Update CHANGELOG

Author: shulhi

CHANGELOG.md

@@ -26,6 +26,7 @@
 - Fix: do not warn for "editor" field in `rescript.json`. https://github.com/rescript-lang/rescript/pull/8084
 - Fix `@val` shadowing (rewrite using `globalThis`). https://github.com/rescript-lang/rescript/pull/8098
 - Fix `@scope` shadowing (rewrite using `globalThis`). https://github.com/rescript-lang/rescript/pull/8100
+- Formatter: normalize underscore placeholders in pipe expressions to canonical form (e.g., `a->map2(_, fn)` formats to `a->map2(fn)`). https://github.com/rescript-lang/rescript/pull/8033
 
 #### :memo: Documentation
 

compiler/syntax/src/res_parsetree_viewer.ml

@@ -142,6 +142,7 @@ let rewrite_underscore_apply expr =
   | _ -> expr
 
 (* For pipe RHS: (__x) => f(__x, a, b) -----> f(a, b)
+   Note: Ppat_var "__x" and Pexp_ident "__x" represent `_` placeholders in user code.
    Omits the first __x argument only if it's the sole occurrence.
    If multiple __x exist (e.g., f(__x, __x, b)), keeps all to preserve semantics. *)
 let rewrite_underscore_apply_in_pipe expr =