Catch more errors on non-wasm32 platforms

This commit tweaks the codegen for imported functions and such (anything
that relies on some imported intrinsic or function filled in by the CLI)
to share as much code as possible on non-wasm32 platforms. This should
help us catch more errors before compiling to wasm and also just make it
easier to write UI tests!

For example a UI test previously couldn't be written for #1528 but now
it can be, and one is include (although the error message is quite bad).

crates/backend/src/codegen.rs

@@ -197,7 +197,6 @@ impl ToTokens for ast::Struct {
             impl wasm_bindgen::__rt::core::convert::From<#name> for
                 wasm_bindgen::JsValue
             {
-                #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
                 fn from(value: #name) -> Self {
                     let ptr = wasm_bindgen::convert::IntoWasmAbi::into_abi(
                         value,
@@ -205,10 +204,16 @@ impl ToTokens for ast::Struct {
                     );
 
                     #[link(wasm_import_module = "__wbindgen_placeholder__")]
+                    #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
                     extern "C" {
                         fn #new_fn(ptr: u32) -> u32;
                     }
 
+                    #[cfg(not(all(target_arch = "wasm32", not(target_os = "emscripten"))))]
+                    unsafe fn #new_fn(ptr: u32) -> u32 {
+                        panic!("cannot convert to JsValue outside of the wasm target")
+                    }
+
                     unsafe {
                         <wasm_bindgen::JsValue as wasm_bindgen::convert::FromWasmAbi>
                             ::from_abi(
@@ -217,11 +222,6 @@ impl ToTokens for ast::Struct {
                             )
                     }
                 }
-
-                #[cfg(not(all(target_arch = "wasm32", not(target_os = "emscripten"))))]
-                fn from(_value: #name) -> Self {
-                    panic!("cannot convert to JsValue outside of the wasm target")
-                }
             }
 
             #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
@@ -712,24 +712,22 @@ impl ToTokens for ast::ImportType {
                 }
 
                 impl JsCast for #rust_name {
-                    #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
                     fn instanceof(val: &JsValue) -> bool {
                         #[link(wasm_import_module = "__wbindgen_placeholder__")]
+                        #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
                         extern "C" {
                             fn #instanceof_shim(val: u32) -> u32;
                         }
+                        #[cfg(not(all(target_arch = "wasm32", not(target_os = "emscripten"))))]
+                        unsafe fn #instanceof_shim(val: u32) -> u32 {
+                            panic!("cannot check instanceof on non-wasm targets");
+                        }
                         unsafe {
                             let idx = val.into_abi(&mut wasm_bindgen::convert::GlobalStack::new());
                             #instanceof_shim(idx) != 0
                         }
                     }
 
-                    #[cfg(not(all(target_arch = "wasm32", not(target_os = "emscripten"))))]
-                    fn instanceof(val: &JsValue) -> bool {
-                        drop(val);
-                        panic!("cannot check instanceof on non-wasm targets");
-                    }
-
                     #is_type_of
 
                     #[inline]
@@ -998,6 +996,7 @@ impl TryToTokens for ast::ImportFunction {
         let import_name = &self.shim;
         let attrs = &self.function.rust_attrs;
         let arguments = &arguments;
+        let abi_arguments = &abi_arguments;
 
         let doc_comment = match &self.doc_comment {
             None => "",
@@ -1012,14 +1011,20 @@ impl TryToTokens for ast::ImportFunction {
         let invocation = quote! {
             #(#attrs)*
             #[allow(bad_style)]
-            #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
             #[doc = #doc_comment]
             #[allow(clippy::all)]
             #vis fn #rust_name(#me #(#arguments),*) #ret {
                 #[link(wasm_import_module = "__wbindgen_placeholder__")]
+                #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
                 extern "C" {
                     fn #import_name(#(#abi_arguments),*) -> #abi_ret;
                 }
+                #[cfg(not(all(target_arch = "wasm32", not(target_os = "emscripten"))))]
+                unsafe fn #import_name(#(#abi_arguments),*) -> #abi_ret {
+                    panic!("cannot call wasm-bindgen imported functions on \
+                            non-wasm targets");
+                }
+
                 unsafe {
                     #exn_data
                     let #ret_ident = {
@@ -1031,17 +1036,6 @@ impl TryToTokens for ast::ImportFunction {
                     #convert_ret
                 }
             }
-
-            #(#attrs)*
-            #[allow(bad_style, unused_variables)]
-            #[cfg(not(all(target_arch = "wasm32", not(target_os = "emscripten"))))]
-            #[doc = #doc_comment]
-            #[allow(clippy::all)]
-            #vis fn #rust_name(#me #(#arguments),*) #ret {
-                panic!("cannot call wasm-bindgen imported functions on \
-                        non-wasm targets");
-            }
-
         };
 
         if let Some(class) = class_ty {
@@ -1164,12 +1158,17 @@ impl ToTokens for ast::ImportStatic {
             #[allow(bad_style)]
             #[allow(clippy::all)]
             #vis static #name: wasm_bindgen::JsStatic<#ty> = {
-                #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
                 fn init() -> #ty {
                     #[link(wasm_import_module = "__wbindgen_placeholder__")]
+                    #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
                     extern "C" {
                         fn #shim_name() -> <#ty as wasm_bindgen::convert::FromWasmAbi>::Abi;
                     }
+                    #[cfg(not(all(target_arch = "wasm32", not(target_os = "emscripten"))))]
+                    unsafe fn #shim_name() -> <#ty as wasm_bindgen::convert::FromWasmAbi>::Abi {
+                        panic!("cannot access imported statics on non-wasm targets")
+                    }
+
                     unsafe {
                         <#ty as wasm_bindgen::convert::FromWasmAbi>::from_abi(
                             #shim_name(),
@@ -1178,10 +1177,6 @@ impl ToTokens for ast::ImportStatic {
 
                     }
                 }
-                #[cfg(not(all(target_arch = "wasm32", not(target_os = "emscripten"))))]
-                fn init() -> #ty {
-                    panic!("cannot access imported statics on non-wasm targets")
-                }
                 thread_local!(static _VAL: #ty = init(););
                 wasm_bindgen::JsStatic {
                     __inner: &_VAL,

crates/macro/ui-tests/missing-catch.rs

@@ -0,0 +1,9 @@
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen]
+extern "C" {
+	#[wasm_bindgen]
+	pub fn foo() -> Result<JsValue, JsValue>;
+}
+
+fn main() {}

crates/macro/ui-tests/missing-catch.stderr

@@ -0,0 +1,7 @@
+error[E0277]: the trait bound `std::result::Result<wasm_bindgen::JsValue, wasm_bindgen::JsValue>: wasm_bindgen::convert::traits::FromWasmAbi` is not satisfied
+ --> $DIR/missing-catch.rs:3:1
+  |
+3 | #[wasm_bindgen]
+  | ^^^^^^^^^^^^^^^ the trait `wasm_bindgen::convert::traits::FromWasmAbi` is not implemented for `std::result::Result<wasm_bindgen::JsValue, wasm_bindgen::JsValue>`
+
+For more information about this error, try `rustc --explain E0277`.