Fix support for WebAssembly (#18)

* Fix support for WebAssembly

The crate previously assumed that `wasm-bindgen` can be used for every
WebAssembly target. However there's essentially the following 4 targets:
 - WebAssembly on the web
 - Freestanding WebAssembly
 - WebAssembly with WASI
 - WebAssembly with Emscripten

Only `WebAssembly on the web` supports `wasm-bindgen`. Unfortunately
that's not a target on its own for historical reasons, so the only way
to properly support that target is through a `js` feature. All
other, unsupported, WebAssembly targets now fall back onto a new fallback
implementation that always returns `None`. The crate now also should be
able to build at all on unsupported targets because of that.

CHANGELOG.md

@@ -4,6 +4,13 @@ Notable changes to this project will be documented in the [keep a changelog](htt
 
 ## [Unreleased]
 
+### Changed
+- The crate now only uses `wasm-bindgen` when targeting WebAssembly on the web.
+  Use the new `js` feature to target the web.
+
+### Fixed
+- The crate now compiles for unsupported platforms.
+
 # [0.2.4] - 2023-03-07
 
 ### Changed

Cargo.toml

@@ -19,7 +19,10 @@ features = [
     "Win32_System_SystemServices"
 ]
 
-[target.'cfg(target_arch = "wasm32")'.dependencies]
-js-sys = "0.3"
-wasm-bindgen = { version = "0.2"}
-web-sys = { version = "0.3", features = ["Window", "WorkerGlobalScope", "Navigator", "WorkerNavigator"] }
+[target.'cfg(all(target_family = "wasm", not(unix)))'.dependencies]
+js-sys = { version = "0.3", optional = true }
+wasm-bindgen = { version = "0.2", optional = true }
+web-sys = { version = "0.3", features = ["Window", "WorkerGlobalScope", "Navigator", "WorkerNavigator"], optional = true }
+
+[features]
+js = ["js-sys", "wasm-bindgen", "web-sys"]

README.md

@@ -15,7 +15,7 @@ Platform support currently includes:
 - iOS
 - macOS
 - Linux, BSD, and other UNIX variations
-- WebAssembly
+- WebAssembly on the web (via the `js` feature)
 - Windows
 
 ```rust

src/lib.rs

@@ -5,7 +5,7 @@
 //! - iOS
 //! - macOS
 //! - Linux, BSD, and other UNIX variations
-//! - WebAssembly
+//! - WebAssembly on the web (via the `js` feature)
 //! - Windows
 #![cfg_attr(
     any(
@@ -40,16 +40,23 @@ mod unix;
 ))]
 use unix as provider;
 
-#[cfg(target_arch = "wasm32")]
+#[cfg(all(target_family = "wasm", feature = "js", not(unix)))]
 mod wasm;
-#[cfg(target_arch = "wasm32")]
+#[cfg(all(target_family = "wasm", feature = "js", not(unix)))]
 use wasm as provider;
 
-#[cfg(target_os = "windows")]
+#[cfg(windows)]
 mod windows;
-#[cfg(target_os = "windows")]
+#[cfg(windows)]
 use windows as provider;
 
+#[cfg(not(any(unix, all(target_family = "wasm", feature = "js", not(unix)), windows)))]
+mod provider {
+    pub fn get() -> Option<alloc::string::String> {
+        None
+    }
+}
+
 /// Returns the active locale for the system or application.
 ///
 /// # Returns