From 6eec601fa6114045724d05ae5670e543ab7ed40e Mon Sep 17 00:00:00 2001
From: Jordan Kiesel <jordantkiesel@gmail.com>
Date: Wed, 24 Jun 2026 23:48:49 -0600
Subject: [PATCH] fix: omit parentheses around lambda body assignment
 expressions

---
 src/printers/helpers.ts                                | 6 +++++-
 test/unit-test/lambda/arrow-parens-always/_input.java  | 4 ++++
 test/unit-test/lambda/arrow-parens-always/_output.java | 4 ++++
 test/unit-test/lambda/arrow-parens-avoid/_input.java   | 4 ++++
 test/unit-test/lambda/arrow-parens-avoid/_output.java  | 4 ++++
 5 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/src/printers/helpers.ts b/src/printers/helpers.ts
index 0892777c..62520417 100644
--- a/src/printers/helpers.ts
+++ b/src/printers/helpers.ts
@@ -680,7 +680,11 @@ export function needsParentheses(path: NamedNodePath) {
         return false;
       }
 
-      if (parent?.type === SyntaxType.AssignmentExpression) {
+      if (
+        parent?.type === SyntaxType.AssignmentExpression ||
+        (parent?.type === SyntaxType.LambdaExpression &&
+          parent.bodyNode === node)
+      ) {
         return false;
       }
 
diff --git a/test/unit-test/lambda/arrow-parens-always/_input.java b/test/unit-test/lambda/arrow-parens-always/_input.java
index b9ce8237..1113789c 100644
--- a/test/unit-test/lambda/arrow-parens-always/_input.java
+++ b/test/unit-test/lambda/arrow-parens-always/_input.java
@@ -337,6 +337,10 @@ void lambdaWithTrailingComments() {
     void lambdaInParentheses() {
         (aaaaaaaaaa -> bbbbbbbbbb.cccccccccc().dddddddddd().eeeeeeeeee().ffffffffff());
     }
+
+    void lambdaWithAssignmentBody() {
+        a -> b = c;
+    }
 }
 
 class T {
diff --git a/test/unit-test/lambda/arrow-parens-always/_output.java b/test/unit-test/lambda/arrow-parens-always/_output.java
index fca16104..28545a8b 100644
--- a/test/unit-test/lambda/arrow-parens-always/_output.java
+++ b/test/unit-test/lambda/arrow-parens-always/_output.java
@@ -571,6 +571,10 @@ void lambdaInParentheses() {
     (aaaaaaaaaa) ->
       bbbbbbbbbb.cccccccccc().dddddddddd().eeeeeeeeee().ffffffffff();
   }
+
+  void lambdaWithAssignmentBody() {
+    (a) -> b = c;
+  }
 }
 
 class T {
diff --git a/test/unit-test/lambda/arrow-parens-avoid/_input.java b/test/unit-test/lambda/arrow-parens-avoid/_input.java
index b9ce8237..1113789c 100644
--- a/test/unit-test/lambda/arrow-parens-avoid/_input.java
+++ b/test/unit-test/lambda/arrow-parens-avoid/_input.java
@@ -337,6 +337,10 @@ void lambdaWithTrailingComments() {
     void lambdaInParentheses() {
         (aaaaaaaaaa -> bbbbbbbbbb.cccccccccc().dddddddddd().eeeeeeeeee().ffffffffff());
     }
+
+    void lambdaWithAssignmentBody() {
+        a -> b = c;
+    }
 }
 
 class T {
diff --git a/test/unit-test/lambda/arrow-parens-avoid/_output.java b/test/unit-test/lambda/arrow-parens-avoid/_output.java
index cfe2af09..e84e93d6 100644
--- a/test/unit-test/lambda/arrow-parens-avoid/_output.java
+++ b/test/unit-test/lambda/arrow-parens-avoid/_output.java
@@ -571,6 +571,10 @@ void lambdaInParentheses() {
     aaaaaaaaaa ->
       bbbbbbbbbb.cccccccccc().dddddddddd().eeeeeeeeee().ffffffffff();
   }
+
+  void lambdaWithAssignmentBody() {
+    a -> b = c;
+  }
 }
 
 class T {