Auto merge of #65345 - davidtwco:issue-64130-async-send-sync-error-improvements, r=nikomatsakis

async/await: improve not-send errors, part 2

Part of #64130. Fixes #65667.

This PR improves the errors introduced in #64895 so that they have specialized messages for `Send` and `Sync`.

r? @nikomatsakis

Author: bors

src/libcore/marker.rs

@@ -29,6 +29,7 @@ use crate::hash::Hasher;
 /// [arc]: ../../std/sync/struct.Arc.html
 /// [ub]: ../../reference/behavior-considered-undefined.html
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "send_trait")]
 #[rustc_on_unimplemented(
     message="`{Self}` cannot be sent between threads safely",
     label="`{Self}` cannot be sent between threads safely"
@@ -440,6 +441,7 @@ pub macro Copy($item:item) { /* compiler built-in */ }
 /// [ub]: ../../reference/behavior-considered-undefined.html
 /// [transmute]: ../../std/mem/fn.transmute.html
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "sync_trait")]
 #[lang = "sync"]
 #[rustc_on_unimplemented(
     message="`{Self}` cannot be shared between threads safely",

src/librustc/traits/error_reporting.rs

@@ -498,10 +498,20 @@ impl Diagnostic {
         self
     }
 
+    pub fn clear_code(&mut self) -> &mut Self {
+        self.code = None;
+        self
+    }
+
     pub fn get_code(&self) -> Option<DiagnosticId> {
         self.code.clone()
     }
 
+    pub fn set_primary_message<M: Into<String>>(&mut self, msg: M) -> &mut Self {
+        self.message[0] = (msg.into(), Style::NoStyle);
+        self
+    }
+
     pub fn message(&self) -> String {
         self.message.iter().map(|i| i.0.as_str()).collect::<String>()
     }

src/librustc_errors/diagnostic.rs

@@ -26,7 +26,6 @@ pub fn from_generator<T: Generator<Yield = ()>>(x: T) -> impl Future<Output = T:
 #[doc(hidden)]
 #[unstable(feature = "gen_future", issue = "50547")]
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
-#[cfg_attr(not(test), rustc_diagnostic_item = "gen_future")]
 struct GenFuture<T: Generator<Yield = ()>>(T);
 
 // We rely on the fact that async/await futures are immovable in order to create

src/libstd/future.rs

@@ -660,6 +660,7 @@ symbols! {
         _Self,
         self_in_typedefs,
         self_struct_ctor,
+        send_trait,
         should_panic,
         simd,
         simd_extract,
@@ -697,6 +698,7 @@ symbols! {
         sty,
         sub_with_overflow,
         suggestion,
+        sync_trait,
         target_feature,
         target_has_atomic,
         target_has_atomic_load_store,

src/libsyntax_pos/symbol.rs

@@ -48,10 +48,10 @@ fn assert_send(_: impl Send) {}
 
 pub fn pass_assert() {
     assert_send(local_dropped_before_await());
-    //~^ ERROR `std::rc::Rc<()>` cannot be sent between threads safely
+    //~^ ERROR future cannot be sent between threads safely
     assert_send(non_send_temporary_in_match());
-    //~^ ERROR `std::rc::Rc<()>` cannot be sent between threads safely
+    //~^ ERROR future cannot be sent between threads safely
     assert_send(non_sync_with_method_call());
-    //~^ ERROR `dyn std::fmt::Write` cannot be sent between threads safely
-    //~^^ ERROR `*mut (dyn std::ops::Fn() + 'static)` cannot be shared between threads safely
+    //~^ ERROR future cannot be sent between threads safely
+    //~^^ ERROR future cannot be sent between threads safely
 }

