Auto merge of #89024 - oli-obk:lazy_tait_is_not_limited_to_being_used_in_return_position, r=nikomatsakis

Lazy TAIT preparation cleanups

Check that TAIT generics are fully generic in mir typeck instead of wf-check, as wf-check can by definition only check TAIT in return position and not account for TAITs defined in the body of the function

r? `@spastorino` `@nikomatsakis`

28 files changed, 279 insertions, 59 deletions

diff --git a/src/test/ui/type-alias-impl-trait/bound_reduction2.rs b/src/test/ui/type-alias-impl-trait/bound_reduction2.rs
index a15074c3593..579067340e8 100644
--- a/src/test/ui/type-alias-impl-trait/bound_reduction2.rs
+++ b/src/test/ui/type-alias-impl-trait/bound_reduction2.rs
@@ -7,6 +7,7 @@ trait TraitWithAssoc {
 }
 
 type Foo<V> = impl Trait<V>;
+//~^ ERROR could not find defining uses
 
 trait Trait<U> {}
 
@@ -14,5 +15,9 @@ impl<W> Trait<W> for () {}
 
 fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
     //~^ ERROR non-defining opaque type use in defining scope
+    //~| ERROR non-defining opaque type use in defining scope
+    //~| ERROR non-defining opaque type use in defining scope
+    //~| ERROR `T` is part of concrete type but not used in parameter list
+    //~| ERROR `T` is part of concrete type but not used in parameter list
     ()
 }
diff --git a/src/test/ui/type-alias-impl-trait/bound_reduction2.stderr b/src/test/ui/type-alias-impl-trait/bound_reduction2.stderr
index c9d6a43b909..a77c0000f12 100644
--- a/src/test/ui/type-alias-impl-trait/bound_reduction2.stderr
+++ b/src/test/ui/type-alias-impl-trait/bound_reduction2.stderr
@@ -1,8 +1,34 @@
+error: type parameter `T` is part of concrete type but not used in parameter list for the `impl Trait` type alias
+  --> $DIR/bound_reduction2.rs:16:60
+   |
+LL |   fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
+   |  ____________________________________________________________^
+LL | |
+LL | |
+LL | |
+...  |
+LL | |     ()
+LL | | }
+   | |_^
+
+error: type parameter `T` is part of concrete type but not used in parameter list for the `impl Trait` type alias
+  --> $DIR/bound_reduction2.rs:16:60
+   |
+LL |   fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
+   |  ____________________________________________________________^
+LL | |
+LL | |
+LL | |
+...  |
+LL | |     ()
+LL | | }
+   | |_^
+
 error: non-defining opaque type use in defining scope
-  --> $DIR/bound_reduction2.rs:15:46
+  --> $DIR/bound_reduction2.rs:16:1
    |
 LL | fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
-   |                                              ^^^^^^^^^^^^^
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: used non-generic type `<T as TraitWithAssoc>::Assoc` for generic parameter
   --> $DIR/bound_reduction2.rs:9:10
@@ -10,5 +36,35 @@ note: used non-generic type `<T as TraitWithAssoc>::Assoc` for generic parameter
 LL | type Foo<V> = impl Trait<V>;
    |          ^
 
-error: aborting due to previous error
+error: non-defining opaque type use in defining scope
+  --> $DIR/bound_reduction2.rs:16:1
+   |
+LL | fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: used non-generic type `_` for generic parameter
+  --> $DIR/bound_reduction2.rs:9:10
+   |
+LL | type Foo<V> = impl Trait<V>;
+   |          ^
+
+error: non-defining opaque type use in defining scope
+  --> $DIR/bound_reduction2.rs:16:1
+   |
+LL | fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: used non-generic type `_` for generic parameter
+  --> $DIR/bound_reduction2.rs:9:10
+   |
+LL | type Foo<V> = impl Trait<V>;
+   |          ^
+
+error: could not find defining uses
+  --> $DIR/bound_reduction2.rs:9:15
+   |
+LL | type Foo<V> = impl Trait<V>;
+   |               ^^^^^^^^^^^^^
+
+error: aborting due to 6 previous errors
 
