rustc_expand: Mark inner #![test] attributes as soft-unstable

src/test/ui/feature-gate/issue-43106-gating-of-test.rs

@@ -1,5 +1,6 @@
 // The non-crate level cases are in issue-43106-gating-of-builtin-attrs.rs.
 
+#![allow(soft_unstable)]
 #![test                    = "4200"]
 //~^ ERROR cannot determine resolution for the attribute macro `test`
 

src/test/ui/feature-gate/issue-43106-gating-of-test.stderr

@@ -1,5 +1,5 @@
 error: cannot determine resolution for the attribute macro `test`
-  --> $DIR/issue-43106-gating-of-test.rs:3:4
+  --> $DIR/issue-43106-gating-of-test.rs:4:4
    |
 LL | #![test                    = "4200"]
    |    ^^^^

src/test/ui/issues/issue-28134.rs

@@ -1,3 +1,4 @@
 // compile-flags: --test
 
+#![allow(soft_unstable)]
 #![test] //~ ERROR cannot determine resolution for the attribute macro `test`

src/test/ui/issues/issue-28134.stderr

@@ -1,5 +1,5 @@
 error: cannot determine resolution for the attribute macro `test`
-  --> $DIR/issue-28134.rs:3:4
+  --> $DIR/issue-28134.rs:4:4
    |
 LL | #![test]
    |    ^^^^

src/test/ui/proc-macro/proc-macro-gates.rs

@@ -45,4 +45,9 @@ fn attrs() {
     //~^ ERROR: custom attributes cannot be applied to expressions
 }
 
+fn test_case() {
+    #![test] //~ ERROR inner macro attributes are unstable
+             //~| WARN this was previously accepted
+}
+
 fn main() {}

src/test/ui/proc-macro/proc-macro-gates.stderr

@@ -76,6 +76,16 @@ LL |     let _x = #[identity_attr] println!();
    = note: see issue #54727 <https://github.com/rust-lang/rust/issues/54727> for more information
    = help: add `#![feature(proc_macro_hygiene)]` to the crate attributes to enable
 
-error: aborting due to 9 previous errors
+error: inner macro attributes are unstable
+  --> $DIR/proc-macro-gates.rs:49:8
+   |
+LL |     #![test]
+   |        ^^^^
+   |
+   = note: `#[deny(soft_unstable)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
+
+error: aborting due to 10 previous errors
 
 For more information about this error, try `rustc --explain E0658`.