src/test/ui/async-await/async-fn-nonsend.rs

@@ -1,79 +1,88 @@
-error[E0277]: `std::rc::Rc<()>` cannot be sent between threads safely
+error: future cannot be sent between threads safely
   --> $DIR/async-fn-nonsend.rs:50:5
    |
 LL | fn assert_send(_: impl Send) {}
    |    -----------         ---- required by this bound in `assert_send`
 ...
 LL |     assert_send(local_dropped_before_await());
-   |     ^^^^^^^^^^^ `std::rc::Rc<()>` cannot be sent between threads safely
+   |     ^^^^^^^^^^^ future returned by `local_dropped_before_await` is not `Send`
    |
    = help: within `impl std::future::Future`, the trait `std::marker::Send` is not implemented for `std::rc::Rc<()>`
-   = note: required because it appears within the type `impl std::fmt::Debug`
-   = note: required because it appears within the type `{impl std::fmt::Debug, impl std::future::Future, impl std::future::Future, ()}`
-   = note: required because it appears within the type `[static generator@$DIR/async-fn-nonsend.rs:21:39: 26:2 {impl std::fmt::Debug, impl std::future::Future, impl std::future::Future, ()}]`
-   = note: required because it appears within the type `std::future::GenFuture<[static generator@$DIR/async-fn-nonsend.rs:21:39: 26:2 {impl std::fmt::Debug, impl std::future::Future, impl std::future::Future, ()}]>`
-   = note: required because it appears within the type `impl std::future::Future`
-   = note: required because it appears within the type `impl std::future::Future`
+note: future is not `Send` as this value is used across an await
+  --> $DIR/async-fn-nonsend.rs:25:5
+   |
+LL |     let x = non_send();
+   |         - has type `impl std::fmt::Debug`
+LL |     drop(x);
+LL |     fut().await;
+   |     ^^^^^^^^^^^ await occurs here, with `x` maybe used later
+LL | }
+   | - `x` is later dropped here
 
-error[E0277]: `std::rc::Rc<()>` cannot be sent between threads safely
+error: future cannot be sent between threads safely
   --> $DIR/async-fn-nonsend.rs:52:5
    |
 LL | fn assert_send(_: impl Send) {}
    |    -----------         ---- required by this bound in `assert_send`
 ...
 LL |     assert_send(non_send_temporary_in_match());
-   |     ^^^^^^^^^^^ `std::rc::Rc<()>` cannot be sent between threads safely
+   |     ^^^^^^^^^^^ future returned by `non_send_temporary_in_match` is not `Send`
    |
    = help: within `impl std::future::Future`, the trait `std::marker::Send` is not implemented for `std::rc::Rc<()>`
-   = note: required because it appears within the type `impl std::fmt::Debug`
-   = note: required because it appears within the type `{impl std::fmt::Debug, std::option::Option<impl std::fmt::Debug>, impl std::future::Future, impl std::future::Future, ()}`
-   = note: required because it appears within the type `[static generator@$DIR/async-fn-nonsend.rs:28:40: 37:2 {impl std::fmt::Debug, std::option::Option<impl std::fmt::Debug>, impl std::future::Future, impl std::future::Future, ()}]`
-   = note: required because it appears within the type `std::future::GenFuture<[static generator@$DIR/async-fn-nonsend.rs:28:40: 37:2 {impl std::fmt::Debug, std::option::Option<impl std::fmt::Debug>, impl std::future::Future, impl std::future::Future, ()}]>`
-   = note: required because it appears within the type `impl std::future::Future`
-   = note: required because it appears within the type `impl std::future::Future`
+note: future is not `Send` as this value is used across an await
+  --> $DIR/async-fn-nonsend.rs:34:20
+   |
+LL |     match Some(non_send()) {
+   |                ---------- has type `impl std::fmt::Debug`
+LL |         Some(_) => fut().await,
+   |                    ^^^^^^^^^^^ await occurs here, with `non_send()` maybe used later
+...
+LL | }
+   | - `non_send()` is later dropped here
 
-error[E0277]: `dyn std::fmt::Write` cannot be sent between threads safely
+error: future cannot be sent between threads safely
   --> $DIR/async-fn-nonsend.rs:54:5
    |
 LL | fn assert_send(_: impl Send) {}
    |    -----------         ---- required by this bound in `assert_send`
 ...
 LL |     assert_send(non_sync_with_method_call());
-   |     ^^^^^^^^^^^ `dyn std::fmt::Write` cannot be sent between threads safely
+   |     ^^^^^^^^^^^ future returned by `non_sync_with_method_call` is not `Send`
    |
    = help: the trait `std::marker::Send` is not implemented for `dyn std::fmt::Write`
-   = note: required because of the requirements on the impl of `std::marker::Send` for `&mut dyn std::fmt::Write`
-   = note: required because it appears within the type `std::fmt::Formatter<'_>`
-   = note: required because of the requirements on the impl of `std::marker::Send` for `&mut std::fmt::Formatter<'_>`
-   = note: required because it appears within the type `for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, bool, impl std::future::Future, impl std::future::Future, ()}`
-   = note: required because it appears within the type `[static generator@$DIR/async-fn-nonsend.rs:39:38: 45:2 for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, bool, impl std::future::Future, impl std::future::Future, ()}]`
-   = note: required because it appears within the type `std::future::GenFuture<[static generator@$DIR/async-fn-nonsend.rs:39:38: 45:2 for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, bool, impl std::future::Future, impl std::future::Future, ()}]>`
-   = note: required because it appears within the type `impl std::future::Future`
-   = note: required because it appears within the type `impl std::future::Future`
+note: future is not `Send` as this value is used across an await
+  --> $DIR/async-fn-nonsend.rs:43:9
+   |
+LL |     let f: &mut std::fmt::Formatter = panic!();
+   |         - has type `&mut std::fmt::Formatter<'_>`
+LL |     if non_sync().fmt(f).unwrap() == () {
+LL |         fut().await;
+   |         ^^^^^^^^^^^ await occurs here, with `f` maybe used later
+LL |     }
+LL | }
+   | - `f` is later dropped here
 
