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/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),
         })
     }