use backticks instead of single quotes when reporting "use of unstabl…

…e library feature"

This is consistent with all other diagnostics I could find containing
features and enables the use of `DiagSymbolList` for generalizing
diagnostics for unstable library features to multiple features.

compiler/rustc_hir_analysis/messages.ftl

@@ -311,8 +311,8 @@ hir_analysis_missing_trait_item_suggestion = implement the missing item: `{$snip
 
 hir_analysis_missing_trait_item_unstable = not all trait items implemented, missing: `{$missing_item_name}`
     .note = default implementation of `{$missing_item_name}` is unstable
-    .some_note = use of unstable library feature '{$feature}': {$reason}
-    .none_note = use of unstable library feature '{$feature}'
+    .some_note = use of unstable library feature `{$feature}`: {$reason}
+    .none_note = use of unstable library feature `{$feature}`
 
 hir_analysis_missing_type_params =
     the type {$parameterCount ->

compiler/rustc_middle/src/middle/stability.rs

@@ -112,8 +112,8 @@ pub fn report_unstable(
     soft_handler: impl FnOnce(&'static Lint, Span, String),
 ) {
     let msg = match reason {
-        Some(r) => format!("use of unstable library feature '{feature}': {r}"),
-        None => format!("use of unstable library feature '{feature}'"),
+        Some(r) => format!("use of unstable library feature `{feature}`: {r}"),
+        None => format!("use of unstable library feature `{feature}`"),
     };
 
     if is_soft {

tests/ui-fulldeps/hash-stable-is-unstable.rs

@@ -1,24 +1,24 @@
 //@ compile-flags: -Zdeduplicate-diagnostics=yes
 extern crate rustc_data_structures;
-//~^ use of unstable library feature 'rustc_private'
+//~^ use of unstable library feature `rustc_private`
 //~| NOTE: issue #27812 <https://github.com/rust-lang/rust/issues/27812> for more information
 //~| NOTE: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 extern crate rustc_macros;
-//~^ use of unstable library feature 'rustc_private'
+//~^ use of unstable library feature `rustc_private`
 //~| NOTE: see issue #27812 <https://github.com/rust-lang/rust/issues/27812> for more information
 //~| NOTE: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 extern crate rustc_query_system;
-//~^ use of unstable library feature 'rustc_private'
+//~^ use of unstable library feature `rustc_private`
 //~| NOTE: see issue #27812 <https://github.com/rust-lang/rust/issues/27812> for more information
 //~| NOTE: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 use rustc_macros::HashStable;
-//~^ use of unstable library feature 'rustc_private'
+//~^ use of unstable library feature `rustc_private`
 //~| NOTE: see issue #27812 <https://github.com/rust-lang/rust/issues/27812> for more information
 //~| NOTE: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 #[derive(HashStable)]
-//~^ use of unstable library feature 'rustc_private'
+//~^ use of unstable library feature `rustc_private`
 //~| NOTE: in this expansion of #[derive(HashStable)]
 //~| NOTE: in this expansion of #[derive(HashStable)]
 //~| NOTE: in this expansion of #[derive(HashStable)]

tests/ui-fulldeps/hash-stable-is-unstable.stderr

@@ -1,4 +1,4 @@
-error[E0658]: use of unstable library feature 'rustc_private': this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
+error[E0658]: use of unstable library feature `rustc_private`: this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
   --> $DIR/hash-stable-is-unstable.rs:2:1
    |
 LL | extern crate rustc_data_structures;
@@ -8,7 +8,7 @@ LL | extern crate rustc_data_structures;
    = help: add `#![feature(rustc_private)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: use of unstable library feature 'rustc_private': this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
+error[E0658]: use of unstable library feature `rustc_private`: this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
   --> $DIR/hash-stable-is-unstable.rs:6:1
    |
 LL | extern crate rustc_macros;
@@ -18,7 +18,7 @@ LL | extern crate rustc_macros;
    = help: add `#![feature(rustc_private)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: use of unstable library feature 'rustc_private': this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
+error[E0658]: use of unstable library feature `rustc_private`: this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
   --> $DIR/hash-stable-is-unstable.rs:10:1
    |
 LL | extern crate rustc_query_system;
@@ -28,7 +28,7 @@ LL | extern crate rustc_query_system;
    = help: add `#![feature(rustc_private)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: use of unstable library feature 'rustc_private': this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
+error[E0658]: use of unstable library feature `rustc_private`: this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
   --> $DIR/hash-stable-is-unstable.rs:15:5
    |
 LL | use rustc_macros::HashStable;
@@ -38,7 +38,7 @@ LL | use rustc_macros::HashStable;
    = help: add `#![feature(rustc_private)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: use of unstable library feature 'rustc_private': this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
+error[E0658]: use of unstable library feature `rustc_private`: this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
   --> $DIR/hash-stable-is-unstable.rs:20:10
    |
 LL | #[derive(HashStable)]

