Dont create trait object if it has errors in it

compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs

@@ -8,7 +8,8 @@ use rustc_lint_defs::builtin::UNUSED_ASSOCIATED_TYPE_BOUNDS;
 use rustc_middle::span_bug;
 use rustc_middle::ty::fold::BottomUpFolder;
 use rustc_middle::ty::{
-    self, DynKind, ExistentialPredicateStableCmpExt as _, Ty, TyCtxt, TypeFoldable, Upcast,
+    self, DynKind, ExistentialPredicateStableCmpExt as _, Ty, TyCtxt, TypeFoldable,
+    TypeVisitableExt, Upcast,
 };
 use rustc_span::{ErrorGuaranteed, Span};
 use rustc_trait_selection::error_reporting::traits::report_dyn_incompatibility;
@@ -103,6 +104,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             let guar = self.report_trait_object_with_no_traits_error(span, &trait_bounds);
             return Ty::new_error(tcx, guar);
         }
+        // Don't create a dyn trait if we have errors in the principal.
+        if let Err(guar) = trait_bounds.error_reported() {
+            return Ty::new_error(tcx, guar);
+        }
 
         // Check that there are no gross dyn-compatibility violations;
         // most importantly, that the supertraits don't contain `Self`,

tests/crashes/130521.rs

@@ -1,7 +1,7 @@
 //@ known-bug: #130521
 
 #![feature(dyn_compatible_for_dispatch)]
-struct Vtable(dyn Cap);
+struct Vtable(dyn Cap<'static>);
 
 trait Cap<'a> {}
 

tests/rustdoc-ui/unable-fulfill-trait.rs

@@ -3,7 +3,6 @@
 pub struct Foo<'a, 'b, T> {
     field1: dyn Bar<'a, 'b>,
     //~^ ERROR
-    //~| ERROR
 }
 
 pub trait Bar<'x, 's, U>

tests/rustdoc-ui/unable-fulfill-trait.stderr

@@ -14,13 +14,6 @@ help: add missing generic argument
 LL |     field1: dyn Bar<'a, 'b, U>,
    |                           +++
 
-error[E0227]: ambiguous lifetime bound, explicit lifetime bound required
-  --> $DIR/unable-fulfill-trait.rs:4:13
-   |
-LL |     field1: dyn Bar<'a, 'b>,
-   |             ^^^^^^^^^^^^^^^
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0107, E0227.
-For more information about an error, try `rustc --explain E0107`.
+For more information about this error, try `rustc --explain E0107`.

tests/ui/const-generics/not_wf_param_in_rpitit.rs

@@ -3,9 +3,6 @@
 trait Trait<const N: dyn Trait = bar> {
     //~^ ERROR: cannot find value `bar` in this scope
     //~| ERROR: cycle detected when computing type of `Trait::N`
-    //~| ERROR: the trait `Trait` cannot be made into an object
-    //~| ERROR: the trait `Trait` cannot be made into an object
-    //~| ERROR: the trait `Trait` cannot be made into an object
     async fn a() {}
 }
 

tests/ui/const-generics/not_wf_param_in_rpitit.stderr

@@ -18,77 +18,7 @@ LL | trait Trait<const N: dyn Trait = bar> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
 
