feat(stdlib): close 6 STEP-3 Deno-ESM gaps surfaced by TS→AS ports (Refs #239, #242)

lib/codegen_deno.ml

@@ -513,6 +513,14 @@ let () =
   b "ensureDir"     (fun a -> Printf.sprintf "__as_ensureDir(%s)" (arg 0 a));
   b "readDirNames"  (fun a -> Printf.sprintf "__as_readDirNames(%s)" (arg 0 a));
   b "statSize"      (fun a -> Printf.sprintf "Deno.statSync(%s).size" (arg 0 a));
+  b "statIsFile"      (fun a -> Printf.sprintf "Deno.statSync(%s).isFile" (arg 0 a));
+  b "statIsDirectory" (fun a -> Printf.sprintf "Deno.statSync(%s).isDirectory" (arg 0 a));
+  b "bytesLength"     (fun a -> Printf.sprintf "(%s).length" (arg 0 a));
+  b "bytesByteAt"     (fun a -> Printf.sprintf "(%s)[%s]" (arg 0 a) (arg 1 a));
+  b "bytesAsciiSlice" (fun a -> Printf.sprintf "String.fromCharCode(...(%s).slice(%s, %s))" (arg 0 a) (arg 1 a) (arg 2 a));
+  (* `import.meta.url` — only legal at module top level, which the
+     Deno-ESM backend's output already is. *)
+  b "importMetaUrl"   (fun _ -> "import.meta.url");
   b "pathJoin"      (fun a -> Printf.sprintf "__as_pathJoin(%s, %s)" (arg 0 a) (arg 1 a));
   b "isNotFound"    (fun a -> Printf.sprintf "__as_isNotFound(%s)" (arg 0 a));
   (* ---- JSON ---- *)
@@ -1238,6 +1246,13 @@ and gen_try_stmt ctx body catch finally =
 
 and gen_stmt ctx (stmt : stmt) : string =
   match stmt with
+  | StmtLet { sl_pat = PatWildcard _; sl_value; _ } ->
+      (* `let _ = X` evaluates X for side effects and drops the value.
+         Emitting `const _ = X;` produces a JS SyntaxError on the second
+         occurrence in the same scope ("Identifier '_' has already been
+         declared"). Drop the binding entirely; the bare expression
+         statement keeps the semantics. *)
+      gen_expr ctx sl_value ^ ";"
   | StmtLet { sl_pat; sl_value; sl_mut; sl_quantity = _; sl_ty = _ } ->
       let kw = if sl_mut then "let" else "const" in
       let js = kw ^ " " ^ gen_pattern ctx sl_pat ^ " = "

stdlib/Deno.affine

@@ -68,11 +68,39 @@ pub extern fn readDirNames(path: String) -> [String];
 /// `Deno.statSync(path).size` in bytes.
 pub extern fn statSize(path: String) -> Int;
 
+/// `Deno.statSync(path).isFile` — true if `path` is a regular file.
+/// Throws on a missing path (pair with `isNotFound` for the absent case).
+pub extern fn statIsFile(path: String) -> Bool;
+
+/// `Deno.statSync(path).isDirectory` — true if `path` is a directory.
+/// Throws on a missing path (pair with `isNotFound` for the absent case).
+pub extern fn statIsDirectory(path: String) -> Bool;
+
 /// Recursive walk under `root` — every file path beneath it, depth-first.
 /// Mirrors `std/fs/walk` for the common case (no glob filter; callers
 /// filter by extension). Throws on a missing root via `Deno.readDirSync`.
 pub extern fn walkRecursive(root: String) -> [String];
 
