compiler: update typecore; tests: add VariantCoercionConstructUsed; d…

AGENTS.md

@@ -1,6 +1,6 @@
-# CLAUDE.md
+# AGENTS.md
 
-This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+Shared guidance for code agents (Claude, Gemini, Codex, etc.) working in this repository. The files `CLAUDE.md` and `GEMINI.md` are symlinks to this document. For Codex‑specific workflow details also see `CODEX.md`.
 
 ## Project Overview
 
@@ -136,4 +136,24 @@ The compiler is designed for fast feedback loops and scales to large codebases.
 - Avoid introducing meaningless symbols
 - Maintain readable JavaScript output
 - Consider compilation speed impact
-- Use appropriate optimization passes in the Lambda and JS IRs
+- Use appropriate optimization passes in the Lambda and JS IRs
+
+## Agent Notes and Gotchas
+
+- **Node version features:** Runtime docstring tests conditionally enable features by Node major version:
+  - 20+: array `toReversed`/`toSorted`
+  - 22+: new `Set` APIs and `Promise.withResolvers`
+  - 24+: `RegExp.escape`
+  Tests auto‑skip unsupported features based on `process.version`.
+- **CPU count in sandboxes:** Some CI/sandboxed environments report `os.cpus().length === 0`.
+  - Clamp concurrency/batch size to at least 1 when using `os.cpus()`.
+  - This pattern is used in `tests/docstring_tests/DocTest.res` and `cli/rescript-legacy/format.js`.
+- **Formatting in tests:** `make test` checks formatting (OCaml, ReScript, JS, Rust). If it fails locally, run `make format` and re‑run tests.
+- **Executables location:** Build copies platform binaries into `packages/@rescript/<platform>/bin/` and convenience folders like `darwinarm64/`.
+- **Direct dune usage:** You can use `dune build`/`dune build -w`, but prefer `make` targets which also copy executables.
+
+## References
+
+- `CODEX.md`: detailed setup, build, testing, and workflows for agented development
+- `README.md`: high‑level repo overview and usage
+- `Makefile`: authoritative list of build/test targets

CHANGELOG.md

@@ -25,6 +25,7 @@
 - Fix generation of interfaces for module types containing multiple type constraints. https://github.com/rescript-lang/rescript/pull/7825
 - JSX preserve mode: fix "make is not a valid component name". https://github.com/rescript-lang/rescript/pull/7831
 - Rewatch: include parser arguments of experimental features. https://github.com/rescript-lang/rescript/pull/7836
+- Suppress spurious “constructor … is never used” warnings when constructors are introduced via variant coercions; still warn for constructors only present on the target side. https://github.com/rescript-lang/rescript/pull/7839
 
 #### :memo: Documentation
 

compiler/ml/typecore.ml

@@ -3018,6 +3018,36 @@ and type_expect_ ~context ?in_function ?(recarg = Rejected) env sexp ty_expected
            raise (Error (loc, env, Not_subtype (tr1, tr2, ctx))));
       (arg, ty', cty')
     in
+    (* After a successful coercion, if we coerced between concrete variant
+       types, mark the intersection of constructors as positively used for the
+       target type to avoid spurious "constructor ... is never used" warnings
+       when values are introduced via coercions. *)
+    (try
+       let _p_src, _p_src_conc, src_decl =
+         Ctype.extract_concrete_typedecl env arg.exp_type
+       in
+       let _, p_tgt_conc, tgt_decl = Ctype.extract_concrete_typedecl env ty' in
+       match (src_decl.type_kind, tgt_decl.type_kind) with
+       | Type_variant src_cons, Type_variant tgt_cons ->
+         let module StringSet = Set.Make (String) in
+         let src_set =
+           List.fold_left
+             (fun acc (c : Types.constructor_declaration) ->
+               StringSet.add (Ident.name c.cd_id) acc)
+             StringSet.empty src_cons
+         in
+         let has_src name = StringSet.mem name src_set in
+         let tgt_ty_name_conc = Path.last p_tgt_conc in
+         (* Mark usage for the concrete target decl (implementation view). *)
+         List.iter
+           (fun (c : Types.constructor_declaration) ->
+             let cname = Ident.name c.cd_id in
+             if has_src cname then
+               Env.mark_constructor_used Env.Positive env tgt_ty_name_conc
+                 tgt_decl cname)
+           tgt_cons
+       | _ -> ()
+     with Not_found -> ());
     rue
       {
         exp_desc = arg.exp_desc;

tests/build_tests/super_errors/expected/VariantCoercionWarnOnC.res.expected

@@ -0,0 +1,13 @@
+
+  Warning number 37
+  /.../fixtures/VariantCoercionWarnOnC.res:9:3-11:7
+
+   7 │   let log: a => unit
+   8 │ } = {
+   9 │   type b =
+  10 │     | ...a
+  11 │     | C
+  12 │ 
+  13 │   let log = (x: a) => Js.log((x :> b))
+
+  unused constructor C.

tests/build_tests/super_errors/fixtures/VariantCoercionWarnOnC.res

@@ -0,0 +1,16 @@
+// Ensure unused-constructor warning still fires for new members introduced
+// only on the target side of a coercion.
+
+type a = A | B
+
+module M: {
+  let log: a => unit
+} = {
+  type b =
+    | ...a
+    | C
+
+  let log = (x: a) => Js.log((x :> b))
+}
+
+let _ = M.log(A)

tests/docstring_tests/DocTest.res

@@ -62,7 +62,11 @@ let extractDocFromFile = async file => {
   }
 }
 
-let batchSize = OS.cpus()->Array.length
+// Some environments may report 0 CPUs; clamp to at least 1 to avoid zero-sized batches
+let batchSize = switch OS.cpus()->Array.length {
+| n if n > 0 => n
+| _ => 1
+}
 
 let runtimePath = Path.join(["packages", "@rescript", "runtime"])
 

tests/tests/src/VariantCoercionConstructUsed.mjs

@@ -0,0 +1,17 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+
+
+function log(x) {
+  console.log(x);
+}
+
+let DoNotWarn = {
+  log: log
+};
+
+console.log("A");
+
+export {
+  DoNotWarn,
+}
+/*  Not a pure module */

tests/tests/src/VariantCoercionConstructUsed.res

@@ -0,0 +1,15 @@
+// Repro for incorrect "constructor ... is never used" warning with coercions
+// This should compile cleanly without warnings when coercing from a -> b.
+
+type a = A | B
+module DoNotWarn: {
+  let log: a => unit
+} = {
+  type b =
+    | ...a
+    | C
+
+  let log = (x: a) => Js.log((x :> b))
+}
+
+let _ = DoNotWarn.log(A)