feat: Minimize diagnostic noise when Pavex attributes emit an error (#559)

Related issue: #538

Author: Duckaet

CONTRIBUTORS.md

@@ -20,4 +20,4 @@ We contributors to Pavex:
 - Oliver Barnes (@oliverbarnes)
 - Joe Hasson (@joehasson)
 - Peter Wischer (@peddermaster2)
-- Paras Sharma (@duckaet)
+- Paras Sharma (@Duckaet)

runtime/pavex_macros/src/utils/fn_like.rs

@@ -1,7 +1,8 @@
 //! Machinery to abstract away the parsing and validation logic that's shared by all
 //! Pavex components that accept function-like inputs.
 use proc_macro2::TokenStream;
-use syn::ImplItemFn;
+use quote::quote;
+use syn::{ImplItemFn, visit_mut::VisitMut};
 
 use crate::utils::{AnnotationCodegen, deny_unreachable_pub_attr, validation::must_be_public};
 
@@ -98,9 +99,17 @@ pub fn direct_entrypoint<M: CallableAnnotation>(
         Ok(output.emit(input))
     }
 
-    match _inner::<M>(metadata, input) {
+    match _inner::<M>(metadata, input.clone()) {
         Ok(t) => t.into(),
-        Err(t) => t,
+        Err(error_tokens) => {
+            let error_tokens = proc_macro2::TokenStream::from(error_tokens);
+            let mut input_item: syn::Item = syn::parse2(input).expect("Input is not a valid syn::Item");
+            crate::utils::PxStripper.visit_item_mut(&mut input_item);
+            quote! {
+                #error_tokens
+                #input_item
+            }.into()
+        }
     }
 }
 

runtime/pavex_macros/src/utils/type_like.rs

@@ -2,8 +2,8 @@
 //! Pavex components that accept type-like inputs.
 use convert_case::{Case, Casing as _};
 use proc_macro2::TokenStream;
-use quote::{ToTokens, format_ident};
-use syn::parse_quote;
+use quote::{quote, ToTokens, format_ident};
+use syn::{parse_quote, visit_mut::VisitMut};
 
 use crate::utils::{AnnotationCodegen, deny_unreachable_pub_attr, validation::must_be_public};
 
@@ -214,9 +214,17 @@ pub fn entrypoint<M: TypeAnnotation>(
         Ok(output.emit(input))
     }
 
-    match _inner::<M>(metadata, input) {
+    match _inner::<M>(metadata, input.clone()) {
         Ok(t) => t.into(),
-        Err(t) => t,
+        Err(error_tokens) => {
+            let error_tokens = proc_macro2::TokenStream::from(error_tokens);
+            let mut input_item: syn::Item = syn::parse2(input).expect("Input is not a valid syn::Item");
+            crate::utils::PxStripper.visit_item_mut(&mut input_item);
+            quote! {
+                #error_tokens
+                #input_item
+            }.into()
+        }
     }
 }
 

runtime/pavex_macros/tests/config/fail/group_rexport.stderr

@@ -11,3 +11,11 @@ error: Star re-exports can't be annotated with #[pavex::config].
   |
 7 | pub use private::*;
   | ^^^^^^^^^^^^^^^^^^^
+
+warning: unused import: `private::*`
+ --> tests/config/fail/group_rexport.rs:7:9
+  |
+7 | pub use private::*;
+  |         ^^^^^^^^^^
+  |
+  = note: `#[warn(unused_imports)]` on by default

runtime/pavex_macros/tests/config/fail/missing_key_with_usage.rs

@@ -0,0 +1,12 @@
+use pavex_macros::config;
+
+#[config]
+pub struct MyConfig {
+    pub value: String,
+}
+
+fn main() {
+    let _config = MyConfig {
+        value: "test".to_string(),
+    };
+}

runtime/pavex_macros/tests/config/fail/missing_key_with_usage.stderr

@@ -0,0 +1,7 @@
+error: Missing field `key`
+ --> tests/config/fail/missing_key_with_usage.rs:3:1
+  |
+3 | #[config]
+  | ^^^^^^^^^
+  |
+  = note: this error originates in the attribute macro `config` (in Nightly builds, run with -Z macro-backtrace for more info)

runtime/pavex_macros/tests/config/fail/not_public.stderr

@@ -39,3 +39,17 @@ error: Configuration types must be public.
    |
 19 | pub(crate) use sub::A as A3;
    | ^^^^^^^^^^
+
+warning: unused import: `sub::A as A2`
+  --> tests/config/fail/not_public.rs:16:5
+   |
+16 | use sub::A as A2;
+   |     ^^^^^^^^^^^^
+   |
+   = note: `#[warn(unused_imports)]` on by default
+
+warning: unused import: `sub::A as A3`
+  --> tests/config/fail/not_public.rs:19:16
+   |
+19 | pub(crate) use sub::A as A3;
+   |                ^^^^^^^^^^^^

runtime/pavex_macros/tests/route/fail/missing_path.rs

@@ -0,0 +1,10 @@
+use pavex_macros::get;
+
+#[get] 
+pub fn my_route() -> pavex::Response {
+    pavex::Response::new(pavex::http::StatusCode::OK)
+}
+
+fn main() {
+    let _response = my_route();
+}

runtime/pavex_macros/tests/route/fail/missing_path.stderr

@@ -0,0 +1,7 @@
+error: Missing field `path`
+ --> tests/route/fail/missing_path.rs:3:1
+  |
+3 | #[get]
+  | ^^^^^^
+  |
+  = note: this error originates in the attribute macro `get` (in Nightly builds, run with -Z macro-backtrace for more info)