help with a Miri ICE

[RalfJung]

This helps with rust-lang/miri#2433, though the example there still ICEs with debug assertions enabled. Due to that, I am not sure what kind of test we could add. Cc @ouz-a @oli-obk

This effectively reverts a behavior change in #99383 that was noticed by @bjorn3 ; I have no clue if that behavior change was intentional or not. I guess the ui test suite will tell us.

Note that I have no clue whatsoever what this change actually does. I don't even understand the words used in this part of the code.

[rust-highfive]

r? @fee1-dead

(rust-highfive has picked a reviewer for you, use r? to override)

[RalfJung]

@bors try
so that I can test Miri against a release build of this

[bors]

⌛ Trying commit 3371a75 with merge 0645e44b518e76c93ea453bf06956214037a6532...

[RalfJung]

ui tests are indeed not happy. No idea if those changes are any good or not.

[bors]

☀️ Try build successful - checks-actions
Build commit: 0645e44b518e76c93ea453bf06956214037a6532 (0645e44b518e76c93ea453bf06956214037a6532)

[RalfJung]

At least I can confirm that this fixes the ICE in Miri using a rustc release build.

There's still the failing debug assertion, of course.

[rust-log-analyzer]

The job x86_64-gnu-llvm-13 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

---- [ui] src/test/ui/impl-trait/issues/issue-99348-impl-compatibility.rs stdout ----
diff of stderr:

- error[E0271]: type mismatch resolving `<Concrete as Bar>::Other == Concrete`
+ error[E0308]: mismatched types
3    |
4 LL | type Tait = impl Sized;

-    |             ---------- the found opaque type
-    |             ---------- the found opaque type
+    |             ---------- the expected opaque type
6 ...
7 LL |     type Item = Concrete;
-    |                 ^^^^^^^^ type mismatch resolving `<Concrete as Bar>::Other == Concrete`
+    |                 ^^^^^^^^ types differ
- note: expected this to be `Concrete`
-   --> $DIR/issue-99348-impl-compatibility.rs:13:18
-    |
-    |
- LL |     type Other = Tait;
-    = note:   expected struct `Concrete`
-            found opaque type `Tait`
- note: required by a bound in `Foo::Item`
-   --> $DIR/issue-99348-impl-compatibility.rs:17:20
-   --> $DIR/issue-99348-impl-compatibility.rs:17:20
-    |
- LL |     type Item: Bar<Other = Self>;
-    |                    ^^^^^^^^^^^^ required by this bound in `Foo::Item`
+    = note: expected opaque type `Tait`
+                    found struct `Concrete`
23 error: aborting due to previous error
24 

