Auto merge of #79576 - m-ou-se:2021, r=Mark-Simulacrum

Add edition 2021.

:fireworks: Happy new ~~year~~ Rust. :champagne:

This adds --edition=2021, and updates suggestions about 2018 to say "2018 *or later*".

Related Cargo PR: https://github.com/rust-lang/cargo/pull/8922

---

Edit: This adds the new edition as *unstable*. Without `-Z unstable-options`, `--edition=2021` results in:
```
$ rustc --edition=2021
error: edition 2021 is unstable and only available with -Z unstable-options.
```

7 files changed, 49 insertions, 42 deletions

diff --git a/src/test/ui/async-await/edition-deny-async-fns-2015.rs b/src/test/ui/async-await/edition-deny-async-fns-2015.rs
index 5d2d186137e..e5dc9c8a5fe 100644
--- a/src/test/ui/async-await/edition-deny-async-fns-2015.rs
+++ b/src/test/ui/async-await/edition-deny-async-fns-2015.rs
@@ -1,21 +1,21 @@
 // edition:2015
 
-async fn foo() {} //~ ERROR `async fn` is not permitted in the 2015 edition
+async fn foo() {} //~ ERROR `async fn` is not permitted in Rust 2015
 
-fn baz() { async fn foo() {} } //~ ERROR `async fn` is not permitted in the 2015 edition
+fn baz() { async fn foo() {} } //~ ERROR `async fn` is not permitted in Rust 2015
 
-async fn async_baz() { //~ ERROR `async fn` is not permitted in the 2015 edition
-    async fn bar() {} //~ ERROR `async fn` is not permitted in the 2015 edition
+async fn async_baz() { //~ ERROR `async fn` is not permitted in Rust 2015
+    async fn bar() {} //~ ERROR `async fn` is not permitted in Rust 2015
 }
 
 struct Foo {}
 
 impl Foo {
-    async fn foo() {} //~ ERROR `async fn` is not permitted in the 2015 edition
+    async fn foo() {} //~ ERROR `async fn` is not permitted in Rust 2015
 }
 
 trait Bar {
-    async fn foo() {} //~ ERROR `async fn` is not permitted in the 2015 edition
+    async fn foo() {} //~ ERROR `async fn` is not permitted in Rust 2015
                       //~^ ERROR functions in traits cannot be declared `async`
 }
 
@@ -23,16 +23,16 @@ fn main() {
     macro_rules! accept_item { ($x:item) => {} }
 
     accept_item! {
-        async fn foo() {} //~ ERROR `async fn` is not permitted in the 2015 edition
+        async fn foo() {} //~ ERROR `async fn` is not permitted in Rust 2015
     }
 
     accept_item! {
         impl Foo {
-            async fn bar() {} //~ ERROR `async fn` is not permitted in the 2015 edition
+            async fn bar() {} //~ ERROR `async fn` is not permitted in Rust 2015
         }
     }
 
