Auto merge of #61044 - Centril:rollup-ztsgb9p, r=Centril

Rollup of 8 pull requests

Successful merges:

 - #60300 (Allow null-pointer-optimized enums in FFI if their underlying representation is FFI safe)
 - #60773 (Always try to project predicates when finding auto traits in rustdoc)
 - #60809 (Add FAQ for NLL migration)
 - #61023 (Migrate from recursion to iterate on qualify consts visitor impl)
 - #61029 (Simplify RefCell minimum_spanning_tree example)
 - #61030 (Make maybe_codegen_consume_direct iterate instead of doing recursion)
 - #61034 (rustc_metadata: parametrize schema::CrateRoot by 'tcx and rip out old unused incremental infra.)
 - #61037 (Update clippy submodule)

Failed merges:

r? @ghost

23 files changed, 135 insertions, 11 deletions

diff --git a/src/test/rustdoc/issue-60726.rs b/src/test/rustdoc/issue-60726.rs
new file mode 100644
index 00000000000..6acc8627738
--- /dev/null
+++ b/src/test/rustdoc/issue-60726.rs
@@ -0,0 +1,35 @@
+use std::marker::PhantomData;
+
+pub struct True;
+pub struct False;
+
+pub trait InterfaceType{
+    type Send;
+}
+
+
+pub struct FooInterface<T>(PhantomData<fn()->T>);
+
+impl<T> InterfaceType for FooInterface<T> {
+    type Send=False;
+}
+
+
+pub struct DynTrait<I>{
+    _interface:PhantomData<fn()->I>,
+    _unsync_unsend:PhantomData<::std::rc::Rc<()>>,
+}
+
+unsafe impl<I> Send for DynTrait<I>
+where
+    I:InterfaceType<Send=True>
+{}
+
+// @has issue_60726/struct.IntoIter.html
+// @has - '//*[@id="synthetic-implementations-list"]/*[@class="impl"]//code' "impl<T> !Send for \
+// IntoIter<T>"
+// @has - '//*[@id="synthetic-implementations-list"]/*[@class="impl"]//code' "impl<T> !Sync for \
+// IntoIter<T>"
+pub struct IntoIter<T>{
+    hello:DynTrait<FooInterface<T>>,
+}
diff --git a/src/test/ui/borrowck/borrowck-anon-fields-variant.stderr b/src/test/ui/borrowck/borrowck-anon-fields-variant.stderr
index 5e86dcb1232..e2d3e417ac3 100644
--- a/src/test/ui/borrowck/borrowck-anon-fields-variant.stderr
+++ b/src/test/ui/borrowck/borrowck-anon-fields-variant.stderr
@@ -12,6 +12,7 @@ LL |     *a += 1;
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error[E0503]: cannot use `y` because it was mutably borrowed
   --> $DIR/borrowck-anon-fields-variant.rs:37:7
diff --git a/src/test/ui/borrowck/borrowck-describe-lvalue.stderr b/src/test/ui/borrowck/borrowck-describe-lvalue.stderr
index fb42e5fbca8..14b9b50f0c3 100644
--- a/src/test/ui/borrowck/borrowck-describe-lvalue.stderr
+++ b/src/test/ui/borrowck/borrowck-describe-lvalue.stderr
@@ -341,6 +341,7 @@ LL |             drop(x);
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 warning[E0502]: cannot borrow `*block.current` as immutable because it is also borrowed as mutable
   --> $DIR/borrowck-describe-lvalue.rs:227:33
@@ -355,6 +356,7 @@ LL |             drop(x);
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error[E0382]: use of moved value: `x`
   --> $DIR/borrowck-describe-lvalue.rs:282:22
diff --git a/src/test/ui/borrowck/borrowck-migrate-to-nll.edition.stderr b/src/test/ui/borrowck/borrowck-migrate-to-nll.edition.stderr
index 8dba34bd808..461fb7d11a5 100644
--- a/src/test/ui/borrowck/borrowck-migrate-to-nll.edition.stderr
+++ b/src/test/ui/borrowck/borrowck-migrate-to-nll.edition.stderr
@@ -6,4 +6,5 @@ LL |                 (|| { let bar = foo; bar.take() })();
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
diff --git a/src/test/ui/borrowck/borrowck-migrate-to-nll.zflag.stderr b/src/test/ui/borrowck/borrowck-migrate-to-nll.zflag.stderr
