[WIP] MCP

compiler/bsc/rescript_compiler_main.ml

@@ -52,6 +52,8 @@ let setup_outcome_printer () = Lazy.force Res_outcome_printer.setup
 
 let setup_runtime_path path = Runtime_package.path := path
 
+let print_suggested_actions_if_any () = Suggested_actions.print_block_if_any ()
+
 let process_file sourcefile ?kind ppf =
   (* This is a better default then "", it will be changed later
      The {!Location.input_name} relies on that we write the binary ast
@@ -114,6 +116,7 @@ let reprint_source_file sourcefile =
       if parse_result.invalid then (
         Res_diagnostics.print_report parse_result.diagnostics
           parse_result.source;
+        print_suggested_actions_if_any ();
         exit 1);
       Res_compmisc.init_path ();
       parse_result.parsetree
@@ -131,6 +134,7 @@ let reprint_source_file sourcefile =
       if parse_result.invalid then (
         Res_diagnostics.print_report parse_result.diagnostics
           parse_result.source;
+        print_suggested_actions_if_any ();
         exit 1);
       Res_compmisc.init_path ();
       parse_result.parsetree
@@ -143,6 +147,7 @@ let reprint_source_file sourcefile =
       print_endline
         ("Invalid input for reprinting ReScript source. Must be a ReScript \
           file: " ^ sourcefile);
+      print_suggested_actions_if_any ();
       exit 2
   in
   res
@@ -198,6 +203,7 @@ let bs_version_string = "ReScript " ^ Bs_version.version
 
 let print_version_string () =
   print_endline bs_version_string;
+  print_suggested_actions_if_any ();
   exit 0
 
 let[@inline] set s : Bsc_args.spec = Unit (Unit_set s)
@@ -358,6 +364,14 @@ let command_line_flags : (string * Bsc_args.spec * string) array =
           Clflags.ignore_parse_errors := true;
           Js_config.cmi_only := true),
       "*internal* Enable editor mode." );
+    ( "-llm-mode",
+      unit_call (fun () ->
+          Js_config.llm_mode := true;
+          Clflags.binary_annotations := false;
+          Clflags.color := Some Never;
+          Location.draw_underline_in_code_frame := true;
+          Warnings.llm_mode := true),
+      "*internal* Enable LLM mode for enhanced tooling" );
     ( "-ignore-parse-errors",
       set Clflags.ignore_parse_errors,
       "*internal* continue after parse errors" );
@@ -443,7 +457,11 @@ let _ : unit =
   try Bsc_args.parse_exn ~argv:Sys.argv command_line_flags anonymous ~usage with
   | Bsc_args.Bad msg ->
     Format.eprintf "%s@." msg;
+    print_suggested_actions_if_any ();
     exit 2
   | x ->
     Location.report_exception ppf x;
+    print_suggested_actions_if_any ();
     exit 2
+
+let _ = print_suggested_actions_if_any ()

compiler/common/js_config.ml

@@ -72,3 +72,5 @@ let jsx_module_of_string = function
 
 let as_pp = ref false
 let self_stack : string Stack.t = Stack.create ()
+
+let llm_mode = ref false

compiler/common/js_config.mli

@@ -101,3 +101,5 @@ val jsx_module_of_string : string -> jsx_module
 val as_pp : bool ref
 
 val self_stack : string Stack.t
+
+val llm_mode : bool ref

compiler/ext/suggested_actions.ml

@@ -0,0 +1,64 @@
+type suggested_action =
+  | ApplyAutomaticMigrationsForFullProject
+  | ApplyAutomaticMigrationsForCurrentFile
+
+type record = {loc: Warnings.loc; action: suggested_action}
+
+let suggestions : record list ref = ref []
+
+let file_of_record (r : record) = r.loc.loc_start.pos_fname
+
+let add r =
+  let exists =
+    List.exists
+      (fun x -> x.action = r.action && file_of_record x = file_of_record r)
+      !suggestions
+  in
+  if not exists then suggestions := r :: !suggestions
+
+let clear () = suggestions := []
+
+let has r =
+  List.exists
+    (fun x -> x.action = r.action && file_of_record x = file_of_record r)
+    !suggestions
+
+let action_id_json = function
+  | ApplyAutomaticMigrationsForFullProject ->
+    "\"ApplyAutomaticMigrationsForFullProject\""
+  | ApplyAutomaticMigrationsForCurrentFile ->
+    "\"ApplyAutomaticMigrationsForCurrentFile\""
+
+let print_block_if_any () =
+  match List.rev !suggestions with
+  | [] -> ()
+  | xs ->
+    let tag_name_of_action = function
+      | ApplyAutomaticMigrationsForCurrentFile -> "apply_all_migrations_in_file"
+      | ApplyAutomaticMigrationsForFullProject ->
+        "apply_all_migrations_in_project"
+    in
+    let description_of_action = function
+      | ApplyAutomaticMigrationsForCurrentFile ->
+        "Applies all automatic migrations in the current file."
+      | ApplyAutomaticMigrationsForFullProject ->
+        "Applies all automatic migrations in the project."
+    in
+    let print_entry ({loc; action} : record) =
+      let path =
+        let f = loc.loc_start.pos_fname in
+        if Filename.is_relative f then Ext_path.absolute_cwd_path f else f
+      in
+      let tag = tag_name_of_action action in
+      Printf.printf "  <%s>\n" tag;
+      Printf.printf "    <description>%s</description>\n"
+        (description_of_action action);
+      print_endline "    <command>";
+      Printf.printf "      perform-action %s %s\n" path (action_id_json action);
+      print_endline "    </command>";
+      Printf.printf "  </%s>\n" tag
+    in
+    print_endline "<suggested_actions>";
+    List.iter print_entry xs;
+    print_endline "</suggested_actions>";
+    flush stdout

