Suggest using move when trying to share ...::channel::{Receiver, Sender}

Extend `rustc_on_unimplemented` to match on ADT without evaluating type
arguments.

Author: estebank

src/libcore/marker.rs

@@ -344,6 +344,14 @@ pub trait Copy : Clone {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[lang = "sync"]
 #[rustc_on_unimplemented(
+    on(
+        _Self="std::sync::mpsc::Receiver<T>",
+        label="`{Self}` cannot be shared safely, if using a closure consider marking it `move`"
+    ),
+    on(
+        _Self="std::sync::mpsc::Sender<T>",
+        label="`{Self}` cannot be shared safely, if using a closure consider marking it `move`"
+    ),
     message="`{Self}` cannot be shared between threads safely",
     label="`{Self}` cannot be shared between threads safely"
 )]

src/librustc/traits/error_reporting.rs

@@ -338,18 +338,15 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             .unwrap_or(trait_ref.def_id());
         let trait_ref = *trait_ref.skip_binder();
 
-        let desugaring;
-        let method;
         let mut flags = vec![];
-        let direct = match obligation.cause.code {
+        match obligation.cause.code {
             ObligationCauseCode::BuiltinDerivedObligation(..) |
-            ObligationCauseCode::ImplDerivedObligation(..) => false,
-            _ => true
-        };
-        if direct {
-            // this is a "direct", user-specified, rather than derived,
-            // obligation.
-            flags.push(("direct".to_string(), None));
+            ObligationCauseCode::ImplDerivedObligation(..) => {}
+            _ => {
+                // this is a "direct", user-specified, rather than derived,
+                // obligation.
+                flags.push(("direct".to_string(), None));
+            }
         }
 
         if let ObligationCauseCode::ItemObligation(item) = obligation.cause.code {
@@ -359,21 +356,27 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             //
             // Currently I'm leaving it for what I need for `try`.
             if self.tcx.trait_of_item(item) == Some(trait_ref.def_id) {
-                method = self.tcx.item_name(item);
+                let method = self.tcx.item_name(item);
                 flags.push(("from_method".to_string(), None));
                 flags.push(("from_method".to_string(), Some(method.to_string())));
             }
         }
 
         if let Some(k) = obligation.cause.span.compiler_desugaring_kind() {
-            desugaring = k.as_symbol().as_str();
+            let desugaring = k.as_symbol().as_str();
             flags.push(("from_desugaring".to_string(), None));
             flags.push(("from_desugaring".to_string(), Some(desugaring.to_string())));
         }
         let generics = self.tcx.generics_of(def_id);
         let self_ty = trait_ref.self_ty();
-        let self_ty_str = self_ty.to_string();
-        flags.push(("_Self".to_string(), Some(self_ty_str.clone())));
+        // This is also included through the generics list as `Self`,
+        // but the parser won't allow you to use it
+        flags.push(("_Self".to_string(), Some(self_ty.to_string())));
+        if let Some(def) = self_ty.ty_adt_def() {
+            // We also want to be able to select self's original
+            // signature with no type arguments resolved
+            flags.push(("_Self".to_string(), Some(self.tcx.type_of(def.did).to_string())));
+        }
 
         for param in generics.types.iter() {
             let name = param.name.as_str().to_string();

src/test/ui/closure-move-sync.rs

@@ -0,0 +1,32 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::thread;
+use std::sync::mpsc::channel;
+
+fn bar() {
+    let (send, recv) = channel();
+    let t = thread::spawn(|| {
+        recv.recv().unwrap();
+        //~^^ ERROR `std::sync::mpsc::Receiver<()>` cannot be shared between threads safely
+    });
+
+    send.send(());
+
+    t.join().unwrap();
+}
+
+fn foo() {
+    let (tx, _rx) = channel();
+    thread::spawn(|| tx.send(()).unwrap());
+    //~^ ERROR `std::sync::mpsc::Sender<()>` cannot be shared between threads safely
+}
+
+fn main() {}

src/test/ui/closure-move-sync.stderr

@@ -0,0 +1,24 @@
+error[E0277]: `std::sync::mpsc::Receiver<()>` cannot be shared between threads safely
+  --> $DIR/closure-move-sync.rs:16:13
+   |
+16 |     let t = thread::spawn(|| {
+   |             ^^^^^^^^^^^^^ `std::sync::mpsc::Receiver<()>` cannot be shared safely, if using a closure consider marking it `move`
+   |
+   = help: the trait `std::marker::Sync` is not implemented for `std::sync::mpsc::Receiver<()>`
+   = note: required because of the requirements on the impl of `std::marker::Send` for `&std::sync::mpsc::Receiver<()>`
+   = note: required because it appears within the type `[closure@$DIR/closure-move-sync.rs:16:27: 19:6 recv:&std::sync::mpsc::Receiver<()>]`
+   = note: required by `std::thread::spawn`
+
+error[E0277]: `std::sync::mpsc::Sender<()>` cannot be shared between threads safely
+  --> $DIR/closure-move-sync.rs:28:5
+   |
+28 |     thread::spawn(|| tx.send(()).unwrap());
+   |     ^^^^^^^^^^^^^ `std::sync::mpsc::Sender<()>` cannot be shared safely, if using a closure consider marking it `move`
+   |
+   = help: the trait `std::marker::Sync` is not implemented for `std::sync::mpsc::Sender<()>`
+   = note: required because of the requirements on the impl of `std::marker::Send` for `&std::sync::mpsc::Sender<()>`
+   = note: required because it appears within the type `[closure@$DIR/closure-move-sync.rs:28:19: 28:42 tx:&std::sync::mpsc::Sender<()>]`
+   = note: required by `std::thread::spawn`
+
+error: aborting due to 2 previous errors
+