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org.scalacheck.Shrink.scala Maven / Gradle / Ivy
/*
* ScalaCheck
* Copyright (c) 2007-2021 Rickard Nilsson. All rights reserved.
* http://www.scalacheck.org
*
* This software is released under the terms of the Revised BSD License.
* There is NO WARRANTY. See the file LICENSE for the full text.
*/
package org.scalacheck
import scala.concurrent.duration.Duration
import scala.concurrent.duration.FiniteDuration
import util.Buildable
import util.SerializableCanBuildFroms.*
sealed abstract class Shrink[T] extends Serializable {
def shrink(x: T): Stream[T]
/** Create a new shrink that only produces values satisfying the given condition.
*/
def suchThat(f: T => Boolean): Shrink[T] = Shrink(v => this.shrink(v).filter(f))
}
trait ShrinkLowPriority {
/** Default shrink instance */
implicit def shrinkAny[T]: Shrink[T] = Shrink(_ => Stream.empty)
}
object Shrink extends ShrinkLowPriority with ShrinkVersionSpecific with time.JavaTimeShrink {
import Stream.{cons, empty}
import scala.collection.*
/** Interleaves two streams */
private def interleave[T](xs: Stream[T], ys: Stream[T]): Stream[T] =
if (xs.isEmpty) ys
else if (ys.isEmpty) xs
else cons(xs.head, cons(ys.head, interleave(xs.tail, ys.tail)))
/** Shrink instance factory */
def apply[T](s: T => Stream[T]): Shrink[T] = new Shrink[T] {
override def shrink(x: T) = s(x)
}
/** Shrink a value */
def shrink[T](x: T)(implicit s: Shrink[T]): Stream[T] = s.shrink(x)
/** Shrink a value, but also return the original value as the first element in the resulting stream
*/
def shrinkWithOrig[T](x: T)(implicit s: Shrink[T]): Stream[T] =
cons(x, s.shrink(x))
/** Shrink instance of container */
implicit def shrinkContainer[C[_], T](implicit
v: C[T] => Traversable[T],
s: Shrink[T],
b: Buildable[T, C[T]]
): Shrink[C[T]] = Shrink { (xs: C[T]) =>
val ys = v(xs)
val zs = ys.toStream
removeChunks(ys.size, zs).append(shrinkOne(zs)).map(b.fromIterable)
}
/** Shrink instance of container2 */
implicit def shrinkContainer2[C[_, _], T, U](implicit
v: C[T, U] => Traversable[(T, U)],
s: Shrink[(T, U)],
b: Buildable[(T, U), C[T, U]]
): Shrink[C[T, U]] = Shrink { (xs: C[T, U]) =>
val ys = v(xs)
val zs = ys.toStream
removeChunks(ys.size, zs).append(shrinkOne(zs)).map(b.fromIterable)
}
private def removeChunks[T](n: Int, xs: Stream[T]): Stream[Stream[T]] =
if (xs.isEmpty) empty
else if (xs.tail.isEmpty) cons(empty, empty)
else {
val n1 = n / 2
val n2 = n - n1
lazy val xs1 = xs.take(n1)
lazy val xs2 = xs.drop(n1)
lazy val xs3 =
for (ys1 <- removeChunks(n1, xs1) if !ys1.isEmpty) yield ys1 append xs2
lazy val xs4 =
for (ys2 <- removeChunks(n2, xs2) if !ys2.isEmpty) yield xs1 append ys2
cons(xs1, cons(xs2, interleave(xs3, xs4)))
}
private def shrinkOne[T: Shrink](zs: Stream[T]): Stream[Stream[T]] =
if (zs.isEmpty) empty
else {
val x = zs.head
val xs = zs.tail
shrink(x).map(cons(_, xs)).append(shrinkOne(xs).map(cons(x, _)))
}
/** Shrink instances for numeric data types */
implicit def shrinkFractional[T: Fractional]: Shrink[T] =
new ShrinkFractional[T]
implicit def shrinkIntegral[T: Integral]: Shrink[T] =
new ShrinkIntegral[T]
/** Shrink instance of String */
implicit lazy val shrinkString: Shrink[String] = Shrink { s =>
