Initial interning implementation

Author: Pauan

Cargo.toml

@@ -49,6 +49,7 @@ wasm-bindgen-test-crate-b = { path = 'tests/crates/b', version = '0.1' }
 [workspace]
 members = [
   "benchmarks",
+  "crates/cache",
   "crates/cli",
   "crates/js-sys",
   "crates/test",
@@ -88,5 +89,6 @@ exclude = ['crates/typescript']
 [patch.crates-io]
 wasm-bindgen = { path = '.' }
 wasm-bindgen-futures = { path = 'crates/futures' }
+wasm-bindgen-cache = { path = 'crates/cache' }
 js-sys = { path = 'crates/js-sys' }
 web-sys = { path = 'crates/web-sys' }

crates/cache/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+authors = ["The wasm-bindgen Developers"]
+description = "Utilities for caching JS objects to avoid expensive copying"
+documentation = "https://docs.rs/wasm-bindgen-cache"
+homepage = "https://rustwasm.github.io/wasm-bindgen/"
+license = "MIT/Apache-2.0"
+name = "wasm-bindgen-cache"
+repository = "https://github.com/rustwasm/wasm-bindgen/tree/master/crates/cache"
+readme = "./README.md"
+version = "0.1.0"
+edition = "2018"
+
+[features]
+disabled = []
+
+[dependencies]
+js-sys = { path = "../js-sys", version = '0.3.24' }
+uluru = "0.3.0"
+
+[target.'cfg(target_arch = "wasm32")'.dev-dependencies]
+wasm-bindgen-test = { path = '../test', version = '0.2.47' }

crates/cache/src/lib.rs

@@ -0,0 +1,100 @@
+#![deny(missing_docs)]
+
+//!
+
+
+///
+pub mod intern {
+    use js_sys::JsString;
+    use std::cell::{Cell, RefCell};
+    use uluru::{LRUCache, Entry};
+
+    struct Pair {
+        key: String,
+        value: JsString,
+    }
+
+    // TODO figure out a good default capacity
+    type Entries = LRUCache::<[Entry<Pair>; 1_024]>;
+
+    struct Cache {
+        enabled: Cell<bool>,
+        max_str_len: Cell<usize>,
+        entries: RefCell<Entries>,
+    }
+
+    // TODO figure out a good max_str_len
+    thread_local! {
+        static CACHE: Cache = Cache {
+            enabled: Cell::new(true),
+            max_str_len: Cell::new(128),
+            entries: RefCell::new(LRUCache::default()),
+        };
+    }
+
+    fn get_js_string(cache: &mut Entries, key: &str) -> JsString {
+        if let Some(p) = cache.find(|p| p.key == key) {
+            p.value.clone()
+
+        } else {
+            let value = JsString::from(key);
+
+            cache.insert(Pair {
+                key: key.to_owned(),
+                value: value.clone(),
+            });
+
+            value
+        }
+    }
+
+    fn cache_str(s: &str) -> JsString {
+        CACHE.with(|cache| {
+            let should_cache =
+                cache.enabled.get() &&
+                s.len() <= cache.max_str_len.get();
+
+            if should_cache {
+                get_js_string(&mut cache.entries.borrow_mut(), s)
+
+            } else {
+                JsString::from(s)
+            }
+        })
+    }
+
+    ///
+    #[inline]
+    pub fn str(s: &str) -> JsString {
+        if cfg!(feature = "disabled") {
+            JsString::from(s)
+
+        } else {
+            cache_str(s)
+        }
+    }
+
+    ///
+    #[inline]
+    pub fn set_max_str_len(len: usize) {
+        if !cfg!(feature = "disabled") {
+            CACHE.with(|cache| cache.max_str_len.set(len));
+        }
+    }
+
+    ///
+    #[inline]
+    pub fn enable() {
+        if !cfg!(feature = "disabled") {
+            CACHE.with(|cache| cache.enabled.set(true));
+        }
+    }
+
+    ///
+    #[inline]
+    pub fn disable() {
+        if !cfg!(feature = "disabled") {
+            CACHE.with(|cache| cache.enabled.set(false));
+        }
+    }
+}