- For more information about this error, try `rustc --explain E0271`.
---
To only update this specific test, also pass `--test-args impl-trait/issues/issue-99348-impl-compatibility.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/impl-trait/issues/issue-99348-impl-compatibility.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/impl-trait/issues/issue-99348-impl-compatibility" "-A" "unused" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/impl-trait/issues/issue-99348-impl-compatibility/auxiliary"
stdout: none
--- stderr -------------------------------
  --> /checkout/src/test/ui/impl-trait/issues/issue-99348-impl-compatibility.rs:8:17
   |
LL | type Tait = impl Sized;
   |             ---------- the expected opaque type
---
221    |
- LL |         async fn ft1() {}
-    |                        ^
-    |                        |
-    |                        checked the `Output` of this `async fn`, found opaque type
-    |
-    = note: while checking the return type of the `async fn`
- note: type in trait
-   --> $DIR/fn-header-semantic-fail.rs:17:23
-   --> $DIR/fn-header-semantic-fail.rs:17:23
-    |
232 LL |         async fn ft1();
-    |                       ^
-    = note: expected fn pointer `fn()`
-               found fn pointer `fn() -> impl Future<Output = ()>`
+    |         --------------- definition of `ft1` from trait
+ ...
+ LL |         async fn ft1() {}
+    |         ^^^^^^^^^^^^^^ impl has extra requirement `(): Future`
- error[E0053]: method `ft5` has an incompatible type for trait
-   --> $DIR/fn-header-semantic-fail.rs:34:48
+ error[E0276]: impl has stricter requirements than trait
+   --> $DIR/fn-header-semantic-fail.rs:34:9
+   --> $DIR/fn-header-semantic-fail.rs:34:9
239    |
- LL |         const async unsafe extern "C" fn ft5() {}
-    |                                                |
-    |                                                |
-    |                                                checked the `Output` of this `async fn`, found opaque type
-    |
-    = note: while checking the return type of the `async fn`
- note: type in trait
-   --> $DIR/fn-header-semantic-fail.rs:21:47
-   --> $DIR/fn-header-semantic-fail.rs:21:47
-    |
250 LL |         const async unsafe extern "C" fn ft5();
-    = note: expected fn pointer `unsafe extern "C" fn()`
-    = note: expected fn pointer `unsafe extern "C" fn()`
-               found fn pointer `unsafe extern "C" fn() -> impl Future<Output = ()>`
+    |         --------------------------------------- definition of `ft5` from trait
+ ...
+ LL |         const async unsafe extern "C" fn ft5() {}
+    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl has extra requirement `(): Future`
254 
255 error[E0391]: cycle detected when computing type of `main::<impl at $DIR/fn-header-semantic-fail.rs:28:5: 28:17>::ft5::{opaque#0}`
256   --> $DIR/fn-header-semantic-fail.rs:34:48
326 
327 error: aborting due to 23 previous errors
328 
- Some errors have detailed explanations: E0053, E0379, E0391, E0706.
---
To only update this specific test, also pass `--test-args parser/fn-header-semantic-fail.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/parser/fn-header-semantic-fail.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/parser/fn-header-semantic-fail" "-A" "unused" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--edition=2018" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/parser/fn-header-semantic-fail/auxiliary"
stdout: none
--- stderr -------------------------------
error: functions cannot be both `const` and `async`
   |
   |
LL |     const async unsafe extern "C" fn ff5() {}
   |     ^^^^^-^^^^^------------------------------
Some tests failed in compiletest suite=ui mode=ui host=x86_64-unknown-linux-gnu target=x86_64-unknown-linux-gnu
Some tests failed in compiletest suite=ui mode=ui host=x86_64-unknown-linux-gnu target=x86_64-unknown-linux-gnu
   |     |     `async` because of this
   |     `const` because of this
error[E0706]: functions in traits cannot be declared `async`
  --> /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:17:9
   |
   |
LL |         async fn ft1(); //~ ERROR functions in traits cannot be declared `async`
   |         |
   |         |
   |         `async` because of this
   |
   = note: `async` trait functions are not currently supported
   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
error[E0379]: functions in traits cannot be declared const
  --> /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:19:9
   |
   |
LL |         const fn ft3(); //~ ERROR functions in traits cannot be declared const

error[E0379]: functions in traits cannot be declared const
  --> /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:21:9
   |
   |
LL |         const async unsafe extern "C" fn ft5();

error[E0706]: functions in traits cannot be declared `async`
  --> /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:21:9
   |
   |
LL |         const async unsafe extern "C" fn ft5();
   |               |
   |               |
   |               `async` because of this
   |
   = note: `async` trait functions are not currently supported
   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait

error: functions cannot be both `const` and `async`
   |
   |
LL |         const async unsafe extern "C" fn ft5();
   |         ^^^^^-^^^^^----------------------------
   |         |     |
   |         |     `async` because of this
   |         `const` because of this
error[E0706]: functions in traits cannot be declared `async`
  --> /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:29:9
   |
   |
LL |         async fn ft1() {} //~ ERROR functions in traits cannot be declared `async`
   |         |
   |         |
   |         `async` because of this
   |
   = note: `async` trait functions are not currently supported
   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
error[E0379]: functions in traits cannot be declared const
  --> /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:32:9
   |
   |
LL |         const fn ft3() {} //~ ERROR functions in traits cannot be declared const

error[E0379]: functions in traits cannot be declared const
  --> /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:34:9
   |
   |
LL |         const async unsafe extern "C" fn ft5() {}

error[E0706]: functions in traits cannot be declared `async`
  --> /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:34:9
   |
   |
LL |         const async unsafe extern "C" fn ft5() {}
   |               |
   |               |
   |               `async` because of this
   |
   = note: `async` trait functions are not currently supported
   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait

error: functions cannot be both `const` and `async`
   |
   |
LL |         const async unsafe extern "C" fn ft5() {}
   |         ^^^^^-^^^^^------------------------------
   |         |     |
   |         |     `async` because of this
   |         `const` because of this

error: functions cannot be both `const` and `async`
   |
   |
LL |         const async unsafe extern "C" fn fi5() {}
   |         ^^^^^-^^^^^------------------------------
   |         |     |
   |         |     `async` because of this
   |         `const` because of this

error: functions in `extern` blocks cannot have qualifiers
   |
LL |     extern "C" {
LL |     extern "C" {
   |     ---------- in this `extern` block
LL |         async fn fe1(); //~ ERROR functions in `extern` blocks cannot have qualifiers
   |
help: remove the qualifiers
   |
   |
LL |         fn fe1(); //~ ERROR functions in `extern` blocks cannot have qualifiers


error: functions in `extern` blocks cannot have qualifiers
   |
LL |     extern "C" {
LL |     extern "C" {
   |     ---------- in this `extern` block
LL |         async fn fe1(); //~ ERROR functions in `extern` blocks cannot have qualifiers
LL |         unsafe fn fe2(); //~ ERROR functions in `extern` blocks cannot have qualifiers
   |
help: remove the qualifiers
   |
   |
LL |         fn fe2(); //~ ERROR functions in `extern` blocks cannot have qualifiers


error: functions in `extern` blocks cannot have qualifiers
   |
LL |     extern "C" {
LL |     extern "C" {
   |     ---------- in this `extern` block
...
LL |         const fn fe3(); //~ ERROR functions in `extern` blocks cannot have qualifiers
   |
help: remove the qualifiers
   |
   |
LL |         fn fe3(); //~ ERROR functions in `extern` blocks cannot have qualifiers


error: functions in `extern` blocks cannot have qualifiers
   |
LL |     extern "C" {
LL |     extern "C" {
   |     ---------- in this `extern` block
...
LL |         extern "C" fn fe4(); //~ ERROR functions in `extern` blocks cannot have qualifiers
   |
help: remove the qualifiers
   |
   |
LL |         fn fe4(); //~ ERROR functions in `extern` blocks cannot have qualifiers


error: functions in `extern` blocks cannot have qualifiers
   |
LL |     extern "C" {
LL |     extern "C" {
   |     ---------- in this `extern` block
...
LL |         const async unsafe extern "C" fn fe5(); //~ ERROR functions in `extern` blocks
   |
help: remove the qualifiers
   |
   |
LL |         fn fe5(); //~ ERROR functions in `extern` blocks


error: functions cannot be both `const` and `async`
   |
   |
LL |         const async unsafe extern "C" fn fe5(); //~ ERROR functions in `extern` blocks
   |         ^^^^^-^^^^^----------------------------
   |         |     |
   |         |     `async` because of this
   |         `const` because of this

error[E0391]: cycle detected when computing type of `main::ff5::{opaque#0}`
   |
   |
LL |     const async unsafe extern "C" fn ff5() {}
   |
   |
note: ...which requires borrow-checking `main::ff5`...
   |
   |
LL |     const async unsafe extern "C" fn ff5() {}
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires processing `main::ff5`...
   |
   |
LL |     const async unsafe extern "C" fn ff5() {}
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires const checking `main::ff5`...
   |
   |
LL |     const async unsafe extern "C" fn ff5() {}
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: ...which requires computing whether `impl core::future::future::Future<Output = ()>` is freeze...
   = note: ...which requires evaluating trait selection obligation `impl core::future::future::Future<Output = ()>: core::marker::Freeze`...
   = note: ...which again requires computing type of `main::ff5::{opaque#0}`, completing the cycle
note: cycle used when checking item types in top-level module
   |
LL | / #![feature(const_extern_fn)]
LL | |
LL | | fn main() {
LL | | fn main() {
LL | |     async fn ff1() {} // OK.
LL | |     }
LL | | }
   | |_^