-error[E0277]: `*mut (dyn std::ops::Fn() + 'static)` cannot be shared between threads safely
+error: future cannot be sent between threads safely
   --> $DIR/async-fn-nonsend.rs:54:5
    |
 LL | fn assert_send(_: impl Send) {}
    |    -----------         ---- required by this bound in `assert_send`
 ...
 LL |     assert_send(non_sync_with_method_call());
-   |     ^^^^^^^^^^^ `*mut (dyn std::ops::Fn() + 'static)` cannot be shared between threads safely
+   |     ^^^^^^^^^^^ future returned by `non_sync_with_method_call` is not `Send`
    |
    = help: within `std::fmt::ArgumentV1<'_>`, the trait `std::marker::Sync` is not implemented for `*mut (dyn std::ops::Fn() + 'static)`
-   = note: required because it appears within the type `std::marker::PhantomData<*mut (dyn std::ops::Fn() + 'static)>`
-   = note: required because it appears within the type `core::fmt::Void`
-   = note: required because it appears within the type `&core::fmt::Void`
-   = note: required because it appears within the type `std::fmt::ArgumentV1<'_>`
-   = note: required because of the requirements on the impl of `std::marker::Send` for `std::slice::Iter<'_, std::fmt::ArgumentV1<'_>>`
-   = note: required because it appears within the type `std::fmt::Formatter<'_>`
-   = note: required because of the requirements on the impl of `std::marker::Send` for `&mut std::fmt::Formatter<'_>`
-   = note: required because it appears within the type `for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, bool, impl std::future::Future, impl std::future::Future, ()}`
-   = note: required because it appears within the type `[static generator@$DIR/async-fn-nonsend.rs:39:38: 45:2 for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, bool, impl std::future::Future, impl std::future::Future, ()}]`
-   = note: required because it appears within the type `std::future::GenFuture<[static generator@$DIR/async-fn-nonsend.rs:39:38: 45:2 for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, bool, impl std::future::Future, impl std::future::Future, ()}]>`
-   = note: required because it appears within the type `impl std::future::Future`
-   = note: required because it appears within the type `impl std::future::Future`
+note: future is not `Send` as this value is used across an await
+  --> $DIR/async-fn-nonsend.rs:43:9
+   |
+LL |     let f: &mut std::fmt::Formatter = panic!();
+   |         - has type `&mut std::fmt::Formatter<'_>`
+LL |     if non_sync().fmt(f).unwrap() == () {
+LL |         fut().await;
+   |         ^^^^^^^^^^^ await occurs here, with `f` maybe used later
+LL |     }
+LL | }
+   | - `f` is later dropped here
 
 error: aborting due to 4 previous errors
 
-For more information about this error, try `rustc --explain E0277`.

src/test/ui/async-await/async-fn-nonsend.stderr

@@ -0,0 +1,23 @@
+#![feature(optin_builtin_traits)]
+// edition:2018
+
+// This tests the the specialized async-await-specific error when futures don't implement an
+// auto trait (which is specifically Sync) due to some type that was captured.
+
+struct Foo;
+
+impl !Sync for Foo {}
+
+fn is_sync<T: Sync>(t: T) { }
+
+async fn bar() {
+    let x = Foo;
+    baz().await;
+}
+
+async fn baz() { }
+
+fn main() {
+    is_sync(bar());
+    //~^ ERROR future cannot be shared between threads safely
+}