tests/ui-fulldeps/pathless-extern-unstable.rs

@@ -4,6 +4,6 @@
 // Test that `--extern rustc_middle` fails with `rustc_private`.
 
 pub use rustc_middle;
-//~^ ERROR use of unstable library feature 'rustc_private'
+//~^ ERROR use of unstable library feature `rustc_private`
 
 fn main() {}

tests/ui-fulldeps/pathless-extern-unstable.stderr

@@ -1,4 +1,4 @@
-error[E0658]: use of unstable library feature 'rustc_private': this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
+error[E0658]: use of unstable library feature `rustc_private`: this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
   --> $DIR/pathless-extern-unstable.rs:6:9
    |
 LL | pub use rustc_middle;

tests/ui/associated-inherent-types/assoc-inherent-unstable.rs

@@ -4,6 +4,6 @@
 #![feature(inherent_associated_types)]
 #![allow(incomplete_features)]
 
-type Data = aux::Owner::Data; //~ ERROR use of unstable library feature 'data'
+type Data = aux::Owner::Data; //~ ERROR use of unstable library feature `data`
 
 fn main() {}

tests/ui/associated-inherent-types/assoc-inherent-unstable.stderr

@@ -1,4 +1,4 @@
-error[E0658]: use of unstable library feature 'data'
+error[E0658]: use of unstable library feature `data`
   --> $DIR/assoc-inherent-unstable.rs:7:13
    |
 LL | type Data = aux::Owner::Data;

tests/ui/async-await/async-fn/edition-2015.rs

@@ -3,7 +3,7 @@ fn foo(x: impl async Fn()) -> impl async Fn() { x }
 //~| ERROR `async` trait bounds are only allowed in Rust 2018 or later
 //~| ERROR async closures are unstable
 //~| ERROR async closures are unstable
-//~| ERROR use of unstable library feature 'async_closure'
-//~| ERROR use of unstable library feature 'async_closure'
+//~| ERROR use of unstable library feature `async_closure`
+//~| ERROR use of unstable library feature `async_closure`
 
 fn main() {}

tests/ui/async-await/async-fn/edition-2015.stderr

@@ -38,7 +38,7 @@ LL | fn foo(x: impl async Fn()) -> impl async Fn() { x }
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
    = help: to use an async block, remove the `||`: `async {`
 
-error[E0658]: use of unstable library feature 'async_closure'
+error[E0658]: use of unstable library feature `async_closure`
   --> $DIR/edition-2015.rs:1:42
    |
 LL | fn foo(x: impl async Fn()) -> impl async Fn() { x }
@@ -48,7 +48,7 @@ LL | fn foo(x: impl async Fn()) -> impl async Fn() { x }
    = help: add `#![feature(async_closure)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: use of unstable library feature 'async_closure'
+error[E0658]: use of unstable library feature `async_closure`
   --> $DIR/edition-2015.rs:1:22
    |
 LL | fn foo(x: impl async Fn()) -> impl async Fn() { x }

tests/ui/box/alloc-unstable-fail.rs

@@ -2,5 +2,5 @@ use std::boxed::Box;
 
 fn main() {
     let _boxed: Box<u32, _> = Box::new(10);
-    //~^ ERROR use of unstable library feature 'allocator_api'
+    //~^ ERROR use of unstable library feature `allocator_api`
 }

