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New footprint calculation scheme (scala#19639)
Since match type reduction is expensive, it is cached. If a type is reduced (or not reduced) in `tryNormalize` we remember that decision and return the previous result - unless something in the context changed since the last attempt which could lead to a different outcome. Relevant here are: - constraints (regular and GADT) over type parameters - instantations of type variables We keep track of these things in a so-called footprint calculation. The old calculation clearly did not work. It either never worked or was broken by the changes to matchtype reduction. I now changed it to a more straightforward scheme that computes the footprint directly instead of relying on TypeComparer to produce the right trace.
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,99 @@ | ||
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| object NamedTuple: | ||
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| opaque type AnyNamedTuple = Any | ||
| opaque type NamedTuple[N <: Tuple, +V <: Tuple] >: V <: AnyNamedTuple = V | ||
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| export NamedTupleDecomposition.{Names, DropNames} | ||
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| /** The type of the named tuple `X` mapped with the type-level function `F`. | ||
| * If `X = (n1 : T1, ..., ni : Ti)` then `Map[X, F] = `(n1 : F[T1], ..., ni : F[Ti])`. | ||
| */ | ||
| type Map[X <: AnyNamedTuple, F[_ <: Tuple.Union[DropNames[X]]]] = | ||
| NamedTuple[Names[X], Tuple.Map[DropNames[X], F]] | ||
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| end NamedTuple | ||
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| object NamedTupleDecomposition: | ||
| import NamedTuple.* | ||
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| /** The names of a named tuple, represented as a tuple of literal string values. */ | ||
| type Names[X <: AnyNamedTuple] <: Tuple = X match | ||
| case NamedTuple[n, _] => n | ||
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| /** The value types of a named tuple represented as a regular tuple. */ | ||
| type DropNames[NT <: AnyNamedTuple] <: Tuple = NT match | ||
| case NamedTuple[_, x] => x | ||
| end NamedTupleDecomposition | ||
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| class Expr[Result] | ||
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| object Expr: | ||
| import NamedTuple.{NamedTuple, AnyNamedTuple} | ||
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| type Of[A] = Expr[A] | ||
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| type StripExpr[E] = E match | ||
| case Expr.Of[b] => b | ||
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| case class Ref[A]($name: String = "") extends Expr.Of[A] | ||
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| case class Join[A <: AnyNamedTuple](a: A) | ||
| extends Expr.Of[NamedTuple.Map[A, StripExpr]] | ||
| end Expr | ||
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| trait Query[A] | ||
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| object Query: | ||
| // Extension methods to support for-expression syntax for queries | ||
| extension [R](x: Query[R]) | ||
| def map[B](f: Expr.Ref[R] => Expr.Of[B]): Query[B] = ??? | ||
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| case class City(zipCode: Int, name: String, population: Int) | ||
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| object Test: | ||
| import Expr.StripExpr | ||
| import NamedTuple.{NamedTuple, AnyNamedTuple} | ||
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| val cities: Query[City] = ??? | ||
| val q6 = | ||
| cities.map: city => | ||
| val x: NamedTuple[ | ||
| ("name", "zipCode"), | ||
| (Expr.Of[String], Expr.Of[Int])] = ??? | ||
| Expr.Join(x) | ||
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| /* Was error: | ||
| -- [E007] Type Mismatch Error: bad-footprint.scala:60:16 ----------------------- | ||
| 60 | cities.map: city => | ||
| | ^ | ||
| |Found: Expr.Ref[City] => | ||
| | Expr[ | ||
| | NamedTuple.NamedTuple[(("name" : String), ("zipCode" : String)), (String, | ||
| | Int)] | ||
| | ] | ||
| |Required: Expr.Ref[City] => | ||
| | Expr[ | ||
| | NamedTuple.NamedTuple[ | ||
| | NamedTupleDecomposition.Names[ | ||
| | NamedTuple.NamedTuple[(("name" : String), ("zipCode" : String)), ( | ||
| | Expr[String], Expr[Int])] | ||
| | ], | ||
| | Tuple.Map[ | ||
| | NamedTupleDecomposition.DropNames[ | ||
| | NamedTuple.NamedTuple[(("name" : String), ("zipCode" : String)), ( | ||
| | Expr[String], Expr[Int])] | ||
| | ], | ||
| | Expr.StripExpr] | ||
| | ] | ||
| | ] | ||
| 61 | val x: NamedTuple[ | ||
| 62 | ("name", "zipCode"), | ||
| 63 | (Expr.Of[String], Expr.Of[Int])] = ??? | ||
| 64 | Expr.Join(x) | ||
| | | ||
| | longer explanation available when compiling with `-explain` | ||
| 1 error found | ||
| */ |