Check all user written definitions for _* return types

Author: nicolasstucki

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

@@ -940,7 +940,7 @@ trait Checking {
 
   /** Check that the signature of the class mamber does not return a repeated parameter type */
   def checkSignatureRepeatedParam(sym: Symbol)(implicit ctx: Context): Unit =
-    if (sym.maybeOwner.isClass && sym.info.finalResultType.isRepeatedParam)
+    if (!sym.isOneOf(Synthetic | InlineProxy | Param) && sym.info.finalResultType.isRepeatedParam)
       ctx.error(em"Cannot return repeated parameter type ${sym.info.finalResultType}", sym.sourcePos)
 
   /** Verify classes extending AnyVal meet the requirements */

tests/neg/i7972.scala

@@ -1,11 +1,11 @@
 object O {
   def m1(a: Int*) = (a: _*) // error: Cannot return repeated parameter type Int*
   def m2(a: Int*) = { // error: Cannot return repeated parameter type Int*
-    val b = (a: _*)
+    val b = (a: _*) // error: Cannot return repeated parameter type Int*
     b
   }
   def m3(a: Int*): Any = {
-    val b = (a: _*) // Ok, does not affect the signature
+    val b = (a: _*) // error: Cannot return repeated parameter type Int*
     b
   }
   def m4(a: 2*) = (a: _*) // error: Cannot return repeated parameter type Int*