i16601 Fix class name in error message

Author: nizhikov

compiler/src/dotty/tools/dotc/transform/PostTyper.scala

@@ -325,7 +325,7 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
                 // Check the constructor type as well; it could be an illegal singleton type
                 // which would not be reflected as `tree.tpe`
                 ctx.typer.checkClassType(nu.tpe, tree.srcPos, traitReq = false, stablePrefixReq = false)
-              Checking.checkInstantiable(tree.tpe, nu.srcPos)
+              Checking.checkInstantiable(nu.tpe, nu.srcPos)
               withNoCheckNews(nu :: Nil)(app1)
             case _ =>
               app1

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

@@ -159,6 +159,7 @@ class CompilationTests {
       compileFile("tests/neg-custom-args/i9517.scala", defaultOptions.and("-Xprint-types")),
       compileFile("tests/neg-custom-args/i11637.scala", defaultOptions.and("-explain")),
       compileFile("tests/neg-custom-args/i15575.scala", defaultOptions.and("-explain")),
+      compileFile("tests/neg-custom-args/i16601a.scala", defaultOptions.and("-explain")),
       compileFile("tests/neg-custom-args/interop-polytypes.scala", allowDeepSubtypes.and("-Yexplicit-nulls")),
       compileFile("tests/neg-custom-args/conditionalWarnings.scala", allowDeepSubtypes.and("-deprecation").and("-Xfatal-warnings")),
       compileFilesInDir("tests/neg-custom-args/isInstanceOf", allowDeepSubtypes and "-Xfatal-warnings"),

tests/neg/i16601.check

@@ -0,0 +1,6 @@
+-- [E042] Type Error: tests/neg/i16601.scala:1:27 ----------------------------------------------------------------------
+1 |@main def Test: Unit = new concurrent.ExecutionContext  // error
+  |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |                           ExecutionContext is a trait; it cannot be instantiated
+  |
+  | longer explanation available when compiling with `-explain`

tests/neg/i16601.scala

@@ -0,0 +1 @@
+@main def Test: Unit = new concurrent.ExecutionContext  // error