From ba8c4c8a592e9070b5a7c1d887daed16e11d732d Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Thu, 3 Nov 2016 19:19:34 +0100
Subject: Fix #1652: Make assertion more robust

An assertion fired giving a false negative after a fuzzing
test which introduced an ill-kinded type argument.
---
 src/dotty/tools/dotc/core/Types.scala | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

(limited to 'src/dotty/tools/dotc/core/Types.scala')

diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 38913a7d0..b67ff8141 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -2527,6 +2527,8 @@ object Types {
       case _: MethodType => true
       case _ => false
     }
+    
+    def isTypeLambda: Boolean = variances.nonEmpty
 
     /** PolyParam references to all type parameters of this type */
     lazy val paramRefs: List[PolyParam] = paramNames.indices.toList.map(PolyParam(this, _))
@@ -2914,9 +2916,15 @@ object Types {
     def instantiate(fromBelow: Boolean)(implicit ctx: Context): Type = {
       val inst = ctx.typeComparer.instanceType(origin, fromBelow)
       if (ctx.typerState.isGlobalCommittable)
-        assert(!inst.isInstanceOf[PolyParam], i"bad inst $this := $inst, constr = ${ctx.typerState.constraint}")
-          // If this fails, you might want to turn on Config.debugCheckConstraintsClosed
-          // to help find the root of the problem.
+        inst match {
+          case inst: PolyParam =>
+            assert(inst.binder.isTypeLambda, i"bad inst $this := $inst, constr = ${ctx.typerState.constraint}")
+              // If this fails, you might want to turn on Config.debugCheckConstraintsClosed
+              // to help find the root of the problem.
+              // Note: Parameters of type lambdas are excluded from the assertion because
+              // they might arise from ill-kinded code. See #1652
+          case _ =>
+        }
       instantiateWith(inst)
     }
 
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