add better error message when using async-trait (#149)

* add better error message when using `async-trait`

* change output file

* move #121 compile tests into trybuild harness

autometrics-macros/src/lib.rs

@@ -1,6 +1,6 @@
 use crate::parse::{AutometricsArgs, Item};
 use percent_encoding::{utf8_percent_encode, NON_ALPHANUMERIC};
-use proc_macro2::TokenStream;
+use proc_macro2::{Span, TokenStream};
 use quote::{quote, ToTokens};
 use std::env;
 use syn::{
@@ -22,6 +22,13 @@ pub fn autometrics(
     item: proc_macro::TokenStream,
 ) -> proc_macro::TokenStream {
     let args = parse_macro_input!(args as parse::AutometricsArgs);
+
+    // if the input has yet to be modified by the `async-trait` crate, we will fail parsing in
+    // in the next line, so lets error early now
+    if let Err(err) = check_async_trait(&item) {
+        return err.into_compile_error().into();
+    }
+
     let item = parse_macro_input!(item as Item);
 
     let result = match item {
@@ -37,6 +44,19 @@ pub fn autometrics(
     output.into()
 }
 
+fn check_async_trait(input: &proc_macro::TokenStream) -> Result<()> {
+    let str = input.to_string();
+
+    if str.contains("#[async_trait]") || str.contains("#[async_trait::async_trait]") {
+        Err(syn::Error::new(
+            Span::call_site(),
+            "#[async_trait] must be defined BEFORE #[autometrics]",
+        ))
+    } else {
+        Ok(())
+    }
+}
+
 #[proc_macro_derive(ResultLabels, attributes(label))]
 pub fn result_labels(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let input = parse_macro_input!(input as syn::DeriveInput);

autometrics/Cargo.toml

@@ -122,6 +122,7 @@ tracing-opentelemetry-0-20 = { package = "tracing-opentelemetry", version = "0.2
 tracing-opentelemetry-0-21 = { package = "tracing-opentelemetry", version = "0.21.0", default-features = false, optional = true }
 
 [dev-dependencies]
+async-trait = "0.1.74"
 axum = { version = "0.6", features = ["tokio"] }
 criterion = "0.5"
 http = "0.2"

autometrics/tests/result_labels/fail/async_trait_support.rs

@@ -0,0 +1,34 @@
+use async_trait::async_trait;
+use autometrics::autometrics;
+
+// https://github.com/autometrics-dev/autometrics-rs/issues/141
+
+#[async_trait]
+trait TestTrait {
+    async fn method() -> bool;
+    async fn self_method(&self) -> bool;
+}
+
+#[derive(Default)]
+struct TestStruct;
+
+#[autometrics]
+#[async_trait]
+impl TestTrait for TestStruct {
+    async fn method() -> bool {
+        true
+    }
+
+    async fn self_method(&self) -> bool {
+        true
+    }
+}
+
+fn main() {
+    let ts = TestStruct::default();
+
+    async move {
+        <TestStruct as TestTrait>::method().await;
+        ts.self_method().await;
+    };
+}

autometrics/tests/result_labels/fail/async_trait_support.stderr

@@ -0,0 +1,29 @@
+error: #[async_trait] must be defined BEFORE #[autometrics]
+  --> tests/result_labels/fail/async_trait_support.rs:15:1
+   |
+15 | #[autometrics]
+   | ^^^^^^^^^^^^^^
+   |
+   = note: this error originates in the attribute macro `autometrics` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `TestStruct: TestTrait` is not satisfied
+  --> tests/result_labels/fail/async_trait_support.rs:31:9
+   |
+31 |         <TestStruct as TestTrait>::method().await;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TestTrait` is not implemented for `TestStruct`
+
+error[E0599]: no method named `self_method` found for struct `TestStruct` in the current scope
+  --> tests/result_labels/fail/async_trait_support.rs:32:12
+   |
+13 | struct TestStruct;
+   | ----------------- method `self_method` not found for this struct
+...
+32 |         ts.self_method().await;
+   |            ^^^^^^^^^^^ method not found in `TestStruct`
+   |
+   = help: items from traits can only be used if the trait is implemented and in scope
+note: `TestTrait` defines an item `self_method`, perhaps you need to implement it
+  --> tests/result_labels/fail/async_trait_support.rs:7:1
+   |
+7  | trait TestTrait {
+   | ^^^^^^^^^^^^^^^

autometrics/tests/compile_test.rs → autometrics/tests/result_labels/pass/generics.rs

@@ -35,9 +35,8 @@ fn issue_121_d() -> Result<impl ToString, impl std::error::Error> {
     }
 }
 
-#[test]
-fn invoke_issue_121() {
-    // we need to handle all three code generation cases
+fn main() {
+    // we need to handle all four code generation cases
     issue_121_a().unwrap();
     issue_121_b().unwrap();
     issue_121_c().unwrap();