Make Option<&dyn FnMut> into impl FnOnce

compiler/rustc_hir_typeck/src/_match.rs

@@ -136,9 +136,7 @@ pub fn check_match(
                 &cause,
                 Some(&arm.body),
                 arm_ty,
-                Some(&mut |err| {
-                    self.suggest_removing_semicolon_for_coerce(err, expr, arm_ty, prior_arm)
-                }),
+                |err| self.suggest_removing_semicolon_for_coerce(err, expr, arm_ty, prior_arm),
                 false,
             );
 
@@ -269,7 +267,7 @@ pub(super) fn if_fallback_coercion<T>(
         coercion.coerce_forced_unit(
             self,
             &cause,
-            &mut |err| {
+            |err| {
                 if let Some((span, msg)) = &ret_reason {
                     err.span_label(*span, msg.clone());
                 } else if let ExprKind::Block(block, _) = &then_expr.kind

compiler/rustc_hir_typeck/src/coercion.rs

@@ -1418,7 +1418,7 @@ pub fn coerce<'a>(
         expression: &'tcx hir::Expr<'tcx>,
         expression_ty: Ty<'tcx>,
     ) {
-        self.coerce_inner(fcx, cause, Some(expression), expression_ty, None, false)
+        self.coerce_inner(fcx, cause, Some(expression), expression_ty, |_| {}, false)
     }
 
     /// Indicates that one of the inputs is a "forced unit". This
@@ -1437,7 +1437,7 @@ pub fn coerce_forced_unit<'a>(
         &mut self,
         fcx: &FnCtxt<'a, 'tcx>,
         cause: &ObligationCause<'tcx>,
-        augment_error: &mut dyn FnMut(&mut Diagnostic),
+        augment_error: impl FnOnce(&mut Diagnostic),
         label_unit_as_expected: bool,
     ) {
         self.coerce_inner(
@@ -1445,7 +1445,7 @@ pub fn coerce_forced_unit<'a>(
             cause,
             None,
             Ty::new_unit(fcx.tcx),
-            Some(augment_error),
+            augment_error,
             label_unit_as_expected,
         )
     }
@@ -1460,7 +1460,7 @@ pub(crate) fn coerce_inner<'a>(
         cause: &ObligationCause<'tcx>,
         expression: Option<&'tcx hir::Expr<'tcx>>,
         mut expression_ty: Ty<'tcx>,
-        augment_error: Option<&mut dyn FnMut(&mut Diagnostic)>,
+        augment_error: impl FnOnce(&mut Diagnostic),
         label_expression_as_expected: bool,
     ) {
         // Incorporate whatever type inference information we have
@@ -1639,9 +1639,7 @@ pub(crate) fn coerce_inner<'a>(
                     }
                 }
 
-                if let Some(augment_error) = augment_error {
-                    augment_error(&mut err);
-                }
+                augment_error(&mut err);
 
                 let is_insufficiently_polymorphic =
                     matches!(coercion_error, TypeError::RegionsInsufficientlyPolymorphic(..));

compiler/rustc_hir_typeck/src/expr.rs

@@ -652,7 +652,7 @@ fn check_expr_break(
                     coerce.coerce_forced_unit(
                         self,
                         &cause,
-                        &mut |mut err| {
+                        |mut err| {
                             self.suggest_mismatched_types_on_tail(
                                 &mut err, expr, ty, e_ty, target_id,
                             );
@@ -748,7 +748,7 @@ fn check_expr_return(
                 coercion.coerce_forced_unit(
                     self,
                     &cause,
-                    &mut |db| {
+                    |db| {
                         let span = fn_decl.output.span();
                         if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
                             db.span_label(
@@ -760,7 +760,7 @@ fn check_expr_return(
                     true,
                 );
             } else {
-                coercion.coerce_forced_unit(self, &cause, &mut |_| (), true);
+                coercion.coerce_forced_unit(self, &cause, |_| (), true);
             }
         }
         self.tcx.types.never

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -1587,9 +1587,9 @@ pub(in super::super) fn check_block_with_expected(
                     &cause,
                     Some(tail_expr),
                     tail_expr_ty,
-                    Some(&mut |diag: &mut Diagnostic| {
+                    |diag| {
                         self.suggest_block_to_brackets(diag, blk, tail_expr_ty, ty_for_diagnostic);
-                    }),
+                    },
                     false,
                 );
             } else {
@@ -1626,7 +1626,7 @@ pub(in super::super) fn check_block_with_expected(
                     coerce.coerce_forced_unit(
                         self,
                         &self.misc(sp),
-                        &mut |err| {
+                        |err| {
                             if let Some(expected_ty) = expected.only_has_type(self) {
                                 if blk.stmts.is_empty() && blk.expr.is_none() {
                                     self.suggest_boxing_when_appropriate(