Backport "Handle TupleXXL in match analysis" to LTS (#20791)

Backports #19212 to the LTS branch.

PR submitted by the release tooling.
[skip ci]

Author: WojciechMazur

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -947,6 +947,7 @@ class Definitions {
   def TupleXXLModule(using Context): Symbol = TupleXXLClass.companionModule
 
     def TupleXXL_fromIterator(using Context): Symbol = TupleXXLModule.requiredMethod("fromIterator")
+    def TupleXXL_unapplySeq(using Context): Symbol = TupleXXLModule.requiredMethod(nme.unapplySeq)
 
   @tu lazy val RuntimeTupleMirrorTypeRef: TypeRef = requiredClassRef("scala.runtime.TupleMirror")
 

compiler/src/dotty/tools/dotc/core/TypeUtils.scala

@@ -72,17 +72,41 @@ class TypeUtils {
             else None
       recur(self.stripTypeVar, bound)
 
-    /** Is this a generic tuple that would fit into the range 1..22,
-     *  but is not already an instance of one of Tuple1..22?
-     *  In this case we need to cast it to make the TupleN/ members accessible.
-     *  This works only for generic tuples of known size up to 22.
-     */
-    def isSmallGenericTuple(using Context): Boolean =
+    /** Is this a generic tuple but not already an instance of one of Tuple1..22? */
+    def isGenericTuple(using Context): Boolean =
       self.derivesFrom(defn.PairClass)
       && !defn.isTupleNType(self.widenDealias)
-      && self.widenTermRefExpr.tupleElementTypesUpTo(Definitions.MaxTupleArity).match
-          case Some(elems) if elems.length <= Definitions.MaxTupleArity => true
-          case _ => false
+
+    /** Is this a generic tuple that would fit into the range 1..22?
+     *  In this case we need to cast it to make the TupleN members accessible.
+     *  This works only for generic tuples of known size up to 22.
+     */
+    def isSmallGenericTuple(using Context): Boolean = genericTupleArityCompare < 0
+
+    /** Is this a generic tuple with an arity above 22? */
+    def isLargeGenericTuple(using Context): Boolean = genericTupleArityCompare > 0
+
+    /** If this is a generic tuple with element types, compare the arity and return:
+     *    * -1, if the generic tuple is small (<= MaxTupleArity)
+     *    * 1, if the generic tuple is large (> MaxTupleArity)
+     *    * 0 if this isn't a generic tuple with element types
+     */
+    def genericTupleArityCompare(using Context): Int =
+      if self.isGenericTuple then
+        self.widenTermRefExpr.tupleElementTypesUpTo(Definitions.MaxTupleArity).match
+          case Some(elems) => if elems.length <= Definitions.MaxTupleArity then -1 else 1
+          case _ => 0
+      else 0
+
+    /** Is this a large generic tuple and is `pat` TupleXXL?
+     *  TupleXXL.unapplySeq extracts values of type TupleXXL
+     *  but large scrutinee terms are typed as large generic tuples.
+     *  This allows them to hold on to their precise element types,
+     *  but it means type-wise, the terms don't conform to the
+     *  extractor's parameter type, so this method identifies case.
+     */
+    def isTupleXXLExtract(pat: Type)(using Context): Boolean =
+      pat.typeSymbol == defn.TupleXXLClass && self.isLargeGenericTuple
 
     /** The `*:` equivalent of an instance of a Tuple class */
     def toNestedPairs(using Context): Type =

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -286,11 +286,9 @@ object SpaceEngine {
     || (unapp.symbol.is(Synthetic) && unapp.symbol.owner.linkedClass.is(Case))  // scala2 compatibility
     || unapplySeqTypeElemTp(unappResult).exists // only for unapplySeq
     || isProductMatch(unappResult, argLen)
-    || {
-      val isEmptyTp = extractorMemberType(unappResult, nme.isEmpty, NoSourcePosition)
-      isEmptyTp <:< ConstantType(Constant(false))
-    }
+    || extractorMemberType(unappResult, nme.isEmpty, NoSourcePosition) <:< ConstantType(Constant(false))
     || unappResult.derivesFrom(defn.NonEmptyTupleClass)
+    || unapp.symbol == defn.TupleXXL_unapplySeq // Fixes TupleXXL.unapplySeq which returns Some but declares Option
   }
 
