ic : cmt_infos)
 
-(** [read filename] opens filename, and extract both the cmi_infos, if
-    it exists, and the cmt_infos, if it exists. Thus, it can be used
-    with .cmi, .cmt and .cmti files.
-
-    The compiler no longer writes a cmi_infos in front of the cmt_infos in
-    .cmt and .cmti files, but files from older compilers may contain one.
-*)
+(** [read filename] reads a .cmi file as its cmi_infos, or a .cmt or .cmti
+    file as its cmt_infos. *)
 let read filename =
   (*  Printf.fprintf stderr "Cmt_format.read %s\n%!" filename; *)
   let ic = open_in_bin (Compiler_request_state.resolve_path filename) in
@@ -118,17 +112,7 @@ let read filename =
     let cmi, cmt =
       if magic_number = Config.cmt_magic_number then (None, Some (input_cmt ic))
       else if magic_number = Config.cmi_magic_number then
-        let cmi = Cmi_format.input_cmi ic in
-        let cmt =
-          try
-            let magic_number = read_magic_number ic in
-            if magic_number = Config.cmt_magic_number then
-              let cmt = input_cmt ic in
-              Some cmt
-            else None
-          with _ -> None
-        in
-        (Some cmi, cmt)
+        (Some (Cmi_format.input_cmi ic), None)
       else raise (Cmi_format.Error (Cmi_format.Not_an_interface filename))
     in
     close_in ic;
diff --git a/compiler/ml/oprint.ml b/compiler/ml/oprint.ml
index 3665f810c2a..398af99b295 100644
--- a/compiler/ml/oprint.ml
+++ b/compiler/ml/oprint.ml
@@ -28,5 +28,3 @@ let out_sig_item : (Format.formatter -> out_sig_item -> unit) ref =
   ref not_set_up
 let out_signature : (Format.formatter -> out_sig_item list -> unit) ref =
   ref not_set_up
-let out_type_extension : (Format.formatter -> out_type_extension -> unit) ref =
-  ref not_set_up
diff --git a/compiler/ml/oprint.mli b/compiler/ml/oprint.mli
index 32b5fe65ed9..8f3b949ce02 100644
--- a/compiler/ml/oprint.mli
+++ b/compiler/ml/oprint.mli
@@ -20,4 +20,3 @@ val out_type : (formatter -> out_type -> unit) ref
 val out_module_type : (formatter -> out_module_type -> unit) ref
 val out_sig_item : (formatter -> out_sig_item -> unit) ref
 val out_signature : (formatter -> out_sig_item list -> unit) ref
-val out_type_extension : (formatter -> out_type_extension -> unit) ref
diff --git a/compiler/ml/platform/native/cmt_format_persistence.ml b/compiler/ml/platform/native/cmt_format_persistence.ml
index 49c13c5caa5..0b1f1c8ba60 100644
--- a/compiler/ml/platform/native/cmt_format_persistence.ml
+++ b/compiler/ml/platform/native/cmt_format_persistence.ml
@@ -46,7 +46,6 @@ let save_cmt filename modname binary_annots sourcefile initial_env =
               (if need_to_clear_env then keep_only_summary initial_env
                else initial_env);
             cmt_imports = List.sort compare (Env.imports ());
-            cmt_interface_digest = None;
             cmt_use_summaries = need_to_clear_env;
             cmt_extra_info = {deprecated_used = deprecated_uses ()};
           }
diff --git a/compiler/syntax/src/res_outcome_printer.ml b/compiler/syntax/src/res_outcome_printer.ml
index 1c8c4095844..7ad5747e513 100644
--- a/compiler/syntax/src/res_outcome_printer.ml
+++ b/compiler/syntax/src/res_outcome_printer.ml
@@ -928,10 +928,6 @@ let print_out_module_type fmt out_module_type =
   Format.pp_print_string fmt
     (Doc.to_string ~width:80 (print_out_module_type_doc out_module_type))
 
-let print_out_type_extension fmt type_extension =
-  Format.pp_print_string fmt
-    (Doc.to_string ~width:80 (print_out_type_extension_doc type_extension))
-
 (* Not supported in ReScript *)
 (* Oprint.out_class_type *)
 let setup =
@@ -939,5 +935,4 @@ let setup =
     (Oprint.out_type := print_out_type;
      Oprint.out_module_type := print_out_module_type;
      Oprint.out_sig_item := print_out_sig_item;
-     Oprint.out_signature := print_out_signature;
-     Oprint.out_type_extension := print_out_type_extension)
+     Oprint.out_signature := print_out_signature)
diff --git a/rewatch-ocaml/tests/failure/Broken.invalid b/rewatch-ocaml/tests/failure/Broken.invalid
deleted file mode 100644
index 0e3ce71961b..00000000000
--- a/rewatch-ocaml/tests/failure/Broken.invalid
+++ /dev/null
@@ -1 +0,0 @@
-let value: string = 42
diff --git a/tests/build_tests/option_transitive_dependency/rescript.json b/tests/build_tests/option_transitive_dependency/rescript.json
deleted file mode 100644
index 2cd03417343..00000000000
--- a/tests/build_tests/option_transitive_dependency/rescript.json
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  "name": "option_transitive_dependency",
-  "sources": []
-}
diff --git a/tests/build_tests/regexp_statement_formatting/rescript.json b/tests/build_tests/regexp_statement_formatting/rescript.json
deleted file mode 100644
index 0517d76218d..00000000000
--- a/tests/build_tests/regexp_statement_formatting/rescript.json
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  "name": "regexp-statement-formatting",
-  "sources": []
-}
diff --git a/tests/ounit_tests/ounit_string_tests.ml b/tests/ounit_tests/ounit_string_tests.ml
index 68a3fd0c3d1..8abc0ffbf00 100644
--- a/tests/ounit_tests/ounit_string_tests.ml
+++ b/tests/ounit_tests/ounit_string_tests.ml
@@ -134,15 +134,6 @@ let suites =
            =~ "AA.js";
            Ext_namespace.js_name_of_modulename "AA-b" Upper ".bs.js"
            =~ "AA.bs.js" );
-         ( __LOC__ >:: fun _ ->
-           let ( =~ ) =
-             OUnit.assert_equal ~printer:(fun x ->
-                 match x with
-                 | None -> ""
-                 | Some (a, b) -> a ^ "," ^ b)
-           in
-           Ext_namespace.try_split_module_name "Js-X" =~ Some ("X", "Js");
-           Ext_namespace.try_split_module_name "Js_X" =~ None );
          ( __LOC__ >:: fun _ ->
            let k = Ext_modulename.js_id_name_of_hint_name in
            k "xx" =~ "Xx";