Allow several addenda for TypeMismatch

It's cleaner to handle the choice what addendum to print in the message
itself.

Author: odersky

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -241,7 +241,7 @@ object messages {
     }
   }
 
-  class TypeMismatch(found: Type, expected: Type, addendum: => String = "")(implicit ctx: Context)
+  class TypeMismatch(found: Type, expected: Type, addenda: => String*)(implicit ctx: Context)
     extends TypeMismatchMsg(TypeMismatchID):
 
     // replace constrained TypeParamRefs and their typevars by their bounds where possible
@@ -269,14 +269,15 @@ object messages {
       val expected1 = reported(expected)
       val (found2, expected2) =
         if (found1 frozen_<:< expected1) (found, expected) else (found1, expected1)
-      val postScript =
-        if !addendum.isEmpty
-           || expected.isAny
-           || expected.isAnyRef
-           || expected.isRef(defn.AnyValClass)
-           || defn.isBottomType(found)
-        then addendum
-        else ctx.typer.importSuggestionAddendum(ViewProto(found.widen, expected))
+      val postScript = addenda.find(!_.isEmpty) match
+        case Some(p) => p
+        case None =>
+          if expected.isAny
+             || expected.isAnyRef
+             || expected.isRef(defn.AnyValClass)
+             || defn.isBottomType(found)
+          then ""
+          else ctx.typer.importSuggestionAddendum(ViewProto(found.widen, expected))
       val (where, printCtx) = Formatting.disambiguateTypes(found2, expected2)
       val whereSuffix = if (where.isEmpty) where else s"\n\n$where"
       val (foundStr, expectedStr) = Formatting.typeDiff(found2, expected2)(printCtx)

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

@@ -102,9 +102,7 @@ object ErrorReporting {
         case If(_, _, elsep @ Literal(Constant(()))) if elsep.span.isSynthetic =>
           "\nMaybe you are missing an else part for the conditional?"
         case _ => ""
-      def addendum = List(implicitFailure.whyNoConversion, missingElse)
-        .find(!_.isEmpty).getOrElse("")
-      errorTree(tree, TypeMismatch(treeTp, pt, addendum))
+      errorTree(tree, TypeMismatch(treeTp, pt, implicitFailure.whyNoConversion, missingElse))
     }
 
     /** A subtype log explaining why `found` does not conform to `expected` */

tests/run/byname-varargs.check

@@ -0,0 +1,5 @@
+a
+b
+a
+b
+result = (ArraySeq(1, 2),ArraySeq(1, 2))

tests/run/byname-varargs.scala

@@ -0,0 +1,12 @@
+def f[T](xs: => T*): (Seq[T], Seq[T]) = (xs, xs)
+
+def a =
+  println("a")
+  1
+
+def b =
+  println("b")
+  2
+
+@main def Test =
+  println(s"result = ${f(a, b)}")