tests/ui/box/alloc-unstable-fail.stderr

@@ -1,4 +1,4 @@
-error[E0658]: use of unstable library feature 'allocator_api'
+error[E0658]: use of unstable library feature `allocator_api`
   --> $DIR/alloc-unstable-fail.rs:4:26
    |
 LL |     let _boxed: Box<u32, _> = Box::new(10);

tests/ui/conditional-compilation/cfg_accessible-unstable.rs

@@ -1,2 +1,2 @@
-#[cfg_accessible(std)] //~ ERROR use of unstable library feature 'cfg_accessible'
+#[cfg_accessible(std)] //~ ERROR use of unstable library feature `cfg_accessible`
 fn main() {}

tests/ui/conditional-compilation/cfg_accessible-unstable.stderr

@@ -1,4 +1,4 @@
-error[E0658]: use of unstable library feature 'cfg_accessible': `cfg_accessible` is not fully implemented
+error[E0658]: use of unstable library feature `cfg_accessible`: `cfg_accessible` is not fully implemented
   --> $DIR/cfg_accessible-unstable.rs:1:3
    |
 LL | #[cfg_accessible(std)]

tests/ui/consts/const-unstable-intrinsic.rs

@@ -15,16 +15,16 @@ const fn const_main() {
     let x = 42;
     unsafe {
         unstable_intrinsic::old_way::size_of_val(&x);
-        //~^ERROR: unstable library feature 'unstable'
+        //~^ERROR: unstable library feature `unstable`
         //~|ERROR: cannot call non-const intrinsic
         unstable_intrinsic::old_way::min_align_of_val(&x);
-        //~^ERROR: unstable library feature 'unstable'
+        //~^ERROR: unstable library feature `unstable`
         //~|ERROR: not yet stable as a const intrinsic
         unstable_intrinsic::new_way::size_of_val(&x);
-        //~^ERROR: unstable library feature 'unstable'
+        //~^ERROR: unstable library feature `unstable`
         //~|ERROR: cannot be (indirectly) exposed to stable
         unstable_intrinsic::new_way::min_align_of_val(&x);
-        //~^ERROR: unstable library feature 'unstable'
+        //~^ERROR: unstable library feature `unstable`
         //~|ERROR: not yet stable as a const intrinsic
 
         old_way::size_of_val(&x);

tests/ui/consts/const-unstable-intrinsic.stderr

@@ -1,4 +1,4 @@
-error[E0658]: use of unstable library feature 'unstable'
+error[E0658]: use of unstable library feature `unstable`
   --> $DIR/const-unstable-intrinsic.rs:17:9
    |
 LL |         unstable_intrinsic::old_way::size_of_val(&x);
@@ -8,7 +8,7 @@ LL |         unstable_intrinsic::old_way::size_of_val(&x);
    = help: add `#![feature(unstable)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: use of unstable library feature 'unstable'
+error[E0658]: use of unstable library feature `unstable`
   --> $DIR/const-unstable-intrinsic.rs:20:9
    |
 LL |         unstable_intrinsic::old_way::min_align_of_val(&x);
@@ -18,7 +18,7 @@ LL |         unstable_intrinsic::old_way::min_align_of_val(&x);
    = help: add `#![feature(unstable)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: use of unstable library feature 'unstable'
+error[E0658]: use of unstable library feature `unstable`
   --> $DIR/const-unstable-intrinsic.rs:23:9
    |
 LL |         unstable_intrinsic::new_way::size_of_val(&x);
@@ -28,7 +28,7 @@ LL |         unstable_intrinsic::new_way::size_of_val(&x);
    = help: add `#![feature(unstable)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: use of unstable library feature 'unstable'
+error[E0658]: use of unstable library feature `unstable`
   --> $DIR/const-unstable-intrinsic.rs:26:9
    |
 LL |         unstable_intrinsic::new_way::min_align_of_val(&x);

