From 88714512d399bb23156852f8f104adad0e249074 Mon Sep 17 00:00:00 2001
From: Tom Grigg <tomegrigg@gmail.com>
Date: Wed, 1 Sep 2021 18:26:45 -0700
Subject: [PATCH] Fix #13440: Avoid capturing var in message closure

---
 compiler/src/dotty/tools/dotc/parsing/Scanners.scala | 3 ++-
 tests/neg-custom-args/fatal-warnings/i13440.check    | 4 ++++
 tests/neg-custom-args/fatal-warnings/i13440.scala    | 3 +++
 3 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 tests/neg-custom-args/fatal-warnings/i13440.check
 create mode 100644 tests/neg-custom-args/fatal-warnings/i13440.scala

diff --git a/compiler/src/dotty/tools/dotc/parsing/Scanners.scala b/compiler/src/dotty/tools/dotc/parsing/Scanners.scala
index 61e31ff1dce8..84a181769e3b 100644
--- a/compiler/src/dotty/tools/dotc/parsing/Scanners.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/Scanners.scala
@@ -247,8 +247,9 @@ object Scanners {
       else keyword
 
     private def treatAsIdent(): Token =
+      val name0 = name  // don't capture the `name` var in the message closure, it may be null later
       report.errorOrMigrationWarning(
-        i"$name is now a keyword, write `$name` instead of $name to keep it as an identifier",
+        i"$name0 is now a keyword, write `$name0` instead of $name0 to keep it as an identifier",
         sourcePos())
       patch(source, Span(offset), "`")
       patch(source, Span(offset + name.length), "`")
diff --git a/tests/neg-custom-args/fatal-warnings/i13440.check b/tests/neg-custom-args/fatal-warnings/i13440.check
new file mode 100644
index 000000000000..0e9dd7dd5e50
--- /dev/null
+++ b/tests/neg-custom-args/fatal-warnings/i13440.check
@@ -0,0 +1,4 @@
+-- Error: tests/neg-custom-args/fatal-warnings/i13440.scala:3:13 -------------------------------------------------------
+3 |case class A(enum: List[Int] = Nil) // error
+  |             ^
+  |             enum is now a keyword, write `enum` instead of enum to keep it as an identifier
diff --git a/tests/neg-custom-args/fatal-warnings/i13440.scala b/tests/neg-custom-args/fatal-warnings/i13440.scala
new file mode 100644
index 000000000000..8e3af76ad3fa
--- /dev/null
+++ b/tests/neg-custom-args/fatal-warnings/i13440.scala
@@ -0,0 +1,3 @@
+import language.`3.0-migration`
+
+case class A(enum: List[Int] = Nil) // error