Add inline and hidden source map modes

Author: mununki

compiler/bsc/rescript_compiler_main.ml

@@ -212,9 +212,14 @@ let[@inline] string_list_add s : Bsc_args.spec = String (String_list_add s)
 let parse_source_map value =
   Js_config.source_map :=
     match String.lowercase_ascii value with
-    | "true" | "linked" -> Linked
+    | "linked" -> Linked
+    | "inline" -> Inline
+    | "hidden" -> Hidden
     | "false" | "none" -> No_source_map
-    | value -> Bsc_args.bad_arg ("Unsupported sourceMap value: " ^ value)
+    | value ->
+      Bsc_args.bad_arg
+        ("Unsupported sourceMap value: " ^ value
+       ^ ". Expected linked, inline, hidden, false, or none")
 
 let parse_bool_ref target value =
   target :=

compiler/common/js_config.ml

@@ -26,7 +26,7 @@
 
 type jsx_version = Jsx_v4
 type jsx_module = React | Generic of {module_name: string}
-type source_map = No_source_map | Linked
+type source_map = No_source_map | Linked | Inline | Hidden
 
 let no_version_header = ref false
 

compiler/common/js_config.mli

@@ -24,7 +24,7 @@
 
 type jsx_version = Jsx_v4
 type jsx_module = React | Generic of {module_name: string}
-type source_map = No_source_map | Linked
+type source_map = No_source_map | Linked | Inline | Hidden
 
 (* val get_packages_info :
    unit -> Js_packages_info.t *)

compiler/core/js_source_map.ml

@@ -14,8 +14,8 @@
       generated position against the original ReScript location.
    4. After printing, the collected mappings are sorted and encoded into the
       compact Source Map v3 "mappings" field using base64 VLQ. The JSON map is
-      emitted next to the generated JavaScript and the JS file receives a
-      sourceMappingURL comment.
+      either emitted next to the generated JavaScript or embedded into it,
+      depending on the configured source map mode.
 
    Original locations come from OCaml Location.t values, whose columns are byte
    offsets. When source contents are available, original columns are converted
@@ -52,7 +52,7 @@ let current : t option ref = ref None
 let source_loc_of_loc (loc : Location.t) =
   match !Js_config.source_map with
   | No_source_map -> None
-  | Linked ->
+  | Linked | Inline | Hidden ->
     if loc.loc_ghost || loc.loc_start.pos_cnum < 0 then None else Some loc
 
 let with_builder builder f =
@@ -283,3 +283,35 @@ let json builder =
 
 let linked_comment ~map_file =
   "//# sourceMappingURL=" ^ Filename.basename map_file ^ "\n"
+
+let base64_chars =
+  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
+
+(* OCaml Stdlib does not provide Base64, and inline source maps only need a
+   small RFC 4648 encoder with padding for the data URI payload. Keep this
+   local instead of adding a package dependency just for this narrow use. *)
+let base64_encode input =
+  let len = String.length input in
+  let output = Buffer.create ((len + 2) / 3 * 4) in
+  let rec loop index =
+    if index < len then (
+      let b0 = Char.code input.[index] in
+      let has_b1 = index + 1 < len in
+      let has_b2 = index + 2 < len in
+      let b1 = if has_b1 then Char.code input.[index + 1] else 0 in
+      let b2 = if has_b2 then Char.code input.[index + 2] else 0 in
+      let chunk = (b0 lsl 16) lor (b1 lsl 8) lor b2 in
+      Buffer.add_char output base64_chars.[(chunk lsr 18) land 0x3f];
+      Buffer.add_char output base64_chars.[(chunk lsr 12) land 0x3f];
+      Buffer.add_char output
+        (if has_b1 then base64_chars.[(chunk lsr 6) land 0x3f] else '=');
+      Buffer.add_char output
+        (if has_b2 then base64_chars.[chunk land 0x3f] else '=');
+      loop (index + 3))
+  in
+  loop 0;
+  Buffer.contents output
+
+let inline_comment ~json =
+  "//# sourceMappingURL=data:application/json;base64," ^ base64_encode json
+  ^ "\n"

compiler/core/js_source_map.mli

@@ -12,3 +12,5 @@ val mark_source_loc : Ext_pp.t -> Location.t option -> unit
 val json : t -> string
 
 val linked_comment : map_file:string -> string
+
+val inline_comment : json:string -> string

compiler/core/lam_compile_main.ml

@@ -300,10 +300,10 @@ let (//) = Filename.concat
 let source_map_enabled () =
   match !Js_config.source_map with
   | No_source_map -> false
-  | Linked -> true
+  | Linked | Inline | Hidden -> true
 