diff --git a/src/test/ui/type-alias-impl-trait/generic_duplicate_lifetime_param.rs b/src/test/ui/type-alias-impl-trait/generic_duplicate_lifetime_param.rs
index 31f992976b1..885aae619d6 100644
--- a/src/test/ui/type-alias-impl-trait/generic_duplicate_lifetime_param.rs
+++ b/src/test/ui/type-alias-impl-trait/generic_duplicate_lifetime_param.rs
@@ -3,6 +3,7 @@
 fn main() {}
 
 type Two<'a, 'b> = impl std::fmt::Debug;
+//~^ ERROR could not find defining uses
 
 fn one<'a>(t: &'a ()) -> Two<'a, 'a> {
     //~^ ERROR non-defining opaque type use
diff --git a/src/test/ui/type-alias-impl-trait/generic_duplicate_lifetime_param.stderr b/src/test/ui/type-alias-impl-trait/generic_duplicate_lifetime_param.stderr
index 08b26b8fc13..b99c6a51f4b 100644
--- a/src/test/ui/type-alias-impl-trait/generic_duplicate_lifetime_param.stderr
+++ b/src/test/ui/type-alias-impl-trait/generic_duplicate_lifetime_param.stderr
@@ -1,5 +1,5 @@
 error: non-defining opaque type use in defining scope
-  --> $DIR/generic_duplicate_lifetime_param.rs:7:26
+  --> $DIR/generic_duplicate_lifetime_param.rs:8:26
    |
 LL | fn one<'a>(t: &'a ()) -> Two<'a, 'a> {
    |                          ^^^^^^^^^^^
@@ -10,5 +10,11 @@ note: lifetime used multiple times
 LL | type Two<'a, 'b> = impl std::fmt::Debug;
    |          ^^  ^^
 
-error: aborting due to previous error
+error: could not find defining uses
+  --> $DIR/generic_duplicate_lifetime_param.rs:5:20
+   |
+LL | type Two<'a, 'b> = impl std::fmt::Debug;
+   |                    ^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use.rs b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use.rs
index a4e40f516dc..33cd2f6ba07 100644
--- a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use.rs
+++ b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use.rs
@@ -6,8 +6,11 @@ fn main() {}
 
 // test that unused generic parameters are ok
 type TwoTys<T, U> = impl Debug;
+//~^ ERROR could not find defining uses
 type TwoLifetimes<'a, 'b> = impl Debug;
+//~^ ERROR could not find defining uses
 type TwoConsts<const X: usize, const Y: usize> = impl Debug;
+//~^ ERROR could not find defining uses
 
 fn one_ty<T: Debug>(t: T) -> TwoTys<T, T> {
     //~^ ERROR non-defining opaque type use in defining scope
diff --git a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use.stderr b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use.stderr
index 641cce26d99..52c60d1777e 100644
--- a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use.stderr
+++ b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use.stderr
@@ -1,5 +1,5 @@
 error: non-defining opaque type use in defining scope
-  --> $DIR/generic_duplicate_param_use.rs:12:30
+  --> $DIR/generic_duplicate_param_use.rs:15:30
    |
 LL | fn one_ty<T: Debug>(t: T) -> TwoTys<T, T> {
    |                              ^^^^^^^^^^^^
@@ -10,29 +10,47 @@ note: type used multiple times
 LL | type TwoTys<T, U> = impl Debug;
    |             ^  ^
 
+error: could not find defining uses
+  --> $DIR/generic_duplicate_param_use.rs:8:21
+   |
+LL | type TwoTys<T, U> = impl Debug;
+   |                     ^^^^^^^^^^
+
 error: non-defining opaque type use in defining scope
-  --> $DIR/generic_duplicate_param_use.rs:17:36
+  --> $DIR/generic_duplicate_param_use.rs:20:36
    |
 LL | fn one_lifetime<'a>(t: &'a u32) -> TwoLifetimes<'a, 'a> {
    |                                    ^^^^^^^^^^^^^^^^^^^^
    |
 note: lifetime used multiple times
-  --> $DIR/generic_duplicate_param_use.rs:9:19
+  --> $DIR/generic_duplicate_param_use.rs:10:19
    |
 LL | type TwoLifetimes<'a, 'b> = impl Debug;
    |                   ^^  ^^
 
