Fix error message when overriding with a lazy val

compiler/src/dotty/tools/dotc/typer/RefChecks.scala

@@ -388,7 +388,7 @@ object RefChecks {
       } else if (member.is(ModuleVal) && !other.isRealMethod && !other.is(Deferred | Lazy)) {
         overrideError("may not override a concrete non-lazy value")
       } else if (member.is(Lazy, butNot = Module) && !other.isRealMethod && !other.is(Lazy) &&
-                 !ctx.testScala2Mode("may not override a non-lazy value", member.sourcePos)) {
+                 !ctx.testScala2Mode(overrideErrorMsg("may not override a non-lazy value"), member.sourcePos)) {
         overrideError("may not override a non-lazy value")
       } else if (other.is(Lazy) && !other.isRealMethod && !member.is(Lazy)) {
         overrideError("must be declared lazy to override a lazy value")

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

@@ -160,6 +160,7 @@ class CompilationTests extends ParallelTesting {
       compileFile("tests/neg-custom-args/implicit-conversions-old.scala", defaultOptions.and("-Xfatal-warnings", "-feature")),
       compileFile("tests/neg-custom-args/i3246.scala", scala2Mode),
       compileFile("tests/neg-custom-args/overrideClass.scala", scala2Mode),
+      compileFile("tests/neg-custom-args/ovlazy.scala", scala2Mode.and("-migration", "-Xfatal-warnings")),
       compileFile("tests/neg-custom-args/autoTuplingTest.scala", defaultOptions.and("-language:noAutoTupling")),
       compileFile("tests/neg-custom-args/nopredef.scala", defaultOptions.and("-Yno-predef")),
       compileFile("tests/neg-custom-args/noimports.scala", defaultOptions.and("-Yno-imports")),

tests/neg-custom-args/ovlazy.check

@@ -0,0 +1,5 @@
+-- Error: tests/neg-custom-args/ovlazy.scala:5:20 ----------------------------------------------------------------------
+5 |  override lazy val x: Int = 2 // error
+  |                    ^
+  |                    error overriding value x in class A of type Int;
+  |                      lazy value x of type Int may not override a non-lazy value

tests/neg-custom-args/ovlazy.scala

@@ -0,0 +1,6 @@
+class A {
+  val x: Int = 1
+}
+class B extends A {
+  override lazy val x: Int = 2 // error
+}