feat(codegen): Deno-ESM target — direct AST→ES module backend (Refs #122)

Adds `lib/codegen_deno.ml`, a direct AffineScript-AST → ES-module
transpiler, plus a `--deno-esm` flag (and `.deno.js` extension) wired
into both compile dispatch paths in `bin/main.ml`.

Why a direct transpiler, not a wasm-wrapping ESM shim (the handoff's
original Phase 1): the motivating consumer (ubicity storage.ts /
wasm-bridge.ts) is pure JS-value orchestration — it JSON-stringifies
opaque objects, JSON-parses file contents back into JS objects, and
returns those to JS callers. AffineScript's wasm ABI is i32-only
(Codegen: params/ret all I32); arbitrary JS objects / JSON.stringify
cannot cross it. There is essentially no computation that belongs in
wasm, so source-to-source emission is the correct tool.

Backend behaviour:
- `pub fn`/`pub const`/`pub enum` -> `export` (ESM, no require).
- `extern fn` -> direct host calls via a lowering table
  (Deno.*Sync / JSON / WebAssembly / path helpers), inlined so output
  is genuinely drop-in (no extra package to resolve).
- struct + receiver-first free functions -> `export class`:
  constructor synthesised from the struct-returning fn (record literal
  -> `this.f = e`), methods from fns whose first param is the struct
  (receiver -> `this`), cross-method calls rewritten to `this.m(...)`.
  This is necessary because the current grammar accepts neither
  inherent `impl Type {}` nor a `self` expression (SELF_KW has no
  expression production — even stdlib/traits.affine fails to parse), so
  an "instance method" must be a free function taking the struct first.
- Methods emitted `async`: the consumer surface is entirely async and
  callers `await`; `await` on a synchronously-returned value is valid
  JS, so the exact API is preserved with no async-extern ABI (#103 not
  required for this consumer; remains documented future work).
- js_reserved trimmed to real ECMAScript reserved words (drops the
  Java-ism primitives Js_codegen carries: double/int/boolean/... are
  valid JS identifiers; mangling them would corrupt a consumer's
  required ESM export surface).

Regression: tests/codegen-deno/class_basic.{affine,harness.mjs} +
tools/run_codegen_deno_tests.sh + a CI step. The harness runs under
Node 20 (CI has no Deno; Phase 1 fixtures are pure logic and the
generated module only touches the Deno global lazily in unused
helpers). `dune build` clean; `dune runtest` unchanged (the 2
pre-existing E2E Node-CJS `--vscode-extension` failures, #116/#117
territory, exist identically on pristine HEAD and are out of #122
scope).

Refs #122, #35, #103.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/ci.yml

@@ -40,6 +40,12 @@ jobs:
       - name: Run codegen WASM tests
         run: opam exec -- ./tools/run_codegen_wasm_tests.sh
 
+      - name: Run codegen Deno-ESM tests (issue #122)
+        # Compiles tests/codegen-deno/*.affine with the --deno-esm backend
+        # and runs the *.harness.mjs under Node (CI has Node 20, not Deno;
+        # the Phase 1 fixtures are pure logic so Node ESM exercises them).
+        run: opam exec -- ./tools/run_codegen_deno_tests.sh
+
       - name: Run face-transformer regression tests
         run: opam exec -- ./tools/run_face_transformer_tests.sh
 

.gitignore

@@ -89,3 +89,9 @@ htmlcov/
 *.bak
 *.wasm
 /a.out
+
+# issue #122: generated Deno-ESM regression outputs (compiled from the
+# committed *.affine fixtures by tools/run_codegen_deno_tests.sh).
+/tests/codegen-deno/*.deno.js
+# Local-only build workaround (see file header); never committed.
+/dune-workspace

