Fix "Arrow functions on the right hand side of |> must be parenthesized"

Author: thekid

.github/workflows/ci.yml

@@ -48,7 +48,7 @@ jobs:
 
     - name: Install dependencies
       run: >
-        curl -sSL https://baltocdn.com/xp-framework/xp-runners/distribution/downloads/e/entrypoint/xp-run-8.8.0.sh > xp-run &&
+        curl -sSL https://github.com/xp-runners/reference/releases/download/v9.2.0/xp-run-9.2.0.sh > xp-run &&
         composer install --prefer-dist &&
         echo "vendor/autoload.php" > composer.pth
 

ChangeLog.md

@@ -3,6 +3,10 @@ XP Compiler ChangeLog
 
 ## ?.?.? / ????-??-??
 
+* Fixed the error *Arrow functions on the right hand side of |> must be
+  parenthesized* - see https://externals.io/message/128473#128554
+  (@thekid)
+
 ## 9.6.0 / 2025-05-22
 
 * Merged PR #185: Implement "clone with", emitting emulating code for

src/main/php/lang/ast/emit/PHP.class.php

@@ -7,6 +7,7 @@
   ArrayLiteral,
   BinaryExpression,
   Block,
+  CallableNewExpression,
   Comment,
   Expression,
   InstanceExpression,
@@ -1165,7 +1166,15 @@ protected function emitNullsafeInstance($result, $instance) {
   protected function emitPipe($result, $pipe) {
     $this->emitOne($result, $pipe->expression);
     $result->out->write('|>');
-    $this->emitOne($result, $pipe->target);
+
+    // `fn() => ...` on the right-hand side of pipe operator must be parenthesized
+    if ($pipe->target instanceof CallableNewExpression) {
+      $result->out->write('(');
+      $this->emitOne($result, $pipe->target);
+      $result->out->write(')');
+    } else {
+      $this->emitOne($result, $pipe->target);
+    }
   }
 
   protected function emitNullsafePipe($result, $pipe) {

src/test/php/lang/ast/unittest/emit/PipelinesTest.class.php

@@ -93,7 +93,7 @@ public function __construct(public string $value) { }
   public function pipe_to_closure() {
     $r= $this->run('class %T {
       public function run() {
-        return "test" |> fn($x) => $x.": OK";
+        return "test" |> (fn($x) => $x.": OK");
       }
     }');
 
@@ -122,7 +122,7 @@ public function run() {
   public function missing_argument() {
     $this->run('class %T {
       public function run() {
-        return 5 |> fn($a, $b) => $a * $b;
+        return 5 |> (fn($a, $b) => $a * $b);
       }
     }');
   }
@@ -175,7 +175,7 @@ public function run() {
   public function addition_precedence() {
     $r= $this->run('class %T {
       public function run() {
-        return 5 + 2 |> fn($i) => $i * 2;
+        return 5 + 2 |> (fn($i) => $i * 2);
       }
     }');
 
@@ -186,7 +186,7 @@ public function run() {
   public function comparison_precedence() {
     $r= $this->run('class %T {
       public function run() {
-        return 5 |> fn($i) => $i * 2 === 10;
+        return 5 |> (fn($i) => $i * 2 === 10);
       }
     }');
 
@@ -249,8 +249,8 @@ public function run() {
         return "Hello World"
           |> "htmlentities"
           |> str_split(...)
-          |> fn($x) => array_map(strtoupper(...), $x)
-          |> fn($x) => array_filter($x, fn($v) => $v != "O")
+          |> (fn($x) => array_map(strtoupper(...), $x))
+          |> (fn($x) => array_filter($x, fn($v) => $v != "O"))
         ;
       }
     }');
@@ -347,13 +347,13 @@ public function run() {
     Assert::equals([2, 3, 4], $r);
   }
 
-  #[Test, Ignore('See https://externals.io/message/128473')]
+  #[Test]
   public function pipe_precedence_challenges() {
     $r= $this->run('class %T {
       public function run() {
         ob_start();
 
-        42 |> fn($x) => $x < 42 |> fn($x) => var_dump($x);
+        42 |> (fn($x) => $x < 42) |> (fn($x) => var_dump($x));
 
         return ob_get_clean();
       }