index 8dba34bd808..461fb7d11a5 100644
--- a/src/test/ui/borrowck/borrowck-migrate-to-nll.zflag.stderr
+++ b/src/test/ui/borrowck/borrowck-migrate-to-nll.zflag.stderr
@@ -6,4 +6,5 @@ LL |                 (|| { let bar = foo; bar.take() })();
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
diff --git a/src/test/ui/borrowck/borrowck-mutate-in-guard.stderr b/src/test/ui/borrowck/borrowck-mutate-in-guard.stderr
index d12d751d89b..ac6bed6137f 100644
--- a/src/test/ui/borrowck/borrowck-mutate-in-guard.stderr
+++ b/src/test/ui/borrowck/borrowck-mutate-in-guard.stderr
@@ -28,6 +28,7 @@ LL |         Enum::A(_) if { x = Enum::B(false); false } => 1,
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 warning[E0510]: cannot mutably borrow `x` in match guard
   --> $DIR/borrowck-mutate-in-guard.rs:15:33
@@ -40,6 +41,7 @@ LL |         Enum::A(_) if { let y = &mut x; *y = Enum::B(false); false } => 1,
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/consts/const_let_refutable.stderr b/src/test/ui/consts/const_let_refutable.stderr
index 20433bbf8b5..2ca76667bd1 100644
--- a/src/test/ui/consts/const_let_refutable.stderr
+++ b/src/test/ui/consts/const_let_refutable.stderr
@@ -21,6 +21,7 @@ LL |     a + b
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 warning[E0381]: use of possibly uninitialized variable: `b`
   --> $DIR/const_let_refutable.rs:4:9
@@ -30,6 +31,7 @@ LL |     a + b
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/consts/min_const_fn/min_const_fn.stderr b/src/test/ui/consts/min_const_fn/min_const_fn.stderr
index 7af37992460..93b57bc24a8 100644
--- a/src/test/ui/consts/min_const_fn/min_const_fn.stderr
+++ b/src/test/ui/consts/min_const_fn/min_const_fn.stderr
@@ -297,6 +297,7 @@ LL | const fn no_dyn_trait_ret() -> &'static dyn std::fmt::Debug { &() }
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error[E0723]: trait bounds other than `Sized` on const fn parameters are unstable
   --> $DIR/min_const_fn.rs:144:41
diff --git a/src/test/ui/consts/min_const_fn/min_const_fn_dyn.stderr b/src/test/ui/consts/min_const_fn/min_const_fn_dyn.stderr
index b6445329db3..9ded93c1672 100644
--- a/src/test/ui/consts/min_const_fn/min_const_fn_dyn.stderr
+++ b/src/test/ui/consts/min_const_fn/min_const_fn_dyn.stderr
@@ -27,6 +27,7 @@ LL | const fn no_inner_dyn_trait_ret() -> Hide { Hide(HasDyn { field: &0 }) }
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/empty/empty-never-array.stderr b/src/test/ui/empty/empty-never-array.stderr
index 6608ad763b2..9911dd4683b 100644
--- a/src/test/ui/empty/empty-never-array.stderr
+++ b/src/test/ui/empty/empty-never-array.stderr
@@ -19,6 +19,7 @@ LL |     u
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/feature-gates/feature-gate-nll.stderr b/src/test/ui/feature-gates/feature-gate-nll.stderr
index ac21241b303..37542d52dc2 100644
--- a/src/test/ui/feature-gates/feature-gate-nll.stderr
+++ b/src/test/ui/feature-gates/feature-gate-nll.stderr
@@ -11,6 +11,7 @@ LL |     m;
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error: compilation successful
   --> $DIR/feature-gate-nll.rs:10:1
diff --git a/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.rs b/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.rs
index f7ff3eb3ac9..9f5c92349e0 100644
--- a/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.rs
+++ b/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.rs
@@ -4,5 +4,6 @@
 
