Gate self span hack on rustc <= 1.46.

Cargo.toml

@@ -24,5 +24,8 @@ tracing-attributes = "0.1.8"
 tracing-futures = "0.2"
 trybuild = { version = "1.0.19", features = ["diff"] }
 
+[build-dependencies]
+version_check = "0.9"
+
 [package.metadata.docs.rs]
 targets = ["x86_64-unknown-linux-gnu"]

build.rs

@@ -0,0 +1,5 @@
+fn main() {
+    if let Some(true) = version_check::is_max_version("1.46") {
+        println!("cargo:rustc-cfg=self_span_hack");
+    }
+}

src/receiver.rs

@@ -108,6 +108,7 @@ impl VisitMut for ReplaceSelf<'_> {
     fn visit_ident_mut(&mut self, i: &mut Ident) {
         if i == "self" {
             *i = quote::format_ident!("{}{}", self.0, i);
+            #[cfg(self_span_hack)]
             i.set_span(self.1);
         }
 

tests/ui/self-span.stderr

@@ -1,10 +1,10 @@
 error[E0308]: mismatched types
-  --> $DIR/self-span.rs:16:21
+  --> $DIR/self-span.rs:17:21
    |
-16 |     async fn method(self) {
-   |                     ^^^^ expected `()`, found struct `S`
 17 |         let _: () = self;
-   |                -- expected due to this
+   |                --   ^^^^ expected `()`, found struct `S`
+   |                |
+   |                expected due to this
 
 error: the `Self` constructor can only be used with tuple or unit structs
   --> $DIR/self-span.rs:18:23
@@ -13,12 +13,12 @@ error: the `Self` constructor can only be used with tuple or unit structs
    |                       ^^^^ help: use curly brackets: `Self { /* fields */ }`
 
 error[E0308]: mismatched types
-  --> $DIR/self-span.rs:24:21
+  --> $DIR/self-span.rs:25:21
    |
-24 |     async fn method(self) {
-   |                     ^^^^ expected `()`, found enum `E`
 25 |         let _: () = self;
-   |                -- expected due to this
+   |                --   ^^^^ expected `()`, found enum `E`
+   |                |
+   |                expected due to this
 
 error[E0533]: expected unit struct, unit variant or constant, found struct variant `Self::V`
   --> $DIR/self-span.rs:26:23