+error: could not find defining uses
+  --> $DIR/generic_duplicate_param_use.rs:10:29
+   |
+LL | type TwoLifetimes<'a, 'b> = impl Debug;
+   |                             ^^^^^^^^^^
+
 error: non-defining opaque type use in defining scope
-  --> $DIR/generic_duplicate_param_use.rs:22:50
+  --> $DIR/generic_duplicate_param_use.rs:25:50
    |
 LL | fn one_const<const N: usize>(t: *mut [u8; N]) -> TwoConsts<N, N> {
    |                                                  ^^^^^^^^^^^^^^^
    |
 note: constant used multiple times
-  --> $DIR/generic_duplicate_param_use.rs:10:22
+  --> $DIR/generic_duplicate_param_use.rs:12:22
    |
 LL | type TwoConsts<const X: usize, const Y: usize> = impl Debug;
    |                      ^               ^
 
-error: aborting due to 3 previous errors
+error: could not find defining uses
+  --> $DIR/generic_duplicate_param_use.rs:12:50
+   |
+LL | type TwoConsts<const X: usize, const Y: usize> = impl Debug;
+   |                                                  ^^^^^^^^^^
+
+error: aborting due to 6 previous errors
 
diff --git a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use2.rs b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use2.rs
index a74731df695..04fb57b39c0 100644
--- a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use2.rs
+++ b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use2.rs
@@ -6,6 +6,7 @@ fn main() {}
 
 // test that unused generic parameters are ok
 type Two<T, U> = impl Debug;
+//~^ ERROR `T` doesn't implement `Debug`
 
 fn one<T: Debug>(t: T) -> Two<T, T> {
     //~^ ERROR non-defining opaque type use in defining scope
diff --git a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use2.stderr b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use2.stderr
index d87e8c5783b..fca9b70d184 100644
--- a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use2.stderr
+++ b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use2.stderr
@@ -1,5 +1,5 @@
 error: non-defining opaque type use in defining scope
-  --> $DIR/generic_duplicate_param_use2.rs:10:27
+  --> $DIR/generic_duplicate_param_use2.rs:11:27
    |
 LL | fn one<T: Debug>(t: T) -> Two<T, T> {
    |                           ^^^^^^^^^
@@ -10,5 +10,17 @@ note: type used multiple times
 LL | type Two<T, U> = impl Debug;
    |          ^  ^
 
-error: aborting due to previous error
+error[E0277]: `T` doesn't implement `Debug`
+  --> $DIR/generic_duplicate_param_use2.rs:8:18
+   |
+LL | type Two<T, U> = impl Debug;
+   |                  ^^^^^^^^^^ `T` cannot be formatted using `{:?}` because it doesn't implement `Debug`
+   |
+help: consider restricting type parameter `T`
+   |
+LL | type Two<T: std::fmt::Debug, U> = impl Debug;
+   |           +++++++++++++++++
+
+error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0277`.
diff --git a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use3.rs b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use3.rs
index 0597b8385d2..1a755d39026 100644
--- a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use3.rs
+++ b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use3.rs
@@ -6,6 +6,7 @@ fn main() {}
 
