Auto merge of rust-lang#148059 - Zalathar:rollup-zkk5prm, r=Zalathar

Rollup of 5 pull requests

Successful merges:

 - rust-lang#148016 (Revert constification of `Borrow` and `Deref for Cow` due to inference failure)
 - rust-lang#148021 ([rustdoc] Simplify module rendering and HTML tags handling)
 - rust-lang#148039 (Add myself to the review rotation)
 - rust-lang#148042 (test(frontmatter): Cover spaces between infostring parts)
 - rust-lang#148054 (Streamline iterator chaining when computing successors.)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

compiler/rustc_middle/src/mir/terminator.rs

@@ -501,6 +501,8 @@ pub use helper::*;
 
 mod helper {
     use super::*;
+    // Note: the methods below use a `slice.chain(Option).chain(Option)` pattern so that all paths
+    // produce an iterator with the same concrete type.
     pub type Successors<'a> = impl DoubleEndedIterator<Item = BasicBlock> + 'a;
 
     impl SwitchTargets {
@@ -510,7 +512,7 @@ mod helper {
         #[define_opaque(Successors)]
         pub fn successors_for_value(&self, value: u128) -> Successors<'_> {
             let target = self.target_for_value(value);
-            (&[]).into_iter().copied().chain(Some(target).into_iter().chain(None))
+            (&[]).into_iter().copied().chain(Some(target)).chain(None)
         }
     }
 
@@ -522,10 +524,7 @@ mod helper {
             match *self {
                 // 3-successors for async drop: target, unwind, dropline (parent coroutine drop)
                 Drop { target: ref t, unwind: UnwindAction::Cleanup(u), drop: Some(d), .. } => {
-                    slice::from_ref(t)
-                        .into_iter()
-                        .copied()
-                        .chain(Some(u).into_iter().chain(Some(d)))
+                    slice::from_ref(t).into_iter().copied().chain(Some(u)).chain(Some(d))
                 }
                 // 2-successors
                 Call { target: Some(ref t), unwind: UnwindAction::Cleanup(u), .. }
@@ -534,7 +533,7 @@ mod helper {
                 | Drop { target: ref t, unwind: _, drop: Some(u), .. }
                 | Assert { target: ref t, unwind: UnwindAction::Cleanup(u), .. }
                 | FalseUnwind { real_target: ref t, unwind: UnwindAction::Cleanup(u) } => {
-                    slice::from_ref(t).into_iter().copied().chain(Some(u).into_iter().chain(None))
+                    slice::from_ref(t).into_iter().copied().chain(Some(u)).chain(None)
                 }
                 // single successor
                 Goto { target: ref t }
@@ -544,7 +543,7 @@ mod helper {
                 | Drop { target: ref t, unwind: _, .. }
                 | Assert { target: ref t, unwind: _, .. }
                 | FalseUnwind { real_target: ref t, unwind: _ } => {
-                    slice::from_ref(t).into_iter().copied().chain(None.into_iter().chain(None))
+                    slice::from_ref(t).into_iter().copied().chain(None).chain(None)
                 }
                 // No successors
                 UnwindResume
@@ -554,23 +553,24 @@ mod helper {
                 | Unreachable
                 | TailCall { .. }
                 | Call { target: None, unwind: _, .. } => {
-                    (&[]).into_iter().copied().chain(None.into_iter().chain(None))
+                    (&[]).into_iter().copied().chain(None).chain(None)
                 }
                 // Multiple successors
                 InlineAsm { ref targets, unwind: UnwindAction::Cleanup(u), .. } => {
-                    targets.iter().copied().chain(Some(u).into_iter().chain(None))
+                    targets.iter().copied().chain(Some(u)).chain(None)
                 }
                 InlineAsm { ref targets, unwind: _, .. } => {
-                    targets.iter().copied().chain(None.into_iter().chain(None))
+                    targets.iter().copied().chain(None).chain(None)
                 }
                 SwitchInt { ref targets, .. } => {
-                    targets.targets.iter().copied().chain(None.into_iter().chain(None))
+                    targets.targets.iter().copied().chain(None).chain(None)
                 }
                 // FalseEdge
                 FalseEdge { ref real_target, imaginary_target } => slice::from_ref(real_target)
                     .into_iter()
                     .copied()
-                    .chain(Some(imaginary_target).into_iter().chain(None)),
+                    .chain(Some(imaginary_target))
+                    .chain(None),
             }
         }
 

library/alloc/src/borrow.rs

@@ -16,12 +16,13 @@ use crate::fmt;
 #[cfg(not(no_global_oom_handling))]
 use crate::string::String;
 
+// FIXME(inference): const bounds removed due to inference regressions found by crater;
+//   see https://github.com/rust-lang/rust/issues/147964
+// #[rustc_const_unstable(feature = "const_convert", issue = "143773")]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
-impl<'a, B: ?Sized> const Borrow<B> for Cow<'a, B>
-where
-    B: ToOwned,
-    B::Owned: [const] Borrow<B>,
+impl<'a, B: ?Sized + ToOwned> Borrow<B> for Cow<'a, B>
+// where
+//     B::Owned: [const] Borrow<B>,
 {
     fn borrow(&self) -> &B {
         &**self
@@ -327,11 +328,13 @@ impl<B: ?Sized + ToOwned> Cow<'_, B> {
     }
 }
 
+// FIXME(inference): const bounds removed due to inference regressions found by crater;
+//   see https://github.com/rust-lang/rust/issues/147964
+// #[rustc_const_unstable(feature = "const_convert", issue = "143773")]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
-impl<B: ?Sized + ToOwned> const Deref for Cow<'_, B>
-where
-    B::Owned: [const] Borrow<B>,
+impl<B: ?Sized + ToOwned> Deref for Cow<'_, B>
+// where
+//     B::Owned: [const] Borrow<B>,
 {
     type Target = B;