attributes: fix tracing::instrument regression around shadowing (tokio-rs#3311)

The change to allow the `dead_code` lint to work on the
`#[instrument]` attribute (tokio-rs#3108) introduced a shadowing
problem which caused compilation failure in certain cases,
as reported in tokio-rs#3306.

The body of the original function was not given its own scope
and `use` statements made there could leak out into the
code inserted by the `#[instrument]`.

This change fixes this problem by explicitly re-introducing the
parenthesis to give the original function body its own scope.

Closes tokio-rs#3306

Author: jplatte

tracing-attributes/src/expand.rs

@@ -87,7 +87,7 @@ pub(crate) fn gen_function<'a, B: ToTokens + 'a>(
     let block = quote! {
         {
             #fake_return_edge
-            #block
+            { #block }
         }
     };
 

tracing-attributes/tests/ui.rs

@@ -1,14 +1,15 @@
-// Only test on nightly, since UI tests are bound to change over time
+// Only test on stable, since UI tests are bound to change over time
+
 #[rustversion::stable]
 #[test]
-fn async_instrument() {
+fn pass() {
     let t = trybuild::TestCases::new();
-    t.compile_fail("tests/ui/async_instrument.rs");
+    t.pass("tests/ui/pass/*.rs");
 }
 
 #[rustversion::stable]
 #[test]
-fn const_instrument() {
+fn compile_fail() {
     let t = trybuild::TestCases::new();
-    t.compile_fail("tests/ui/const_instrument.rs");
+    t.compile_fail("tests/ui/fail/*.rs");
 }

tracing-attributes/tests/ui/async_instrument.rs renamed to tracing-attributes/tests/ui/fail/async_instrument.rs

@@ -1,31 +1,31 @@
 error[E0308]: mismatched types
- --> tests/ui/async_instrument.rs:5:5
+ --> tests/ui/fail/async_instrument.rs:5:5
   |
 5 |     ""
   |     ^^ expected `()`, found `&str`
   |
 note: return type inferred to be `()` here
- --> tests/ui/async_instrument.rs:4:10
+ --> tests/ui/fail/async_instrument.rs:4:10
   |
 4 | async fn unit() {
   |          ^^^^
 
 error[E0308]: mismatched types
-  --> tests/ui/async_instrument.rs:10:5
+  --> tests/ui/fail/async_instrument.rs:10:5
    |
 10 |     ""
    |     ^^- help: try using a conversion method: `.to_string()`
    |     |
    |     expected `String`, found `&str`
    |
 note: return type inferred to be `String` here
-  --> tests/ui/async_instrument.rs:9:31
+  --> tests/ui/fail/async_instrument.rs:9:31
    |
 9  | async fn simple_mismatch() -> String {
    |                               ^^^^^^
 
 error[E0277]: `(&str,)` doesn't implement `std::fmt::Display`
-  --> tests/ui/async_instrument.rs:14:57
+  --> tests/ui/fail/async_instrument.rs:14:57
    |
 14 |   async fn opaque_unsatisfied() -> impl std::fmt::Display {
    |  _________________________________________________________-
@@ -40,7 +40,7 @@ error[E0277]: `(&str,)` doesn't implement `std::fmt::Display`
    = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 
 error[E0277]: `(&str,)` doesn't implement `std::fmt::Display`
-  --> tests/ui/async_instrument.rs:14:34
+  --> tests/ui/fail/async_instrument.rs:14:34
    |
 14 | async fn opaque_unsatisfied() -> impl std::fmt::Display {
    |                                  ^^^^^^^^^^^^^^^^^^^^^^ `(&str,)` cannot be formatted with the default formatter
@@ -49,15 +49,15 @@ error[E0277]: `(&str,)` doesn't implement `std::fmt::Display`
    = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 
 error[E0308]: mismatched types
-  --> tests/ui/async_instrument.rs:22:5
+  --> tests/ui/fail/async_instrument.rs:22:5
    |
 22 |     ""
    |     ^^ expected `Wrapper<_>`, found `&str`
    |
    = note: expected struct `Wrapper<_>`
            found reference `&'static str`
 note: return type inferred to be `Wrapper<_>` here
-  --> tests/ui/async_instrument.rs:21:36
+  --> tests/ui/fail/async_instrument.rs:21:36
    |
 21 | async fn mismatch_with_opaque() -> Wrapper<impl std::fmt::Display> {
    |                                    ^^^^^^^
@@ -67,33 +67,33 @@ help: try wrapping the expression in `Wrapper`
    |     ++++++++  +
 
