Developer playground: genType support and sourcemap scaffolding

CHANGELOG.md

@@ -43,7 +43,7 @@
 - Preserve trailing comments between the type and `=` in locally abstract value constraints (`let f: type a. t /* comment */ = value`). https://github.com/rescript-lang/rescript/pull/8575
 - Enforce function arity in interface/module inclusion and type coercion. Previously a curried implementation (e.g. `int => int => int`) could satisfy an uncurried interface (`(int, int) => int`) or be coerced to it, which could miscompile calls made through the interface type. Such mismatches are now compile errors with an explanatory hint. https://github.com/rescript-lang/rescript/pull/8559
 - Fix termination-analysis false positives for functions whose progress flows through un-annotated helpers: collecting the callees of a function binding was accidentally disabled in 2024 (the collection guard required a node shape that uncurried code never produces), so helpers calling `@progress` functions were no longer added to the function table. https://github.com/rescript-lang/rescript/pull/8568
-- Fix default values of optional parameters being computed at the wrong time for curried functions: in `(~x=default, y) => (~z=default, w) => ...`, `x`'s default was only computed when the *inner* function was applied. Each default is now computed when its own parameter group is applied. https://github.com/rescript-lang/rescript/pull/8568
+- Fix default values of optional parameters being computed at the wrong time for curried functions: in `(~x=default, y) => (~z=default, w) => ...`, `x`'s default was only computed when the _inner_ function was applied. Each default is now computed when its own parameter group is applied. https://github.com/rescript-lang/rescript/pull/8568
 - Fix bare labeled arrow types (`~x: int => string`) getting no arity: they printed identically to their parenthesized form (`(~x: int) => string`) but did not unify with it. https://github.com/rescript-lang/rescript/pull/8563
 - Fix losses of fidelity when code passes through an external PPX: the internal `@res.async` marker no longer leaks into the program, attributes on an arrow type or on an `await` expression are no longer dropped or relocated (previously this could crash the formatter), JSX elements keep their closing tag, and PPX-emitted OCaml-style `function` is desugared instead of crashing the compiler. https://github.com/rescript-lang/rescript/pull/8561
 - Preserve multibyte characters when wrapping long source lines in compiler code frames. https://github.com/rescript-lang/rescript/pull/8520
@@ -60,6 +60,7 @@
 
 #### :house: Internal
 
+- Add genType and source map controls and output to the developer playground. https://github.com/rescript-lang/rescript/pull/8448
 - Rework the object-type representation end to end: object rows are plain field chains carrying a per-field mutability state (no phantom setter members), object literals are typed directly and property access and assignment are first-class AST and Lambda nodes shared between the Lambda and JS pipelines, and dead class-system remnants (the field-presence lattice, the class-abbreviation memo on object types, method-send typing) are removed. https://github.com/rescript-lang/rescript/pull/8597
 - Upgrade the development toolchain and primary CI builds to OCaml 5.5 while retaining OCaml 5.0 as the minimum supported version. https://github.com/rescript-lang/rescript/pull/8589
 - Upgrade the vendored Flow parser from 0.267.0 to 0.320.0, the final release of the OCaml implementation. https://github.com/rescript-lang/rescript/pull/8588

compiler/core/js_source_map.ml

@@ -41,6 +41,7 @@ type t = {
   generated_dir: string;
   source_root: string;
   sources_content: bool;
+  provided_source_contents: (string, string) Hashtbl.t;
   sources: (string, int) Hashtbl.t;
   mutable source_list: source list;
   mutable mappings: mapping list;
@@ -109,20 +110,27 @@ let relative_path ~from_dir ~to_file =
     let parts = repeat ".." (List.length from_rest) @ to_rest in
     if parts = [] then Filename.basename to_file else String.concat "/" parts
 
-let make ~generated_file ~source_root ~sources_content =
+let make ~source_contents ~generated_file ~source_root ~sources_content =
+  let provided_source_contents = Hashtbl.create (List.length source_contents) in
+  source_contents
+  |> List.iter (fun (filename, content) ->
+      Hashtbl.replace provided_source_contents (absolute_path filename) content);
   {
     generated_file = Filename.basename generated_file;
     generated_dir = Filename.dirname generated_file;
     source_root;
     sources_content;
+    provided_source_contents;
     sources = Hashtbl.create 4;
     source_list = [];
     mappings = [];
     last_generated = None;
   }
 
-let load_content filename =
-  try Some (Ext_io.load_file filename) with _ -> None
+let load_content builder filename =
+  match Hashtbl.find_opt builder.provided_source_contents filename with
+  | Some content -> Some content
+  | None -> ( try Some (Ext_io.load_file filename) with _ -> None)
 
 let add_source builder filename =
   let filename =
@@ -138,7 +146,7 @@ let add_source builder filename =
       {
         relative_path =
           relative_path ~from_dir:builder.generated_dir ~to_file:filename;
-        content = load_content filename;
+        content = load_content builder filename;
       }
     in
     let index = List.length builder.source_list in

compiler/core/js_source_map.mli

@@ -1,7 +1,11 @@
 type t
 
 val make :
-  generated_file:string -> source_root:string -> sources_content:bool -> t
+  source_contents:(string * string) list ->
+  generated_file:string ->
+  source_root:string ->
+  sources_content:bool ->
+  t
 
 val with_builder : t -> (unit -> 'a) -> 'a
 

compiler/core/lam_compile_main.ml

@@ -437,7 +437,7 @@ let remove_stale_source_map ?(remove_stale_map = true) target_file =
 let dump_deps_program_with_source_map ?(remove_stale_map = true) ~target_file
     ~output_prefix module_system lambda_output chan =
   let builder =
-    Js_source_map.make ~generated_file:target_file
+    Js_source_map.make ~source_contents:[] ~generated_file:target_file
       ~source_root:!Js_config.source_map_root
       ~sources_content:!Js_config.source_map_sources_content
   in

compiler/jsoo/dune

@@ -7,4 +7,4 @@
   (= %{profile} browser))
  (flags
   (:standard -w +a-4-9-40-42-44-45))
- (libraries core syntax ml js_of_ocaml))
+ (libraries core syntax ml gentype js_of_ocaml))