Auto merge of #72202 - Dylan-DPC:rollup-6lbxh1s, r=Dylan-DPC

Rollup of 8 pull requests

Successful merges:

 - #71910 (Fix unused_parens false positive when using binary operations)
 - #72087 (Fix hang in lexical_region_resolve)
 - #72126 (Change `WorkProduct::saved_files` to an `Option`.)
 - #72127 (add long error explanation for E0228)
 - #72141 (Warn against thread::sleep in async fn)
 - #72170 (use `require_lang_item` over `unwrap`.)
 - #72191 (Clean up E0589 explanation)
 - #72194 (Don't ICE on missing `Unsize` impl)

Failed merges:

r? @ghost

2 files changed, 42 insertions, 0 deletions

diff --git a/src/librustc_error_codes/error_codes/E0228.md b/src/librustc_error_codes/error_codes/E0228.md
new file mode 100644
index 00000000000..3443a5ae863
--- /dev/null
+++ b/src/librustc_error_codes/error_codes/E0228.md
@@ -0,0 +1,40 @@
+The lifetime bound for this object type cannot be deduced from context and must
+be specified.
+
+Erroneous code example:
+
+```compile_fail,E0228
+trait Trait { }
+
+struct TwoBounds<'a, 'b, T: Sized + 'a + 'b> {
+    x: &'a i32,
+    y: &'b i32,
+    z: T,
+}
+
+type Foo<'a, 'b> = TwoBounds<'a, 'b, dyn Trait>;
+```
+
+When a trait object is used as a type argument of a generic type, Rust will try
+to infer its lifetime if unspecified. However, this isn't possible when the
+containing type has more than one lifetime bound.
+
+The above example can be resolved by either reducing the number of lifetime
+bounds to one or by making the trait object lifetime explicit, like so:
+
+```
+trait Trait { }
+
+struct TwoBounds<'a, 'b, T: Sized + 'a + 'b> {
+    x: &'a i32,
+    y: &'b i32,
+    z: T,
+}
+
+type Foo<'a, 'b> = TwoBounds<'a, 'b, dyn Trait + 'b>;
+```
+
+For more information, see [RFC 599] and its amendment [RFC 1156].
+
+[RFC 599]: https://github.com/rust-lang/rfcs/blob/master/text/0599-default-object-bound.md
+[RFC 1156]: https://github.com/rust-lang/rfcs/blob/master/text/1156-adjust-default-object-bounds.md
diff --git a/src/librustc_error_codes/error_codes/E0589.md b/src/librustc_error_codes/error_codes/E0589.md
index 5e15a875b0b..8a4f8d21725 100644
--- a/src/librustc_error_codes/error_codes/E0589.md
+++ b/src/librustc_error_codes/error_codes/E0589.md
@@ -1,6 +1,8 @@
 The value of `N` that was specified for `repr(align(N))` was not a power
 of two, or was greater than 2^29.
 
+Erroneous code example:
+
 ```compile_fail,E0589
 #[repr(align(15))] // error: invalid `repr(align)` attribute: not a power of two
 enum Foo {