-error[E0038]: the trait `Trait` cannot be made into an object
-  --> $DIR/not_wf_param_in_rpitit.rs:3:22
-   |
-LL | trait Trait<const N: dyn Trait = bar> {
-   |                      ^^^^^^^^^ `Trait` cannot be made into an object
-   |
-note: for a trait to be "dyn-compatible" 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>
-  --> $DIR/not_wf_param_in_rpitit.rs:9:14
-   |
-LL | trait Trait<const N: dyn Trait = bar> {
-   |       ----- this trait cannot be made into an object...
-...
-LL |     async fn a() {}
-   |              ^ ...because associated function `a` has no `self` parameter
-help: consider turning `a` into a method by giving it a `&self` argument
-   |
-LL |     async fn a(&self) {}
-   |                +++++
-help: alternatively, consider constraining `a` so it does not apply to trait objects
-   |
-LL |     async fn a() where Self: Sized {}
-   |                  +++++++++++++++++
-
-error[E0038]: the trait `Trait` cannot be made into an object
-  --> $DIR/not_wf_param_in_rpitit.rs:3:13
-   |
-LL | trait Trait<const N: dyn Trait = bar> {
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^ `Trait` cannot be made into an object
-   |
-note: for a trait to be "dyn-compatible" 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>
-  --> $DIR/not_wf_param_in_rpitit.rs:9:14
-   |
-LL | trait Trait<const N: dyn Trait = bar> {
-   |       ----- this trait cannot be made into an object...
-...
-LL |     async fn a() {}
-   |              ^ ...because associated function `a` has no `self` parameter
-help: consider turning `a` into a method by giving it a `&self` argument
-   |
-LL |     async fn a(&self) {}
-   |                +++++
-help: alternatively, consider constraining `a` so it does not apply to trait objects
-   |
-LL |     async fn a() where Self: Sized {}
-   |                  +++++++++++++++++
-
-error[E0038]: the trait `Trait` cannot be made into an object
-  --> $DIR/not_wf_param_in_rpitit.rs:3:13
-   |
-LL | trait Trait<const N: dyn Trait = bar> {
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^ `Trait` cannot be made into an object
-   |
-note: for a trait to be "dyn-compatible" 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>
-  --> $DIR/not_wf_param_in_rpitit.rs:9:14
-   |
-LL | trait Trait<const N: dyn Trait = bar> {
-   |       ----- this trait cannot be made into an object...
-...
-LL |     async fn a() {}
-   |              ^ ...because associated function `a` has no `self` parameter
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-help: consider turning `a` into a method by giving it a `&self` argument
-   |
-LL |     async fn a(&self) {}
-   |                +++++
-help: alternatively, consider constraining `a` so it does not apply to trait objects
-   |
-LL |     async fn a() where Self: Sized {}
-   |                  +++++++++++++++++
-
-error: aborting due to 5 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0038, E0391, E0425.
-For more information about an error, try `rustc --explain E0038`.
+Some errors have detailed explanations: E0391, E0425.
+For more information about an error, try `rustc --explain E0391`.

tests/ui/issues/issue-23024.rs

@@ -8,5 +8,4 @@ fn main()
     println!("{:?}",(vfnfer[0] as dyn Fn)(3));
     //~^ ERROR the precise format of `Fn`-family traits'
     //~| ERROR missing generics for trait `Fn`
-    //~| ERROR the value of the associated type `Output` in `FnOnce`
 }

tests/ui/issues/issue-23024.stderr

@@ -19,13 +19,7 @@ help: add missing generic argument
 LL |     println!("{:?}",(vfnfer[0] as dyn Fn<Args>)(3));
    |                                         ++++++
 
-error[E0191]: the value of the associated type `Output` in `FnOnce` must be specified
-  --> $DIR/issue-23024.rs:8:39
-   |
-LL |     println!("{:?}",(vfnfer[0] as dyn Fn)(3));
-   |                                       ^^ help: specify the associated type: `Fn::<Output = Type>`
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0107, E0191, E0658.
+Some errors have detailed explanations: E0107, E0658.
 For more information about an error, try `rustc --explain E0107`.

tests/ui/issues/issue-34373.rs

@@ -6,7 +6,6 @@ trait Trait<T> {
 
 pub struct Foo<T = Box<Trait<DefaultFoo>>>;  //~ ERROR cycle detected
 //~^ ERROR `T` is never used
-//~| ERROR `Trait` cannot be made into an object
 type DefaultFoo = Foo;
 
 fn main() {

tests/ui/issues/issue-34373.stderr

@@ -5,7 +5,7 @@ LL | pub struct Foo<T = Box<Trait<DefaultFoo>>>;
    |                              ^^^^^^^^^^
    |
 note: ...which requires expanding type alias `DefaultFoo`...
-  --> $DIR/issue-34373.rs:10:19
+  --> $DIR/issue-34373.rs:9:19
    |
 LL | type DefaultFoo = Foo;
    |                   ^^^
@@ -17,28 +17,6 @@ LL | pub struct Foo<T = Box<Trait<DefaultFoo>>>;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
 
