WebAssembly frontend — statically typed, IR-shaped; experimental

• Type: feature — frontend (experimental folder rules apply: never a prio ticket; upscale only for genuine AST/IR work on its own merits)
• Opened: 2026-07-09 (user decision, from the JS-frontend advice session: "wasm — trivial. worth a ticket")
• Owner: —

Why this one is actually compilable

Unlike JS ([[feature-js-frontend-parked]]), wasm is exactly the shape the shared IR eats: statically typed (i32/i64/f32/f64 map 1:1 onto existing TTypeKinds), a validated stack machine (the Whitespace probe already proved stack-discipline folds into AST expression trees at parse time), structured control flow (block/loop/if/br map onto AN_IF/AN_WHILE/ AN_BREAK-family — no irreducible CFGs by construction), linear memory (one big byte array + load/store = the raw-pointer math the C frontend does all day). MVP wasm has no GC, no exceptions, no threads.

Honest scope notes (why "trivial-adjacent", not trivial)

• Two input formats. .wat (text, s-exprs — a lexer/parser like any other frontend) vs .wasm (binary — a decoder, no lexer at all; arguably easier and more useful). Pick ONE for the skeleton: .wat is more probe-like, .wasm is more real-world. Suggest .wat first (pure parser, zero tooling needed to write tests by hand).
• The stack discipline needs folding into expression trees (Whitespace precedent) OR explicit temp locals per stack slot (simpler, always correct, slightly worse code). Start with temps; fold later if fun.
• Imports are the actual boundary. A wasm module importing wasi_snapshot_preview1.fd_write etc needs a host shim layer. Skeleton: support exactly one import shape (a print_i64-style debug hook wired to the shared write machinery) and exported functions called from a generated entry stub. Real WASI = its own later sub-ticket, on demand.
• Value proposition (distinct from the JS goal): consume the compiled polyglot ecosystem — C/Rust/Zig/Go code shipped as .wasm — not JS libraries (those are mostly not shipped as wasm; the JS answer is [[feature-c-corpus-quickjs]]).

Skeleton scope (if/when picked up — esoteric-probe sized)

.wat subset: (module (func (export ...) (param i64...) (result i64) local.get/set, i64.const, i64.add/sub/mul/div_s, i64.eq/lt_s/gt_s, block/ loop/if/else/end, br/br_if, call, return)) + one debug-print import. Lower onto existing AN_*/IR only; x86-64 only; test wired into make test next to the other probe skeletons. Everything else (memories, globals, tables, f32/f64, .wasm binary decoding, WASI) stays out until wanted.

Log

• 2026-07-09 — filed per user decision; parked in experimental/ alongside the other optional frontends.