bin/main.ml

@@ -478,7 +478,7 @@ let repl_cmd_fn () =
     compilation errors.  With [--wasm-gc], targets the WebAssembly GC
     proposal instead of WASM 1.0 linear memory. *)
 let compile_file face json wasm_gc vscode_ext vscode_adapter vscode_no_lc
-    path output =
+    deno_esm path output =
   let face = resolve_face ~quiet:json face path in
   if json then begin
     let diags = ref [] in
@@ -512,8 +512,9 @@ let compile_file face json wasm_gc vscode_ext vscode_adapter vscode_no_lc
                use the original [prog] because they handle imports natively
                via Codegen.gen_imports / the import section. *)
             let flat_prog = Affinescript.Module_loader.flatten_imports loader prog in
+            let is_deno = deno_esm || Filename.check_suffix output ".deno.js" in
             let is_julia = Filename.check_suffix output ".jl" in
-            let is_js = Filename.check_suffix output ".js" in
+            let is_js = (not is_deno) && Filename.check_suffix output ".js" in
             let is_c = Filename.check_suffix output ".c" in
             let is_wgsl = Filename.check_suffix output ".wgsl" in
             let is_faust = Filename.check_suffix output ".dsp" in
@@ -534,7 +535,17 @@ let compile_file face json wasm_gc vscode_ext vscode_adapter vscode_no_lc
             let is_why3 = Filename.check_suffix output ".mlw" in
             let is_lean = Filename.check_suffix output ".lean" in
             let is_spirv = Filename.check_suffix output ".spv" in
-            if is_julia then begin
+            if is_deno then begin
+              match Affinescript.Codegen_deno.codegen_deno flat_prog resolve_ctx.symbols with
+              | Error msg ->
+                add { severity = Error; code = "E0824";
+                      message = Printf.sprintf "Deno-ESM codegen error: %s" msg;
+                      span = Affinescript.Span.dummy; help = None; labels = [] }
+              | Ok esm_code ->
+                let oc = open_out output in
+                output_string oc esm_code;
+                close_out oc
+            end else if is_julia then begin
               match Affinescript.Julia_codegen.codegen_julia flat_prog resolve_ctx.symbols with
               | Error msg ->
                 add { severity = Error; code = "E0800";
@@ -725,8 +736,9 @@ let compile_file face json wasm_gc vscode_ext vscode_adapter vscode_no_lc
                cross-module imports for backends that don't have native
                module-system support. Wasm/Wasm-GC keep the original [prog]. *)
             let flat_prog = Affinescript.Module_loader.flatten_imports loader prog in
+            let is_deno = deno_esm || Filename.check_suffix output ".deno.js" in
             let is_julia = Filename.check_suffix output ".jl" in
-            let is_js = Filename.check_suffix output ".js" in
+            let is_js = (not is_deno) && Filename.check_suffix output ".js" in
             let is_c = Filename.check_suffix output ".c" in
             let is_wgsl = Filename.check_suffix output ".wgsl" in
             let is_faust = Filename.check_suffix output ".dsp" in
@@ -747,7 +759,18 @@ let compile_file face json wasm_gc vscode_ext vscode_adapter vscode_no_lc
             let is_why3 = Filename.check_suffix output ".mlw" in
             let is_lean = Filename.check_suffix output ".lean" in
             let is_spirv = Filename.check_suffix output ".spv" in
-            if is_julia then
+            if is_deno then
+              (match Affinescript.Codegen_deno.codegen_deno flat_prog resolve_ctx.symbols with
+              | Error e ->
+                Format.eprintf "@[<v>Deno-ESM codegen error: %s@]@." e;
+                `Error (false, "Deno-ESM codegen error")
+              | Ok esm_code ->
+                let oc = open_out output in
+                output_string oc esm_code;
+                close_out oc;
+                Format.printf "Compiled %s -> %s (Deno-ESM)@." path output;
+                `Ok ())
+            else if is_julia then
               (match Affinescript.Julia_codegen.codegen_julia flat_prog resolve_ctx.symbols with
               | Error e ->
                 Format.eprintf "@[<v>Julia codegen error: %s@]@." e;
@@ -1178,6 +1201,20 @@ let vscode_no_lc_arg =
           dependency for extensions that ship no language client; the \
           wiring passes null in its place.")
 
+(* Issue #122: --deno-esm. Selects the direct AST -> ES-module backend
+   ({!Affinescript.Codegen_deno}) regardless of output extension, so a
+   drop-in `.js` ES module can be produced (e.g. `-o src/storage.js
+   --deno-esm`). A `.deno.js` output extension also routes here without
+   the flag, as a convenience for the test corpus / ad-hoc use. *)
+let deno_esm_arg =
+  Arg.(value & flag & info ["deno-esm"]
+    ~doc:"Emit a standalone Deno/Node ES module directly from the AST \
+          (issue #122): `export class` for struct+impl, `export` for \
+          public fns/consts, and `extern fn` lowered to direct host \
+          calls (Deno.*Sync / JSON / WebAssembly). No wasm, no require, \
+          no handle table — the output is a drop-in importable ESM. A \
+          `.deno.js` output extension selects this backend implicitly.")
+
 (** Shared --face flag: select the parser surface-syntax face. *)
 let face_arg =
   let faces = Arg.enum [
@@ -1524,7 +1561,7 @@ let compile_cmd =
   let doc = "Compile a file to WebAssembly (1.0 or GC proposal), Julia (.jl), JavaScript (.js), C (.c), a WGSL compute kernel (.wgsl), a Faust DSP program (.dsp), or an ONNX model (.onnx)" in
   let info = Cmd.info "compile" ~doc in
   Cmd.v info Term.(ret (const compile_file $ face_arg $ json_arg $ wasm_gc_arg
-    $ vscode_ext_arg $ vscode_adapter_arg $ vscode_no_lc_arg
+    $ vscode_ext_arg $ vscode_adapter_arg $ vscode_no_lc_arg $ deno_esm_arg
     $ path_arg $ output_arg))
 
 let fmt_cmd =