error[E0276]: impl has stricter requirements than trait
  --> /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:29:9
   |
LL |         async fn ft1(); //~ ERROR functions in traits cannot be declared `async`
   |         --------------- definition of `ft1` from trait
...
LL |         async fn ft1() {} //~ ERROR functions in traits cannot be declared `async`
   |         ^^^^^^^^^^^^^^ impl has extra requirement `(): Future`
error[E0276]: impl has stricter requirements than trait
  --> /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:34:9
   |
   |
LL |         const async unsafe extern "C" fn ft5();
   |         --------------------------------------- definition of `ft5` from trait
...
LL |         const async unsafe extern "C" fn ft5() {}
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl has extra requirement `(): Future`

error[E0391]: cycle detected when computing type of `main::<impl at /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:28:5: 28:17>::ft5::{opaque#0}`
   |
   |
LL |         const async unsafe extern "C" fn ft5() {}
   |
   |
note: ...which requires borrow-checking `main::<impl at /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:28:5: 28:17>::ft5`...
   |
   |
LL |         const async unsafe extern "C" fn ft5() {}
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires processing `main::<impl at /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:28:5: 28:17>::ft5`...
   |
   |
LL |         const async unsafe extern "C" fn ft5() {}
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires const checking `main::<impl at /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:28:5: 28:17>::ft5`...
   |
   |
LL |         const async unsafe extern "C" fn ft5() {}
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: ...which requires computing whether `impl core::future::future::Future<Output = ()>` is freeze...
   = note: ...which requires evaluating trait selection obligation `impl core::future::future::Future<Output = ()>: core::marker::Freeze`...
   = note: ...which again requires computing type of `main::<impl at /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:28:5: 28:17>::ft5::{opaque#0}`, completing the cycle
note: cycle used when checking item types in top-level module
   |
LL | / #![feature(const_extern_fn)]
LL | |
LL | | fn main() {
LL | | fn main() {
LL | |     async fn ff1() {} // OK.
LL | |     }
LL | | }
   | |_^


error[E0391]: cycle detected when computing type of `main::<impl at /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:42:5: 42:11>::fi5::{opaque#0}`
   |
   |
LL |         const async unsafe extern "C" fn fi5() {}
   |
   |
note: ...which requires borrow-checking `main::<impl at /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:42:5: 42:11>::fi5`...
   |
   |
LL |         const async unsafe extern "C" fn fi5() {}
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires processing `main::<impl at /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:42:5: 42:11>::fi5`...
   |
   |
LL |         const async unsafe extern "C" fn fi5() {}
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires const checking `main::<impl at /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:42:5: 42:11>::fi5`...
   |
   |
LL |         const async unsafe extern "C" fn fi5() {}
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: ...which requires computing whether `impl core::future::future::Future<Output = ()>` is freeze...
   = note: ...which requires evaluating trait selection obligation `impl core::future::future::Future<Output = ()>: core::marker::Freeze`...
   = note: ...which again requires computing type of `main::<impl at /checkout/src/test/ui/parser/fn-header-semantic-fail.rs:42:5: 42:11>::fi5::{opaque#0}`, completing the cycle
note: cycle used when checking item types in top-level module
   |
LL | / #![feature(const_extern_fn)]
LL | |
LL | | fn main() {
LL | | fn main() {
LL | |     async fn ff1() {} // OK.
LL | |     }
LL | | }
   | |_^

---

---- [ui] src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.rs stdout ----
diff of stderr:

44    = note: `async` trait functions are not currently supported
45    = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
- error[E0053]: method `associated` has an incompatible type for trait
-   --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:15:26
+ error[E0276]: impl has stricter requirements than trait
+   --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:15:5
+   --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:15:5
49    |
50 LL |     async fn associated();
-    |                          ^
-    |                          |
-    |                          checked the `Output` of this `async fn`, found opaque type
-    |
-    = note: while checking the return type of the `async fn`
- note: type in trait
-   --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:11:26
-   --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:11:26
-    |
+    |     ---------------------- definition of `associated` from trait
+ ...
60 LL |     async fn associated();
-    |                          ^
-    = note: expected fn pointer `fn()`
-               found fn pointer `fn() -> impl Future<Output = ()>`
+    |     ^^^^^^^^^^^^^^^^^^^^^^ impl has extra requirement `(): Future`
65 error: aborting due to 6 previous errors
66 

