Merge release 0.1.5 into master

Author: dtolnay

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "async-trait"
-version = "0.1.4"
+version = "0.1.5"
 authors = ["David Tolnay <dtolnay@gmail.com>"]
 edition = "2018"
 license = "MIT OR Apache-2.0"
@@ -16,3 +16,10 @@ proc-macro = true
 proc-macro2 = "0.4"
 quote = "0.6"
 syn = { version = "0.15.41", features = ["full", "visit-mut"] }
+
+[features]
+# Alternative implementation that produces worse error messages but potentially
+# works on old nightlies without https://github.com/rust-lang/rust/pull/61775 in
+# some cases where the default implementation does not. This feature is semver
+# exempt and might get removed without notice in any patch version.
+support_old_nightly = []

src/expand.rs

@@ -225,6 +225,15 @@ fn transform_block(
     has_self: bool,
     is_local: bool,
 ) {
+    if cfg!(feature = "support_old_nightly") {
+        let brace = block.brace_token;
+        *block = parse_quote!({
+            core::pin::Pin::from(Box::new(async move #block))
+        });
+        block.brace_token = brace;
+        return;
+    }
+
     let inner = Ident::new(&format!("__{}", sig.ident), sig.ident.span());
     let args = sig
         .decl