     let inside_closure = || {
-        async fn bar() {} //~ ERROR `async fn` is not permitted in the 2015 edition
+        async fn bar() {} //~ ERROR `async fn` is not permitted in Rust 2015
     };
 }
diff --git a/src/test/ui/async-await/edition-deny-async-fns-2015.stderr b/src/test/ui/async-await/edition-deny-async-fns-2015.stderr
index 8bffeb2131d..43364a8e858 100644
--- a/src/test/ui/async-await/edition-deny-async-fns-2015.stderr
+++ b/src/test/ui/async-await/edition-deny-async-fns-2015.stderr
@@ -1,80 +1,80 @@
-error[E0670]: `async fn` is not permitted in the 2015 edition
+error[E0670]: `async fn` is not permitted in Rust 2015
   --> $DIR/edition-deny-async-fns-2015.rs:3:1
    |
 LL | async fn foo() {}
-   | ^^^^^ to use `async fn`, switch to Rust 2018
+   | ^^^^^ to use `async fn`, switch to Rust 2018 or later
    |
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
-error[E0670]: `async fn` is not permitted in the 2015 edition
+error[E0670]: `async fn` is not permitted in Rust 2015
   --> $DIR/edition-deny-async-fns-2015.rs:5:12
    |
 LL | fn baz() { async fn foo() {} }
-   |            ^^^^^ to use `async fn`, switch to Rust 2018
+   |            ^^^^^ to use `async fn`, switch to Rust 2018 or later
    |
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
-error[E0670]: `async fn` is not permitted in the 2015 edition
+error[E0670]: `async fn` is not permitted in Rust 2015
   --> $DIR/edition-deny-async-fns-2015.rs:7:1
    |
 LL | async fn async_baz() {
-   | ^^^^^ to use `async fn`, switch to Rust 2018
+   | ^^^^^ to use `async fn`, switch to Rust 2018 or later
    |
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
-error[E0670]: `async fn` is not permitted in the 2015 edition
+error[E0670]: `async fn` is not permitted in Rust 2015
   --> $DIR/edition-deny-async-fns-2015.rs:8:5
    |
 LL |     async fn bar() {}
-   |     ^^^^^ to use `async fn`, switch to Rust 2018
+   |     ^^^^^ to use `async fn`, switch to Rust 2018 or later
    |
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
-error[E0670]: `async fn` is not permitted in the 2015 edition
+error[E0670]: `async fn` is not permitted in Rust 2015
   --> $DIR/edition-deny-async-fns-2015.rs:14:5
    |
 LL |     async fn foo() {}
-   |     ^^^^^ to use `async fn`, switch to Rust 2018
+   |     ^^^^^ to use `async fn`, switch to Rust 2018 or later
    |
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
-error[E0670]: `async fn` is not permitted in the 2015 edition
+error[E0670]: `async fn` is not permitted in Rust 2015
   --> $DIR/edition-deny-async-fns-2015.rs:18:5
    |
 LL |     async fn foo() {}
-   |     ^^^^^ to use `async fn`, switch to Rust 2018
+   |     ^^^^^ to use `async fn`, switch to Rust 2018 or later
    |
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
-error[E0670]: `async fn` is not permitted in the 2015 edition
+error[E0670]: `async fn` is not permitted in Rust 2015
   --> $DIR/edition-deny-async-fns-2015.rs:36:9
    |
 LL |         async fn bar() {}
-   |         ^^^^^ to use `async fn`, switch to Rust 2018
+   |         ^^^^^ to use `async fn`, switch to Rust 2018 or later
    |
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
-error[E0670]: `async fn` is not permitted in the 2015 edition
+error[E0670]: `async fn` is not permitted in Rust 2015
   --> $DIR/edition-deny-async-fns-2015.rs:26:9
    |
 LL |         async fn foo() {}
-   |         ^^^^^ to use `async fn`, switch to Rust 2018
+   |         ^^^^^ to use `async fn`, switch to Rust 2018 or later
    |
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
-error[E0670]: `async fn` is not permitted in the 2015 edition
+error[E0670]: `async fn` is not permitted in Rust 2015
   --> $DIR/edition-deny-async-fns-2015.rs:31:13
    |
 LL |             async fn bar() {}
-   |             ^^^^^ to use `async fn`, switch to Rust 2018
+   |             ^^^^^ to use `async fn`, switch to Rust 2018 or later
    |
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
diff --git a/src/test/ui/async-await/suggest-switching-edition-on-await.stderr b/src/test/ui/async-await/suggest-switching-edition-on-await.stderr
index 695d7dd59fb..9ac2bc5cc89 100644
--- a/src/test/ui/async-await/suggest-switching-edition-on-await.stderr
+++ b/src/test/ui/async-await/suggest-switching-edition-on-await.stderr
@@ -4,7 +4,7 @@ error[E0609]: no field `await` on type `await_on_struct_missing::S`
 LL |     x.await;
    |       ^^^^^ unknown field
    |
-   = note: to `.await` a `Future`, switch to Rust 2018
+   = note: to `.await` a `Future`, switch to Rust 2018 or later
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
@@ -14,7 +14,7 @@ error[E0609]: no field `await` on type `await_on_struct_similar::S`
 LL |     x.await;
    |       ^^^^^ help: a field with a similar name exists: `awai`
    |
-   = note: to `.await` a `Future`, switch to Rust 2018
+   = note: to `.await` a `Future`, switch to Rust 2018 or later
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
@@ -24,7 +24,7 @@ error[E0609]: no field `await` on type `Pin<&mut dyn Future<Output = ()>>`
 LL |     x.await;
    |       ^^^^^ unknown field
    |
-   = note: to `.await` a `Future`, switch to Rust 2018
+   = note: to `.await` a `Future`, switch to Rust 2018 or later
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
@@ -34,7 +34,7 @@ error[E0609]: no field `await` on type `impl Future<Output = ()>`
 LL |     x.await;
    |       ^^^^^
    |
-   = note: to `.await` a `Future`, switch to Rust 2018
+   = note: to `.await` a `Future`, switch to Rust 2018 or later
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
diff --git a/src/test/ui/editions/async-block-2015.rs b/src/test/ui/editions/async-block-2015.rs
index 985606a6f25..92eae9e3c14 100644
--- a/src/test/ui/editions/async-block-2015.rs
+++ b/src/test/ui/editions/async-block-2015.rs
@@ -1,13 +1,13 @@
 async fn foo() {
-//~^ ERROR `async fn` is not permitted in the 2015 edition
-//~| NOTE to use `async fn`, switch to Rust 2018
+//~^ ERROR `async fn` is not permitted in Rust 2015
+//~| NOTE to use `async fn`, switch to Rust 2018 or later
 //~| HELP set `edition = "2018"` in `Cargo.toml`
 //~| NOTE for more on editions, read https://doc.rust-lang.org/edition-guide
 
