Do not silence some sized errors as they would cause ICEs

Author: estebank

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -641,30 +641,21 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
 
                         if Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
                             if !self.tcx.object_safety_violations(trait_ref.def_id()).is_empty() {
-                                match (
-                                    obligation.cause.code(),
-                                    trait_ref.skip_binder().self_ty().kind(),
-                                ) {
-                                    (
-                                        ObligationCauseCode::WhereClauseInExpr(..),
-                                        ty::Dynamic(..),
-                                    ) => {
+                                if let ObligationCauseCode::SizedCallReturnType(did)
+                                    = obligation.cause.code()
+                                {
+                                    let fn_sig = self.tcx.fn_sig(did);
+                                    let ret_kind =
+                                        fn_sig.skip_binder().output().skip_binder().kind();
+                                    if let ty::Param(param_ty) = ret_kind
+                                        && param_ty.name == kw::SelfUpper
+                                    {
                                         return err.delay_as_bug();
                                     }
-                                    (ObligationCauseCode::SizedCallReturnType(did), _) => {
-                                        let fn_sig = self.tcx.fn_sig(did);
-                                        let ret_kind =
-                                            fn_sig.skip_binder().output().skip_binder().kind();
-                                        if let ty::Param(param_ty) = ret_kind
-                                            && param_ty.name == kw::SelfUpper
-                                        {
-                                            return err.delay_as_bug();
-                                        }
-                                    }
-                                    _ => {}
                                 }
                             }
                         }
+
                         if let ObligationCauseCode::Coercion { source, target } =
                             *obligation.cause.code().peel_derives()
                         {

tests/ui/dyn-keyword/trait-missing-dyn-in-qualified-path.edition2018.stderr

@@ -21,6 +21,16 @@ LL |     let x: u32 = <Default>::default();
    = note: the trait cannot be made into an object because it requires `Self: Sized`
    = note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
 
+error[E0277]: the size for values of type `dyn Default` cannot be known at compilation time
+  --> $DIR/trait-missing-dyn-in-qualified-path.rs:5:19
+   |
+LL |     let x: u32 = <Default>::default();
+   |                   ^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `dyn Default`
+note: required by a bound in `default`
+  --> $SRC_DIR/core/src/default.rs:LL:COL
+
 error[E0308]: mismatched types
   --> $DIR/trait-missing-dyn-in-qualified-path.rs:5:18
    |
@@ -42,7 +52,7 @@ LL |     let x: u32 = <Default>::default();
    = note: the trait cannot be made into an object because it requires `Self: Sized`
    = note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
 
-error: aborting due to 3 previous errors; 1 warning emitted
+error: aborting due to 4 previous errors; 1 warning emitted
 
-Some errors have detailed explanations: E0038, E0308.
+Some errors have detailed explanations: E0038, E0277, E0308.
 For more information about an error, try `rustc --explain E0038`.

tests/ui/dyn-keyword/trait-missing-dyn-in-qualified-path.rs

@@ -9,4 +9,5 @@ fn main() {
     //[edition2018]~| ERROR trait `Default` cannot be made into an object
     //[edition2018]~| ERROR trait `Default` cannot be made into an object
     //[edition2018]~| ERROR mismatched types
+    //[edition2018]~| ERROR the size for values of type `dyn Default` cannot be known at compilation time
 }

tests/ui/traits/bad-sized.rs

@@ -5,4 +5,5 @@ pub fn main() {
     //~^ ERROR only auto traits can be used as additional traits in a trait object
     //~| ERROR the size for values of type
     //~| ERROR the size for values of type
+    //~| ERROR the size for values of type
 }

tests/ui/traits/bad-sized.stderr

@@ -19,6 +19,16 @@ LL |     let x: Vec<dyn Trait + Sized> = Vec::new();
 note: required by an implicit `Sized` bound in `Vec`
   --> $SRC_DIR/alloc/src/vec/mod.rs:LL:COL
 
+error[E0277]: the size for values of type `dyn Trait` cannot be known at compilation time
+  --> $DIR/bad-sized.rs:4:37
+   |
+LL |     let x: Vec<dyn Trait + Sized> = Vec::new();
+   |                                     ^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `dyn Trait`
+note: required by a bound in `Vec::<T>::new`
+  --> $SRC_DIR/alloc/src/vec/mod.rs:LL:COL
+
 error[E0277]: the size for values of type `dyn Trait` cannot be known at compilation time
   --> $DIR/bad-sized.rs:4:37
    |
@@ -29,7 +39,7 @@ LL |     let x: Vec<dyn Trait + Sized> = Vec::new();
 note: required by an implicit `Sized` bound in `Vec`
   --> $SRC_DIR/alloc/src/vec/mod.rs:LL:COL
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
 
 Some errors have detailed explanations: E0225, E0277.
 For more information about an error, try `rustc --explain E0225`.