Make LetChainsPolicy public for rustfmt usage

Author: mohe2015

compiler/rustc_parse/src/parser/expr.rs

@@ -2742,7 +2742,7 @@ impl<'a> Parser<'a> {
     /// The specified `edition` in `let_chains_policy` should be that of the whole `if` construct,
     /// i.e. the same span we use to later decide whether the drop behaviour should be that of
     /// edition `..=2021` or that of `2024..`.
-    // Public because it is used in rustfmt forks such as https://github.com/tucant/rustfmt/blob/30c83df9e1db10007bdd16dafce8a86b404329b2/src/parse/macros/html.rs#L57 for custom if expressions.
+    // Public to use it for custom `if` expressions in rustfmt forks like https://github.com/tucant/rustfmt
     pub fn parse_expr_cond(
         &mut self,
         let_chains_policy: LetChainsPolicy,

compiler/rustc_parse/src/parser/mod.rs

@@ -22,6 +22,8 @@ use std::{fmt, mem, slice};
 use attr_wrapper::{AttrWrapper, UsePreAttrPos};
 pub use diagnostics::AttemptLocalParseRecovery;
 pub(crate) use expr::ForbiddenLetReason;
+// Public to use it for custom `if` expressions in rustfmt forks like https://github.com/tucant/rustfmt
+pub use expr::LetChainsPolicy;
 pub(crate) use item::{FnContext, FnParseMode};
 pub use pat::{CommaRecoveryMode, RecoverColon, RecoverComma};
 pub use path::PathStyle;