feat(parser,desugar): extern abi blocks (clean — replaces #47/#53)#54
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Second slice of #43. After the slash-paths PR (#46), the next concrete parse error on `hyperpolymath/hypatia`'s `bridge.eph` is the `extern "gossamer" { type Window; fn window_open(…): Window; … }` block. This commit makes that parse. What lands: * **Pest grammar** (`ephapax-parser/src/ephapax.pest`): new `extern_block` / `extern_item` / `extern_type_item` / `extern_fn_item` rules. Top-level `declaration` rule extended to admit `extern_block`. `"extern"` added to `keyword` and `keyword_boundary` so identifiers can't shadow it. * **Core AST** (`ephapax-syntax`): new `Decl::Extern { abi, items }` variant plus `ExternItem { Type { name } | Fn { name, params, ret_ty } }` enum. Item params/ret carry core `Ty`. * **Surface AST** (`ephapax-surface`): mirror `SurfaceDecl::Extern { abi, items, span }` and `SurfaceExternItem` with the same shape but `SurfaceTy`. The span lives on the block, not on individual items, matching how `DataDecl` carries one block-level span. * **Core parser** (`lib.rs`): `parse_declaration` routes `Rule::extern_block` to a new `parse_extern_block` → `parse_extern_item` pair. The ABI string is unquoted and unescaped via a minimal helper that handles `\"` and `\\` (sufficient for ABI tags; extend if richer escapes appear). * **Surface parser** (`surface.rs`): same plumbing against `SurfaceExternItem`, types staying in `SurfaceTy` until the desugar pass. * **Desugar** (`ephapax-desugar`): `SurfaceDecl::Extern` lowers to `Decl::Extern` by walking each item and mapping its surface types through `desugar_ty`. Extern types pass through as-is (just the name). The block carries no body so there's no expression-level desugaring. * **Downstream stubs** so the workspace builds: every exhaustive match on `Decl` now handles `Decl::Extern` — typecheck (no-op for now, registered as TODO), affine/linear discipline (no body → nothing to check), wasm codegen (skipped — wasm imports are phase 2B), IR s-expr printer (renders the block with `extern-type` / `extern-fn` tagged sub-forms), LSP symbol extractor (`filter_map` to drop extern blocks from the outline — phase 2B will expose them as navigable symbols). Tests: * `parse_empty_extern_block` — `extern "gossamer" { }` round-trips with empty items. * `parse_extern_block_with_type_and_fn_items` — full hypatia shape: `type Window` + `fn window_open(title, body): Window`. * `parse_bridge_eph_shaped_prelude` — slash-pathed module + extern block + regular fn all in one file (the canonical bridge.eph prelude). * `test_parse_extern_block_core` — same shape through the core parser, asserting `ExternItem::Type` / `ExternItem::Fn` and param arity. * `desugar_extern_block` — `SurfaceDecl::Extern` → `Decl::Extern`, with `SurfaceTy::String(region)` → `Ty::String(region)` and `SurfaceTy::Base(I32)` → `Ty::Base(I32)` covered. `cargo test --workspace` passes. `cargo check --workspace` clean. Out of scope (phase 2B follow-up, tracked in #43): * **Typechecker**: register extern types as opaque nominal types and extern fns as ambient bindings in the module env so other decls can call them. * **Wasm codegen**: emit `(import "<abi>" "<name>" (func ...))` for fn items, treat type items as opaque (i32) externs. This is what actually unblocks `bridge.eph → bridge.wasm`. * **LSP**: surface extern items as navigable symbols. After phase 2B, the `compile-eph` / `compile-affine` clap aliases land as trivial 3-line additions (the original #36 ask), and hypatia's `build-gossamer-gui.yml` workflow flips from `::warning::` to an actual wasm artifact. Stacked on #46. Rebase target switches to `main` when #46 merges. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This was referenced May 15, 2026
This was referenced May 15, 2026
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Clean replacement for #47/#53 (which were blocked by sha-different slash-paths commit on main). Cherry-picked f9f8657 onto a fresh branch off current main — single-commit PR, no force-push needed.
Close #53 alongside merging this.
Closes part of #43 (v2 grammar phase 2A).