From 5244ecdd525330f8ee0202859cf68bf14367c39e Mon Sep 17 00:00:00 2001
From: Shulhi Sapli <shulhi@gmail.com>
Date: Sun, 30 Mar 2025 10:07:39 +0800
Subject: [PATCH 1/2] Fix superfluous parens for underscore application

---
 compiler/syntax/src/res_parens.ml                         | 1 +
 .../data/printer/expr/expected/callback.res.txt           | 8 ++++----
 .../data/printer/expr/expected/underscoreApply.res.txt    | 7 ++++++-
 tests/syntax_tests/data/printer/expr/underscoreApply.res  | 5 +++++
 4 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/compiler/syntax/src/res_parens.ml b/compiler/syntax/src/res_parens.ml
index 8034e7cf59..2094a2c5fa 100644
--- a/compiler/syntax/src/res_parens.ml
+++ b/compiler/syntax/src/res_parens.ml
@@ -185,6 +185,7 @@ let flatten_operand_rhs parent_operator rhs =
     prec_parent >= prec_child || rhs.pexp_attributes <> []
   | Pexp_constraint ({pexp_desc = Pexp_pack _}, {ptyp_desc = Ptyp_package _}) ->
     false
+  | Pexp_fun {lhs = {ppat_desc = Ppat_var {txt = "__x"}}} -> false
   | Pexp_fun _ | Pexp_newtype _ | Pexp_setfield _ | Pexp_constraint _ -> true
   | _ when ParsetreeViewer.is_ternary_expr rhs -> true
   | _ -> false
diff --git a/tests/syntax_tests/data/printer/expr/expected/callback.res.txt b/tests/syntax_tests/data/printer/expr/expected/callback.res.txt
index a2d661ce40..e7ee3eeb80 100644
--- a/tests/syntax_tests/data/printer/expr/expected/callback.res.txt
+++ b/tests/syntax_tests/data/printer/expr/expected/callback.res.txt
@@ -218,14 +218,14 @@ let f = () => {
 }
 
 myPromise
-->(Js.Promise.then_(value => {
+->Js.Promise.then_(value => {
   Js.log(value)
   Js.Promise.resolve(value + 2)
-}, _))
-->(Js.Promise.then_(value => {
+}, _)
+->Js.Promise.then_(value => {
   Js.log(value)
   Js.Promise.resolve(value + 3)
-}, _))
+}, _)
 ->Js.Promise.catch(err => {
   Js.log2("Failure!!", err)
   Js.Promise.resolve(-2)
diff --git a/tests/syntax_tests/data/printer/expr/expected/underscoreApply.res.txt b/tests/syntax_tests/data/printer/expr/expected/underscoreApply.res.txt
index dc50fb21da..315faac753 100644
--- a/tests/syntax_tests/data/printer/expr/expected/underscoreApply.res.txt
+++ b/tests/syntax_tests/data/printer/expr/expected/underscoreApply.res.txt
@@ -36,7 +36,7 @@ f((a, b) => List.length(_), a, b)
 f(a, b, _)(x, y)
 -f(a, b, _)
 f(a, b, _) + g(x, _, z)
-f(a, b, _) + (g(x, _, z)) + h(alpha, beta, _)
+f(a, b, _) + g(x, _, z) + h(alpha, beta, _)
 
 assert(f(a, b, _))
 
@@ -66,3 +66,8 @@ x => {
   // Comment 2
   something()
 }, _)
+
+let status =
+  json
+  ->optional(field("status", string, _), _)
+  ->Option.mapOr(Status.Active, Status.fromString)
diff --git a/tests/syntax_tests/data/printer/expr/underscoreApply.res b/tests/syntax_tests/data/printer/expr/underscoreApply.res
index 6740f76784..91d8b053fe 100644
--- a/tests/syntax_tests/data/printer/expr/underscoreApply.res
+++ b/tests/syntax_tests/data/printer/expr/underscoreApply.res
@@ -71,3 +71,8 @@ underscoreWithComments(
   },
   _,
 )
+
+let status =
+    json
+    ->optional(field("status", string, _), _)
+    ->Option.mapOr(Status.Active, Status.fromString)

From af4b4871f3ceb334d373f8c0fb9b65272c3e97a3 Mon Sep 17 00:00:00 2001
From: Shulhi Sapli <shulhi@gmail.com>
Date: Sun, 30 Mar 2025 10:16:20 +0800
Subject: [PATCH 2/2] Update CHANGELOG

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 070d0df456..ee0ca01bfa 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,7 @@
 #### :bug: Bug fix
 
 - Fix `Error.fromException`. https://github.com/rescript-lang/rescript/pull/7364
+- Fix formatter adds superfluous parens in pipe chain. https://github.com/rescript-lang/rescript/pull/7370
 
 #### :house: Internal