Auto merge of #61988 - Centril:there-is-only-loop, r=matthewjasper

[let_chains, 3/6] And then there was only Loop

Here we remove `hir::ExprKind::While`.
Instead, we desugar: `'label: while $cond $body` into:

```rust
'label: loop {
    match DropTemps($cond) {
        true => $body,
        _ => break,
    }
}
```

Per https://github.com/rust-lang/rust/issues/53667#issuecomment-471583239.
This is a follow up to https://github.com/rust-lang/rust/pull/59288 which did the same for `if` expressions.

r? @matthewjasper

1 files changed, 3 insertions, 2 deletions

diff --git a/src/libsyntax_pos/hygiene.rs b/src/libsyntax_pos/hygiene.rs
index 4dbd4ccda91..a6c8c76cf23 100644
--- a/src/libsyntax_pos/hygiene.rs
+++ b/src/libsyntax_pos/hygiene.rs
@@ -723,7 +723,8 @@ pub enum CompilerDesugaringKind {
     /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`.
     /// However, we do not want to blame `c` for unreachability but rather say that `i`
     /// is unreachable. This desugaring kind allows us to avoid blaming `c`.
-    IfTemporary,
+    /// This also applies to `while` loops.
+    CondTemporary,
     QuestionMark,
     TryBlock,
     /// Desugaring of an `impl Trait` in return type position
@@ -738,7 +739,7 @@ pub enum CompilerDesugaringKind {
 impl CompilerDesugaringKind {
     pub fn name(self) -> Symbol {
         Symbol::intern(match self {
-            CompilerDesugaringKind::IfTemporary => "if",
+            CompilerDesugaringKind::CondTemporary => "if and while condition",
             CompilerDesugaringKind::Async => "async",
             CompilerDesugaringKind::Await => "await",
             CompilerDesugaringKind::QuestionMark => "?",