Auto merge of #120558 - oli-obk:missing_impl_item_ice, r=estebank

Stop bailing out from compilation just because there were incoherent traits

fixes #120343

but also has a lot of "type annotations needed" fallout. Some are fixed in the second commit.

tests/ui/error-codes/E0117.rs

@@ -1,4 +1,5 @@
 impl Drop for u32 {} //~ ERROR E0117
 //~| ERROR the `Drop` trait may only be implemented for local structs, enums, and unions
+//~| ERROR not all trait items implemented
 
 fn main() {}

tests/ui/error-codes/E0117.stderr

@@ -15,7 +15,15 @@ error[E0120]: the `Drop` trait may only be implemented for local structs, enums,
 LL | impl Drop for u32 {}
    |               ^^^ must be a struct, enum, or union in the current crate
 
-error: aborting due to 2 previous errors
+error[E0046]: not all trait items implemented, missing: `drop`
+  --> $DIR/E0117.rs:1:1
+   |
+LL | impl Drop for u32 {}
+   | ^^^^^^^^^^^^^^^^^ missing `drop` in implementation
+   |
+   = help: implement the missing item: `fn drop(&mut self) { todo!() }`
 
-Some errors have detailed explanations: E0117, E0120.
-For more information about an error, try `rustc --explain E0117`.
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0046, E0117, E0120.
+For more information about an error, try `rustc --explain E0046`.

tests/ui/error-codes/E0120.rs

@@ -3,6 +3,7 @@ trait MyTrait { fn foo() {} }
 impl Drop for dyn MyTrait {
               //~^ ERROR E0120
     fn drop(&mut self) {}
+
 }
 
 fn main() {}

tests/ui/error-codes/E0374.rs

@@ -1,7 +1,7 @@
 #![feature(coerce_unsized)]
 use std::ops::CoerceUnsized;
 
-struct Foo<T: ?Sized> {
+struct Foo<T: ?Sized> { //~ ERROR `T` is never used
     a: i32,
 }
 

tests/ui/error-codes/E0374.stderr

@@ -7,6 +7,15 @@ LL | |     where T: CoerceUnsized<U> {}
    |
    = note: expected a single field to be coerced, none found
 
-error: aborting due to 1 previous error
+error[E0392]: type parameter `T` is never used
+  --> $DIR/E0374.rs:4:12
+   |
+LL | struct Foo<T: ?Sized> {
+   |            ^ unused type parameter
+   |
+   = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
 
-For more information about this error, try `rustc --explain E0374`.
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0374, E0392.
+For more information about an error, try `rustc --explain E0374`.

tests/ui/error-codes/E0375.rs

@@ -3,7 +3,7 @@ use std::ops::CoerceUnsized;
 
 struct Foo<T: ?Sized, U: ?Sized> {
     a: i32,
-    b: T,
+    b: T, //~ ERROR E0277
     c: U,
 }
 

tests/ui/error-codes/E0375.stderr

@@ -7,6 +7,32 @@ LL | impl<T, U> CoerceUnsized<Foo<U, T>> for Foo<T, U> {}
    = note: `CoerceUnsized` may only be implemented for a coercion between structures with one field being coerced
    = note: currently, 2 fields need coercions: `b` (`T` to `U`), `c` (`U` to `T`)
 
-error: aborting due to 1 previous error
+error[E0277]: the size for values of type `T` cannot be known at compilation time
+  --> $DIR/E0375.rs:6:8
+   |
+LL | struct Foo<T: ?Sized, U: ?Sized> {
+   |            - this type parameter needs to be `Sized`
+LL |     a: i32,
+LL |     b: T,
+   |        ^ doesn't have a size known at compile-time
+   |
+   = note: only the last field of a struct may have a dynamically sized type
+   = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL - struct Foo<T: ?Sized, U: ?Sized> {
+LL + struct Foo<T, U: ?Sized> {
+   |
+help: borrowed types always have a statically known size
+   |
+LL |     b: &T,
+   |        +
+help: the `Box` type always has a statically known size and allocates its contents in the heap
+   |
+LL |     b: Box<T>,
+   |        ++++ +
 
-For more information about this error, try `rustc --explain E0375`.
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0277, E0375.
+For more information about an error, try `rustc --explain E0277`.