Fixes #2418: Enhance wiggle to generate its UserErrorConverstion trait with a function that returns Result<abi_err, String> (#2419)

* Enhance wiggle to generate its UserErrorConverstion trait with a function that returns
a Result<abi_err, String>.  This enhancement allows hostcall implementations using wiggle
to return an actionable error to the instance (the abi_err) or to terminate the instance
using the String as fatal error information.

* Enhance wiggle to generate its UserErrorConverstion trait with a function that returns
a Result<abi_err, String>.  This enhancement allows hostcall implementations using wiggle
to return an actionable error to the instance (the abi_err) or to terminate the instance
using the String as fatal error information.

* Enhance the wiggle/wasmtime integration to leverage new work in ab7e9c6.  Hostcall
implementations generated by wiggle now return an Result<abi_error, Trap>.  As a
result, hostcalls experiencing fatal errors may trap, thereby terminating the
wasmtime instance.  This enhancement has been performed for both wasi snapshot1
and wasi snapshot0.

* Update wasi-nn crate to reflect enhancement in issue #2418.

* Update wiggle test-helpers for wiggle enhancement made in issue #2418.

* Address PR feedback; omit verbose return statement.

* Address PR feedback; manually format within a proc macro.

* Address PR feedback; manually format proc macro.

* Restore return statements to wasi.rs.

* Restore return statements in funcs.rs.

* Address PR feedback; omit TODO and fix formatting.

* Ok-wrap error type in assert statement.

crates/wasi-common/src/wasi.rs

@@ -23,9 +23,9 @@ impl types::GuestErrorConversion for WasiCtx {
 }
 
 impl types::UserErrorConversion for WasiCtx {
-    fn errno_from_error(&self, e: Error) -> Errno {
+    fn errno_from_error(&self, e: Error) -> Result<Errno, String> {
         debug!("Error: {:?}", e);
-        e.into()
+        Ok(e.into())
     }
 }
 

crates/wasi-common/wig/src/hostcalls.rs

@@ -13,8 +13,6 @@ pub fn define(args: TokenStream) -> TokenStream {
 
     let mut ret = TokenStream::new();
 
-    let old = true;
-
     for module in doc.modules() {
         for func in module.funcs() {
             // `proc_exit` is special; it's essentially an unwinding primitive,
@@ -24,14 +22,14 @@ pub fn define(args: TokenStream) -> TokenStream {
                 continue;
             }
 
-            ret.extend(generate_wrappers(&func, old));
+            ret.extend(generate_wrappers(&func));
         }
     }
 
     return ret;
 }
 
-fn generate_wrappers(func: &witx::InterfaceFunc, old: bool) -> TokenStream {
+fn generate_wrappers(func: &witx::InterfaceFunc) -> TokenStream {
     let name = format_ident!("{}", func.name.as_str());
     let mut arg_declarations = Vec::new();
     let mut arg_names = Vec::new();
@@ -101,33 +99,13 @@ fn generate_wrappers(func: &witx::InterfaceFunc, old: bool) -> TokenStream {
         }
     };
 
-    let c_abi_name = if old {
-        format_ident!("old_wasi_common_{}", name)
-    } else {
-        format_ident!("wasi_common_{}", name)
-    };
-
     quote! {
         pub unsafe fn #name(
             wasi_ctx: &mut super::WasiCtx,
             memory: &mut [u8],
             #(#arg_declarations,)*
-        ) -> #ret {
-            #body
-        }
-
-        #[no_mangle]
-        pub unsafe fn #c_abi_name(
-            wasi_ctx: *mut super::WasiCtx,
-            memory: *mut u8,
-            memory_len: usize,
-            #(#arg_declarations,)*
-        ) -> #ret {
-            #name(
-                &mut *wasi_ctx,
-                std::slice::from_raw_parts_mut(memory, memory_len),
-                #(#arg_names,)*
-            )
+        ) -> Result<#ret, String> {
+            Ok({#body})
         }
     }
 }

crates/wasi-common/wig/src/wasi.rs

@@ -168,7 +168,7 @@ pub fn define_struct(args: TokenStream) -> TokenStream {
 
             // The first result is returned bare right now...
             if let Some(ret) = results.next() {
-                handle_early_error = quote! { return e.into() };
+                handle_early_error = quote! { return Ok(e.into()) };
                 match &*ret.tref.type_() {
                     // Eventually we'll want to add support for more returned
                     // types, but for now let's just conform to what `*.witx`
@@ -200,7 +200,7 @@ pub fn define_struct(args: TokenStream) -> TokenStream {
                 let my_cx = cx.clone();
                 let #name_ident = wasmtime::Func::wrap(
                     store,
-                    move |caller: wasmtime::Caller<'_> #(,#shim_arg_decls)*| -> #ret_ty {
+                    move |caller: wasmtime::Caller<'_> #(,#shim_arg_decls)*| -> Result<#ret_ty, wasmtime::Trap> {
                         tracing::trace!(
                             #format_str,
                             #(#format_args),*
@@ -214,11 +214,15 @@ pub fn define_struct(args: TokenStream) -> TokenStream {
                                     #handle_early_error
                                 }
                             };
-                            hostcalls::#name_ident(
+                            let result = hostcalls::#name_ident(
                                 &mut my_cx.borrow_mut(),
                                 memory.data_unchecked_mut(),
                                 #(#hostcall_args),*
-                            ) #cvt_ret
+                            );
+                            match result {
+                                Ok(r) => { return Ok(r #cvt_ret); },
+                                Err(err) => { return Err(wasmtime::Trap::new(err)); },
+                            }
                         }
                     }
                 );