Fix inconsistent typeSize calculation for TupleN vs recursive pair encodings
#24743
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typeSize calculation for TupleN vs recursive pair encodings
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 scala#24730
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Currently,
typeSizereports inconsistent values for standard tuple types (e.g.,(A, B)) compared to their semantically equivalent recursive pair encodings (e.g.,A *: B *: EmptyTuple).This discrepancy arises because
TupleNis represented as a flatAppliedType, whereas the nested encoding forms a deeper tree structure. AstypeSizeis often used as a heuristic for complexity or optimization limits, this inconsistency can lead to divergent behavior in the compiler depending on how a tuple is represented syntactically.This PR modifies
TypeSizeAccumulatorto canonicalizeTupleNtypes into their recursive*:representation before calculating their size. This ensures that the size metric is consistent regardless of whether the tuple is represented as a flatAppliedTypeor a nested structural type.I have added a new unit test in
TypesTestthat assertsTuple3[Int, Boolean, Double]andInt *: Boolean *: Double *: EmptyTupleboth yield identicaltypeSizeequal to 3.Thanks to @mbovel for providing the unit test that effectively reproduces this issue and validates the fix.
Fixes #24730