feat(es/transforms): Add an API for returning metadata to JS (#9022)

crates/swc_core/Cargo.toml

@@ -21,6 +21,7 @@ version       = "0.92.11"
     "ecma_loader",
     "ecma_ast",
     "trace_macro",
+    "transform_common",
     "plugin_transform",
   ]
   rustdoc-args = ["--cfg", "docsrs"]
@@ -40,6 +41,8 @@ doctest = false
 # swc_common/ahash
 common_ahash = ["swc_common/ahash"]
 
+transform_common = []
+
 # swc_ecma_loader/cache*
 ecma_loader_lru         = ["swc_ecma_loader/lru"]
 ecma_loader_parking_lot = ["swc_ecma_loader/parking_lot"]
@@ -371,6 +374,7 @@ swc_plugin                       = { optional = true, version = "0.90.0", path =
 swc_plugin_macro                 = { optional = true, version = "0.9.16", path = "../swc_plugin_macro" }
 swc_plugin_proxy                 = { optional = true, version = "0.42.1", path = "../swc_plugin_proxy" }
 swc_trace_macro                  = { optional = true, version = "0.1.3", path = "../swc_trace_macro" }
+swc_transform_common             = { optional = true, version = "0.1.0", path = "../swc_transform_common" }
 testing                          = { optional = true, version = "0.35.24", path = "../testing" }
 # TODO: eventually swc_plugin_runner needs to remove default features
 swc_plugin_runner = { optional = true, version = "0.107.1", path = "../swc_plugin_runner", default-features = false }

crates/swc_core/src/lib.rs

@@ -184,6 +184,12 @@ pub mod trace_macro {
     pub use swc_trace_macro::*;
 }
 
+#[cfg(feature = "transform_common")]
+#[cfg_attr(docsrs, doc(cfg(feature = "transform_common")))]
+pub mod transform_common {
+    pub use swc_transform_common::*;
+}
+
 // swc_bundler
 #[cfg(feature = "__bundler")]
 #[cfg_attr(docsrs, doc(cfg(feature = "__bundler")))]

crates/swc_transform_common/src/output.rs

@@ -1,3 +1,7 @@
+//! (Experimental) Output capturing.
+//!
+//! This module provides a way to emit metadata to the JS caller.
+
 use std::cell::RefCell;
 
 use better_scoped_tls::scoped_tls;
@@ -6,6 +10,9 @@ use serde_json::Value;
 
 scoped_tls!(static OUTPUT: RefCell<FxHashMap<String, Value>>);
 
+/// (Experimental) Captures output.
+///
+/// This is not stable and may be removed in the future.
 pub fn capture<Ret>(f: impl FnOnce() -> Ret) -> (Ret, FxHashMap<String, Value>) {
     let output = RefCell::new(FxHashMap::default());
 
@@ -14,6 +21,9 @@ pub fn capture<Ret>(f: impl FnOnce() -> Ret) -> (Ret, FxHashMap<String, Value>)
     (ret, output.into_inner())
 }
 
+/// (Experimental) Emits a value to the JS caller.
+///
+/// This is not stable and may be removed in the future.
 pub fn emit(key: String, value: Value) {
     OUTPUT.with(|output| {
         let previous = output.borrow_mut().insert(key, value);