wiggle: introduce wiggle::Trap, which can be either a String or I32

also, make noreturn functions always return a Trap

wasmtime-wiggle can trivially turn a wiggle::Trap into a wasmtime::Trap.
lucet will have to do the same.

crates/wiggle/generate/src/funcs.rs

@@ -36,12 +36,6 @@ pub fn define_func(
             witx::CoreParamSignifies::Value(atom) => names.atom_type(atom),
             _ => unreachable!("ret should always be passed by value"),
         }
-    } else if func.noreturn {
-        // Ideally we would return `quote!(!)` here, but, we'd have to change
-        // the error handling logic in all the marshalling code to never return,
-        // and instead provide some other way to bail to the context...
-        // noreturn func
-        unimplemented!("noreturn funcs not supported yet!")
     } else {
         quote!(())
     };
@@ -174,7 +168,23 @@ pub fn define_func(
     let mod_name = &module.name.as_str();
     let func_name = &func.name.as_str();
 
-    quote!(pub fn #ident(#abi_args) -> Result<#abi_ret, String> {
+    if func.noreturn {
+        quote!(pub fn #ident(#abi_args) -> Result<#abi_ret, wiggle::Trap> {
+            let _span = #rt::tracing::span!(
+                #rt::tracing::Level::TRACE,
+                "wiggle abi",
+                module = #mod_name,
+                function = #func_name
+            );
+            let _enter = _span.enter();
+
+            #(#marshal_args)*
+            #log_marshalled_args
+            let trap = #trait_name::#ident(ctx, #(#trait_args),*);
+            Err(trap)
+        })
+    } else {
+        quote!(pub fn #ident(#abi_args) -> Result<#abi_ret, wiggle::Trap> {
             let _span = #rt::tracing::span!(
                 #rt::tracing::Level::TRACE,
                 "wiggle abi",
@@ -194,6 +204,7 @@ pub fn define_func(
             #success
         })
     }
+}
 
 fn marshal_arg(
     names: &Names,

crates/wiggle/generate/src/lib.rs

@@ -40,7 +40,7 @@ pub fn generate(doc: &witx::Document, names: &Names, errs: &ErrorTransform) -> T
         let abi_typename = names.type_ref(&errtype.abi_type(), anon_lifetime());
         let user_typename = errtype.typename();
         let methodname = names.user_error_conversion_method(&errtype);
-        quote!(fn #methodname(&self, e: super::#user_typename) -> Result<#abi_typename, String>;)
+        quote!(fn #methodname(&self, e: super::#user_typename) -> Result<#abi_typename, wiggle::Trap>;)
     });
     let user_error_conversion = quote! {
         pub trait UserErrorConversion {

crates/wiggle/generate/src/module_trait.rs

@@ -48,6 +48,8 @@ pub fn define_module_trait(names: &Names, m: &Module, errxform: &ErrorTransform)
             };
             quote!(#arg_name: #arg_type)
         });
+
+        let result = if !f.noreturn {
             let rets = f
                 .results
                 .iter()
@@ -65,11 +67,15 @@ pub fn define_module_trait(names: &Names, m: &Module, errxform: &ErrorTransform)
                     }
                 })
                 .unwrap_or(quote!(()));
+            quote!( Result<(#(#rets),*), #err> )
+        } else {
+            quote!(wiggle::Trap)
+        };
 
         if is_anonymous {
-            quote!(fn #funcname(&self, #(#args),*) -> Result<(#(#rets),*), #err>;)
+            quote!(fn #funcname(&self, #(#args),*) -> #result; )
         } else {
-            quote!(fn #funcname<#lifetime>(&self, #(#args),*) -> Result<(#(#rets),*), #err>;)
+            quote!(fn #funcname<#lifetime>(&self, #(#args),*) -> #result;)
         }
     });
     quote! {

crates/wiggle/src/lib.rs

@@ -928,3 +928,9 @@ impl Pointee for str {
         <[u8]>::debug(pointer, f)
     }
 }
+
+#[derive(Debug, Clone)]
+pub enum Trap {
+    I32(i32),
+    String(String),
+}

crates/wiggle/wasmtime/macro/src/lib.rs

@@ -199,8 +199,9 @@ fn generate_func(
                         #(#arg_names),*
                     );
                     match result {
-                        Ok(r) => {return Ok(r.into());},
-                        Err(err) => { return Err(wasmtime::Trap::new(err)); },
+                        Ok(r) => Ok(r.into()),
+                        Err(wasmtime_wiggle::Trap::String(err)) => Err(wasmtime::Trap::new(err)),
+                        Err(wasmtime_wiggle::Trap::I32(err)) => Err(wasmtime::Trap::i32_exit(err)),
                     }
                 }
             }