compiler/ext/suggested_actions.mli

@@ -0,0 +1,10 @@
+type suggested_action =
+  | ApplyAutomaticMigrationsForFullProject
+  | ApplyAutomaticMigrationsForCurrentFile
+
+type record = {loc: Warnings.loc; action: suggested_action}
+
+val add : record -> unit
+val clear : unit -> unit
+val has : record -> bool
+val print_block_if_any : unit -> unit

compiler/ext/warnings.ml

@@ -296,6 +296,8 @@ let reset () =
 
 let () = reset ()
 
+let llm_mode = ref false
+
 let message = function
   | Comment_start -> "this is the start of a comment."
   | Comment_not_end -> "this is not the end of a comment."
@@ -310,10 +312,15 @@ let message = function
     ^
     if can_be_automigrated then
       "\n\n\
-      \  This can be automatically migrated by the ReScript migration tool. \
-       Run `rescript-tools migrate-all <project-root>` to run all automatic \
-       migrations available in your project, or `rescript-tools migrate \
-       <file>` to migrate a single file."
+      \  This can be automatically migrated by the ReScript migration tool. "
+      ^
+      if !llm_mode then
+        "Run the perform-action MCP tool for automatic migration, suggested \
+         below, to fix this automatically."
+      else
+        "Run `rescript-tools migrate-all <project-root>` to run all automatic \
+         migrations available in your project, or `rescript-tools migrate \
+         <file>` to migrate a single file."
     else ""
   | Fragile_match "" -> "this pattern-matching is fragile."
   | Fragile_match s ->

compiler/ext/warnings.mli

@@ -131,3 +131,5 @@ val loc_to_string : loc -> string
 (**
 Turn the location into a string with (line,column--line,column) format.
 *)
+
+val llm_mode : bool ref

compiler/ml/code_frame.ml

@@ -104,7 +104,7 @@ end
 
 let setup = Color.setup
 
-type gutter = Number of int | Elided
+type gutter = Number of int | Elided | UnderlinedRow
 type highlighted_string = {s: string; start: int; end_: int}
 type line = {gutter: gutter; content: highlighted_string list}
 
