From 8408339e4fcfbfaa430971276166cb25fe33e28f Mon Sep 17 00:00:00 2001
From: odersky <odersky@gmail.com>
Date: Wed, 18 Jun 2025 18:44:42 +0200
Subject: [PATCH] Print update modifier when printing update method definitions

I verified by printing i23389.scala -Xprint:cc. I did not manage to
make up a test case for this.
---
 .../tools/dotc/printing/RefinedPrinter.scala  |  6 ++--
 tests/neg-custom-args/captures/i23389.scala   | 36 +++++++++++++++++++
 2 files changed, 40 insertions(+), 2 deletions(-)
 create mode 100644 tests/neg-custom-args/captures/i23389.scala

diff --git a/compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala b/compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala
index 324d4f0c1d23..2578bbba6316 100644
--- a/compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala
+++ b/compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala
@@ -994,8 +994,9 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
   protected def valDefToText[T <: Untyped](tree: ValDef[T]): Text = {
     dclTextOr(tree) {
       modText(tree.mods, tree.symbol, keywordStr(if (tree.mods.is(Mutable)) "var" else "val"), isType = false) ~~
-        valDefText(nameIdText(tree)) ~ optAscription(tree.tpt) ~
-        withEnclosingDef(tree) { rhsValDef(tree) }
+        valDefText(nameIdText(tree))
+        ~ optAscription(tree.tpt)
+        ~ withEnclosingDef(tree) { rhsValDef(tree) }
     }
   }
 
@@ -1170,6 +1171,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
     if (rawFlags.is(Param)) flagMask = flagMask &~ Given
     val flags = rawFlags & flagMask
     var flagsText = toTextFlags(sym, flags)
+    if sym.isUpdateMethod then flagsText ~~= keywordStr("update")
     val annotTexts =
       if sym.exists then
         sym.annotationsUNSAFE.filterNot(ann => dropAnnotForModText(ann.symbol)).map(toText)
diff --git a/tests/neg-custom-args/captures/i23389.scala b/tests/neg-custom-args/captures/i23389.scala
new file mode 100644
index 000000000000..cb62a5e69a2c
--- /dev/null
+++ b/tests/neg-custom-args/captures/i23389.scala
@@ -0,0 +1,36 @@
+import language.experimental.captureChecking
+import caps.*
+
+package test1:
+
+  trait Collection[T] extends Mutable:
+    update def add(elem: T): Unit
+    update def remove(elem: T): Unit
+    def get(index: Int): Option[T]
+
+  object Collection:
+    def empty[T]: Collection[T] = ???
+
+  trait Foo:
+    val thunks: Collection[() => Unit] // that's fine
+
+  object FooImpl1 extends Foo:
+    val thunks: Collection[() => Unit] = Collection.empty // error
+    val thunks2: Collection[() => Unit] = Collection.empty[() => Unit] // error
+    val thunks3: Collection[() => Unit] = Collection.empty[() => Unit] // error
+
+package test2:
+
+  trait Collection[+T] extends Mutable:
+    def get(index: Int): Option[T]
+
+  object Collection:
+    def empty[T]: Collection[T] = ???
+
+  trait Foo:
+    val thunks: Collection[() => Unit] // that's fine
+
+  object FooImpl1 extends Foo:
+    val thunks: Collection[() => Unit] = Collection.empty // error
+    val thunks2: Collection[() => Unit] = Collection.empty[() => Unit] // error
+    val thunks3: Collection[() => Unit] = Collection.empty[() => Unit] // error
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