-error[E0038]: the trait `Trait` cannot be made into an object
-  --> $DIR/issue-34373.rs:7:24
-   |
-LL | pub struct Foo<T = Box<Trait<DefaultFoo>>>;
-   |                        ^^^^^^^^^^^^^^^^^ `Trait` cannot be made into an object
-   |
-note: for a trait to be "dyn-compatible" 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>
-  --> $DIR/issue-34373.rs:4:8
-   |
-LL | trait Trait<T> {
-   |       ----- this trait cannot be made into an object...
-LL |     fn foo(_: T) {}
-   |        ^^^ ...because associated function `foo` has no `self` parameter
-help: consider turning `foo` into a method by giving it a `&self` argument
-   |
-LL |     fn foo(&self, _: T) {}
-   |            ++++++
-help: alternatively, consider constraining `foo` so it does not apply to trait objects
-   |
-LL |     fn foo(_: T) where Self: Sized {}
-   |                  +++++++++++++++++
-
 error[E0392]: type parameter `T` is never used
   --> $DIR/issue-34373.rs:7:16
    |
@@ -48,7 +26,7 @@ LL | pub struct Foo<T = Box<Trait<DefaultFoo>>>;
    = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
    = help: if you intended `T` to be a const parameter, use `const T: /* Type */` instead
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0038, E0391, E0392.
-For more information about an error, try `rustc --explain E0038`.
+Some errors have detailed explanations: E0391, E0392.
+For more information about an error, try `rustc --explain E0391`.

tests/ui/suggestions/use-type-argument-instead-of-assoc-type.rs

@@ -5,8 +5,7 @@ pub trait T<X, Y> {
 }
 pub struct Foo {
     i: Box<dyn T<usize, usize, usize, usize, B=usize>>,
-    //~^ ERROR must be specified
-    //~| ERROR trait takes 2 generic arguments but 4 generic arguments were supplied
+    //~^ ERROR trait takes 2 generic arguments but 4 generic arguments were supplied
 }
 
 

tests/ui/suggestions/use-type-argument-instead-of-assoc-type.stderr

@@ -14,19 +14,6 @@ help: replace the generic bounds with the associated types
 LL |     i: Box<dyn T<usize, usize, A = usize, C = usize, B=usize>>,
    |                                +++        +++
 
-error[E0191]: the value of the associated types `C` and `A` in `T` must be specified
-  --> $DIR/use-type-argument-instead-of-assoc-type.rs:7:16
-   |
-LL |     type A;
-   |     ------ `A` defined here
-LL |     type B;
-LL |     type C;
-   |     ------ `C` defined here
-...
-LL |     i: Box<dyn T<usize, usize, usize, usize, B=usize>>,
-   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ associated types `A`, `C` must be specified
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0107, E0191.
-For more information about an error, try `rustc --explain E0107`.
+For more information about this error, try `rustc --explain E0107`.

tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.rs

@@ -1,21 +1,13 @@
 trait Trait<const N: Trait = bar> {
     //~^ ERROR cannot find value `bar` in this scope
     //~| ERROR cycle detected when computing type of `Trait::N`
-    //~| ERROR the trait `Trait` cannot be made into an object
-    //~| ERROR the trait `Trait` cannot be made into an object
-    //~| ERROR the trait `Trait` cannot be made into an object
-    //~| WARN trait objects without an explicit `dyn` are deprecated [bare_trait_objects]
-    //~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
     //~| WARN trait objects without an explicit `dyn` are deprecated [bare_trait_objects]
     //~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
     fn fnc<const N: Trait = u32>(&self) -> Trait {
         //~^ ERROR the name `N` is already used for a generic parameter in this item's generic parameters
         //~| ERROR expected value, found builtin type `u32`
         //~| ERROR defaults for const parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
         //~| ERROR associated item referring to unboxed trait object for its own trait
-        //~| ERROR the trait `Trait` cannot be made into an object
-        //~| WARN trait objects without an explicit `dyn` are deprecated [bare_trait_objects]
-        //~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
         //~| WARN trait objects without an explicit `dyn` are deprecated [bare_trait_objects]
         //~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
         //~| WARN trait objects without an explicit `dyn` are deprecated [bare_trait_objects]