@@ -116,7 +116,7 @@ type line = {gutter: gutter; content: highlighted_string list}
   - center snippet when it's heavily indented
   - ellide intermediate lines when the reported range is huge
 *)
-let print ~is_warning ~src ~(start_pos : Lexing.position)
+let print ~is_warning ~draw_underline ~src ~(start_pos : Lexing.position)
     ~(end_pos : Lexing.position) =
   let indent = 2 in
   let highlight_line_start_line = start_pos.pos_lnum in
@@ -134,27 +134,22 @@ let print ~is_warning ~src ~(start_pos : Lexing.position)
   let max_line_digits_count = digits_count last_shown_line in
   (* TODO: change this back to a fixed 100? *)
   (* 3 for separator + the 2 spaces around it *)
-  let line_width = 78 - max_line_digits_count - indent - 3 in
+  let line_width = max 1 (78 - max_line_digits_count - indent - 3) in
   let lines =
-    if
-      start_line_line_offset >= 0
-      && end_line_line_end_offset >= start_line_line_offset
-    then
-      String.sub src start_line_line_offset
-        (end_line_line_end_offset - start_line_line_offset)
-      |> String.split_on_char '\n'
-      |> filter_mapi (fun i line ->
-             let line_number = i + first_shown_line in
-             if more_than_5_highlighted_lines then
-               if line_number = highlight_line_start_line + 2 then
-                 Some (Elided, line)
-               else if
-                 line_number > highlight_line_start_line + 2
-                 && line_number < highlight_line_end_line - 1
-               then None
-               else Some (Number line_number, line)
-             else Some (Number line_number, line))
-    else []
+    String.sub src start_line_line_offset
+      (end_line_line_end_offset - start_line_line_offset)
+    |> String.split_on_char '\n'
+    |> filter_mapi (fun i line ->
+           let line_number = i + first_shown_line in
+           if more_than_5_highlighted_lines then
+             if line_number = highlight_line_start_line + 2 then
+               Some (Elided, line)
+             else if
+               line_number > highlight_line_start_line + 2
+               && line_number < highlight_line_end_line - 1
+             then None
+             else Some (Number line_number, line)
+           else Some (Number line_number, line))
   in
   let leading_space_to_cut =
     lines
@@ -178,41 +173,98 @@ let print ~is_warning ~src ~(start_pos : Lexing.position)
                String.sub line leading_space_to_cut
                  (String.length line - leading_space_to_cut)
                |> break_long_line line_width
-               |> List.mapi (fun i line ->
+               |> List.mapi (fun i chunk ->
                       match gutter with
-                      | Elided -> {s = line; start = 0; end_ = 0}
+                      | Elided | UnderlinedRow ->
+                        {s = chunk; start = 0; end_ = 0}
                       | Number line_number ->
-                        let highlight_line_start_offset =
+                        let hl_start_off =
                           start_pos.pos_cnum - start_pos.pos_bol
                         in
-                        let highlight_line_end_offset =
-                          end_pos.pos_cnum - end_pos.pos_bol
+                        let hl_end_off = end_pos.pos_cnum - end_pos.pos_bol in
+                        (* Offsets within the trimmed line (after leading-space cut) *)
+                        let trimmed_hl_start =
+                          if line_number = highlight_line_start_line then
+                            max 0 (hl_start_off - leading_space_to_cut)
+                          else if line_number > highlight_line_start_line then 0
+                          else (* before start line *) max_int
                         in
-                        let start =
-                          if i = 0 && line_number = highlight_line_start_line
-                          then
-                            highlight_line_start_offset - leading_space_to_cut
+                        let trimmed_hl_end =
+                          if line_number < highlight_line_start_line then 0
+                          else if line_number = highlight_line_start_line
+                                  && line_number = highlight_line_end_line
+                          then max 0 (hl_end_off - leading_space_to_cut)
+                          else if line_number = highlight_line_start_line then
+                            (* highlight runs through end of this line *)
+                            String.length chunk (* placeholder; refined below *)
+                          else if line_number < highlight_line_end_line then
+                            (* full line highlight for interior lines *)
+                            String.length chunk (* placeholder; refined below *)
+                          else if line_number = highlight_line_end_line then
+                            max 0 (hl_end_off - leading_space_to_cut)
                           else 0
                         in
-                        let end_ =
-                          if line_number < highlight_line_start_line then 0
-                          else if
+                        (* Map highlight to this chunk using its offset *)
+                        let chunk_offset = i * line_width in
+                        let clen = String.length chunk in
+                        let start_rel =
+                          if trimmed_hl_start = max_int then 0
+                          else trimmed_hl_start - chunk_offset
+                        in
+                        let end_rel =
+                          if
                             line_number = highlight_line_start_line
-                            && line_number = highlight_line_end_line
-                          then highlight_line_end_offset - leading_space_to_cut
-                          else if line_number = highlight_line_start_line then
-                            String.length line
+                            && line_number <> highlight_line_end_line
+                            && i = 0
+                          then clen
                           else if
                             line_number > highlight_line_start_line
                             && line_number < highlight_line_end_line
-                          then String.length line
-                          else if line_number = highlight_line_end_line then
-                            highlight_line_end_offset - leading_space_to_cut
-                          else 0
+                          then clen
+                          else trimmed_hl_end - chunk_offset
                         in
-                        {s = line; start; end_})
+                        let start = max 0 (min clen start_rel) in
+                        let end_ = max 0 (min clen end_rel) in
+                        let start, end_ =
+                          if start >= end_ then (0, 0) else (start, end_)
+                        in
+                        {s = chunk; start; end_})
            in
-           {gutter; content = new_content})
+           if draw_underline then
+             let has_highlight =
+               List.exists (fun {start; end_} -> start < end_) new_content
+             in
+             if has_highlight then
+               let underline_content =
+                 List.map
+                   (fun {start; end_} ->
+                     if start < end_ then
+                       let overline_char = "^" in
+                       let underline_length = end_ - start in
+                       let underline =
+                         String.concat ""
+                           (List.init underline_length (fun _ -> overline_char))
+                       in
+                       [
+                         {
+                           s = String.make start ' ' ^ underline;
+                           start = 0;
+                           end_ = 0;
+                         };
+                       ]
+                     else [{s = ""; start = 0; end_ = 0}])
+                   new_content
+               in
+               [
+                 {gutter; content = new_content};
+                 {
+                   gutter = UnderlinedRow;
+                   content = List.flatten underline_content;
+                 };
+               ]
+             else [{gutter; content = new_content}]
+           else [{gutter; content = new_content}])
+    |> List.flatten
   in
   let buf = Buffer.create 100 in
   let open Color in
@@ -280,5 +332,11 @@ let print ~is_warning ~src ~(start_pos : Lexing.position)
                            else NoColor
                          in
                          add_ch c ch);
+                  add_ch NoColor '\n')
+         | UnderlinedRow ->
+           content
+           |> List.iter (fun line ->
+                  draw_gutter NoColor "";
+                  line.s |> String.iter (fun ch -> add_ch NoColor ch);
                   add_ch NoColor '\n'));
   Buffer.contents buf