wiggle: allow disable tracing in Wiggle-generated code (#5146)

Wiggle generates code that instruments APIs with tracing code. This is
handy for diagnosing issues at runtime, but when inspecting the output
of Wiggle, it can make the generated code difficult for a human to
decipher. This change makes tracing a default but optional feature,
allowing users to avoid tracing code with commands like `cargo expand
--no-default-features`. This should be no change for current crates
depending on `wiggle`, `wiggle-macro`, and `wiggle-generate`.

review: add 'tracing' feature to wasi-common

review: switch to using macro configuration parsing

Co-authored-by: Andrew Brown <andrew.brown@intel.com>

crates/wasi-common/src/snapshots/preview_1.rs

@@ -25,7 +25,7 @@ wiggle::from_witx!({
     // keeping that set the same in this macro and the wasmtime_wiggle / lucet_wiggle macros is
     // tedious, and there is no cost to having a sync function be async in this case.
     async: *,
-    wasmtime: false
+    wasmtime: false,
 });
 
 impl wiggle::GuestErrorType for types::Errno {

crates/wiggle/generate/src/codegen_settings.rs

@@ -12,6 +12,10 @@ pub struct CodegenSettings {
     pub errors: ErrorTransform,
     pub async_: AsyncConf,
     pub wasmtime: bool,
+    // Disabling this feature makes it possible to remove all of the tracing
+    // code emitted in the Wiggle-generated code; this can be helpful while
+    // inspecting the code (e.g., with `cargo expand`).
+    pub tracing: bool,
 }
 impl CodegenSettings {
     pub fn new(
@@ -19,12 +23,14 @@ impl CodegenSettings {
         async_: &AsyncConf,
         doc: &Document,
         wasmtime: bool,
+        tracing: bool,
     ) -> Result<Self, Error> {
         let errors = ErrorTransform::new(error_conf, doc)?;
         Ok(Self {
             errors,
             async_: async_.clone(),
             wasmtime,
+            tracing,
         })
     }
     pub fn get_async(&self, module: &Module, func: &InterfaceFunc) -> Asyncness {

crates/wiggle/generate/src/config.rs

@@ -15,6 +15,7 @@ pub struct Config {
     pub errors: ErrorConf,
     pub async_: AsyncConf,
     pub wasmtime: bool,
+    pub tracing: bool,
 }
 
 mod kw {
@@ -24,6 +25,7 @@ mod kw {
     syn::custom_keyword!(errors);
     syn::custom_keyword!(target);
     syn::custom_keyword!(wasmtime);
+    syn::custom_keyword!(tracing);
 }
 
 #[derive(Debug, Clone)]
@@ -32,6 +34,7 @@ pub enum ConfigField {
     Error(ErrorConf),
     Async(AsyncConf),
     Wasmtime(bool),
+    Tracing(bool),
 }
 
 impl Parse for ConfigField {
@@ -67,6 +70,10 @@ impl Parse for ConfigField {
             input.parse::<kw::wasmtime>()?;
             input.parse::<Token![:]>()?;
             Ok(ConfigField::Wasmtime(input.parse::<syn::LitBool>()?.value))
+        } else if lookahead.peek(kw::tracing) {
+            input.parse::<kw::tracing>()?;
+            input.parse::<Token![:]>()?;
+            Ok(ConfigField::Tracing(input.parse::<syn::LitBool>()?.value))
         } else {
             Err(lookahead.error())
         }
@@ -79,6 +86,7 @@ impl Config {
         let mut errors = None;
         let mut async_ = None;
         let mut wasmtime = None;
+        let mut tracing = None;
         for f in fields {
             match f {
                 ConfigField::Witx(c) => {
@@ -105,6 +113,12 @@ impl Config {
                     }
                     wasmtime = Some(c);
                 }
+                ConfigField::Tracing(c) => {
+                    if tracing.is_some() {
+                        return Err(Error::new(err_loc, "duplicate `tracing` field"));
+                    }
+                    tracing = Some(c);
+                }
             }
         }
         Ok(Config {
@@ -114,6 +128,7 @@ impl Config {
             errors: errors.take().unwrap_or_default(),
             async_: async_.take().unwrap_or_default(),
             wasmtime: wasmtime.unwrap_or(true),
+            tracing: tracing.unwrap_or(true),
         })
     }
 

crates/wiggle/generate/src/funcs.rs

@@ -84,6 +84,16 @@ fn _define_func(
         );
     );
     if settings.get_async(&module, &func).is_sync() {
+        let traced_body = if settings.tracing {
+            quote!(
+                #mk_span
+                _span.in_scope(|| {
+                  #body
+                })
+            )
+        } else {
+            quote!(#body)
+        };
         (
             quote!(
                 #[allow(unreachable_code)] // deals with warnings in noreturn functions
@@ -93,15 +103,23 @@ fn _define_func(
                     #(#abi_params),*
                 ) -> Result<#abi_ret, #rt::wasmtime_crate::Trap> {
                     use std::convert::TryFrom as _;
-                    #mk_span
+                    #traced_body
-                    _span.in_scope(|| {
-                      #body
-                    })
                 }
             ),
             bounds,
         )
     } else {
+        let traced_body = if settings.tracing {
+            quote!(
+                use #rt::tracing::Instrument as _;
+                #mk_span
+                async move {
+                    #body
+                }.instrument(_span)
+            )
+        } else {
+            quote!(#body)
+        };
         (
             quote!(
                 #[allow(unreachable_code)] // deals with warnings in noreturn functions
@@ -111,11 +129,7 @@ fn _define_func(
                     #(#abi_params),*
                 ) -> impl std::future::Future<Output = Result<#abi_ret, #rt::wasmtime_crate::Trap>> + 'a {
                     use std::convert::TryFrom as _;
-                    use #rt::tracing::Instrument as _;
+                    #traced_body
-                    #mk_span
-                    async move {
-                        #body
-                    }.instrument(_span)
                 }
             ),
             bounds,
@@ -243,7 +257,7 @@ impl witx::Bindgen for Rust<'_> {
                         args.push(quote!(#name));
                     }
                 }
-                if func.params.len() > 0 {
+                if self.settings.tracing && func.params.len() > 0 {
                     let args = func
                         .params
                         .iter()
@@ -272,12 +286,14 @@ impl witx::Bindgen for Rust<'_> {
                         let ret = #trait_name::#ident(ctx, #(#args),*).await;
                     })
                 };
+                if self.settings.tracing {
                     self.src.extend(quote! {
                         #rt::tracing::event!(
                             #rt::tracing::Level::TRACE,
                             result = #rt::tracing::field::debug(&ret),
                         );
                     });
+                }
 
                 if func.results.len() > 0 {
                     results.push(quote!(ret));

crates/wiggle/macro/src/lib.rs

@@ -153,6 +153,7 @@ pub fn from_witx(args: TokenStream) -> TokenStream {
         &config.async_,
         &doc,
         config.wasmtime,
+        config.tracing,
     )
     .expect("validating codegen settings");
 
@@ -189,8 +190,13 @@ pub fn wasmtime_integration(args: TokenStream) -> TokenStream {
     let doc = config.c.load_document();
     let names = wiggle_generate::Names::new(quote!(wiggle));
 
-    let settings =
+    let settings = wiggle_generate::CodegenSettings::new(
-        wiggle_generate::CodegenSettings::new(&config.c.errors, &config.c.async_, &doc, true)
+        &config.c.errors,
+        &config.c.async_,
+        &doc,
+        true,
+        config.c.tracing,
+    )
     .expect("validating codegen settings");
 
     let modules = doc.modules().map(|module| {