shrinkContainer[List, Char].shrink(s.toList).map(_.mkString)
}
/** Shrink instance of Option */
implicit def shrinkOption[T: Shrink]: Shrink[Option[T]] = Shrink {
case None => empty
case Some(x) => cons(None, for (y <- shrink(x)) yield Some(y))
}
/** Shrink instance of 2-tuple */
implicit def shrinkTuple2[
T1: Shrink,
T2: Shrink
]: Shrink[(T1, T2)] =
Shrink { case (t1, t2) =>
shrink(t1).map((_, t2)) append
shrink(t2).map((t1, _))
}
/** Shrink instance of 3-tuple */
implicit def shrinkTuple3[
T1: Shrink,
T2: Shrink,
T3: Shrink
]: Shrink[(T1, T2, T3)] =
Shrink { case (t1, t2, t3) =>
shrink(t1).map((_, t2, t3)) append
shrink(t2).map((t1, _, t3)) append
shrink(t3).map((t1, t2, _))
}
/** Shrink instance of 4-tuple */
implicit def shrinkTuple4[
T1: Shrink,
T2: Shrink,
T3: Shrink,
T4: Shrink
]: Shrink[(T1, T2, T3, T4)] =
Shrink { case (t1, t2, t3, t4) =>
shrink(t1).map((_, t2, t3, t4)) append
shrink(t2).map((t1, _, t3, t4)) append
shrink(t3).map((t1, t2, _, t4)) append
shrink(t4).map((t1, t2, t3, _))
}
/** Shrink instance of 5-tuple */
implicit def shrinkTuple5[
T1: Shrink,
T2: Shrink,
T3: Shrink,
T4: Shrink,
T5: Shrink
]: Shrink[(T1, T2, T3, T4, T5)] =
Shrink { case (t1, t2, t3, t4, t5) =>
shrink(t1).map((_, t2, t3, t4, t5)) append
shrink(t2).map((t1, _, t3, t4, t5)) append
shrink(t3).map((t1, t2, _, t4, t5)) append
shrink(t4).map((t1, t2, t3, _, t5)) append
shrink(t5).map((t1, t2, t3, t4, _))
}
/** Shrink instance of 6-tuple */
implicit def shrinkTuple6[
T1: Shrink,
T2: Shrink,
T3: Shrink,
T4: Shrink,
T5: Shrink,
T6: Shrink
]: Shrink[(T1, T2, T3, T4, T5, T6)] =
Shrink { case (t1, t2, t3, t4, t5, t6) =>
shrink(t1).map((_, t2, t3, t4, t5, t6)) append
shrink(t2).map((t1, _, t3, t4, t5, t6)) append
shrink(t3).map((t1, t2, _, t4, t5, t6)) append
shrink(t4).map((t1, t2, t3, _, t5, t6)) append
shrink(t5).map((t1, t2, t3, t4, _, t6)) append
shrink(t6).map((t1, t2, t3, t4, t5, _))
}
/** Shrink instance of 7-tuple */
implicit def shrinkTuple7[
T1: Shrink,
T2: Shrink,
T3: Shrink,
T4: Shrink,
T5: Shrink,
T6: Shrink,
T7: Shrink
]: Shrink[(T1, T2, T3, T4, T5, T6, T7)] =
Shrink { case (t1, t2, t3, t4, t5, t6, t7) =>
shrink(t1).map((_, t2, t3, t4, t5, t6, t7)) append
shrink(t2).map((t1, _, t3, t4, t5, t6, t7)) append
shrink(t3).map((t1, t2, _, t4, t5, t6, t7)) append
shrink(t4).map((t1, t2, t3, _, t5, t6, t7)) append
shrink(t5).map((t1, t2, t3, t4, _, t6, t7)) append
shrink(t6).map((t1, t2, t3, t4, t5, _, t7)) append
shrink(t7).map((t1, t2, t3, t4, t5, t6, _))
}
/** Shrink instance of 8-tuple */
implicit def shrinkTuple8[
T1: Shrink,
T2: Shrink,
T3: Shrink,
T4: Shrink,
T5: Shrink,
T6: Shrink,
T7: Shrink,
T8: Shrink
]: Shrink[(T1, T2, T3, T4, T5, T6, T7, T8)] =
Shrink { case (t1, t2, t3, t4, t5, t6, t7, t8) =>
shrink(t1).map((_, t2, t3, t4, t5, t6, t7, t8)) append
shrink(t2).map((t1, _, t3, t4, t5, t6, t7, t8)) append
shrink(t3).map((t1, t2, _, t4, t5, t6, t7, t8)) append
shrink(t4).map((t1, t2, t3, _, t5, t6, t7, t8)) append
shrink(t5).map((t1, t2, t3, t4, _, t6, t7, t8)) append
shrink(t6).map((t1, t2, t3, t4, t5, _, t7, t8)) append
shrink(t7).map((t1, t2, t3, t4, t5, t6, _, t8)) append
shrink(t8).map((t1, t2, t3, t4, t5, t6, t7, _))
}
/** Shrink instance of 9-tuple */