tests/ui/derives/rustc-decodable-issue-123156.stderr

@@ -1,5 +1,5 @@
 Future incompatibility report: Future breakage diagnostic:
-warning: use of unstable library feature 'rustc_encodable_decodable': derive macro for `rustc-serialize`; should not be used in new code
+warning: use of unstable library feature `rustc_encodable_decodable`: derive macro for `rustc-serialize`; should not be used in new code
   --> $DIR/rustc-decodable-issue-123156.rs:10:10
    |
 LL | #[derive(RustcDecodable)]

tests/ui/explore-issue-38412.rs

@@ -18,7 +18,7 @@ fn main() {
 
     let Record { a_stable_pub: _, a_unstable_declared_pub: _, a_unstable_undeclared_pub: _, .. } =
         Record::new();
-    //~^^ ERROR use of unstable library feature 'unstable_undeclared'
+    //~^^ ERROR use of unstable library feature `unstable_undeclared`
 
     let r = Record::new();
     let t = Tuple::new();

tests/ui/explore-issue-38412.stderr

@@ -1,4 +1,4 @@
-error[E0658]: use of unstable library feature 'unstable_undeclared'
+error[E0658]: use of unstable library feature `unstable_undeclared`
   --> $DIR/explore-issue-38412.rs:19:63
    |
 LL |     let Record { a_stable_pub: _, a_unstable_declared_pub: _, a_unstable_undeclared_pub: _, .. } =
@@ -8,7 +8,7 @@ LL |     let Record { a_stable_pub: _, a_unstable_declared_pub: _, a_unstable_un
    = help: add `#![feature(unstable_undeclared)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: use of unstable library feature 'unstable_undeclared'
+error[E0658]: use of unstable library feature `unstable_undeclared`
   --> $DIR/explore-issue-38412.rs:28:5
    |
 LL |     r.a_unstable_undeclared_pub;
@@ -36,7 +36,7 @@ error[E0616]: field `d_priv` of struct `Record` is private
 LL |     r.d_priv;
    |       ^^^^^^ private field
 
-error[E0658]: use of unstable library feature 'unstable_undeclared'
+error[E0658]: use of unstable library feature `unstable_undeclared`
   --> $DIR/explore-issue-38412.rs:35:5
    |
 LL |     t.2;
@@ -64,7 +64,7 @@ error[E0616]: field `5` of struct `pub_and_stability::Tuple` is private
 LL |     t.5;
    |       ^ private field
 
-error[E0658]: use of unstable library feature 'unstable_undeclared'
+error[E0658]: use of unstable library feature `unstable_undeclared`
   --> $DIR/explore-issue-38412.rs:42:7
    |
 LL |     r.unstable_undeclared_trait_method();
@@ -74,7 +74,7 @@ LL |     r.unstable_undeclared_trait_method();
    = help: add `#![feature(unstable_undeclared)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: use of unstable library feature 'unstable_undeclared'
+error[E0658]: use of unstable library feature `unstable_undeclared`
   --> $DIR/explore-issue-38412.rs:46:7
    |
 LL |     r.unstable_undeclared();
@@ -117,7 +117,7 @@ LL |     r.private();
 LL |         fn private(&self) -> i32 { self.d_priv }
    |         ------------------------ private method defined here
 
-error[E0658]: use of unstable library feature 'unstable_undeclared'
+error[E0658]: use of unstable library feature `unstable_undeclared`
   --> $DIR/explore-issue-38412.rs:55:7
    |
 LL |     t.unstable_undeclared_trait_method();
@@ -127,7 +127,7 @@ LL |     t.unstable_undeclared_trait_method();
    = help: add `#![feature(unstable_undeclared)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: use of unstable library feature 'unstable_undeclared'
+error[E0658]: use of unstable library feature `unstable_undeclared`
   --> $DIR/explore-issue-38412.rs:59:7
    |
 LL |     t.unstable_undeclared();

tests/ui/feature-gates/bench.rs

@@ -1,9 +1,9 @@
 //@ edition:2018
 
-#[bench] //~ ERROR use of unstable library feature 'test'
+#[bench] //~ ERROR use of unstable library feature `test`
          //~| WARN this was previously accepted
 fn bench() {}
 
