Implement async function support

Author: tailhook

src/lib.rs

@@ -56,9 +56,24 @@ pub fn context(args: TokenStream, input: TokenStream) -> TokenStream {
 
     let body = &input.block;
     let return_ty = &input.sig.output;
-    input.block = syn::parse_quote!({
-        (|| #return_ty #body)().map_err(|err| err.context(format!(#args)).into())
-    });
+    if input.sig.asyncness.is_some() {
+        match return_ty {
+            syn::ReturnType::Default => {
+                return syn::Error::new_spanned(return_ty,
+                    "function should return Result").to_compile_error().into()
+            }
+            syn::ReturnType::Type(_, return_ty) => {
+                input.block = syn::parse_quote!({
+                    let result: #return_ty = async { #body }.await;
+                    result.map_err(|err| err.context(format!(#args)).into())
+                });
+            }
+        }
+    } else {
+        input.block = syn::parse_quote!({
+            (|| #return_ty #body)().map_err(|err| err.context(format!(#args)).into())
+        });
+    }
 
     quote!(#input).into()
 }

tests/async_without_return.rs

@@ -0,0 +1,8 @@
+use fn_error_context::context;
+
+#[context("context")]
+async fn async_something() {
+}
+
+fn main() {
+}

tests/async_without_return.stderr

@@ -0,0 +1,7 @@
+error: function should return Result
+ --> $DIR/async_without_return.rs:3:1
+  |
+3 | #[context("context")]
+  | ^^^^^^^^^^^^^^^^^^^^^
+  |
+  = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)

tests/inherent.rs

@@ -7,6 +7,11 @@ impl Foo {
     fn do_stuff(&self) -> anyhow::Result<()> {
         anyhow::bail!("error {}", self.0)
     }
+
+    #[context("context")]
+    async fn do_async_stuff(&self) -> anyhow::Result<()> {
+        anyhow::bail!("error {}", self.0)
+    }
 }
 
 fn main() {

tests/tests.rs

@@ -15,4 +15,5 @@ fn tests() {
     tests.compile_fail("tests/fmt_missing_arg.rs");
     tests.compile_fail("tests/fmt_unused_arg.rs");
     tests.pass("tests/fmt_named_arg.rs");
+    tests.compile_fail("tests/async_without_return.rs");
 }