Fix #5256: add regression test

Author: nicolasstucki

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -171,6 +171,7 @@ class CompilationTests extends ParallelTesting {
   @Test def runAll: Unit = {
     implicit val testGroup: TestGroup = TestGroup("runAll")
     compileFilesInDir("tests/run-custom-args/Yretain-trees", defaultOptions and "-Yretain-trees") +
+    compileFile("tests/run-custom-args/i5256.scala", allowDeepSubtypes) +
     compileFilesInDir("tests/run", defaultOptions)
   }.checkRuns()
 

tests/run-custom-args/i5256.check

@@ -0,0 +1 @@
+276

tests/run-custom-args/i5256.scala

@@ -0,0 +1,11 @@
+object Test {
+
+  def main(args: Array[String]): Unit = {
+    val f23: ((Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int)) => Int = {
+      (x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15, x16, x17, x18, x19, x20, x21, x22, x23) =>
+        x1 + x2 + x3 + x4 + x5 + x6 + x7 + x8 + x9 + x10 + x11 + x12 + x13 + x14 + x15 + x16 + x17 + x18 + x19 + x20 + x21 + x22 + x23
+    }
+
+    println(f23((1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)))
+  }
+}