From 4328f3feb8f3bf70c78ce1cd07ef6d71a92a9506 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Fri, 22 May 2020 13:26:19 +0200
Subject: [PATCH] Fix #9023: Check that names of vals and vars do not end with
 `_=`

---
 .../src/dotty/tools/dotc/typer/Namer.scala    |  2 ++
 tests/neg/i9023.scala                         | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 tests/neg/i9023.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Namer.scala b/compiler/src/dotty/tools/dotc/typer/Namer.scala
index 329135a02b32..3c3142906015 100644
--- a/compiler/src/dotty/tools/dotc/typer/Namer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Namer.scala
@@ -389,6 +389,8 @@ class Namer { typer: Typer =>
         val name = checkNoConflict(tree.name, flags.is(Private), tree.span)
         tree match
           case tree: ValOrDefDef =>
+            if tree.isInstanceOf[ValDef] && !flags.is(Param) && name.endsWith("_=") then
+              ctx.error("Names of vals or vars may not end in `_=`", tree.namePos)
             if tree.unforcedRhs == EmptyTree
                && !flags.isOneOf(TermParamOrAccessor)
                && !tree.name.isConstructorName
diff --git a/tests/neg/i9023.scala b/tests/neg/i9023.scala
new file mode 100644
index 000000000000..d27cdcbf1f8b
--- /dev/null
+++ b/tests/neg/i9023.scala
@@ -0,0 +1,19 @@
+class C {
+  var __= : Int = 42 // error
+  var x_= : Int = 42 // error
+}
+
+class D {
+  val __= : Int = 42 // error
+  val x_= : Int = 42 // error
+}
+
+class E {
+  lazy val __= : Int = 42 // error
+  lazy val x_= : Int = 42 // error
+}
+
+class F {
+  def __= : Int = 42
+  def x_= : Int = 42
+}