wiggle GuestError: improve Display of InFunc, InDataField

crates/wiggle/generate/src/funcs.rs

@@ -139,10 +139,12 @@ impl witx::Bindgen for Rust<'_> {
     ) {
         let rt = self.rt;
         let wrap_err = |location: &str| {
+            let modulename = self.module.name.as_str();
             let funcname = self.funcname;
             quote! {
                 |e| {
                     #rt::GuestError::InFunc {
+                        modulename: #modulename,
                         funcname: #funcname,
                         location: #location,
                         err: Box::new(#rt::GuestError::from(e)),

crates/wiggle/src/error.rs

@@ -19,14 +19,15 @@ pub enum GuestError {
     BorrowCheckerOutOfHandles,
     #[error("Slice length mismatch")]
     SliceLengthsDiffer,
-    #[error("In func {funcname}:{location}:")]
+    #[error("In func {modulename}::{funcname} at {location}: {err}")]
     InFunc {
+        modulename: &'static str,
         funcname: &'static str,
         location: &'static str,
         #[source]
         err: Box<GuestError>,
     },
-    #[error("In data {typename}.{field}:")]
+    #[error("In data {typename}.{field}: {err}")]
     InDataField {
         typename: String,
         field: String,