src/test/ui/async-await/issue-64130-1-sync.rs

@@ -0,0 +1,22 @@
+error: future cannot be shared between threads safely
+  --> $DIR/issue-64130-1-sync.rs:21:5
+   |
+LL | fn is_sync<T: Sync>(t: T) { }
+   |    -------    ---- required by this bound in `is_sync`
+...
+LL |     is_sync(bar());
+   |     ^^^^^^^ future returned by `bar` is not `Sync`
+   |
+   = help: within `impl std::future::Future`, the trait `std::marker::Sync` is not implemented for `Foo`
+note: future is not `Sync` as this value is used across an await
+  --> $DIR/issue-64130-1-sync.rs:15:5
+   |
+LL |     let x = Foo;
+   |         - has type `Foo`
+LL |     baz().await;
+   |     ^^^^^^^^^^^ await occurs here, with `x` maybe used later
+LL | }
+   | - `x` is later dropped here
+
+error: aborting due to previous error
+

src/test/ui/async-await/issue-64130-1-sync.stderr

@@ -0,0 +1,23 @@
+#![feature(optin_builtin_traits)]
+// edition:2018
+
+// This tests the the specialized async-await-specific error when futures don't implement an
+// auto trait (which is specifically Send) due to some type that was captured.
+
+struct Foo;
+
+impl !Send for Foo {}
+
+fn is_send<T: Send>(t: T) { }
+
+async fn bar() {
+    let x = Foo;
+    baz().await;
+}
+
+async fn baz() { }
+
+fn main() {
+    is_send(bar());
+    //~^ ERROR future cannot be sent between threads safely
+}

src/test/ui/async-await/issue-64130-2-send.rs

@@ -0,0 +1,22 @@
+error: future cannot be sent between threads safely
+  --> $DIR/issue-64130-2-send.rs:21:5
+   |
+LL | fn is_send<T: Send>(t: T) { }
+   |    -------    ---- required by this bound in `is_send`
+...
+LL |     is_send(bar());
+   |     ^^^^^^^ future returned by `bar` is not `Send`
+   |
+   = help: within `impl std::future::Future`, the trait `std::marker::Send` is not implemented for `Foo`
+note: future is not `Send` as this value is used across an await
+  --> $DIR/issue-64130-2-send.rs:15:5
+   |
+LL |     let x = Foo;
+   |         - has type `Foo`
+LL |     baz().await;
+   |     ^^^^^^^^^^^ await occurs here, with `x` maybe used later
+LL | }
+   | - `x` is later dropped here
+
+error: aborting due to previous error
+

src/test/ui/async-await/issue-64130-2-send.stderr

@@ -0,0 +1,25 @@
+#![feature(optin_builtin_traits)]
+// edition:2018
+
+// This tests the the unspecialized async-await-specific error when futures don't implement an
+// auto trait (which is not Send or Sync) due to some type that was captured.
+
+auto trait Qux { }
+
+struct Foo;
+
+impl !Qux for Foo {}
+
+fn is_qux<T: Qux>(t: T) { }
+
+async fn bar() {
+    let x = Foo;
+    baz().await;
+}
+
+async fn baz() { }
+
+fn main() {
+    is_qux(bar());
+    //~^ ERROR the trait bound `Foo: Qux` is not satisfied in `impl std::future::Future`
+}

src/test/ui/async-await/issue-64130-3-other.rs

@@ -0,0 +1,24 @@
+error[E0277]: the trait bound `Foo: Qux` is not satisfied in `impl std::future::Future`
+  --> $DIR/issue-64130-3-other.rs:23:5
+   |
+LL | fn is_qux<T: Qux>(t: T) { }
+   |    ------    --- required by this bound in `is_qux`
+...
+LL |     is_qux(bar());
+   |     ^^^^^^ within `impl std::future::Future`, the trait `Qux` is not implemented for `Foo`
+   |
+   = help: the following implementations were found:
+             <Foo as Qux>
+note: future does not implement `Qux` as this value is used across an await
+  --> $DIR/issue-64130-3-other.rs:17:5
+   |
+LL |     let x = Foo;
+   |         - has type `Foo`
+LL |     baz().await;
+   |     ^^^^^^^^^^^ await occurs here, with `x` maybe used later
+LL | }
+   | - `x` is later dropped here
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/async-await/issue-64130-3-other.stderr

@@ -0,0 +1,28 @@
+// edition:2018
+use std::any::Any;
+use std::future::Future;
+
+struct Client(Box<dyn Any + Send>);
+
+impl Client {
+    fn status(&self) -> u16 {
+        200
+    }
+}
+
+async fn get() { }
+
+pub fn foo() -> impl Future + Send {
+    //~^ ERROR future cannot be sent between threads safely
+    let client = Client(Box::new(true));
+    async move {
+        match client.status() {
+            200 => {
+                let _x = get().await;
+            },
+            _ => (),
+        }
+    }
+}
+
+fn main() {}