Reject impl Trait within ?Trait generics or assoc ty bounds

compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs

@@ -103,7 +103,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 continue;
             }
             // There was a `?Trait` bound, but it was not `?Sized`; warn.
-            self.dcx().span_warn(
+            self.dcx().span_err(
                 unbound.span,
                 "relaxing a default bound only does something for `?Sized`; \
                 all other traits are not bound by default",

tests/ui/diagnostic-flags/allow-non-lint-warnings.rs

@@ -1,8 +1,7 @@
 // ignore-tidy-linelength
 //! Check that `-A warnings` cli flag applies to non-lint warnings as well.
 //!
-//! This test tries to exercise that by checking that the "relaxing a default bound only does
-//! something for `?Sized`; all other traits are not bound by default" non-lint warning (normally
+//! This test tries to exercise that by checking that a non-lint warning (normally
 //! warn-by-default) is suppressed if the `-A warnings` cli flag is passed.
 //!
 //! Take special note that `warnings` is a special pseudo lint group in relationship to non-lint
@@ -14,14 +13,14 @@
 //! - Original impl PR: <https://github.com/rust-lang/rust/pull/21248>.
 //! - RFC 507 "Release channels":
 //!   <https://github.com/rust-lang/rfcs/blob/c017755b9bfa0421570d92ba38082302e0f3ad4f/text/0507-release-channels.md>.
-#![crate_type = "lib"]
+#![feature(rustc_attrs)]
 
 //@ revisions: without_flag with_flag
 
 //@[with_flag] compile-flags: -Awarnings
 
 //@ check-pass
 
-pub trait Trait {}
-pub fn f<T: ?Trait>() {}
-//[without_flag]~^ WARN relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+#[rustc_error(warn)]
+fn main() {}
+//[without_flag]~^ WARN unexpected annotation used with `#[rustc_error(...)]`!

tests/ui/diagnostic-flags/allow-non-lint-warnings.without_flag.stderr

@@ -1,8 +1,8 @@
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
-  --> $DIR/allow-non-lint-warnings.rs:26:13
+warning: unexpected annotation used with `#[rustc_error(...)]`!
+  --> $DIR/allow-non-lint-warnings.rs:25:1
    |
-LL | pub fn f<T: ?Trait>() {}
-   |             ^^^^^^
+LL | fn main() {}
+   | ^^^^^^^^^
 
 warning: 1 warning emitted
 

tests/ui/feature-gates/feature-gate-more-maybe-bounds.rs

@@ -11,14 +11,14 @@ fn foo(_: Box<dyn Trait1 + ?Trait2>) {}
 //~^  ERROR `?Trait` is not permitted in trait object types
 fn bar<T: ?Trait1 + ?Trait2>(_: T) {}
 //~^ ERROR type parameter has more than one relaxed default bound, only one is supported
-//~| WARN relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
-//~| WARN relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+//~| ERROR relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+//~| ERROR relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
 
 trait Trait {}
 // Do not suggest `#![feature(more_maybe_bounds)]` for repetitions
 fn baz<T: ?Trait + ?Trait>(_ : T) {}
 //~^ ERROR type parameter has more than one relaxed default bound, only one is supported
-//~| WARN relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
-//~| WARN relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+//~| ERROR relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+//~| ERROR relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
 