- Some errors have detailed explanations: E0053, E0706.
---
To only update this specific test, also pass `--test-args resolve/issue-70736-async-fn-no-body-def-collector.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/resolve/issue-70736-async-fn-no-body-def-collector" "-A" "unused" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--edition=2018" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/resolve/issue-70736-async-fn-no-body-def-collector/auxiliary"
stdout: none
--- stderr -------------------------------
error: free function without a body
   |
   |
LL | async fn free(); //~ ERROR without a body
   |                |
   |                |
   |                help: provide a definition for the function: `{ <body> }`

error: associated function in `impl` without body
   |
   |
LL |     async fn inherent(); //~ ERROR without body
   |                        |
   |                        |
   |                        help: provide a definition for the function: `{ <body> }`
error[E0706]: functions in traits cannot be declared `async`
  --> /checkout/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.rs:11:5
   |
LL |     async fn associated();
LL |     async fn associated();
   |     -----^^^^^^^^^^^^^^^^^
   |     |
   |     `async` because of this
   |
   = note: `async` trait functions are not currently supported
   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait

error: associated function in `impl` without body
   |
   |
LL |     async fn associated(); //~ ERROR without body
   |                          |
   |                          |
   |                          help: provide a definition for the function: `{ <body> }`
error[E0706]: functions in traits cannot be declared `async`
  --> /checkout/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.rs:15:5
   |
   |
LL |     async fn associated(); //~ ERROR without body
   |     |
   |     |
   |     `async` because of this
   |
   = note: `async` trait functions are not currently supported
   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
error[E0276]: impl has stricter requirements than trait
  --> /checkout/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.rs:15:5
   |
LL |     async fn associated();
LL |     async fn associated();
   |     ---------------------- definition of `associated` from trait
...
LL |     async fn associated(); //~ ERROR without body
   |     ^^^^^^^^^^^^^^^^^^^^^^ impl has extra requirement `(): Future`
error: aborting due to 6 previous errors

Some errors have detailed explanations: E0276, E0706.
For more information about an error, try `rustc --explain E0276`.
For more information about an error, try `rustc --explain E0276`.
------------------------------------------


---- [ui] src/test/ui/type-alias-impl-trait/issue-57961.rs stdout ----
diff of stderr:

- error[E0271]: expected `std::vec::IntoIter<u32>` to be an iterator that yields `X`, but it yields `u32`
+ error[E0308]: mismatched types
3    |
3    |
4 LL | type X = impl Sized;
5    |          ---------- the expected opaque type
6 ...
7 LL |     type Bar = std::vec::IntoIter<u32>;
-    |                ^^^^^^^^^^^^^^^^^^^^^^^ expected opaque type, found `u32`
---

- note: required by a bound in `Foo::Bar`
-   --> $DIR/issue-57961.rs:6:24
-    |
- LL |     type Bar: Iterator<Item = X>;
-    |                        ^^^^^^^^ required by this bound in `Foo::Bar`
18 error: aborting due to previous error
19 

- For more information about this error, try `rustc --explain E0271`.
---
To only update this specific test, also pass `--test-args type-alias-impl-trait/issue-57961.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/type-alias-impl-trait/issue-57961.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/type-alias-impl-trait/issue-57961" "-A" "unused" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/type-alias-impl-trait/issue-57961/auxiliary"
stdout: none
--- stderr -------------------------------
  --> /checkout/src/test/ui/type-alias-impl-trait/issue-57961.rs:10:16
   |
   |
LL | type X = impl Sized;
...
LL |     type Bar = std::vec::IntoIter<u32>;
   |                ^^^^^^^^^^^^^^^^^^^^^^^ types differ
   |

[ouz-a]

There's still the failing debug assertion, of course.

Although I have an idea why this change makes miri build without ICE, I don't know why debug assertions cause problems.

[RalfJung]

@ouz-a I am confused by the question. A debug assertion causes problems when it does not hold? That's completely expected.

Regular release builds of Miri have debug assertions disabled, that's why we did not notice when this started.

[ouz-a]

@ouz-a I am confused by the question. A debug assertion causes problems when it does not hold? That's completely expected.

Regular release builds of Miri have debug assertions disabled, that's why we did not notice when this started.

Ahh okay, this shouldn't be hard to fix then I will try to push it tonight.

[ouz-a]

Opened #100967, it should fix problems related to my PR. @RalfJung

[RalfJung]

Superseded by #100967