Canonicalize capture variable subtype comparisons #22289
Conversation
Fixes scala#22103 Subtype problems where at least one side is a type variable representing a capture variable are canonicalized to capturing type comparisons on the special `CapSet` for the universe capture sets. For example, `C <: CapSet^{C^}` becomes `CapSet^{C^} <: CapSet^{C^}`, and `A <: B` becomes `CapSet^{A^} <: CapSet^{B^}` if both `A` and `B` are capture variables.
| val c3: C = d_e_f1 // error | ||
| val c4: C = f1 // error | ||
| val e4: E = f1 // error | ||
| val e5: E = d1 // error |
There was a problem hiding this comment.
This should fail but currently doesn't. We now canonicalize the subtype test D <: E (fails) to CapSet^{D^} <: CapSet^{E^} (succeeds). It appears the subcapturing implementation does not handle this correctly.
|
Can you push this to dotty-staging? Then we can collaborate to maybe fix the problem with the failing test. |
|
I think the problem of the failing test is with And if we handle this correctly, it should also be possible to write things like def f[C^, D^, E <: C | D](...) = ...which means that or: def f[C^, D^, E <: C & D](...) = ...which means that |
|
@Linyxus exactly! That will be the next step. |
|
The continuation: #22299 |
Fixes #22103
Subtype problems where at least one side is a type variable representing a capture variable are canonicalized to capturing type comparisons on the special
CapSetfor the universe of capture sets. For example,C <: CapSet^{C^}becomesCapSet^{C^} <: CapSet^{C^}, andA <: BbecomesCapSet^{A^} <: CapSet^{B^}if bothAandBare capture variables.Supersedes #22183. This solution is overall cleaner and does not require adding a new bit to the TypeComparer's ApproxState.