 error[E0308]: mismatched types
-  --> tests/ui/async_instrument.rs:28:16
+  --> tests/ui/fail/async_instrument.rs:28:16
    |
 28 |         return "";
    |                ^^ expected `()`, found `&str`
    |
 note: return type inferred to be `()` here
-  --> tests/ui/async_instrument.rs:26:10
+  --> tests/ui/fail/async_instrument.rs:26:10
    |
 26 | async fn early_return_unit() {
    |          ^^^^^^^^^^^^^^^^^
 
 error[E0308]: mismatched types
-  --> tests/ui/async_instrument.rs:35:16
+  --> tests/ui/fail/async_instrument.rs:35:16
    |
 35 |         return "";
    |                ^^- help: try using a conversion method: `.to_string()`
    |                |
    |                expected `String`, found `&str`
    |
 note: return type inferred to be `String` here
-  --> tests/ui/async_instrument.rs:33:28
+  --> tests/ui/fail/async_instrument.rs:33:28
    |
 33 | async fn early_return() -> String {
    |                            ^^^^^^
 
 error[E0308]: mismatched types
-  --> tests/ui/async_instrument.rs:40:1
+  --> tests/ui/fail/async_instrument.rs:40:1
    |
 40 | #[tracing::instrument]
    | ^^^^^^^^^^^^^^^^^^^^^^ expected `i32`, found `()`

tracing-attributes/tests/ui/async_instrument.stderr renamed to tracing-attributes/tests/ui/fail/async_instrument.stderr

@@ -1,13 +1,13 @@
 error: macros that expand to items must be delimited with braces or followed by a semicolon
- --> tests/ui/const_instrument.rs:3:1
+ --> tests/ui/fail/const_instrument.rs:3:1
   |
 3 | #[tracing::instrument]
   | ^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this error originates in the attribute macro `tracing::instrument` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: the `#[instrument]` attribute may not be used with `const fn`s
- --> tests/ui/const_instrument.rs:3:1
+ --> tests/ui/fail/const_instrument.rs:3:1
   |
 3 | #[tracing::instrument]
   | ^^^^^^^^^^^^^^^^^^^^^^

tracing-attributes/tests/ui/const_instrument.rs renamed to tracing-attributes/tests/ui/fail/const_instrument.rs

@@ -0,0 +1,6 @@
+#![deny(dead_code)]
+
+#[tracing::instrument]
+fn never_used() {}
+
+fn main() {}

tracing-attributes/tests/ui/const_instrument.stderr renamed to tracing-attributes/tests/ui/fail/const_instrument.stderr

@@ -0,0 +1,11 @@
+error: function `never_used` is never used
+ --> tests/ui/fail/unused_instrumented_fn.rs:4:4
+  |
+4 | fn never_used() {}
+  |    ^^^^^^^^^^
+  |
+note: the lint level is defined here
+ --> tests/ui/fail/unused_instrumented_fn.rs:1:9
+  |
+1 | #![deny(dead_code)]
+  |         ^^^^^^^^^

tracing-attributes/tests/ui/fail/unused_instrumented_fn.rs

@@ -0,0 +1,17 @@
+//! This program is a regression test for [#3306], where shadowing
+//! caused compilation failure in certain cases due to the original
+//! function body not getting its own scope.
+//!
+//! [#3306]: https://github.com/tokio-rs/tracing/issues/3306
+type Foo = ();
+enum Bar {
+    Foo,
+}
+
+#[tracing::instrument]
+fn this_is_fine() -> Foo {
+    // glob import imports Bar::Foo, shadowing Foo
+    use Bar::*;
+}
+
+fn main() {}