Auto merge of rust-lang#93069 - matthiaskrgr:rollup-gx1vkp7, r=matthiaskrgr

Rollup of 10 pull requests

Successful merges:

 - rust-lang#88642 (Formally implement let chains)
 - rust-lang#89621 (doc: guarantee call order for sort_by_cached_key)
 - rust-lang#91278 (Use iterator instead of recursion in `codegen_place`)
 - rust-lang#92124 (Little improves in CString `new` when creating from slice)
 - rust-lang#92783 (Annotate dead code lint with notes about ignored derived impls)
 - rust-lang#92797 (Remove horizontal lines at top of page)
 - rust-lang#92920 (Move expr- and item-related pretty printing functions to modules)
 - rust-lang#93041 (Remove some unused ordering derivations based on `DefId`)
 - rust-lang#93051 (Add Option::is_some_with and Result::is_{ok,err}_with)
 - rust-lang#93062 (Update books)

Failed merges:

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

Author: bors

compiler/rustc_ast_lowering/src/expr.rs

@@ -392,14 +392,20 @@ impl<'hir> LoweringContext<'_, 'hir> {
     // If `cond` kind is `let`, returns `let`. Otherwise, wraps and returns `cond`
     // in a temporary block.
     fn manage_let_cond(&mut self, cond: &'hir hir::Expr<'hir>) -> &'hir hir::Expr<'hir> {
-        match cond.kind {
-            hir::ExprKind::Let(..) => cond,
-            _ => {
-                let span_block =
-                    self.mark_span_with_reason(DesugaringKind::CondTemporary, cond.span, None);
-                self.expr_drop_temps(span_block, cond, AttrVec::new())
+        fn has_let_expr<'hir>(expr: &'hir hir::Expr<'hir>) -> bool {
+            match expr.kind {
+                hir::ExprKind::Binary(_, lhs, rhs) => has_let_expr(lhs) || has_let_expr(rhs),
+                hir::ExprKind::Let(..) => true,
+                _ => false,
             }
         }
+        if has_let_expr(cond) {
+            cond
+        } else {
+            let reason = DesugaringKind::CondTemporary;
+            let span_block = self.mark_span_with_reason(reason, cond.span, None);
+            self.expr_drop_temps(span_block, cond, AttrVec::new())
+        }
     }
 
     // We desugar: `'label: while $cond $body` into:

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -707,11 +707,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
         "`if let` guards are experimental",
         "you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`"
     );
-    gate_all!(
-        let_chains,
-        "`let` expressions in this position are experimental",
-        "you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`"
-    );
+    gate_all!(let_chains, "`let` expressions in this position are unstable");
     gate_all!(
         async_closure,
         "async closures are unstable",