 fn main() {}

tests/ui/feature-gates/feature-gate-more-maybe-bounds.stderr

@@ -35,13 +35,13 @@ LL | fn bar<T: ?Trait1 + ?Trait2>(_: T) {}
    = help: add `#![feature(more_maybe_bounds)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/feature-gate-more-maybe-bounds.rs:12:11
    |
 LL | fn bar<T: ?Trait1 + ?Trait2>(_: T) {}
    |           ^^^^^^^
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/feature-gate-more-maybe-bounds.rs:12:21
    |
 LL | fn bar<T: ?Trait1 + ?Trait2>(_: T) {}
@@ -53,19 +53,19 @@ error[E0203]: type parameter has more than one relaxed default bound, only one i
 LL | fn baz<T: ?Trait + ?Trait>(_ : T) {}
    |           ^^^^^^   ^^^^^^
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/feature-gate-more-maybe-bounds.rs:19:11
    |
 LL | fn baz<T: ?Trait + ?Trait>(_ : T) {}
    |           ^^^^^^
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/feature-gate-more-maybe-bounds.rs:19:20
    |
 LL | fn baz<T: ?Trait + ?Trait>(_ : T) {}
    |                    ^^^^^^
 
-error: aborting due to 5 previous errors; 4 warnings emitted
+error: aborting due to 9 previous errors
 
 Some errors have detailed explanations: E0203, E0658.
 For more information about an error, try `rustc --explain E0203`.

tests/ui/impl-trait/opt-out-bound-not-satisfied.rs

@@ -0,0 +1,11 @@
+//! Regression test for ICE https://github.com/rust-lang/rust/issues/135730
+//! This used
+
+use std::future::Future;
+fn foo() -> impl ?Future<Output = impl Send> {
+    //~^ ERROR: relaxing a default bound only does something for `?Sized`
+    //~| ERROR: relaxing a default bound only does something for `?Sized`
+    ()
+}
+
+pub fn main() {}

tests/ui/impl-trait/opt-out-bound-not-satisfied.stderr

@@ -0,0 +1,16 @@
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+  --> $DIR/opt-out-bound-not-satisfied.rs:2:18
+   |
+LL | fn foo() -> impl ?Future<Output = impl Send> {
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+  --> $DIR/opt-out-bound-not-satisfied.rs:2:18
+   |
+LL | fn foo() -> impl ?Future<Output = impl Send> {
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: aborting due to 2 previous errors
+

tests/ui/issues/issue-37534.rs

@@ -1,5 +1,5 @@
 struct Foo<T: ?Hash> {}
 //~^ ERROR expected trait, found derive macro `Hash`
-//~| WARN relaxing a default bound only does something for `?Sized`
+//~| ERROR relaxing a default bound only does something for `?Sized`
 
 fn main() {}

tests/ui/issues/issue-37534.stderr

@@ -9,12 +9,12 @@ help: consider importing this trait instead
 LL + use std::hash::Hash;
    |
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/issue-37534.rs:1:15
    |
 LL | struct Foo<T: ?Hash> {}
    |               ^^^^^
 
-error: aborting due to 1 previous error; 1 warning emitted
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0404`.

tests/ui/issues/issue-87199.rs

@@ -6,12 +6,12 @@
 
 // Check that these function definitions only emit warnings, not errors
 fn arg<T: ?Send>(_: T) {}
-//~^ warning: relaxing a default bound only does something for `?Sized`
+//~^ ERROR: relaxing a default bound only does something for `?Sized`
 fn ref_arg<T: ?Send>(_: &T) {}
-//~^ warning: relaxing a default bound only does something for `?Sized`
+//~^ ERROR: relaxing a default bound only does something for `?Sized`
 fn ret() -> impl Iterator<Item = ()> + ?Send { std::iter::empty() }
-//~^ warning: relaxing a default bound only does something for `?Sized`
-//~| warning: relaxing a default bound only does something for `?Sized`
+//~^ ERROR: relaxing a default bound only does something for `?Sized`
+//~| ERROR: relaxing a default bound only does something for `?Sized`
 