-use bench as _; //~ ERROR use of unstable library feature 'test'
+use bench as _; //~ ERROR use of unstable library feature `test`
                 //~| WARN this was previously accepted
 fn main() {}

tests/ui/feature-gates/bench.stderr

@@ -1,4 +1,4 @@
-error: use of unstable library feature 'test': `bench` is a part of custom test frameworks which are unstable
+error: use of unstable library feature `test`: `bench` is a part of custom test frameworks which are unstable
   --> $DIR/bench.rs:3:3
    |
 LL | #[bench]
@@ -8,7 +8,7 @@ LL | #[bench]
    = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
    = note: `#[deny(soft_unstable)]` on by default
 
-error: use of unstable library feature 'test': `bench` is a part of custom test frameworks which are unstable
+error: use of unstable library feature `test`: `bench` is a part of custom test frameworks which are unstable
   --> $DIR/bench.rs:7:5
    |
 LL | use bench as _;
@@ -20,7 +20,7 @@ LL | use bench as _;
 error: aborting due to 2 previous errors
 
 Future incompatibility report: Future breakage diagnostic:
-error: use of unstable library feature 'test': `bench` is a part of custom test frameworks which are unstable
+error: use of unstable library feature `test`: `bench` is a part of custom test frameworks which are unstable
   --> $DIR/bench.rs:3:3
    |
 LL | #[bench]
@@ -31,7 +31,7 @@ LL | #[bench]
    = note: `#[deny(soft_unstable)]` on by default
 
 Future breakage diagnostic:
-error: use of unstable library feature 'test': `bench` is a part of custom test frameworks which are unstable
+error: use of unstable library feature `test`: `bench` is a part of custom test frameworks which are unstable
   --> $DIR/bench.rs:7:5
    |
 LL | use bench as _;

tests/ui/feature-gates/feature-gate-alloc-error-handler.rs

@@ -5,7 +5,7 @@
 
 use core::alloc::Layout;
 
-#[alloc_error_handler] //~ ERROR use of unstable library feature 'alloc_error_handler'
+#[alloc_error_handler] //~ ERROR use of unstable library feature `alloc_error_handler`
 fn oom(info: Layout) -> ! {
     loop {}
 }

tests/ui/feature-gates/feature-gate-alloc-error-handler.stderr

@@ -1,4 +1,4 @@
-error[E0658]: use of unstable library feature 'alloc_error_handler'
+error[E0658]: use of unstable library feature `alloc_error_handler`
   --> $DIR/feature-gate-alloc-error-handler.rs:8:3
    |
 LL | #[alloc_error_handler]

tests/ui/feature-gates/feature-gate-autodiff-use.has_support.stderr

@@ -1,4 +1,4 @@
-error[E0658]: use of unstable library feature 'autodiff'
+error[E0658]: use of unstable library feature `autodiff`
   --> $DIR/feature-gate-autodiff-use.rs:13:3
    |
 LL | #[autodiff(dfoo, Reverse)]
@@ -8,7 +8,7 @@ LL | #[autodiff(dfoo, Reverse)]
    = help: add `#![feature(autodiff)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: use of unstable library feature 'autodiff'
+error[E0658]: use of unstable library feature `autodiff`
   --> $DIR/feature-gate-autodiff-use.rs:9:5
    |
 LL | use std::autodiff::autodiff;

tests/ui/feature-gates/feature-gate-autodiff-use.no_support.stderr

@@ -1,4 +1,4 @@
-error[E0658]: use of unstable library feature 'autodiff'
+error[E0658]: use of unstable library feature `autodiff`
   --> $DIR/feature-gate-autodiff-use.rs:13:3
    |
 LL | #[autodiff(dfoo, Reverse)]
@@ -14,7 +14,7 @@ error: this rustc version does not support autodiff
 LL | #[autodiff(dfoo, Reverse)]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error[E0658]: use of unstable library feature 'autodiff'
+error[E0658]: use of unstable library feature `autodiff`
   --> $DIR/feature-gate-autodiff-use.rs:9:5
    |
 LL | use std::autodiff::autodiff;