+// ── Bytes accessors ────────────────────────────────────────────────
+//
+// The opaque `Bytes` type (a Uint8Array under the hood) gets minimal
+// inspectors so AffineScript can peek at file magic, parse fixed-width
+// binary headers, and recover ASCII slices without crossing back through
+// `readTextFile`. Bounds-check via `bytesLength` — `bytesByteAt` with
+// an out-of-range index returns `undefined → NaN` coerced to 0.
+
+/// `b.length` — number of bytes.
+pub extern fn bytesLength(b: Bytes) -> Int;
+
+/// `b[i]` — byte value at index `i` (0..255). Bounds-check via `bytesLength`.
+pub extern fn bytesByteAt(b: Bytes, i: Int) -> Int;
+
+/// `String.fromCharCode(...b.slice(start, end))` — decode `[start, end)`
+/// as a Latin-1 / ASCII-safe string. Each byte becomes one code point
+/// (0..255). Use this for ASCII-only headers (PDF magic, MZ, ELF, etc.);
+/// for full UTF-8, prefer `readTextFile` directly.
+pub extern fn bytesAsciiSlice(b: Bytes, start: Int, end: Int) -> String;
+
 // ── Path ───────────────────────────────────────────────────────────
 
 /// Single-segment join with a `/` separator (idempotent on a trailing
@@ -121,6 +149,15 @@ pub extern fn dateNow() -> Int;
 /// returns epoch millis as `Int`.
 pub extern fn dateNowIso() -> String;
 
+// ── Module identity ────────────────────────────────────────────────
+
+/// `import.meta.url` — the absolute URL of the importing module. The JS
+/// idiom for "find my own location" (cf. `__dirname` / `__filename`). At
+/// Deno-ESM top level, lowers to the bare `import.meta.url` expression;
+/// callers parse it (`new URL(...)`/`fileURLToPath`/string split) for
+/// directory-relative behaviour.
+pub extern fn importMetaUrl() -> String;
+
 // ── CLI ────────────────────────────────────────────────────────────
 
 /// `Deno.args` — command-line arguments (excludes argv[0]).

stdlib/string.affine

@@ -68,7 +68,7 @@ fn starts_with(s: String, prefix: String) -> Bool {
 }
 
 /// Check if string ends with the given suffix
-fn ends_with(s: String, suffix: String) -> Bool {
+pub fn ends_with(s: String, suffix: String) -> Bool {
   let slen = len(s);
   let sfxlen = len(suffix);
   if sfxlen > slen {

tests/codegen-deno/deno_scripting_part2.affine

@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: MPL-2.0
+// campaign #239 STEP 3 — second batch of Deno-scripting stdlib gaps
+// surfaced during STEP 2 ports (panic-attack#82, session-sentinel#25,
+// tropical-resource-typing#15, nafa-app#23).
+//
+// New externs / fixes exercised:
+//   - statIsFile / statIsDirectory         (gap 3)
+//   - bytesLength / bytesByteAt /
+//     bytesAsciiSlice                      (gap 4)
+//   - importMetaUrl                        (gap 5)
+//   - let _ = X wildcard binding emits
+//     a bare expression statement          (gap 7)
+//
+// Signatures stay in primitives so the harness can stub the host.
+
+use Deno::{ statIsFile, statIsDirectory, bytesLength, bytesByteAt, bytesAsciiSlice, importMetaUrl, readFileBytes };
+
+pub fn classify_path(p: String) -> Int {
+  if statIsFile(p) {
+    1
+  } else {
+    if statIsDirectory(p) {
+      2
+    } else {
+      0
+    }
+  }
+}
+
+pub fn first_byte(p: String) -> Int {
+  let b = readFileBytes(p);
+  if bytesLength(b) == 0 {
+    0
+  } else {
+    bytesByteAt(b, 0)
+  }
+}
+
+pub fn header_string(p: String, n: Int) -> String {
+  let b = readFileBytes(p);
+  let lim = bytesLength(b);
+  let end = if n > lim { lim } else { n };
+  bytesAsciiSlice(b, 0, end)
+}
+
+pub fn module_url_has_scheme() -> Bool {
+  let u = importMetaUrl();
+  // Any well-formed module URL starts with `file:` or `http`.
+  len(u) > 4
+}
+
+fn side(n: Int) -> Int { n + 1 }
+
+pub fn discard_chain() -> Int {
+  // Three back-to-back `let _ = side(N)` discards. Before the fix this
+  // tripped JS `SyntaxError: Identifier '_' has already been declared`
+  // because the AS pattern lowered to `const _ = ...` thrice. Now they
+  // lower to bare expression statements.
+  let _ = side(1);
+  let _ = side(2);
+  let _ = side(3);
+  42
+}