 // Check that there's no `?Sized` relaxation!
 fn main() {

tests/ui/issues/issue-87199.stderr

@@ -1,22 +1,22 @@
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/issue-87199.rs:8:11
    |
 LL | fn arg<T: ?Send>(_: T) {}
    |           ^^^^^
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/issue-87199.rs:10:15
    |
 LL | fn ref_arg<T: ?Send>(_: &T) {}
    |               ^^^^^
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/issue-87199.rs:12:40
    |
 LL | fn ret() -> impl Iterator<Item = ()> + ?Send { std::iter::empty() }
    |                                        ^^^^^
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/issue-87199.rs:12:40
    |
 LL | fn ret() -> impl Iterator<Item = ()> + ?Send { std::iter::empty() }
@@ -41,6 +41,6 @@ help: consider relaxing the implicit `Sized` restriction
 LL | fn ref_arg<T: ?Send + ?Sized>(_: &T) {}
    |                     ++++++++
 
-error: aborting due to 1 previous error; 4 warnings emitted
+error: aborting due to 5 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

tests/ui/trait-bounds/maybe-bound-has-path-args.rs

@@ -2,6 +2,6 @@ trait Trait {}
 
 fn test<T: ?self::<i32>::Trait>() {}
 //~^ ERROR type arguments are not allowed on module `maybe_bound_has_path_args`
-//~| WARN relaxing a default bound only does something for `?Sized`
+//~| ERROR relaxing a default bound only does something for `?Sized`
 
 fn main() {}

tests/ui/trait-bounds/maybe-bound-has-path-args.stderr

@@ -1,4 +1,4 @@
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/maybe-bound-has-path-args.rs:3:12
    |
 LL | fn test<T: ?self::<i32>::Trait>() {}
@@ -12,6 +12,6 @@ LL | fn test<T: ?self::<i32>::Trait>() {}
    |             |
    |             not allowed on module `maybe_bound_has_path_args`
 
-error: aborting due to 1 previous error; 1 warning emitted
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0109`.

tests/ui/trait-bounds/maybe-bound-with-assoc.rs

@@ -2,11 +2,11 @@ trait HasAssoc {
     type Assoc;
 }
 fn hasassoc<T: ?HasAssoc<Assoc = ()>>() {}
-//~^ WARN relaxing a default bound
+//~^ ERROR relaxing a default bound
 
 trait NoAssoc {}
 fn noassoc<T: ?NoAssoc<Missing = ()>>() {}
-//~^ WARN relaxing a default bound
+//~^ ERROR relaxing a default bound
 //~| ERROR associated type `Missing` not found for `NoAssoc`
 
 fn main() {}

tests/ui/trait-bounds/maybe-bound-with-assoc.stderr

@@ -1,10 +1,10 @@
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/maybe-bound-with-assoc.rs:4:16
    |
 LL | fn hasassoc<T: ?HasAssoc<Assoc = ()>>() {}
    |                ^^^^^^^^^^^^^^^^^^^^^
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/maybe-bound-with-assoc.rs:8:15
    |
 LL | fn noassoc<T: ?NoAssoc<Missing = ()>>() {}
@@ -16,6 +16,6 @@ error[E0220]: associated type `Missing` not found for `NoAssoc`
 LL | fn noassoc<T: ?NoAssoc<Missing = ()>>() {}
    |                        ^^^^^^^ associated type `Missing` not found
 
-error: aborting due to 1 previous error; 2 warnings emitted
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0220`.

tests/ui/traits/maybe-polarity-pass.rs

@@ -1,5 +1,3 @@
-//@ check-pass
-
 #![feature(auto_traits)]
 #![feature(more_maybe_bounds)]
 #![feature(negative_impls)]
@@ -12,9 +10,9 @@ trait Trait4 where Self: Trait1 {}
 
 fn foo(_: Box<(dyn Trait3 + ?Trait2)>) {}
 fn bar<T: ?Sized + ?Trait2 + ?Trait1 + ?Trait4>(_: &T) {}
-//~^ WARN relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
-//~| WARN relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
-//~| WARN relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+//~^ ERROR relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+//~| ERROR relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+//~| ERROR relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
 