 #[rustc_variance] //~ ERROR the `#[rustc_variance]` attribute is just used for rustc unit tests and will never be stable
 #[rustc_error] //~ ERROR the `#[rustc_error]` attribute is just used for rustc unit tests and will never be stable
+#[rustc_nonnull_optimization_guaranteed] //~ ERROR the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable niche optimizations in libcore and will never be stable
 
 fn main() {}
diff --git a/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.stderr b/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.stderr
index 882feb87f42..ed98484e13c 100644
--- a/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.stderr
+++ b/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.stderr
@@ -16,6 +16,15 @@ LL | #[rustc_error]
    = note: for more information, see https://github.com/rust-lang/rust/issues/29642
    = help: add #![feature(rustc_attrs)] to the crate attributes to enable
 
-error: aborting due to 2 previous errors
+error[E0658]: the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable niche optimizations in libcore and will never be stable
+  --> $DIR/feature-gate-rustc-attrs-1.rs:7:1
+   |
+LL | #[rustc_nonnull_optimization_guaranteed]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/29642
+   = help: add #![feature(rustc_attrs)] to the crate attributes to enable
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0658`.
diff --git a/src/test/ui/issues/issue-15381.stderr b/src/test/ui/issues/issue-15381.stderr
index 0f44a0f170f..7b11d85ead8 100644
--- a/src/test/ui/issues/issue-15381.stderr
+++ b/src/test/ui/issues/issue-15381.stderr
@@ -12,6 +12,7 @@ LL |         println!("y={}", y);
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issues/issue-40510-1.migrate.stderr b/src/test/ui/issues/issue-40510-1.migrate.stderr
index 17d1c48d075..28aaa2a797e 100644
--- a/src/test/ui/issues/issue-40510-1.migrate.stderr
+++ b/src/test/ui/issues/issue-40510-1.migrate.stderr
@@ -10,6 +10,7 @@ LL |         &mut x
    = note: ...therefore, they cannot allow references to captured variables to escape
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error: compilation successful
   --> $DIR/issue-40510-1.rs:20:1
diff --git a/src/test/ui/issues/issue-40510-3.migrate.stderr b/src/test/ui/issues/issue-40510-3.migrate.stderr
index 692aa105377..f00690efc31 100644
--- a/src/test/ui/issues/issue-40510-3.migrate.stderr
+++ b/src/test/ui/issues/issue-40510-3.migrate.stderr
@@ -12,6 +12,7 @@ LL | |         }
    = note: ...therefore, they cannot allow references to captured variables to escape
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error: compilation successful
   --> $DIR/issue-40510-3.rs:22:1
diff --git a/src/test/ui/issues/issue-45696-scribble-on-boxed-borrow.migrate.stderr b/src/test/ui/issues/issue-45696-scribble-on-boxed-borrow.migrate.stderr
index 8cc9f1eb2a6..479b724ad18 100644
--- a/src/test/ui/issues/issue-45696-scribble-on-boxed-borrow.migrate.stderr
+++ b/src/test/ui/issues/issue-45696-scribble-on-boxed-borrow.migrate.stderr
@@ -11,6 +11,7 @@ LL | }
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 warning[E0713]: borrow may still be in use when destructor runs
   --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:62:5
@@ -25,6 +26,7 @@ LL | }
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 warning[E0713]: borrow may still be in use when destructor runs
   --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:73:5
@@ -39,6 +41,7 @@ LL | }
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error: compilation successful
   --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:80:1
diff --git a/src/test/ui/issues/issue-49824.stderr b/src/test/ui/issues/issue-49824.stderr
index c66ee69cb2b..d5f1af88e13 100644
--- a/src/test/ui/issues/issue-49824.stderr
+++ b/src/test/ui/issues/issue-49824.stderr
@@ -15,6 +15,7 @@ LL | |         }
    = note: ...therefore, they cannot allow references to captured variables to escape
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error: compilation successful
   --> $DIR/issue-49824.rs:6:1
diff --git a/src/test/ui/lint/lint-ctypes-enum.rs b/src/test/ui/lint/lint-ctypes-enum.rs
index f347c2761c3..d3e11d2f7ed 100644
--- a/src/test/ui/lint/lint-ctypes-enum.rs
+++ b/src/test/ui/lint/lint-ctypes-enum.rs
@@ -1,6 +1,8 @@
 #![deny(improper_ctypes)]
 #![allow(dead_code)]
 
