Fix inconsistent typeSize for TupleN vs nested pairs

Previously, `typeSize` reported different values for standard `TupleN` types (e.g., `(A, B)`) compared to their equivalent recursive pair encodings (e.g., `A *: B *: EmptyTuple`). This discrepancy occurred because `TupleN` is a flat `AppliedType`, while the nested encoding forms a deeper tree structure. This patch modifies `TypeSizeAccumulator` to canonicalize `TupleN` types into their recursive `*:` representation before calculating the size. This ensures that the size metric is consistent regardless of whether the tuple is represented syntactically or structurally. This change is verified by a new unit test in `TypesTest`, which confirms that both `Tuple3[Int, Boolean, Double]` and its recursive equivalent `Int *: Boolean *: Double *: EmptyTuple` now yield identical `typeSize` values. Fixes#24730

Author: Lluc24

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

@@ -7124,7 +7124,15 @@ object Types extends TypeUtils{
 classTypeSizeAccumulator(usingContext) extendsTypeAccumulator[Int]{
 varseen= util.HashSet[Type](initialCapacity =8)
 defapply(n: Int, tp: Type):Int=
- tp match{
+
+valcanonicTp= tp match
+caseAppliedType(_, args) if defn.isTupleNType(tp) =>
+ args.foldRight(defn.EmptyTupleClass.typeRef:Type){(elemType, acc) =>
+ defn.PairClass.typeRef.appliedTo(elemType, acc)
+ }
+case _ => tp
+
+ canonicTp match{
 casetp: AppliedType=>
 valtpNorm= tp.tryNormalize
 if tpNorm.exists then apply(n, tpNorm)

compiler/test/dotty/tools/dotc/core/TypesTest.scala

@@ -0,0 +1,18 @@
+packagedotty.tools.dotc.core
+
+importdotty.tools.DottyTest
+importdotty.tools.dotc.core.Symbols.defn
+importdotty.tools.dotc.core.TypeOps
+
+importorg.junit.Test
+importorg.junit.Assert.assertEquals
+
+classTypesTestextendsDottyTest:
+
+@Testdeftuple3TypeSize=
+valtpe= defn.TupleType(3).nn.appliedTo(List(defn.IntType, defn.BooleanType, defn.DoubleType))
+ assertEquals(3, tpe.typeSize)
+
+@Testdeftuple3ConsTypeSize=
+valtpe=TypeOps.nestedPairs(List(defn.IntType, defn.BooleanType, defn.DoubleType))
+ assertEquals(3, tpe.typeSize)