 struct S;
 impl !Trait2 for S {}

tests/ui/traits/maybe-polarity-pass.stderr

@@ -1,20 +1,20 @@
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
-  --> $DIR/maybe-polarity-pass.rs:14:20
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+  --> $DIR/maybe-polarity-pass.rs:12:20
    |
 LL | fn bar<T: ?Sized + ?Trait2 + ?Trait1 + ?Trait4>(_: &T) {}
    |                    ^^^^^^^
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
-  --> $DIR/maybe-polarity-pass.rs:14:30
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+  --> $DIR/maybe-polarity-pass.rs:12:30
    |
 LL | fn bar<T: ?Sized + ?Trait2 + ?Trait1 + ?Trait4>(_: &T) {}
    |                              ^^^^^^^
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
-  --> $DIR/maybe-polarity-pass.rs:14:40
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+  --> $DIR/maybe-polarity-pass.rs:12:40
    |
 LL | fn bar<T: ?Sized + ?Trait2 + ?Trait1 + ?Trait4>(_: &T) {}
    |                                        ^^^^^^^
 
-warning: 3 warnings emitted
+error: aborting due to 3 previous errors
 

tests/ui/traits/maybe-polarity-repeated.rs

@@ -3,7 +3,7 @@
 trait Trait {}
 fn foo<T: ?Trait + ?Trait>(_: T) {}
 //~^ ERROR type parameter has more than one relaxed default bound, only one is supported
-//~| WARN relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
-//~| WARN relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+//~| ERROR relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+//~| ERROR relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
 
 fn main() {}

tests/ui/traits/maybe-polarity-repeated.stderr

@@ -4,18 +4,18 @@ error[E0203]: type parameter has more than one relaxed default bound, only one i
 LL | fn foo<T: ?Trait + ?Trait>(_: T) {}
    |           ^^^^^^   ^^^^^^
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/maybe-polarity-repeated.rs:4:11
    |
 LL | fn foo<T: ?Trait + ?Trait>(_: T) {}
    |           ^^^^^^
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/maybe-polarity-repeated.rs:4:20
    |
 LL | fn foo<T: ?Trait + ?Trait>(_: T) {}
    |                    ^^^^^^
 
-error: aborting due to 1 previous error; 2 warnings emitted
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0203`.

tests/ui/unsized/maybe-bounds-where.rs

@@ -11,11 +11,11 @@ trait Trait<'a> {}
 
 struct S4<T>(T) where for<'a> T: ?Trait<'a>;
 //~^ ERROR `?Trait` bounds are only permitted at the point where a type parameter is declared
-//~| WARN relaxing a default bound only does something for `?Sized`
+//~| ERROR relaxing a default bound only does something for `?Sized`
 
 struct S5<T>(*const T) where T: ?Trait<'static> + ?Sized;
 //~^ ERROR type parameter has more than one relaxed default bound
-//~| WARN relaxing a default bound only does something for `?Sized`
+//~| ERROR relaxing a default bound only does something for `?Sized`
 
 impl<T> S1<T> {
     fn f() where T: ?Sized {}

tests/ui/unsized/maybe-bounds-where.stderr

@@ -43,7 +43,7 @@ LL |     fn f() where T: ?Sized {}
    = help: add `#![feature(more_maybe_bounds)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/maybe-bounds-where.rs:12:34
    |
 LL | struct S4<T>(T) where for<'a> T: ?Trait<'a>;
@@ -58,13 +58,13 @@ LL | struct S5<T>(*const T) where T: ?Trait<'static> + ?Sized;
    = help: add `#![feature(more_maybe_bounds)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+error: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
   --> $DIR/maybe-bounds-where.rs:16:33
    |
 LL | struct S5<T>(*const T) where T: ?Trait<'static> + ?Sized;
    |                                 ^^^^^^^^^^^^^^^
 
-error: aborting due to 6 previous errors; 2 warnings emitted
+error: aborting due to 8 previous errors
 
 Some errors have detailed explanations: E0203, E0658.
 For more information about an error, try `rustc --explain E0203`.