Show root of stackoverflow in IsFullyDefinedAccumulator by odersky · Pull Request #12649 · scala/scala3

odersky · 2021-05-30T15:20:21Z

This gives a better diagnosis for #12640.

smarter · 2021-05-30T15:31:10Z

+        case tp =>
+          foldOver(x, tp)
+      catch case ex: Throwable =>
+        handleRecursive("traverse ", s"${tp.show}" , ex)


Might be useful to print the constraints here too, since the loop might be due to cyclic constraints as we traverse type variables.

Here you go. With that we get:

-- Error: i12640.scala:15:42 --------------------------------------------------- 15 | case Some(s1,a) => Cons(a, () => unfold(s1,f)) | ^ |Recursion limit exceeded. |Maybe there is an illegal cyclic reference? |If that's not the case, you could also try to increase the stacksize using the -Xss JVM option. |A recurring operation is (inner to outer): | | traverse (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] |) => R in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse ([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] |] in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse ((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] |) => R in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse ([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] |] in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse ((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] |) => R in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse ([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | ... | | traverse x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] |] in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse ((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] |) => R in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] |) => R in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse ([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse Nothing in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse Nothing[Option[((S, S => F[Option[(S, T)]]), Nothing)]] in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |) | traverse ((S, S => F[Option[(S, T)]])) => | Nothing[Option[((S, S => F[Option[(S, T)]]), Nothing)]] in Constraint( | uninstantiated variables: | constrained types: [A, B](fa: F[A])(f: A => F[B]): F[B], | [F[_$3], T](head: T, tailFun: () => F[x.CpsStream[F, T]]): x.Cons[F, T] |, | [S, F[_$5], T] | (s0: S) | (f: S => F[Option[(S, T)]]) | (implicit evidence$1: x.CpsMonad[F]): F[x.CpsStream[F, T]] | bounds: | A := Option[(S, T)] | B := x.CpsStream[F, T] | F := | [R] =>> (((S, S => F[Option[(S, T)]])) => | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), | Option[((S, S => F[Option[(S, T)]]), Nothing)] | ] | ) => R | T | >: (a : T) | | x.CpsStream[ | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R) | , | T] | , Nothing] | S := (S, S => F[Option[(S, T)]]) | F := | [T] =>> | x.CpsStream[([R] =>> (((S, S => F[Option[(S, T)]])) => Nothing) => R), T] | T | ordering: |)

@rssh My gut feeling is that you are trying to push higher-kinded types too far here. I mean nobody stops you, but if you want code to be widely used then crazy types and constraints like this are a show-stopper. Even if the compiler survives this, how will anybody be able to debug type errors when they arise?

Interestingly, that original (unminimized) bug source is an attempt to create adapter for a well-known library [fs2 if anybody care], so the genie was already released from the bottle a long time ago.

smarter

Actually it looks like this is already fixed on master, if I run the testcase there I only get type errors and no stackoverflow, in this PR we get a stackoverflow because it's based on a week-old version of master but meanwhile e58ece8 already added stackoverflow handling.

odersky · 2021-05-30T20:55:36Z

I added a regression test. I still have some doubts what goes on here since with the added handleRecursion the stackoverflow problem gets reported. Bit without it, the SO goes away and we see the other errors instead.

smarter · 2021-05-30T21:03:07Z

That's because handleRecursive throws a RecursionOverflow so it's not caught by the catch ex: StackOverflowError added in e58ece8

odersky · 2021-05-31T07:35:51Z

Doh! Completely forgot about that one.

odersky mentioned this pull request May 30, 2021

Compiler crash when attempt to write async unfold signature with incorrect number of parameters #12640

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smarter reviewed May 30, 2021

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Add regression test

b0b74d5

odersky force-pushed the fix-12640 branch from 23ea2fd to b0b74d5 Compare May 30, 2021 19:48

odersky merged commit d28b891 into scala:master May 31, 2021

odersky deleted the fix-12640 branch May 31, 2021 07:36

smarter mentioned this pull request Jun 4, 2021

Test tests/neg/i12640.scala intermittently fails on the CI #12693

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Show root of stackoverflow in IsFullyDefinedAccumulator#12649

Show root of stackoverflow in IsFullyDefinedAccumulator#12649
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odersky commented May 30, 2021

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