Fix #4815: Illegal modifier on local def

During parsing, disallow the use of "final" in local definitions.

e.g.

def foo = {
  final def bar = 42 // error: final in local def is disallowed
  final var x = 42 // error
  final type X = Int // error
}

Author: abeln

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -2545,7 +2545,12 @@ object Parsers {
     def localDef(start: Int, implicitMods: Modifiers = EmptyModifiers): Tree = {
       var mods = defAnnotsMods(localModifierTokens)
       for (imod <- implicitMods.mods) mods = addMod(mods, imod)
-      defOrDcl(start, mods)
+      if (mods.is(Final)) {
+        // A final modifier means the local definition is "class-like".
+        tmplDef(start, mods)
+      } else {
+        defOrDcl(start, mods)
+      }
     }
 
     /** BlockStatSeq ::= { BlockStat semi } [ResultExpr]

language-server/src/dotty/tools/languageserver/Memory.scala

@@ -37,11 +37,11 @@ object Memory {
   }
 
   def stats(): String = {
-    final val M = 2 << 20
+    val M = 2 << 20
     val runtime = Runtime.getRuntime
     def total = runtime.totalMemory / M
     def maximal = runtime.maxMemory / M
     def free = runtime.freeMemory / M
     s"total used memory: $total MB, free: $free MB, maximal available = $maximal MB"
   }
-}
+}

tests/neg/t4815.scala

@@ -0,0 +1,26 @@
+class Test {
+  def foo = {
+    final def bar = 1 // error: local def may not be final
+    final val v = 42 // error: local val may not be final
+    final var v2 = 100 // error: local var may not be final
+    final type T = Int // error: local type def may not be final
+  }
+
+  {
+    final def foo(x: Int) = x // error: local def may not be final
+  }
+
+  final def foo2(x: Int) = x // ok: final allowed in class field
+
+  object Foo {
+    final def foo(x: Int) = x // ok, but redundant
+  }
+
+  abstract class Bar {
+    def foo: Int
+  }
+
+  val x = new Bar {
+    override final def foo = 42 // ok: def is a field
+  }
+}

tests/run/tasty-eval/quoted_2.scala

@@ -2,10 +2,11 @@
 import Macros._
 
 object Test {
+  final val y = 5
+
   def main(args: Array[String]): Unit = {
     println(foo(1)) // "Some(1)"
     println(foo(1 + 7)) // "Some(8)"
-    final val y = 5
     println(foo(y)) // "Some(5)"
     println(foo(y + 1))
     val x = 4