 // test that unused generic parameters are ok
 type Two<T, U> = impl Debug;
+//~^ ERROR `T` doesn't implement `Debug`
 
 fn one<T: Debug>(t: T) -> Two<T, T> {
     //~^ ERROR non-defining opaque type use in defining scope
@@ -17,5 +18,6 @@ fn two<T: Debug, U>(t: T, _: U) -> Two<T, U> {
 }
 
 fn three<T, U: Debug>(_: T, u: U) -> Two<T, U> {
+    //~^ ERROR concrete type differs from previous defining opaque type use
     u
 }
diff --git a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use3.stderr b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use3.stderr
index 711de855f0d..90b04c043a0 100644
--- a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use3.stderr
+++ b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use3.stderr
@@ -1,5 +1,5 @@
 error: non-defining opaque type use in defining scope
-  --> $DIR/generic_duplicate_param_use3.rs:10:27
+  --> $DIR/generic_duplicate_param_use3.rs:11:27
    |
 LL | fn one<T: Debug>(t: T) -> Two<T, T> {
    |                           ^^^^^^^^^
@@ -10,5 +10,29 @@ note: type used multiple times
 LL | type Two<T, U> = impl Debug;
    |          ^  ^
 
-error: aborting due to previous error
+error: concrete type differs from previous defining opaque type use
+  --> $DIR/generic_duplicate_param_use3.rs:20:1
+   |
+LL | fn three<T, U: Debug>(_: T, u: U) -> Two<T, U> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `T`, got `U`
+   |
+note: previous use here
+  --> $DIR/generic_duplicate_param_use3.rs:16:1
+   |
+LL | fn two<T: Debug, U>(t: T, _: U) -> Two<T, U> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: `T` doesn't implement `Debug`
+  --> $DIR/generic_duplicate_param_use3.rs:8:18
+   |
+LL | type Two<T, U> = impl Debug;
+   |                  ^^^^^^^^^^ `T` cannot be formatted using `{:?}` because it doesn't implement `Debug`
+   |
+help: consider restricting type parameter `T`
+   |
+LL | type Two<T: std::fmt::Debug, U> = impl Debug;
+   |           +++++++++++++++++
+
+error: aborting due to 3 previous errors
 
+For more information about this error, try `rustc --explain E0277`.
diff --git a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use4.rs b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use4.rs
index e77c94988f7..50d95c83d58 100644
--- a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use4.rs
+++ b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use4.rs
@@ -6,6 +6,7 @@ fn main() {}
 
 // test that unused generic parameters are ok
 type Two<T, U> = impl Debug;
+//~^ ERROR `U` doesn't implement `Debug`
 
 fn one<T: Debug>(t: T) -> Two<T, T> {
     //~^ ERROR non-defining opaque type use in defining scope
diff --git a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use4.stderr b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use4.stderr
index fcf01f5164a..c4be2fa83f1 100644
--- a/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use4.stderr
+++ b/src/test/ui/type-alias-impl-trait/generic_duplicate_param_use4.stderr
@@ -1,5 +1,5 @@
 error: non-defining opaque type use in defining scope
-  --> $DIR/generic_duplicate_param_use4.rs:10:27
+  --> $DIR/generic_duplicate_param_use4.rs:11:27
    |
 LL | fn one<T: Debug>(t: T) -> Two<T, T> {
    |                           ^^^^^^^^^
@@ -10,5 +10,17 @@ note: type used multiple times
 LL | type Two<T, U> = impl Debug;
    |          ^  ^
 
-error: aborting due to previous error
+error[E0277]: `U` doesn't implement `Debug`
+  --> $DIR/generic_duplicate_param_use4.rs:8:18
+   |
+LL | type Two<T, U> = impl Debug;
+   |                  ^^^^^^^^^^ `U` cannot be formatted using `{:?}` because it doesn't implement `Debug`
+   |
+help: consider restricting type parameter `U`
+   |
+LL | type Two<T, U: std::fmt::Debug> = impl Debug;
+   |              +++++++++++++++++
+
+error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0277`.
diff --git a/src/test/ui/type-alias-impl-trait/generic_nondefining_use.rs b/src/test/ui/type-alias-impl-trait/generic_nondefining_use.rs
index 7ee5f7b068f..cf43085877f 100644
--- a/src/test/ui/type-alias-impl-trait/generic_nondefining_use.rs
+++ b/src/test/ui/type-alias-impl-trait/generic_nondefining_use.rs
@@ -5,8 +5,11 @@ use std::fmt::Debug;
 fn main() {}
 
 type OneTy<T> = impl Debug;
+//~^ ERROR could not find defining uses
 type OneLifetime<'a> = impl Debug;
+//~^ ERROR could not find defining uses
 type OneConst<const X: usize> = impl Debug;
+//~^ ERROR could not find defining uses
 