+use std::num;
+
 enum Z { }
 enum U { A }
 enum B { C, D }
@@ -15,14 +17,39 @@ enum U8 { A, B, C }
 #[repr(isize)]
 enum Isize { A, B, C }
 
+#[repr(transparent)]
+struct Transparent<T>(T, std::marker::PhantomData<Z>);
+
+struct Rust<T>(T);
+
 extern {
    fn zf(x: Z);
    fn uf(x: U); //~ ERROR enum has no representation hint
    fn bf(x: B); //~ ERROR enum has no representation hint
    fn tf(x: T); //~ ERROR enum has no representation hint
-   fn reprc(x: ReprC);
-   fn u8(x: U8);
-   fn isize(x: Isize);
+   fn repr_c(x: ReprC);
+   fn repr_u8(x: U8);
+   fn repr_isize(x: Isize);
+   fn option_ref(x: Option<&'static u8>);
+   fn option_fn(x: Option<extern "C" fn()>);
+   fn nonnull(x: Option<std::ptr::NonNull<u8>>);
+   fn nonzero_u8(x: Option<num::NonZeroU8>);
+   fn nonzero_u16(x: Option<num::NonZeroU16>);
+   fn nonzero_u32(x: Option<num::NonZeroU32>);
+   fn nonzero_u64(x: Option<num::NonZeroU64>);
+   fn nonzero_u128(x: Option<num::NonZeroU128>);
+   //~^ ERROR 128-bit integers don't currently have a known stable ABI
+   fn nonzero_usize(x: Option<num::NonZeroUsize>);
+   fn nonzero_i8(x: Option<num::NonZeroI8>);
+   fn nonzero_i16(x: Option<num::NonZeroI16>);
+   fn nonzero_i32(x: Option<num::NonZeroI32>);
+   fn nonzero_i64(x: Option<num::NonZeroI64>);
+   fn nonzero_i128(x: Option<num::NonZeroI128>);
+   //~^ ERROR 128-bit integers don't currently have a known stable ABI
+   fn nonzero_isize(x: Option<num::NonZeroIsize>);
+   fn repr_transparent(x: Option<Transparent<num::NonZeroU8>>);
+   fn repr_rust(x: Option<Rust<num::NonZeroU8>>); //~ ERROR enum has no representation hint
+   fn no_result(x: Result<(), num::NonZeroI32>); //~ ERROR enum has no representation hint
 }
 
 pub fn main() { }
diff --git a/src/test/ui/lint/lint-ctypes-enum.stderr b/src/test/ui/lint/lint-ctypes-enum.stderr
index 92f76cfc38a..6b807f48aaa 100644
--- a/src/test/ui/lint/lint-ctypes-enum.stderr
+++ b/src/test/ui/lint/lint-ctypes-enum.stderr
@@ -1,5 +1,5 @@
 error: `extern` block uses type `U` which is not FFI-safe: enum has no representation hint
-  --> $DIR/lint-ctypes-enum.rs:20:13
+  --> $DIR/lint-ctypes-enum.rs:27:13
    |
 LL |    fn uf(x: U);
    |             ^
@@ -11,36 +11,64 @@ LL | #![deny(improper_ctypes)]
    |         ^^^^^^^^^^^^^^^
    = help: consider adding a #[repr(...)] attribute to this enum
 note: type defined here
-  --> $DIR/lint-ctypes-enum.rs:5:1
+  --> $DIR/lint-ctypes-enum.rs:7:1
    |
 LL | enum U { A }
    | ^^^^^^^^^^^^
 
