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Fixes issue #912: Executes liftF effect twice in a product composition #914

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Merged
sloshy merged 1 commit into from
Jan 22, 2026
Merged

Fixes issue #912: Executes liftF effect twice in a product composition #914

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12 changes: 6 additions & 6 deletions fetch/src/main/scala/fetch.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -301,9 +301,9 @@ object `package` {
case (Done(a), Done(b)) =>
Done[F, Z](f(a, b))
case (Done(a), Blocked(br, c)) =>
Blocked[F, Z](br, map2(fa, c)(f))
Blocked[F, Z](br, c.map(b => f(a, b)))
case (Blocked(br, c), Done(b)) =>
Blocked[F, Z](br, map2(c, fb)(f))
Blocked[F, Z](br, c.map(a => f(a, b)))
case (Blocked(br, c), Blocked(br2, c2)) =>
Blocked[F, Z](combineRequestMaps(br, br2), map2(c, c2)(f))
case (_, Throw(e)) =>
Expand All @@ -324,9 +324,9 @@ object `package` {
case (Done(a), Done(b)) =>
Done[F, (A, B)]((a, b))
case (Done(a), Blocked(br, c)) =>
Blocked[F, (A, B)](br, product(fa, c))
Blocked[F, (A, B)](br, c.map((a, _)))
case (Blocked(br, c), Done(b)) =>
Blocked[F, (A, B)](br, product(c, fb))
Blocked[F, (A, B)](br, c.map((_, b)))
case (Blocked(br, c), Blocked(br2, c2)) =>
Blocked[F, (A, B)](combineRequestMaps(br, br2), product(c, c2))
case (_, Throw(e)) =>
Expand All @@ -343,9 +343,9 @@ object `package` {
case (Done(a), Done(b)) =>
Done[F, B](b)
case (Done(a), Blocked(br, c)) =>
Blocked[F, B](br, productR(fa)(c))
Blocked[F, B](br, c)
case (Blocked(br, c), Done(b)) =>
Blocked[F, B](br, productR(c)(fb))
Blocked[F, B](br, c.as(b))
case (Blocked(br, c), Blocked(br2, c2)) =>
Blocked[F, B](combineRequestMaps(br, br2), productR(c)(c2))
case (_, Throw(e)) =>
Expand Down
47 changes: 47 additions & 0 deletions fetch/src/test/scala/FetchTests.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -942,4 +942,51 @@ class FetchTests extends FetchSpec {

io.map(_ shouldEqual List(0, 1, 2, 42)).unsafeToFuture()
}

// Side effect re-execution tests (Issue #912)

"Product should not re-execute side effects from completed fetches" in {
Ref[IO]
.of(0)
.flatMap { counter =>
val fetchWithSideEffect: Fetch[IO, Unit] = Fetch.liftF(counter.update(_ + 1))

val program = (
List.range(1, 10).map(one[IO]).reduce(_ >> _),
fetchWithSideEffect
).tupled

Fetch.run[IO](program) >> counter.get.map(_ shouldEqual 1)
}
.unsafeToFuture()
}

"ProductR should not re-execute side effects from completed fetches" in {
Ref[IO]
.of(0)
.flatMap { counter =>
val fetchWithSideEffect: Fetch[IO, Unit] = Fetch.liftF(counter.update(_ + 1))

val program = List.range(1, 10).map(one[IO]).reduce(_ >> _) *> fetchWithSideEffect

Fetch.run[IO](program) >> counter.get.map(_ shouldEqual 1)
}
.unsafeToFuture()
}

"mapN should not re-execute side effects from completed fetches" in {
Ref[IO]
.of(0)
.flatMap { counter =>
val fetchWithSideEffect: Fetch[IO, Int] = Fetch.liftF(counter.updateAndGet(_ + 1))

val program = (
List.range(1, 10).map(one[IO]).reduce(_ >> _),
fetchWithSideEffect
).mapN((_, n) => n)

Fetch.run[IO](program) >> counter.get.map(_ shouldEqual 1)
}
.unsafeToFuture()
}
}
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