 // Not defining uses, because they doesn't define *all* possible generics.
 
diff --git a/src/test/ui/type-alias-impl-trait/generic_nondefining_use.stderr b/src/test/ui/type-alias-impl-trait/generic_nondefining_use.stderr
index 5b42f10a6ee..3aa42a25484 100644
--- a/src/test/ui/type-alias-impl-trait/generic_nondefining_use.stderr
+++ b/src/test/ui/type-alias-impl-trait/generic_nondefining_use.stderr
@@ -1,5 +1,5 @@
 error: non-defining opaque type use in defining scope
-  --> $DIR/generic_nondefining_use.rs:13:21
+  --> $DIR/generic_nondefining_use.rs:16:21
    |
 LL | fn concrete_ty() -> OneTy<u32> {
    |                     ^^^^^^^^^^
@@ -10,8 +10,14 @@ note: used non-generic type `u32` for generic parameter
 LL | type OneTy<T> = impl Debug;
    |            ^
 
+error: could not find defining uses
+  --> $DIR/generic_nondefining_use.rs:7:17
+   |
+LL | type OneTy<T> = impl Debug;
+   |                 ^^^^^^^^^^
+
 error: non-defining opaque type use in defining scope
-  --> $DIR/generic_nondefining_use.rs:18:27
+  --> $DIR/generic_nondefining_use.rs:21:27
    |
 LL | type OneLifetime<'a> = impl Debug;
    |                  -- cannot use static lifetime; use a bound lifetime instead or remove the lifetime parameter from the opaque type
@@ -19,17 +25,29 @@ LL | type OneLifetime<'a> = impl Debug;
 LL | fn concrete_lifetime() -> OneLifetime<'static> {
    |                           ^^^^^^^^^^^^^^^^^^^^
 
+error: could not find defining uses
+  --> $DIR/generic_nondefining_use.rs:9:24
+   |
+LL | type OneLifetime<'a> = impl Debug;
+   |                        ^^^^^^^^^^
+
 error: non-defining opaque type use in defining scope
-  --> $DIR/generic_nondefining_use.rs:23:24
+  --> $DIR/generic_nondefining_use.rs:26:24
    |
 LL | fn concrete_const() -> OneConst<{ 123 }> {
    |                        ^^^^^^^^^^^^^^^^^
    |
 note: used non-generic constant `123_usize` for generic parameter
-  --> $DIR/generic_nondefining_use.rs:9:21
+  --> $DIR/generic_nondefining_use.rs:11:21
    |
 LL | type OneConst<const X: usize> = impl Debug;
    |                     ^
 
-error: aborting due to 3 previous errors
+error: could not find defining uses
+  --> $DIR/generic_nondefining_use.rs:11:33
+   |
+LL | type OneConst<const X: usize> = impl Debug;
+   |                                 ^^^^^^^^^^
+
+error: aborting due to 6 previous errors
 
diff --git a/src/test/ui/type-alias-impl-trait/incomplete-inference.rs b/src/test/ui/type-alias-impl-trait/incomplete-inference.rs
index 955d1288a45..4c8bf2cfca1 100644
--- a/src/test/ui/type-alias-impl-trait/incomplete-inference.rs
+++ b/src/test/ui/type-alias-impl-trait/incomplete-inference.rs
@@ -8,7 +8,6 @@ fn bar() -> Foo {
 }
 
 fn baz() -> Foo {
-    //~^ ERROR: concrete type differs from previous defining opaque type use
     Some(())
 }
 
diff --git a/src/test/ui/type-alias-impl-trait/incomplete-inference.stderr b/src/test/ui/type-alias-impl-trait/incomplete-inference.stderr
index 53cdf9e5b38..0cdd4cc8dc3 100644
--- a/src/test/ui/type-alias-impl-trait/incomplete-inference.stderr
+++ b/src/test/ui/type-alias-impl-trait/incomplete-inference.stderr
@@ -4,18 +4,6 @@ error[E0282]: type annotations needed
 LL |     None
    |     ^^^^ cannot infer type for type parameter `T` declared on the enum `Option`
 
