Use mixed-site spans to avoid clippy 'uri!' error.

Closes #2630.

core/codegen/src/attribute/route/mod.rs

@@ -10,6 +10,7 @@ use crate::proc_macro_ext::StringLit;
 use crate::syn_ext::{IdentExt, TypeExt as _};
 use crate::http_codegen::{Method, Optional};
 use crate::attribute::param::Guard;
+use crate::exports::mixed;
 
 use self::parse::{Route, Attribute, MethodAttribute};
 
@@ -242,7 +243,7 @@ fn responder_outcome_expr(route: &Route) -> TokenStream {
         .map(|a| quote_spanned!(a.span() => .await));
 
     define_spanned_export!(ret_span => __req, _route);
-    quote_spanned! { Span::mixed_site().located_at(ret_span) =>
+    quote_spanned! { mixed(ret_span) =>
         let ___responder = #user_handler_fn_name(#(#parameter_names),*) #_await;
         #_route::Outcome::from(#__req, ___responder)
     }

core/codegen/src/bang/uri.rs

@@ -126,7 +126,7 @@ fn add_binding<P: fmt::Part>(to: &mut Vec<TokenStream>, ident: &Ident, ty: &Type
     let tmp_ident = ident.clone().with_span(expr.span());
     let let_stmt = quote_spanned!(span => let #tmp_ident = #expr);
 
-    to.push(quote_spanned!(span =>
+    to.push(quote_spanned!(mixed(span) =>
         #[allow(non_snake_case)] #let_stmt;
         let #ident = <#ty as #_fmt::FromUriParam<#part, _>>::from_uri_param(#tmp_ident);
     ));

core/codegen/src/exports.rs

@@ -106,3 +106,9 @@ define_exported_paths! {
 macro_rules! define_spanned_export {
     ($span:expr => $($name:ident),*) => ($(define!($span => $name $name);)*)
 }
+
+/// Convenience: returns a "mixed site" span located at `span`.
+#[inline(always)]
+pub fn mixed(span: Span) -> Span {
+    Span::mixed_site().located_at(span)
+}