Improve span label

Author: tmandry

src/librustc_trait_selection/traits/error_reporting/suggestions.rs

@@ -10,7 +10,7 @@ use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::Visitor;
-use rustc_hir::Node;
+use rustc_hir::{GeneratorKind, AsyncGeneratorKind, Node};
 use rustc_middle::ty::TypeckTables;
 use rustc_middle::ty::{
     self, AdtKind, DefIdTree, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
@@ -1204,15 +1204,23 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             let original_span = err.span.primary_span().unwrap();
             let mut span = MultiSpan::from_span(original_span);
 
-            let message = if let Some(name) = outer_generator
-                .and_then(|generator_did| self.tcx.parent(generator_did))
-                .and_then(|parent_did| hir.as_local_hir_id(parent_did))
-                .and_then(|parent_hir_id| hir.opt_name(parent_hir_id))
-            {
-                format!("future returned by `{}` is not {}", name, trait_name)
-            } else {
-                format!("future is not {}", trait_name)
-            };
+            let message = outer_generator
+                .and_then(|generator_did| Some(
+                    match self.tcx.generator_kind(generator_did).unwrap() {
+                        GeneratorKind::Gen => format!("generator is not {}", trait_name),
+                        GeneratorKind::Async(AsyncGeneratorKind::Fn) =>
+                            self.tcx.parent(generator_did)
+                                .and_then(|parent_did| hir.as_local_hir_id(parent_did))
+                                .and_then(|parent_hir_id| hir.opt_name(parent_hir_id))
+                                .map(|name| format!("future returned by `{}` is not {}",
+                                                    name, trait_name))?,
+                        GeneratorKind::Async(AsyncGeneratorKind::Block) =>
+                            format!("future created by async block is not {}", trait_name),
+                        GeneratorKind::Async(AsyncGeneratorKind::Closure) =>
+                            format!("future created by async closure is not {}", trait_name),
+                    }
+                ))
+                .unwrap_or_else(|| format!("future is not {}", trait_name));
 
             span.push_span_label(original_span, message);
             err.set_span(span);

src/test/ui/async-await/issue-64130-4-async-move.stderr

@@ -2,7 +2,7 @@ error: future cannot be sent between threads safely
   --> $DIR/issue-64130-4-async-move.rs:15:17
    |
 LL |   pub fn foo() -> impl Future + Send {
-   |                   ^^^^^^^^^^^^^^^^^^ future returned by `foo` is not `Send`
+   |                   ^^^^^^^^^^^^^^^^^^ future created by async block is not `Send`
 ...
 LL | /     async move {
 LL | |         match client.status() {

src/test/ui/async-await/issue-67252-unnamed-future.stderr

@@ -5,7 +5,7 @@ LL | fn spawn<T: Send>(_: T) {}
    |    -----    ---- required by this bound in `spawn`
 ...
 LL |     spawn(async {
-   |     ^^^^^ future is not `Send`
+   |     ^^^^^ future created by async block is not `Send`
    |
    = help: within `impl std::future::Future`, the trait `std::marker::Send` is not implemented for `*mut ()`
 note: future is not `Send` as this value is used across an await

src/test/ui/async-await/issue-68112.stderr

@@ -5,7 +5,7 @@ LL | fn require_send(_: impl Send) {}
    |    ------------         ---- required by this bound in `require_send`
 ...
 LL |     require_send(send_fut);
-   |     ^^^^^^^^^^^^ future returned by `test1` is not `Send`
+   |     ^^^^^^^^^^^^ future created by async block is not `Send`
    |
    = help: the trait `std::marker::Sync` is not implemented for `std::cell::RefCell<i32>`
 note: future is not `Send` as this value is used across an await

src/test/ui/async-await/issues/issue-65436-raw-ptr-not-send.stderr

@@ -5,7 +5,7 @@ LL | fn assert_send<T: Send>(_: T) {}
    |    -----------    ---- required by this bound in `assert_send`
 ...
 LL |     assert_send(async {
-   |     ^^^^^^^^^^^ future returned by `main` is not `Send`
+   |     ^^^^^^^^^^^ future created by async block is not `Send`
    |
    = help: within `impl std::future::Future`, the trait `std::marker::Send` is not implemented for `*const u8`
 note: future is not `Send` as this value is used across an await

src/test/ui/generator/issue-68112.stderr

@@ -5,7 +5,7 @@ LL | fn require_send(_: impl Send) {}
    |    ------------         ---- required by this bound in `require_send`
 ...
 LL |     require_send(send_gen);
-   |     ^^^^^^^^^^^^ future returned by `test1` is not `Send`
+   |     ^^^^^^^^^^^^ generator is not `Send`
    |
    = help: the trait `std::marker::Sync` is not implemented for `std::cell::RefCell<i32>`
 note: future is not `Send` as this value is used across an yield

src/test/ui/generator/not-send-sync.stderr

@@ -18,7 +18,7 @@ LL |     fn assert_sync<T: Sync>(_: T) {}
    |        -----------    ---- required by this bound in `main::assert_sync`
 ...
 LL |     assert_sync(|| {
-   |     ^^^^^^^^^^^ future returned by `main` is not `Sync`
+   |     ^^^^^^^^^^^ generator is not `Sync`
    |
    = help: within `[generator@$DIR/not-send-sync.rs:9:17: 13:6 {std::cell::Cell<i32>, ()}]`, the trait `std::marker::Sync` is not implemented for `std::cell::Cell<i32>`
 note: future is not `Sync` as this value is used across an yield