implicit def shrinkTuple9[
T1: Shrink,
T2: Shrink,
T3: Shrink,
T4: Shrink,
T5: Shrink,
T6: Shrink,
T7: Shrink,
T8: Shrink,
T9: Shrink
]: Shrink[(T1, T2, T3, T4, T5, T6, T7, T8, T9)] =
Shrink { case (t1, t2, t3, t4, t5, t6, t7, t8, t9) =>
shrink(t1).map((_, t2, t3, t4, t5, t6, t7, t8, t9)) append
shrink(t2).map((t1, _, t3, t4, t5, t6, t7, t8, t9)) append
shrink(t3).map((t1, t2, _, t4, t5, t6, t7, t8, t9)) append
shrink(t4).map((t1, t2, t3, _, t5, t6, t7, t8, t9)) append
shrink(t5).map((t1, t2, t3, t4, _, t6, t7, t8, t9)) append
shrink(t6).map((t1, t2, t3, t4, t5, _, t7, t8, t9)) append
shrink(t7).map((t1, t2, t3, t4, t5, t6, _, t8, t9)) append
shrink(t8).map((t1, t2, t3, t4, t5, t6, t7, _, t9)) append
shrink(t9).map((t1, t2, t3, t4, t5, t6, t7, t8, _))
}
implicit def shrinkEither[T1: Shrink, T2: Shrink]: Shrink[Either[T1, T2]] =
Shrink { x =>
x.fold(shrink(_).map(Left(_)), shrink(_).map(Right(_)))
}
implicit val shrinkFiniteDuration: Shrink[FiniteDuration] =
xmap[Long, FiniteDuration](Duration.fromNanos, _.toNanos)
implicit val shrinkDuration: Shrink[Duration] = Shrink {
case d: FiniteDuration => shrinkFiniteDuration.shrink(d)
case _ => Stream.empty
}
/** Transform a Shrink[T] to a Shrink[U] where T and U are two isomorphic types whose relationship is described by the
* provided transformation functions. (exponential functor map)
*/
def xmap[T, U](from: T => U, to: U => T)(implicit st: Shrink[T]): Shrink[U] = Shrink[U] { (u: U) =>
st.shrink(to(u)).map(from)
}
}
final class ShrinkIntegral[T](implicit ev: Integral[T]) extends Shrink[T] {
import ev.{fromInt, gteq, quot, negate, equiv, zero, one}
val two = fromInt(2)
// see if T supports negative values or not. this makes some
// assumptions about how Integral[T] is defined, which work for
// Integral[Char] at least. we can't be sure user-defined
// Integral[T] instances will be reasonable.
val skipNegation = gteq(negate(one), one)
// assumes x is non-zero.
private def halves(x: T): Stream[T] = {
val q = quot(x, two)
if (equiv(q, zero)) Stream(zero)
else if (skipNegation) q #:: halves(q)
else q #:: negate(q) #:: halves(q)
}
def shrink(x: T): Stream[T] =
if (equiv(x, zero)) Stream.empty[T] else halves(x)
}
final class ShrinkFractional[T](implicit ev: Fractional[T]) extends Shrink[T] {
import ev.{fromInt, abs, zero, one, div, lteq, negate, lt}
val two = fromInt(2)
// this makes some assumptions, namely that we can support 1e-5 as a
// fractional value. fortunately, if that is not true, it's likely
// that our divisions will converge to zero quickly enough anyway.
val small = div(one, fromInt(100000))
def closeToZero(x: T): Boolean = lteq(abs(x), small)
// assumes x is not close to zero
private def halves(x: T): Stream[T] = {
val q = div(x, two)
if (closeToZero(q)) Stream(zero)
else q #:: negate(q) #:: halves(q)
}
// this catches things like NaN and Infinity. it's not clear that we
// should be shrinking those values, since they are sentinels.
def isUnusual(x0: T): Boolean = {
val x = abs(x0)
// the negation here is important -- if we wrote this as gteq(...)
// then it would not handle the NaN case correctly.
!lt(div(x, two), x)
}
def shrink(x: T): Stream[T] =
if (closeToZero(x) || isUnusual(x)) Stream.empty[T]
else halves(x)
}