-error: concrete type differs from previous defining opaque type use
-  --> $DIR/incomplete-inference.rs:10:1
-   |
-LL | fn baz() -> Foo {
-   | ^^^^^^^^^^^^^^^ expected `[type error]`, got `Option<()>`
-   |
-note: previous use here
-  --> $DIR/incomplete-inference.rs:5:1
-   |
-LL | fn bar() -> Foo {
-   | ^^^^^^^^^^^^^^^
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0282`.
diff --git a/src/test/ui/type-alias-impl-trait/issue-60371.rs b/src/test/ui/type-alias-impl-trait/issue-60371.rs
index 37a2f28ce07..9d2ba849c86 100644
--- a/src/test/ui/type-alias-impl-trait/issue-60371.rs
+++ b/src/test/ui/type-alias-impl-trait/issue-60371.rs
@@ -11,6 +11,7 @@ impl Bug for &() {
 
     const FUN: fn() -> Self::Item = || ();
     //~^ ERROR the trait bound `(): Bug` is not satisfied
+    //~| ERROR non-defining opaque type use in defining scope
 }
 
 fn main() {}
diff --git a/src/test/ui/type-alias-impl-trait/issue-60371.stderr b/src/test/ui/type-alias-impl-trait/issue-60371.stderr
index 1710e07644d..62ab7eb4560 100644
--- a/src/test/ui/type-alias-impl-trait/issue-60371.stderr
+++ b/src/test/ui/type-alias-impl-trait/issue-60371.stderr
@@ -16,7 +16,16 @@ LL |     const FUN: fn() -> Self::Item = || ();
    = help: the following implementations were found:
              <&() as Bug>
 
-error: aborting due to 2 previous errors
+error: non-defining opaque type use in defining scope
+  --> $DIR/issue-60371.rs:12:37
+   |
+LL | impl Bug for &() {
+   |              - cannot use static lifetime; use a bound lifetime instead or remove the lifetime parameter from the opaque type
+...
+LL |     const FUN: fn() -> Self::Item = || ();
+   |                                     ^^^^^
+
+error: aborting due to 3 previous errors
 
 Some errors have detailed explanations: E0277, E0658.
 For more information about an error, try `rustc --explain E0277`.
diff --git a/src/test/ui/type-alias-impl-trait/issue-60564.rs b/src/test/ui/type-alias-impl-trait/issue-60564.rs
index 78def0d1136..44dcec2c3da 100644
--- a/src/test/ui/type-alias-impl-trait/issue-60564.rs
+++ b/src/test/ui/type-alias-impl-trait/issue-60564.rs
@@ -6,6 +6,7 @@ trait IterBits {
 }
 
 type IterBitsIter<T, E, I> = impl std::iter::Iterator<Item = I>;
+//~^ ERROR could not find defining uses
 
 impl<T: Copy, E> IterBits for T
 where
diff --git a/src/test/ui/type-alias-impl-trait/issue-60564.stderr b/src/test/ui/type-alias-impl-trait/issue-60564.stderr
index 66fa862ef9d..6b73fbef011 100644
--- a/src/test/ui/type-alias-impl-trait/issue-60564.stderr
+++ b/src/test/ui/type-alias-impl-trait/issue-60564.stderr
@@ -1,5 +1,5 @@
 error: non-defining opaque type use in defining scope
-  --> $DIR/issue-60564.rs:19:34
+  --> $DIR/issue-60564.rs:20:34
    |
 LL |     fn iter_bits(self, n: u8) -> Self::BitsIter {
    |                                  ^^^^^^^^^^^^^^
@@ -10,5 +10,11 @@ note: used non-generic type `u8` for generic parameter
 LL | type IterBitsIter<T, E, I> = impl std::iter::Iterator<Item = I>;
    |                         ^
 
