Add build guards for invalid build configs (#866)

Cargo.toml

@@ -38,6 +38,7 @@ serde_yaml = { version = "0.8.3", optional = true }
 slab = "0.4"
 stdweb = { version = "0.4.20", optional = true }
 toml = { version = "0.5", optional = true }
+wasm-bindgen = { version = "0.2.58", optional = true }
 yew-macro = { version = "0.11.1", path = "crates/macro" }
 
 [dependencies.web-sys]
@@ -91,9 +92,7 @@ features = [
   "WorkerOptions",
 ]
 
-[target.'cfg(all(target_arch = "wasm32", not(target_os="wasi"), not(cargo_web)))'.dependencies]
-wasm-bindgen = "0.2.58"
-
+# Changes here must be reflected in `build.rs`
 [target.'cfg(all(target_arch = "wasm32", not(target_os="wasi"), not(cargo_web)))'.dev-dependencies]
 wasm-bindgen-test = "0.3.4"
 
@@ -108,7 +107,7 @@ rustversion = "1.0"
 [features]
 default = ["services", "agent"]
 std_web = ["stdweb"]
-web_sys = ["console_error_panic_hook", "gloo", "js-sys", "web-sys"]
+web_sys = ["console_error_panic_hook", "gloo", "js-sys", "web-sys", "wasm-bindgen"]
 doc_test = []
 web_test = []
 wasm_test = []

build.rs

@@ -2,14 +2,26 @@ use std::env;
 
 pub fn main() {
     if cfg!(all(feature = "web_sys", feature = "std_web")) {
-        panic!("the `web_sys` and `std_web` cargo features cannot be used simultaneously")
+        panic!("Yew does not allow the `web_sys` and `std_web` cargo features to be used simultaneously");
     } else if cfg!(not(any(feature = "web_sys", feature = "std_web"))) {
-        panic!("please select either the `web_sys` or `std_web` cargo feature")
+        panic!("Yew requires selecting either the `web_sys` or `std_web` cargo feature");
     }
 
-    let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap_or_default();
+    let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap_or_default();
+    let using_wasi = target_os == "wasi";
+
     let cargo_web = env::var("COMPILING_UNDER_CARGO_WEB").unwrap_or_default();
-    if target_arch == "wasm32" && cargo_web != "1" {
+    let using_cargo_web = cargo_web == "1";
+    if using_cargo_web && cfg!(feature = "web_sys") {
+        panic!("cargo-web is not compatible with web-sys");
+    }
+
+    let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap_or_default();
+    let using_wasm_bindgen = target_arch == "wasm32" && !using_cargo_web && !using_wasi;
+    if using_wasm_bindgen {
         println!("cargo:rustc-cfg=feature=\"wasm_bindgen_test\"");
+    } else if cfg!(all(feature = "web_sys", not(feature = "doc_test"))) {
+        let target = env::var("TARGET").unwrap_or_default();
+        panic!("Selected target `{}` is not compatible with web-sys", target);
     }
 }