Rollup merge of #119239 - compiler-errors:yield-coercion, r=davidtwco

Remove unnecessary arm in `check_expr_yield`

We always set up the `resume_yield_tys` for async blocks and fns, so this arm was unreachable.

compiler/rustc_hir/src/hir.rs

@@ -2110,12 +2110,6 @@ pub enum YieldSource {
     Yield,
 }
 
-impl YieldSource {
-    pub fn is_await(&self) -> bool {
-        matches!(self, YieldSource::Await { .. })
-    }
-}
-
 impl fmt::Display for YieldSource {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.write_str(match self {

compiler/rustc_hir_typeck/src/expr.rs

@@ -349,7 +349,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             ExprKind::Index(base, idx, brackets_span) => {
                 self.check_expr_index(base, idx, expr, brackets_span)
             }
-            ExprKind::Yield(value, ref src) => self.check_expr_yield(value, expr, src),
+            ExprKind::Yield(value, _) => self.check_expr_yield(value, expr),
             hir::ExprKind::Err(guar) => Ty::new_error(tcx, guar),
         }
     }
@@ -3162,7 +3162,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         &self,
         value: &'tcx hir::Expr<'tcx>,
         expr: &'tcx hir::Expr<'tcx>,
-        src: &'tcx hir::YieldSource,
     ) -> Ty<'tcx> {
         match self.resume_yield_tys {
             Some((resume_ty, yield_ty)) => {
@@ -3170,14 +3169,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
                 resume_ty
             }
-            // Given that this `yield` expression was generated as a result of lowering a `.await`,
-            // we know that the yield type must be `()`; however, the context won't contain this
-            // information. Hence, we check the source of the yield expression here and check its
-            // value's type against `()` (this check should always hold).
-            None if src.is_await() => {
-                self.check_expr_coercible_to_type(value, Ty::new_unit(self.tcx), None);
-                Ty::new_unit(self.tcx)
-            }
             _ => {
                 self.dcx().emit_err(YieldExprOutsideOfCoroutine { span: expr.span });
                 // Avoid expressions without types during writeback (#78653).