Check that main/start is not async

* Add new error code E0752
* Add span to hir::IsAsync::Yes
* Emit an error if main or the start function is marked as async
* Add two regression tests

Fix formatting errors and bless test outputs
* move tests to ui/async-await

fix test error text

remove span from IsAsync

2 files changed, 7 insertions, 12 deletions

diff --git a/src/librustc_trait_selection/traits/error_reporting/on_unimplemented.rs b/src/librustc_trait_selection/traits/error_reporting/on_unimplemented.rs
index 1ecc7fdafc4..3b6c741b890 100644
--- a/src/librustc_trait_selection/traits/error_reporting/on_unimplemented.rs
+++ b/src/librustc_trait_selection/traits/error_reporting/on_unimplemented.rs
@@ -82,10 +82,9 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         match &node {
             hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, _, body_id), .. }) => {
                 self.describe_generator(*body_id).or_else(|| {
-                    Some(if let hir::FnHeader { asyncness: hir::IsAsync::Async, .. } = sig.header {
-                        "an async function"
-                    } else {
-                        "a function"
+                    Some(match sig.header {
+                        hir::FnHeader { asyncness: hir::IsAsync::Async, .. } => "an async function",
+                        _ => "a function",
                     })
                 })
             }
@@ -97,10 +96,9 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 kind: hir::ImplItemKind::Fn(sig, body_id),
                 ..
             }) => self.describe_generator(*body_id).or_else(|| {
-                Some(if let hir::FnHeader { asyncness: hir::IsAsync::Async, .. } = sig.header {
-                    "an async method"
-                } else {
-                    "a method"
+                Some(match sig.header {
+                    hir::FnHeader { asyncness: hir::IsAsync::Async, .. } => "an async method",
+                    _ => "a method",
                 })
             }),
             hir::Node::Expr(hir::Expr {
diff --git a/src/librustc_trait_selection/traits/error_reporting/suggestions.rs b/src/librustc_trait_selection/traits/error_reporting/suggestions.rs
index 254db6cb869..982ceec7dca 100644
--- a/src/librustc_trait_selection/traits/error_reporting/suggestions.rs
+++ b/src/librustc_trait_selection/traits/error_reporting/suggestions.rs
@@ -1313,10 +1313,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
 
         let is_async = inner_generator_body
             .and_then(|body| body.generator_kind())
-            .map(|generator_kind| match generator_kind {
-                hir::GeneratorKind::Async(..) => true,
-                _ => false,
-            })
+            .map(|generator_kind| matches!(generator_kind, hir::GeneratorKind::Async(..)))
             .unwrap_or(false);
         let (await_or_yield, an_await_or_yield) =
             if is_async { ("await", "an await") } else { ("yield", "a yield") };