   /** Is the unapply or unapplySeq irrefutable?
@@ -514,6 +512,7 @@ object SpaceEngine {
   def isSubType(tp1: Type, tp2: Type)(using Context): Boolean = trace(i"$tp1 <:< $tp2", debug, show = true) {
     if tp1 == ConstantType(Constant(null)) && !ctx.mode.is(Mode.SafeNulls)
     then tp2 == ConstantType(Constant(null))
+    else if tp1.isTupleXXLExtract(tp2) then true // See isTupleXXLExtract, fixes TupleXXL parameter type
     else tp1 <:< tp2
   }
 
@@ -838,7 +837,8 @@ object SpaceEngine {
     def isCheckable(tp: Type): Boolean =
       val tpw = tp.widen.dealias
       val classSym = tpw.classSymbol
-      classSym.is(Sealed) ||
+      classSym.is(Sealed) && !tpw.isLargeGenericTuple || // exclude large generic tuples from exhaustivity
+                                                         // requires an unknown number of changes to make work
       tpw.isInstanceOf[OrType] ||
       (tpw.isInstanceOf[AndType] && {
         val and = tpw.asInstanceOf[AndType]

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

@@ -911,7 +911,10 @@ trait Checking {
       false
     }
 
-    def check(pat: Tree, pt: Type): Boolean = (pt <:< pat.tpe) || fail(pat, pt, Reason.NonConforming)
+    def check(pat: Tree, pt: Type): Boolean =
+      pt.isTupleXXLExtract(pat.tpe) // See isTupleXXLExtract, fixes TupleXXL parameter type
+      || pt <:< pat.tpe
+      || fail(pat, pt, Reason.NonConforming)
 
     def recur(pat: Tree, pt: Type): Boolean =
       !sourceVersion.isAtLeast(`3.2`)

tests/pos/i14588.scala

@@ -0,0 +1,20 @@
+//> using options -Werror
+
+class Test:
+  def t1: Unit =
+    (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23) match
+      case (x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15, x16, x17, x18, x19, x20, x21, x22, x23) =>
+  def t2: Unit =
+    (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23) match
+      case (x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15, x16, x17, x18, x19, x20, x21, x22, x23, x24) =>
+  def t3: Unit =
+    (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24) match
+      case (x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15, x16, x17, x18, x19, x20, x21, x22, x23) =>
+
+object Main:
+  def main(args: Array[String]): Unit = {
+    val t = new Test
+    t.t1
+    try { t.t2; ??? } catch case _: MatchError => ()
+    try { t.t3; ??? } catch case _: MatchError => ()
+  }

tests/pos/i16186.scala

@@ -0,0 +1,9 @@
+//> using options -Werror
+
+class Test:
+  val x = 42
+  val tup23 = (x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x)
+
+  tup23 match {
+    case (_, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _) => "Tuple Pattern"
+  }

tests/pos/i16657.scala

@@ -0,0 +1,13 @@
+//> using options -Werror
+
+class Test:
+  val (_, (
+    _, _, _, _, _, _, _, _, _, _, // 10
+    _, _, _, _, _, _, _, _, _, _, // 20
+    _, c22, _                     // 23
+  )) = // nested pattern has 23 elems
+    (0, (
+      1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
+      1, 2, 3, 4, 5, 6, 7, 8, 9, 20,
+      1, 2, 3
+    )) // ok, exhaustive, reachable, conforming and irrefutable

tests/pos/i19084.scala

@@ -0,0 +1,14 @@
+//> using options -Werror
+
+class Test:
+  def t1(y: (
+    Int, Int, Int, Int, Int, Int, Int, Int, Int, Int,
+    "Bob", Int, 33, Int,
+    Int, Int, Int, Int, Int, Int, Int, Int, Int, Int)
+        ): Unit = y match
+    case b @ (x0, x1, x2, x3, x4, x5, x6, x7, x8, x9,
+          "Bob", y1, 33, y2,
+          z0, z1, z2, z3, z4, z5, z6, z7, z8, z9)
+     => // was: !!! spurious unreachable case warning
+      ()
+    case _ => ()

tests/warn/i19084.scala

@@ -0,0 +1,17 @@
+
+
+class Test:
+  def t1(y: (
+    Int, Int, Int, Int, Int, Int, Int, Int, Int, Int,
+    "Bob", Int, 33, Int,
+    Int, Int, Int, Int, Int, Int, Int, Int, Int, Int)
+        ): Unit = y match
+    case b @ (x0, x1, x2, x3, x4, x5, x6, x7, x8, x9,
+          "Bob", y1, 33, y2,
+          z0, z1, z2, z3, z4, z5, z6, z7, z8, z9)
+     => ()
+    case b @ (x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, // warn: unreachable
+          "Bob", y1, 33, y2,
+          z0, z1, z2, z3, z4, z5, z6, z7, z8, z9)
+     => ()
+    case _ => ()