From e6fa1ab1135d8504d7020c10962b7eb059499fd9 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Sun, 8 Nov 2020 16:04:08 +0100
Subject: [PATCH] Fix #10062: Avoid bad case during typing

---
 compiler/src/dotty/tools/dotc/typer/Applications.scala | 4 ++--
 tests/run/i10062.scala                                 | 9 +++++++++
 2 files changed, 11 insertions(+), 2 deletions(-)
 create mode 100644 tests/run/i10062.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Applications.scala b/compiler/src/dotty/tools/dotc/typer/Applications.scala
index b90d72ab2996..fb7d69d0b86b 100644
--- a/compiler/src/dotty/tools/dotc/typer/Applications.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Applications.scala
@@ -600,8 +600,8 @@ trait Applications extends Compatibility {
             args match {
               case arg :: Nil if isVarArg(arg) =>
                 addTyped(arg, formal)
-              case Typed(Literal(Constant(null)), _) :: Nil =>
-                addTyped(args.head, formal)
+              case (arg as Typed(Literal(Constant(null)), _)) :: Nil if ctx.isAfterTyper =>
+                addTyped(arg, formal)
               case _ =>
                 val elemFormal = formal.widenExpr.argTypesLo.head
                 val typedArgs =
diff --git a/tests/run/i10062.scala b/tests/run/i10062.scala
new file mode 100644
index 000000000000..900145852ae7
--- /dev/null
+++ b/tests/run/i10062.scala
@@ -0,0 +1,9 @@
+class X
+
+object X {
+  extension (x: List[X]) { def isNull = x.head == null }
+}
+
+@main def Test =
+  assert(List(null: X).isNull)
+  assert(List((null: X)).isNull)