From 3dd34948f21c53bd8e39bd6a99dfdb340f12fcb7 Mon Sep 17 00:00:00 2001
From: Matt Bovel <matthieu@bovel.net>
Date: Mon, 21 Oct 2024 19:51:53 +0200
Subject: [PATCH] Move AmbiguousNamedTupleAssignment check to Typer
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Co-Authored-By: Nicolas Stucki <3648029+nicolasstucki@users.noreply.github.com>
Co-Authored-By: Oliver Bračevac <bracevac@users.noreply.github.com>
---
 compiler/src/dotty/tools/dotc/ast/Desugar.scala |  2 --
 compiler/src/dotty/tools/dotc/typer/Typer.scala | 13 +++++++++++++
 tests/pos/21681d.scala                          | 16 ++++++++++++++++
 tests/warn/21681b.check                         |  7 +++++++
 tests/warn/21681b.scala                         |  3 +++
 5 files changed, 39 insertions(+), 2 deletions(-)
 create mode 100644 tests/pos/21681d.scala
 create mode 100644 tests/warn/21681b.check
 create mode 100644 tests/warn/21681b.scala

diff --git a/compiler/src/dotty/tools/dotc/ast/Desugar.scala b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
index 482210845fea..e66c71731b4f 100644
--- a/compiler/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
@@ -1639,8 +1639,6 @@ object desugar {
       if ctx.mode.is(Mode.Type) then
         AppliedTypeTree(ref(defn.NamedTupleTypeRef), namesTuple :: tup :: Nil)
       else
-        if names.length == 1 && ctx.scope.lookup(names.head).is(Flags.Mutable) then
-          report.migrationWarning(AmbiguousNamedTupleAssignment(names.head, elemValues.head), tree.srcPos)
         Apply(
           Apply(
             TypeApply(
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index 89ce01231fed..e7bd7d874634 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -3398,6 +3398,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
   /** Translate tuples of all arities */
   def typedTuple(tree: untpd.Tuple, pt: Type)(using Context): Tree =
     val tree1 = desugar.tuple(tree, pt)
+    checkAmbiguousNamedTupleAssignment(tree)
     if tree1 ne tree then typed(tree1, pt)
     else
       val arity = tree.trees.length
@@ -3423,6 +3424,18 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
           val resTpe = TypeOps.nestedPairs(elemTpes)
           app1.cast(resTpe)
 
+ /** Checks if `tree` is a named tuple with one element that could be
+  *  interpreted as an assignment, such as `(x = 1)`. If so, issues a warning.
+  */
+  def checkAmbiguousNamedTupleAssignment(tree: untpd.Tuple)(using Context): Unit =
+    tree.trees match
+      case List(NamedArg(name, value)) =>
+        val typedName = typedIdent(untpd.Ident(name), WildcardType)
+        val sym = typedName.symbol
+        if sym.exists && (sym.is(Flags.Mutable) || sym.setter.exists) then
+          report.migrationWarning(AmbiguousNamedTupleAssignment(name, value), tree.srcPos)
+      case _ => ()
+
   /** Retrieve symbol attached to given tree */
   protected def retrieveSym(tree: untpd.Tree)(using Context): Symbol = tree.removeAttachment(SymOfTree) match {
     case Some(sym) =>
diff --git a/tests/pos/21681d.scala b/tests/pos/21681d.scala
new file mode 100644
index 000000000000..97a01dec74aa
--- /dev/null
+++ b/tests/pos/21681d.scala
@@ -0,0 +1,16 @@
+def test1() =
+  class Person:
+    def age: Int = ???
+    def age_=(x: Int): Unit = ???
+
+  val person = Person()
+  
+  (person.age = 29) // no warn (interpreted as `person.age_=(29)`)
+
+def test2() =
+  class Person:
+    var age: Int = 28
+
+  val person = Person()
+  
+  (person.age = 29) // no warn (interpreted as `person.age_=(29)`)
diff --git a/tests/warn/21681b.check b/tests/warn/21681b.check
new file mode 100644
index 000000000000..32760e00ebb6
--- /dev/null
+++ b/tests/warn/21681b.check
@@ -0,0 +1,7 @@
+-- [E203] Syntax Migration Warning: tests/warn/21681b.scala:3:2 --------------------------------------------------------
+3 |  (age = 29) // warn
+  |  ^^^^^^^^^^
+  |  Ambiguous syntax: this is interpreted as a named tuple with one element,
+  |  not as an assignment.
+  |
+  |  To assign a value, use curly braces: `{age = 29}`.
diff --git a/tests/warn/21681b.scala b/tests/warn/21681b.scala
new file mode 100644
index 000000000000..710d69b0dd23
--- /dev/null
+++ b/tests/warn/21681b.scala
@@ -0,0 +1,3 @@
+object Test:
+  var age: Int = 28
+  (age = 29) // warn