Merge pull request #15748 from dotty-staging/fix-15687

odersky · web-flow · commit 03da9dd108bf · 2022-07-26T20:02:27.000+02:00
Avoid null types when reducing match types
diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -2988,7 +2988,7 @@ class TrackingTypeComparer(initctx: Context) extends TypeComparer(initctx) {
       def redux(canApprox: Boolean): MatchResult =
         caseLambda match
           case caseLambda: HKTypeLambda =>
-            val instances = paramInstances(canApprox)(new Array(caseLambda.paramNames.length), pat)
+            val instances = paramInstances(canApprox)(Array.fill(caseLambda.paramNames.length)(NoType), pat)
             instantiateParams(instances)(body) match
               case Range(lo, hi) =>
                 MatchResult.NoInstance {
diff --git a/tests/neg/i15687.scala b/tests/neg/i15687.scala
@@ -0,0 +1,2 @@
+val _ = summon[Tuple.IsMappedBy[[X] =>> Int][(4, 2)]] // error
+

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	`+val _ = summon[Tuple.IsMappedBy[[X] =>> Int][(4, 2)]] // error`
	`2`	`+`