     let x = async {};
     //~^ ERROR cannot find struct, variant or union type `async` in this scope
-    //~| NOTE `async` blocks are only allowed in the 2018 edition
-    let y = async { //~ NOTE `async` blocks are only allowed in the 2018 edition
+    //~| NOTE `async` blocks are only allowed in Rust 2018 or later
+    let y = async { //~ NOTE `async` blocks are only allowed in Rust 2018 or later
         let x = 42;
         //~^ ERROR expected identifier, found keyword `let`
         //~| NOTE expected identifier, found keyword
@@ -15,7 +15,7 @@ async fn foo() {
         //~| NOTE for more on editions, read https://doc.rust-lang.org/edition-guide
         42
     };
-    let z = async { //~ NOTE `async` blocks are only allowed in the 2018 edition
+    let z = async { //~ NOTE `async` blocks are only allowed in Rust 2018 or later
         42
         //~^ ERROR expected identifier, found `42`
         //~| NOTE expected identifier
diff --git a/src/test/ui/editions/async-block-2015.stderr b/src/test/ui/editions/async-block-2015.stderr
index 8e5e5d8bfab..e42747c804c 100644
--- a/src/test/ui/editions/async-block-2015.stderr
+++ b/src/test/ui/editions/async-block-2015.stderr
@@ -1,8 +1,8 @@
-error[E0670]: `async fn` is not permitted in the 2015 edition
+error[E0670]: `async fn` is not permitted in Rust 2015
   --> $DIR/async-block-2015.rs:1:1
    |
 LL | async fn foo() {
-   | ^^^^^ to use `async fn`, switch to Rust 2018
+   | ^^^^^ to use `async fn`, switch to Rust 2018 or later
    |
    = help: set `edition = "2018"` in `Cargo.toml`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
@@ -11,7 +11,7 @@ error: expected identifier, found keyword `let`
   --> $DIR/async-block-2015.rs:11:9
    |
 LL |     let y = async {
-   |             ----- `async` blocks are only allowed in the 2018 edition
+   |             ----- `async` blocks are only allowed in Rust 2018 or later
 LL |         let x = 42;
    |         ^^^ expected identifier, found keyword
    |
@@ -22,7 +22,7 @@ error: expected identifier, found `42`
   --> $DIR/async-block-2015.rs:19:9
    |
 LL |     let z = async {
-   |             ----- `async` blocks are only allowed in the 2018 edition
+   |             ----- `async` blocks are only allowed in Rust 2018 or later
 LL |         42
    |         ^^ expected identifier
    |
@@ -33,7 +33,7 @@ error[E0422]: cannot find struct, variant or union type `async` in this scope
   --> $DIR/async-block-2015.rs:7:13
    |
 LL |     let x = async {};
-   |             ^^^^^ `async` blocks are only allowed in the 2018 edition
+   |             ^^^^^ `async` blocks are only allowed in Rust 2018 or later
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/hello2021.rs b/src/test/ui/hello2021.rs
new file mode 100644
index 00000000000..738f151b0f6
--- /dev/null
+++ b/src/test/ui/hello2021.rs
@@ -0,0 +1,7 @@
+// run-pass
+// edition:2021
+// compile-flags: -Zunstable-options
+
+fn main() {
+    println!("hello, 2021");
+}
diff --git a/src/test/ui/try-block/try-block-in-edition2015.stderr b/src/test/ui/try-block/try-block-in-edition2015.stderr
index 78cdfb2cc7f..0f3c14b1386 100644
--- a/src/test/ui/try-block/try-block-in-edition2015.stderr
+++ b/src/test/ui/try-block/try-block-in-edition2015.stderr
@@ -13,7 +13,7 @@ error[E0574]: expected struct, variant or union type, found macro `try`
 LL |     let try_result: Option<_> = try {
    |                                 ^^^ not a struct, variant or union type
    |
-   = note: if you want the `try` keyword, you need to be in the 2018 edition
+   = note: if you want the `try` keyword, you need Rust 2018 or later
 help: use `!` to invoke the macro
    |
 LL |     let try_result: Option<_> = try! {