Even better model panics

crates/fj-proc/src/lib.rs

@@ -2,11 +2,7 @@ mod expand;
 mod parse;
 
 use proc_macro::TokenStream;
-use proc_macro2::{Ident, Span};
-use syn::{
-    parse_macro_input, punctuated::Punctuated, token::Paren, Expr, ExprCall,
-    ExprPath, FnArg, ItemFn, PathArguments, PathSegment, Stmt,
-};
+use syn::{parse_macro_input, FnArg, ItemFn};
 
 /// Define a function-based model.
 ///
@@ -95,67 +91,26 @@ pub fn model(_: TokenStream, input: TokenStream) -> TokenStream {
 
     match parse::parse(&item) {
         Ok(init) => {
-            let mut item = without_param_attrs(item);
+            let item = without_param_attrs(item);
 
-            // Yes, all of this is to add `fj::abi::initialize_panic_handling();` to the top of the function.
-            item.block.stmts.insert(
-                0,
-                Stmt::Semi(
-                    Expr::Call(ExprCall {
-                        attrs: vec![],
-                        func: Box::new(Expr::Path(ExprPath {
-                            attrs: vec![],
-                            qself: None,
-                            path: syn::Path {
-                                leading_colon: None,
-                                segments: {
-                                    let mut segments = Punctuated::new();
+            let attrs = item.attrs;
+            let vis = item.vis;
+            let sig = item.sig;
+            let statements = item.block.stmts;
 
-                                    segments.push(PathSegment {
-                                        ident: Ident::new(
-                                            "fj",
-                                            Span::call_site(),
-                                        ),
-                                        arguments: PathArguments::None,
-                                    });
-
-                                    segments.push(PathSegment {
-                                        ident: Ident::new(
-                                            "abi",
-                                            Span::call_site(),
-                                        ),
-                                        arguments: PathArguments::None,
-                                    });
-
-                                    segments.push(PathSegment {
-                                        ident: Ident::new(
-                                            "initialize_panic_handling",
-                                            Span::call_site(),
-                                        ),
-                                        arguments: PathArguments::None,
-                                    });
-
-                                    segments
-                                },
-                            },
-                        })),
-                        paren_token: Paren {
-                            span: Span::call_site(),
-                        },
-                        args: Punctuated::new(),
-                    }),
-                    syn::token::Semi::default(),
-                ),
-            );
+            let item = quote::quote! {
+                #(#attrs)* #vis #sig {
+                    fj::abi::initialize_panic_handling();
+                    #(#statements)*
+                }
+            };
 
             let tokens = quote::quote! {
                 #item
                 #init
 
             };
 
-            eprintln!("TOKENS: {}", tokens);
-
             tokens.into()
         }
         Err(e) => e.into_compile_error().into(),

crates/fj/Cargo.toml

@@ -17,6 +17,7 @@ anyhow = "1.0.70"
 
 [dependencies]
 fj-proc.workspace = true
+backtrace = "0.3.67"
 
 [dependencies.serde]
 version = "1.0.158"

crates/fj/src/abi/mod.rs

@@ -43,6 +43,7 @@ mod host;
 mod metadata;
 mod model;
 
+use backtrace::Backtrace;
 use std::{any::Any, fmt::Display, panic, sync::Mutex};
 
 pub use self::{
@@ -122,6 +123,7 @@ pub const INIT_FUNCTION_NAME: &str = "fj_model_init";
 struct PanicInfo {
     message: Option<String>,
     location: Option<Location>,
+    backtrace: Backtrace,
 }
 
 impl Display for PanicInfo {
@@ -139,6 +141,8 @@ impl Display for PanicInfo {
             write!(f, "no location given")?;
         }
 
+        writeln!(f, "\nBacktrace:\n{:?}", self.backtrace)?;
+
         Ok(())
     }
 }
@@ -180,7 +184,12 @@ pub fn initialize_panic_handling() {
             column: location.column(),
         });
 
-        *last_panic = Some(PanicInfo { message, location });
+        let backtrace = backtrace::Backtrace::new();
+        *last_panic = Some(PanicInfo {
+            message,
+            location,
+            backtrace,
+        });
     }));
 }