Fix scala#11008: Support generic tuples as a valid unapply result

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

@@ -8,7 +8,7 @@ import collection.mutable
 import Symbols._, Contexts._, Types._, StdNames._, NameOps._
 import ast.Trees._
 import util.Spans._
-import typer.Applications.{isProductMatch, isGetMatch, isProductSeqMatch, productSelectors, productArity, unapplySeqTypeElemTp}
+import typer.Applications.*
 import SymUtils._
 import Flags._, Constants._
 import Decorators._
@@ -325,15 +325,16 @@ object PatternMatcher {
         def isSyntheticScala2Unapply(sym: Symbol) =
           sym.isAllOf(SyntheticCase) && sym.owner.is(Scala2x)
 
+        def tupleApp(i: Int, receiver: Tree) = // manually inlining the call to NonEmptyTuple#apply, because it's an inline method
+          ref(defn.RuntimeTuplesModule)
+            .select(defn.RuntimeTuples_apply)
+            .appliedTo(receiver, Literal(Constant(i)))
+            .cast(args(i).tpe.widen)
+
         if (isSyntheticScala2Unapply(unapp.symbol) && caseAccessors.length == args.length)
           def tupleSel(sym: Symbol) = ref(scrutinee).select(sym)
-          def tupleApp(i: Int) = // manually inlining the call to NonEmptyTuple#apply, because it's an inline method
-            ref(defn.RuntimeTuplesModule)
-              .select(defn.RuntimeTuples_apply)
-              .appliedTo(ref(scrutinee), Literal(Constant(i)))
-              .cast(args(i).tpe.widen)
           val isGenericTuple = defn.isTupleClass(caseClass) && !defn.isTupleNType(tree.tpe)
-          val components = if isGenericTuple then caseAccessors.indices.toList.map(tupleApp) else caseAccessors.map(tupleSel)
+          val components = if isGenericTuple then caseAccessors.indices.toList.map(tupleApp(_, ref(scrutinee))) else caseAccessors.map(tupleSel)
           matchArgsPlan(components, args, onSuccess)
         else if (unapp.tpe <:< (defn.BooleanType))
           TestPlan(GuardTest, unapp, unapp.span, onSuccess)
@@ -345,6 +346,9 @@ object PatternMatcher {
                 .map(ref(unappResult).select(_))
               matchArgsPlan(selectors, args, onSuccess)
             }
+            else if unappResult.info <:< defn.NonEmptyTupleTypeRef then
+              val components = (0 until foldApplyTupleType(unappResult.denot.info).length).toList.map(tupleApp(_, ref(unappResult)))
+              matchArgsPlan(components, args, onSuccess)
             else if (isUnapplySeq && isProductSeqMatch(unapp.tpe.widen, args.length, unapp.srcPos)) {
               val arity = productArity(unapp.tpe.widen, unapp.srcPos)
               unapplyProductSeqPlan(unappResult, args, arity)

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

@@ -193,10 +193,22 @@ object Applications {
         productSelectorTypes(unapplyResult, pos)
           // this will cause a "wrong number of arguments in pattern" error later on,
           // which is better than the message in `fail`.
+      else if unapplyResult.derivesFrom(defn.NonEmptyTupleClass) then
+        foldApplyTupleType(unapplyResult)
       else fail
     }
   }
 
+  def foldApplyTupleType(tp: Type)(using Context): List[Type] =
+    object tupleFold extends TypeAccumulator[List[Type]]:
+      override def apply(accum: List[Type], t: Type): List[Type] =
+        t match
+          case AppliedType(tycon, x :: x2 :: Nil) if tycon.typeSymbol == defn.PairClass =>
+            apply(x :: accum, x2)
+          case x => foldOver(accum, x)
+    end tupleFold
+    tupleFold(Nil, tp).reverse
+
   def wrapDefs(defs: mutable.ListBuffer[Tree], tree: Tree)(using Context): Tree =
     if (defs != null && defs.nonEmpty) tpd.Block(defs.toList, tree) else tree
 

tests/run/i11008.check

@@ -0,0 +1,2 @@
+hello
+hello and 10

tests/run/i11008.scala

@@ -0,0 +1,13 @@
+object A:
+  def unapply(s: String): String *: EmptyTuple = Tuple1(s)
+
+object B:
+  def unapply(s:String): String *: Int *: EmptyTuple = Tuple2(s, 10)
+
+@main def Test =
+  "hello" match
+    case A(x) =>
+      println(x)
+  "hello" match
+    case B(x, y) =>
+      println(s"$x and $y")