From 004c40af4d90c59045e5ec2fcbac07f85c9e4600 Mon Sep 17 00:00:00 2001
From: Jacob O'Toole <jacob@jotpot.co.uk>
Date: Wed, 12 Mar 2025 23:44:53 +0000
Subject: [PATCH] Fix inconsistent identifier spans in route codegen

Previously, identifiers such as `__req` were output with inconsistent
spans. For example, in
[`query_decls`](https://github.com/rwf2/Rocket/blob/28891e8072136f4641a33fb8c3f2aafce9d88d5b/core/codegen/src/attribute/route/mod.rs#L43),
it was defined with `Span::call_site()`, but in
[`request_guard_decl`](https://github.com/rwf2/Rocket/blob/28891e8072136f4641a33fb8c3f2aafce9d88d5b/core/codegen/src/attribute/route/mod.rs#L127)
as `guard.ty.span()`. The problem is, when used with macros, these spans
can be different and cause the identifiers to fail to resolve.

A simple failure example is:

```rust
macro_rules! empty_get {
    ($name:ident) => {
        #[get("/")]
        async fn $name() {}
    }
}

empty_get!(test);
```

In this case, the inconsistency arises because:

- In
  [`codegen_route`](https://github.com/rwf2/Rocket/blob/28891e8072136f4641a33fb8c3f2aafce9d88d5b/core/codegen/src/attribute/route/mod.rs#L380),
  no span for `__req` is specified, which I believe means it defaults to
  `Span::call_site()`, so inside `macro_rules!`, then
- in
  [`responder_outcome_expr`](https://github.com/rwf2/Rocket/blob/28891e8072136f4641a33fb8c3f2aafce9d88d5b/core/codegen/src/attribute/route/mod.rs#L299),
  the span used is from the identifier of the function, which is outside
  of `macro_rules!`.

This causes the `__req` in `responder_outcome` not to resolve to the
`__req` defined in the `monomorphized_function` arguments.

The span is now always `Span::call_site()`, which resolves these issues.

I believe `call_site` is acceptable, since it was already used as the
span for these variables elsewhere. In addition, I didn't spot anywhere
in the code where this could cause a problem.
---
 core/codegen/src/attribute/route/mod.rs | 14 +++++++-------
 core/codegen/tests/route.rs             | 10 ++++++++++
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/core/codegen/src/attribute/route/mod.rs b/core/codegen/src/attribute/route/mod.rs
index 506102499c..4a51c2629c 100644
--- a/core/codegen/src/attribute/route/mod.rs
+++ b/core/codegen/src/attribute/route/mod.rs
@@ -63,7 +63,7 @@ fn query_decls(route: &Route) -> Option<TokenStream> {
                 _ => quote!(#name)
             };
 
-            define_spanned_export!(ty.span() => FromForm, _form);
+            define_spanned_export!(Span::call_site() => FromForm, _form);
 
             let ty = quote_spanned!(ty.span() => <#ty as #FromForm>);
             let init = quote_spanned!(ty.span() => #ty::init(#_form::Options::Lenient));
@@ -124,8 +124,8 @@ fn query_decls(route: &Route) -> Option<TokenStream> {
 
 fn request_guard_decl(guard: &Guard) -> TokenStream {
     let (ident, ty) = (guard.fn_ident.rocketized(), &guard.ty);
-    define_spanned_export!(ty.span() =>
-        __req, __data, _request, display_hack, FromRequest, Outcome
+    define_spanned_export!(Span::call_site() =>
+        __req, __data, display_hack, FromRequest, Outcome
     );
 
     quote_spanned! { ty.span() =>
@@ -162,7 +162,7 @@ fn request_guard_decl(guard: &Guard) -> TokenStream {
 
 fn param_guard_decl(guard: &Guard) -> TokenStream {
     let (i, name, ty) = (guard.index, &guard.name, &guard.ty);
-    define_spanned_export!(ty.span() =>
+    define_spanned_export!(Span::call_site() =>
         __req, __data, _None, _Some, _Ok, _Err,
         Outcome, FromSegments, FromParam, Status, display_hack
     );
@@ -219,7 +219,7 @@ fn param_guard_decl(guard: &Guard) -> TokenStream {
 
 fn data_guard_decl(guard: &Guard) -> TokenStream {
     let (ident, ty) = (guard.fn_ident.rocketized(), &guard.ty);
-    define_spanned_export!(ty.span() => __req, __data, display_hack, FromData, Outcome);
+    define_spanned_export!(Span::call_site() => __req, __data, display_hack, FromData, Outcome);
 
     quote_spanned! { ty.span() =>
         let #ident: #ty = match <#ty as #FromData>::from_data(#__req, #__data).await {
@@ -307,7 +307,7 @@ fn responder_outcome_expr(route: &Route) -> TokenStream {
     let _await = route.handler.sig.asyncness
         .map(|a| quote_spanned!(a.span() => .await));
 
-    define_spanned_export!(ret_span => __req, _route);
+    define_spanned_export!(Span::call_site() => __req, _route);
     quote_spanned! { mixed(ret_span) =>
         let ___responder = #user_handler_fn_name(#(#parameter_names),*) #_await;
         #_route::Outcome::from(#__req, ___responder)
@@ -363,7 +363,7 @@ fn sentinels_expr(route: &Route) -> TokenStream {
         .map(|child| (child.parent, child.ty));
 
     let sentinel = eligible_types.map(|(parent, ty)| {
-        define_spanned_export!(ty.span() => _sentinel);
+        define_spanned_export!(Span::call_site() => _sentinel);
 
         match parent {
             Some(p) if p.is_concrete(&generic_idents) => {
diff --git a/core/codegen/tests/route.rs b/core/codegen/tests/route.rs
index f9a1bf66e9..33c73a8833 100644
--- a/core/codegen/tests/route.rs
+++ b/core/codegen/tests/route.rs
@@ -347,3 +347,13 @@ fn test_inclusive_segments() {
     assert_eq!(get("//a//b////c/d/e"), "nonempty+c/d/e");
     assert_eq!(get("//a//b////c/d/e/"), "nonempty+c/d/e/");
 }
+
+macro_rules! empty_get {
+    ($name:ident) => {
+        #[allow(dead_code)]
+        #[get("/")]
+        async fn $name() {}
+    }
+}
+
+empty_get!(test);