-error: aborting due to previous error
+error: could not find defining uses
+  --> $DIR/issue-60564.rs:8:30
+   |
+LL | type IterBitsIter<T, E, I> = impl std::iter::Iterator<Item = I>;
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use-2.rs b/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use-2.rs
new file mode 100644
index 00000000000..2e6354088ac
--- /dev/null
+++ b/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use-2.rs
@@ -0,0 +1,14 @@
+// Regression test for issue #68368
+// Ensures that we don't ICE when emitting an error
+// for a non-defining use when lifetimes are involved
+
+#![feature(type_alias_impl_trait)]
+trait Trait<T> {}
+type Alias<'a, U> = impl Trait<U>;
+//~^ ERROR could not find defining uses
+fn f<'a>() -> Alias<'a, ()> {}
+//~^ ERROR non-defining opaque type use in defining scope
+
+fn main() {}
+
+impl<X> Trait<X> for () {}
diff --git a/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use-2.stderr b/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use-2.stderr
new file mode 100644
index 00000000000..721f99a3f0d
--- /dev/null
+++ b/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use-2.stderr
@@ -0,0 +1,20 @@
+error: non-defining opaque type use in defining scope
+  --> $DIR/issue-68368-non-defining-use-2.rs:9:15
+   |
+LL | fn f<'a>() -> Alias<'a, ()> {}
+   |               ^^^^^^^^^^^^^
+   |
+note: used non-generic type `()` for generic parameter
+  --> $DIR/issue-68368-non-defining-use-2.rs:7:16
+   |
+LL | type Alias<'a, U> = impl Trait<U>;
+   |                ^
+
+error: could not find defining uses
+  --> $DIR/issue-68368-non-defining-use-2.rs:7:21
+   |
+LL | type Alias<'a, U> = impl Trait<U>;
+   |                     ^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
diff --git a/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use.rs b/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use.rs
index 3b6decbe9c6..3addd8dcc4f 100644
--- a/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use.rs
+++ b/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use.rs
@@ -5,6 +5,7 @@
 #![feature(type_alias_impl_trait)]
 trait Trait<T> {}
 type Alias<'a, U> = impl Trait<U>;
+//~^ ERROR could not find defining uses
 fn f<'a>() -> Alias<'a, ()> {}
 //~^ ERROR non-defining opaque type use in defining scope
 
diff --git a/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use.stderr b/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use.stderr
index c2fa54f50f8..f5b8fccf65d 100644
--- a/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use.stderr
+++ b/src/test/ui/type-alias-impl-trait/issue-68368-non-defining-use.stderr
@@ -1,5 +1,5 @@
 error: non-defining opaque type use in defining scope
-  --> $DIR/issue-68368-non-defining-use.rs:8:15
+  --> $DIR/issue-68368-non-defining-use.rs:9:15
    |
 LL | fn f<'a>() -> Alias<'a, ()> {}
    |               ^^^^^^^^^^^^^
@@ -10,5 +10,11 @@ note: used non-generic type `()` for generic parameter
 LL | type Alias<'a, U> = impl Trait<U>;
    |                ^
 
-error: aborting due to previous error
+error: could not find defining uses
+  --> $DIR/issue-68368-non-defining-use.rs:7:21
+   |
+LL | type Alias<'a, U> = impl Trait<U>;
+   |                     ^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn3.rs b/src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn3.rs
index bcd9aeff6b4..11a922443e6 100644
--- a/src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn3.rs
+++ b/src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn3.rs
@@ -11,7 +11,6 @@ fn f<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<B, A>)
 }
 
