feat(fmt): prototype SWC Next 0.2.0 via crate and decoder

Cargo.toml

@@ -14,6 +14,8 @@ napi-build = "2.4.1"
 napi-derive = "3.6.3"
 pathdiff = "0.2.3"
 rstack-ignore = { path = "crates/rstack-ignore" }
+# The wire format must match @swc-next/decoder exactly.
+swc_next_bridge = { version = "=0.2.0", features = ["parser"] }
 
 # Local development: 16 codegen units are sufficient for this small workspace while preserving
 # parallel compilation and full debugging support.

crates/rstack-binding/Cargo.toml

@@ -14,6 +14,7 @@ test = false
 napi.workspace = true
 napi-derive.workspace = true
 rstack-ignore.workspace = true
+swc_next_bridge.workspace = true
 
 [build-dependencies]
 napi-build.workspace = true

crates/rstack-binding/src/lib.rs

@@ -1,5 +1,9 @@
 #![deny(clippy::all)]
 
+mod parser;
+
+pub use parser::parse_swc_next;
+
 use std::path::Path;
 
 use napi::{bindgen_prelude::Uint8Array, Error, Status};

crates/rstack-binding/src/parser.rs

@@ -0,0 +1,43 @@
+use napi::{bindgen_prelude::Buffer, Error, Status};
+use napi_derive::napi;
+use swc_next_bridge::{parse_to_buffer, CommentMode, Lang, ParserOptions, SourceType};
+
+/// Returns the SWC Next 0.2.0 wire format consumed by @swc-next/decoder.
+/// Keep parsing and serialization in the upstream crate, not in the NAPI adapter.
+#[napi]
+pub fn parse_swc_next(source: String, lang: String, source_type: String) -> napi::Result<Buffer> {
+    let lang = match lang.as_str() {
+        "js" => Lang::Js,
+        "jsx" => Lang::Jsx,
+        "ts" => Lang::Ts,
+        "tsx" => Lang::Tsx,
+        "dts" => Lang::Dts,
+        _ => {
+            return Err(Error::new(
+                Status::InvalidArg,
+                "Unsupported SWC Next language.",
+            ))
+        }
+    };
+    let source_type = match source_type.as_str() {
+        "module" => SourceType::Module,
+        "commonjs" => SourceType::CommonJs,
+        _ => {
+            return Err(Error::new(
+                Status::InvalidArg,
+                "Unsupported SWC Next source type.",
+            ))
+        }
+    };
+
+    Ok(parse_to_buffer(
+        &source,
+        Some(ParserOptions {
+            lang: Some(lang),
+            source_type: Some(source_type),
+            preserve_parens: Some(true),
+            comments: Some(CommentMode::Flat),
+        }),
+    )
+    .into())
+}

packages/rstack/SWC_NEXT_POC.md

@@ -0,0 +1,32 @@
+# SWC next formatter PoC
+
+This branch replaces the default Yuku parser in `rs fmt` with SWC Next 0.2.0 while retaining Prettier's ESTree printer and the existing formatting adapter.
+
+`swc_next_bridge = "=0.2.0"` compiles parsing and serialization into the existing rstack native binding. A thin NAPI function returns a Buffer to `@swc-next/decoder@0.2.0`; the generated loader is resolved lazily when parsing starts. No parser npm package or separate SWC Next native binary is installed.
+
+Inferred JavaScript, JSX, TypeScript, TSX, and embedded script formatting use SWC Next. Explicit `babel` and `typescript` options still select Prettier's own parsers, and project plugins retain precedence. The experimental explicit parser names are `swc-next` and `swc-next-ts`, replacing `yuku` and `yuku-ts`.
+
+The cache namespace includes the parser version and integration route so switching between the original formatter and either PoC cannot reuse stale formatting results. The decoder and Rust serializer must be upgraded together; all SWC Next packages in this PoC are locked to 0.2.0.
+
+## Try it
+
+```sh
+pnpm install
+pnpm build
+pnpm --filter rstack build:native
+printf 'const view=<Component value={{foo:1}} />' | pnpm exec rs fmt --stdin-filepath example.tsx
+pnpm test
+pnpm check
+```
+
+Native changes also require `cargo fmt --all -- --check`, `cargo clippy --workspace --all-targets --locked -- -D warnings`, and `cargo test --workspace --locked`.
+
+## Compatibility and limits
+
+SWC Next 0.2.0 accepts function implementations in declaration files, for example `export function value() { return 1; }` in `example.d.ts`. Yuku previously rejected this with an ambient-context diagnostic. The tests explicitly record this upstream difference; valid declarations, comments, Unicode locations, JSX/TSX, CommonJS, pragmas, and syntax errors remain covered. No fallback to another parser hides SWC Next errors.
+
+Validation is on macOS arm64 with the repository's Node.js, pnpm, and Rust versions. The complete formatter/CLI suite covers worker execution, stdin, LSP, Vue, Svelte, and caching. Cross-platform binaries and formatter-wide conformance against Prettier's upstream corpus have not been validated. No throughput advantage is claimed by this PoC.
+
+## Upstream
+
+[SWC Next 0.2.0 source](https://github.com/swc-project/swc-next/tree/v0.2.0)

packages/rstack/THIRD_PARTY_NOTICES.md

@@ -29,9 +29,9 @@ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 
-## Prettier yuku parser adapter
+## Prettier SWC next parser adapter
 
-The local Yuku parser adapter includes portions derived from
+The local SWC Next parser adapter includes portions derived from
 [@prettier/plugin-yuku](https://github.com/prettier/prettier/tree/main/packages/plugin-yuku)
 and Prettier's JavaScript parser postprocessing. The adapter reuses the public
 ESTree printer, formatter options, and parser utilities from the installed

packages/rstack/binding.cjs

@@ -702,3 +702,7 @@ if (!nativeBinding) {
 module.exports = nativeBinding
 module.exports.GitIgnoreMatcher = nativeBinding.GitIgnoreMatcher
 module.exports.IgnoreMatcher = nativeBinding.IgnoreMatcher
+module.exports.parseSwcNext = nativeBinding.parseSwcNext
+module.exports.CommentMode = nativeBinding.CommentMode
+module.exports.Lang = nativeBinding.Lang
+module.exports.SourceType = nativeBinding.SourceType