Remove delay_as_bug for fn call with unsized Self that return Self.

Author: estebank

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

@@ -48,7 +48,7 @@ use rustc_middle::ty::{
 use rustc_middle::{bug, span_bug};
 use rustc_session::Limit;
 use rustc_span::def_id::LOCAL_CRATE;
-use rustc_span::symbol::{kw, sym};
+use rustc_span::symbol::sym;
 use rustc_span::{BytePos, ExpnKind, Span, Symbol, DUMMY_SP};
 use std::borrow::Cow;
 use std::fmt;
@@ -638,28 +638,6 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                             err.span_label(span, explanation);
                         }
 
-                        if Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait()
-                            && 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
-                            {
-                                // We expect the return type of an fn call is expected to be
-                                // `Sized`. In the test `trait-missing-dyn-in-qualified-path.rs`
-                                // under edition 2018, when writing `<Default>::default()`, we will
-                                // check both `dyn Default` and `<dyn Default>::default()` for
-                                // being `Sized`, but in every case where an associated function
-                                // like `Default::default` which returns `Self`, if the returned
-                                // value is `!Sized`, so will be the `Self`, so we'd always have
-                                // two redundat errors.
-                                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

@@ -68,7 +68,16 @@ 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: aborting due to 4 previous errors; 1 warning emitted
+error[E0277]: the size for values of type `dyn Default` cannot be known at compilation time
+  --> $DIR/trait-missing-dyn-in-qualified-path.rs:5:18
+   |
+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: the return type of a function must have a statically known size
+
+error: aborting due to 5 previous errors; 1 warning emitted
 
 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

@@ -8,6 +8,7 @@ fn main() {
     //[edition2018]~| WARNING this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021!
     //[edition2018]~| ERROR trait `Default` cannot be made into an object
     //[edition2018]~| ERROR trait `Default` cannot be made into an object
+    //[edition2018]~| ERROR the size for values of type `dyn Default` cannot be known at compilation time
     //[edition2018]~| ERROR mismatched types
     //[edition2018]~| ERROR the size for values of type `dyn Default` cannot be known at compilation time
 }