 fn g<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<A, B>) {
-    //~^ ERROR concrete type differs from previous defining opaque type
     (a, b)
     //~^ ERROR mismatched types
 }
diff --git a/src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn3.stderr b/src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn3.stderr
index 3d943b77af5..bbe709dccab 100644
--- a/src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn3.stderr
+++ b/src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn3.stderr
@@ -1,11 +1,10 @@
 error[E0308]: mismatched types
-  --> $DIR/multiple-def-uses-in-one-fn3.rs:15:9
+  --> $DIR/multiple-def-uses-in-one-fn3.rs:14:9
    |
 LL | fn g<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<A, B>) {
    |      -                    - found type parameter
    |      |
    |      expected type parameter
-LL |
 LL |     (a, b)
    |         ^ expected type parameter `A`, found type parameter `B`
    |
@@ -14,18 +13,6 @@ LL |     (a, b)
    = note: a type parameter was expected, but a different one was found; you might be missing a type parameter or trait bound
    = note: for more information, visit https://doc.rust-lang.org/book/ch10-02-traits.html#traits-as-parameters
 
-error: concrete type differs from previous defining opaque type use
-  --> $DIR/multiple-def-uses-in-one-fn3.rs:13:1
-   |
-LL | fn g<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<A, B>) {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `A`, got `[type error]`
-   |
-note: previous use here
-  --> $DIR/multiple-def-uses-in-one-fn3.rs:9:1
-   |
-LL | fn f<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<B, A>) {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/type-alias-impl-trait/not_a_defining_use.rs b/src/test/ui/type-alias-impl-trait/not_a_defining_use.rs
index f29b980dfd0..107cd394579 100644
--- a/src/test/ui/type-alias-impl-trait/not_a_defining_use.rs
+++ b/src/test/ui/type-alias-impl-trait/not_a_defining_use.rs
@@ -5,6 +5,7 @@ use std::fmt::Debug;
 fn main() {}
 
 type Two<T, U> = impl Debug;
+//~^ ERROR `T` doesn't implement `Debug`
 
 fn two<T: Debug>(t: T) -> Two<T, u32> {
     //~^ ERROR non-defining opaque type use in defining scope
@@ -26,6 +27,7 @@ impl Bar for u32 {
 }
 
 fn four<T: Debug, U: Bar>(t: T) -> Two<T, U> {
+    //~^ ERROR concrete type differs from previous
     (t, <U as Bar>::FOO)
 }
 
diff --git a/src/test/ui/type-alias-impl-trait/not_a_defining_use.stderr b/src/test/ui/type-alias-impl-trait/not_a_defining_use.stderr
index 2fa236b373a..08e49845521 100644
--- a/src/test/ui/type-alias-impl-trait/not_a_defining_use.stderr
+++ b/src/test/ui/type-alias-impl-trait/not_a_defining_use.stderr
@@ -1,5 +1,5 @@
 error: non-defining opaque type use in defining scope
-  --> $DIR/not_a_defining_use.rs:9:27
+  --> $DIR/not_a_defining_use.rs:10:27
    |
 LL | fn two<T: Debug>(t: T) -> Two<T, u32> {
    |                           ^^^^^^^^^^^
@@ -10,5 +10,30 @@ note: used non-generic type `u32` for generic parameter
 LL | type Two<T, U> = impl Debug;
    |             ^
 
-error: aborting due to previous error
+error: concrete type differs from previous defining opaque type use
+  --> $DIR/not_a_defining_use.rs:29:1
+   |
+LL | fn four<T: Debug, U: Bar>(t: T) -> Two<T, U> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `(T, i8)`, got `(T, <U as Bar>::Blub)`
+   |
+note: previous use here
+  --> $DIR/not_a_defining_use.rs:15:1
+   |
+LL | fn three<T: Debug, U>(t: T) -> Two<T, U> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: `T` doesn't implement `Debug`
+  --> $DIR/not_a_defining_use.rs:7:18
+   |
+LL | type Two<T, U> = impl Debug;
+   |                  ^^^^^^^^^^ `T` cannot be formatted using `{:?}` because it doesn't implement `Debug`
+   |
+   = note: required because of the requirements on the impl of `Debug` for `(T, i8)`
+help: consider restricting type parameter `T`
+   |
+LL | type Two<T: std::fmt::Debug, U> = impl Debug;
+   |           +++++++++++++++++
+
+error: aborting due to 3 previous errors
 
+For more information about this error, try `rustc --explain E0277`.