For implementation reasons we want the requirement signature of a
protocol to directly include all protocol refinement relationships,
even if they can be derived via same-type requirements between Self
and some nested type.
Therefore, a protocol refinement rule [P].[Q] => [P] can only be
replaced with a generating conformance equation that consists
entirely of other conformance rules.
This exactly simulates the existing behavior of the GSB's redundant
requirements algorithm.
After forming a reference to an entry in a DenseMap, we have to be
careful not touch the reference after calling any code which might
re-entrantly invalidate the reference by mutating the DenseMap.
Fixes rdar://problem/83891298.
We would skip recording a conformance access path if the subject
type canonicalized to a concrete type, but this was incorrect.
The correct formulation is to use the _canonical anchor_ and not
the canonical type as the caching key; that is, we always want it
to be a type parameter, even if it is fixed to a concrete type,
because type parameters fixed to concrete types can appear in
the middle of conformance access paths, as the example in the
radar demonstrates.
Fixes rdar://problem/83687967.
This was manifesting as module interfaces printing generic parameters
as `τ_0_0` in some cases.
Note that the GSB has the same bug, so this test case will fail with
-requirement-machine=off. I don't plan on fixing the bug in the GSB
unless we need to.
Fixes rdar://problem/78977127.
- Skip permanent rules (there's no point, we'll add them back next time)
- Skip conformance rules (these will be handled separately)
- Delete 3-cells that are entirely "in-context" (but don't quote me on
this one, I'm not quite yet convinced it's correct, but it feels right)
The canonical order on associated types compares the name before the
protocol, so for example T.[P2:A] < T.[P1:B]. Make sure the reduction
order does the same so that we correctly compute canonical types in
this case.
The left and right hand side of a merged associated type candidate rule
have a common prefix except for the associated type symbol at the end.
Instead of passing two MutableTerms, we can pass a single uniqued
Term and a Symbol.
Also, we can compute the merged symbol before pushing the candidate
onto the vector. This avoids unnecessary work if the merged symbol
is equal to the right hand side's symbol.