 error: `extern` block uses type `B` which is not FFI-safe: enum has no representation hint
-  --> $DIR/lint-ctypes-enum.rs:21:13
+  --> $DIR/lint-ctypes-enum.rs:28:13
    |
 LL |    fn bf(x: B);
    |             ^
    |
    = help: consider adding a #[repr(...)] attribute to this enum
 note: type defined here
-  --> $DIR/lint-ctypes-enum.rs:6:1
+  --> $DIR/lint-ctypes-enum.rs:8:1
    |
 LL | enum B { C, D }
    | ^^^^^^^^^^^^^^^
 
 error: `extern` block uses type `T` which is not FFI-safe: enum has no representation hint
-  --> $DIR/lint-ctypes-enum.rs:22:13
+  --> $DIR/lint-ctypes-enum.rs:29:13
    |
 LL |    fn tf(x: T);
    |             ^
    |
    = help: consider adding a #[repr(...)] attribute to this enum
 note: type defined here
-  --> $DIR/lint-ctypes-enum.rs:7:1
+  --> $DIR/lint-ctypes-enum.rs:9:1
    |
 LL | enum T { E, F, G }
    | ^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 3 previous errors
+error: `extern` block uses type `u128` which is not FFI-safe: 128-bit integers don't currently have a known stable ABI
+  --> $DIR/lint-ctypes-enum.rs:40:23
+   |
+LL |    fn nonzero_u128(x: Option<num::NonZeroU128>);
+   |                       ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: `extern` block uses type `i128` which is not FFI-safe: 128-bit integers don't currently have a known stable ABI
+  --> $DIR/lint-ctypes-enum.rs:47:23
+   |
+LL |    fn nonzero_i128(x: Option<num::NonZeroI128>);
+   |                       ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: `extern` block uses type `std::option::Option<Rust<std::num::NonZeroU8>>` which is not FFI-safe: enum has no representation hint
+  --> $DIR/lint-ctypes-enum.rs:51:20
+   |
+LL |    fn repr_rust(x: Option<Rust<num::NonZeroU8>>);
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider adding a #[repr(...)] attribute to this enum
+
+error: `extern` block uses type `std::result::Result<(), std::num::NonZeroI32>` which is not FFI-safe: enum has no representation hint
+  --> $DIR/lint-ctypes-enum.rs:52:20
+   |
+LL |    fn no_result(x: Result<(), num::NonZeroI32>);
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider adding a #[repr(...)] attribute to this enum
+
+error: aborting due to 7 previous errors
 
diff --git a/src/test/ui/pattern/pattern-bindings-after-at.stderr b/src/test/ui/pattern/pattern-bindings-after-at.stderr
index 3a2cffcbf45..70452a930ee 100644
--- a/src/test/ui/pattern/pattern-bindings-after-at.stderr
+++ b/src/test/ui/pattern/pattern-bindings-after-at.stderr
@@ -18,6 +18,7 @@ LL |             **z = None;
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/recursion/recursive-types-are-not-uninhabited.stderr b/src/test/ui/recursion/recursive-types-are-not-uninhabited.stderr
index 940ab94a613..9203f893fdb 100644
--- a/src/test/ui/recursion/recursive-types-are-not-uninhabited.stderr
+++ b/src/test/ui/recursion/recursive-types-are-not-uninhabited.stderr
@@ -12,6 +12,7 @@ LL |     x
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/thread-local-in-ctfe.stderr b/src/test/ui/thread-local-in-ctfe.stderr
index bba5b0c74d9..6869109e67f 100644
--- a/src/test/ui/thread-local-in-ctfe.stderr
+++ b/src/test/ui/thread-local-in-ctfe.stderr
@@ -20,6 +20,7 @@ LL | static C: &u32 = &A;
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error[E0625]: thread-local statics cannot be accessed at compile-time
   --> $DIR/thread-local-in-ctfe.rs:15:16
@@ -43,6 +44,7 @@ LL | const E: &u32 = &A;
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+   = note: for more information, try `rustc --explain E0729`
 
 error[E0625]: thread-local statics cannot be accessed at compile-time
   --> $DIR/thread-local-in-ctfe.rs:25:5