warning: `#[derive]` does nothing on macro invocations
  --> $DIR/issue-49934.rs:20:5
   |
LL |     #[derive(Debug)]
   |     ^^^^^^^^^^^^^^^^
   |
   = note: this may become a hard error in a future release

warning: unused attribute
  --> $DIR/issue-49934.rs:6:8
   |
LL | fn foo<#[derive(Debug)] T>() {
   |        ^^^^^^^^^^^^^^^^
   |
note: lint level defined here
  --> $DIR/issue-49934.rs:4:9
   |
LL | #![warn(unused_attributes)]
   |         ^^^^^^^^^^^^^^^^^

warning: unused attribute
  --> $DIR/issue-49934.rs:8:9
   |
LL |         #[derive(Debug)]
   |         ^^^^^^^^^^^^^^^^

warning: unused attribute
  --> $DIR/issue-49934.rs:26:5
   |
LL |     #[derive(Debug)]
   |     ^^^^^^^^^^^^^^^^

warning: unused attribute
  --> $DIR/issue-49934.rs:30:5
   |
LL |     #[derive(Debug)]
   |     ^^^^^^^^^^^^^^^^

warning: unused attribute
  --> $DIR/issue-49934.rs:34:13
   |
LL |     let _ = #[derive(Debug)] "Hello, world!";
   |             ^^^^^^^^^^^^^^^^

warning: unused attribute
  --> $DIR/issue-49934.rs:39:9
   |
LL |         #[derive(Debug)]
   |         ^^^^^^^^^^^^^^^^