-let dump_deps_program_with_source_map ~target_file ~output_prefix module_system
-    lambda_output chan =
+let dump_deps_program_with_source_map ?(remove_stale_map = true) ~target_file
+    ~output_prefix module_system lambda_output chan =
   let builder =
     if source_map_enabled () then
       Some
@@ -315,11 +315,23 @@ let dump_deps_program_with_source_map ~target_file ~output_prefix module_system
   Js_source_map.with_builder builder (fun () ->
       Js_dump_program.pp_deps_program ~output_prefix module_system lambda_output
         (Ext_pp.from_channel chan));
+  let map_file = target_file ^ ".map" in
+  let remove_map_file () =
+    if remove_stale_map && not !Clflags.dont_write_files then
+      Misc.remove_file map_file
+  in
   match (builder, !Js_config.source_map) with
   | Some builder, Linked ->
-    let map_file = target_file ^ ".map" in
+    let json = Js_source_map.json builder in
     output_string chan (Js_source_map.linked_comment ~map_file);
+    Ext_io.write_file map_file json
+  | Some builder, Hidden ->
     Ext_io.write_file map_file (Js_source_map.json builder)
+  | Some builder, Inline ->
+    output_string chan
+      (Js_source_map.inline_comment ~json:(Js_source_map.json builder));
+    remove_map_file ()
+  | _, No_source_map -> remove_map_file ()
   | _ -> ()
 
 let lambda_as_module 
@@ -328,7 +340,18 @@ let lambda_as_module
   : unit = 
   let package_info = Js_packages_state.get_packages_info () in 
   if Js_packages_info.is_empty package_info && !Js_config.js_stdout then begin    
-    Js_dump_program.dump_deps_program ~output_prefix Commonjs (lambda_output) stdout
+    match !Js_config.source_map with
+    | Inline ->
+      let target_file =
+        Ext_namespace.change_ext_ns_suffix
+          (Filename.basename output_prefix)
+          Literals.suffix_js
+      in
+      dump_deps_program_with_source_map ~remove_stale_map:false ~target_file
+        ~output_prefix Commonjs lambda_output stdout
+    | _ ->
+      Js_dump_program.dump_deps_program ~output_prefix Commonjs lambda_output
+        stdout
   end else
     Js_packages_info.iter package_info (fun {module_system; path; suffix} -> 
         let basename =  

docs/docson/build-schema.json

@@ -61,8 +61,8 @@
               "description": "`dev` generates source maps only during watch mode. `always` generates source maps during both build and watch."
             },
             "mode": {
-              "enum": ["linked"],
-              "description": "Generate a separate .js.map file next to each generated JavaScript file and append a sourceMappingURL comment. Only linked source maps are supported for now."
+              "enum": ["linked", "inline", "hidden"],
+              "description": "`linked` generates a separate .js.map file and appends a sourceMappingURL comment. `inline` appends the source map as a data URI and does not generate a .js.map file. `hidden` generates a separate .js.map file without appending a sourceMappingURL comment. When `inline` is combined with `sourcesContent: true`, original .res source text is embedded directly into the generated JS."
             },
             "sourcesContent": {
               "type": "boolean",

rewatch/src/build/compile.rs

@@ -1067,6 +1067,8 @@ fn compile_file(
                     if source_map.exists() {
                         let _ = std::fs::copy(&source_map, &destination_map)
                             .expect("copying source map file failed");
+                    } else {
+                        let _ = std::fs::remove_file(&destination_map);
                     }
                 }
             });