Diagnose when a same-type constraint (to a concrete type) is made
redundant by another same-type constraint. Slightly improve the
diagnostic that handles collisions between two same-type constraints.
Track each same-type-to-concrete constraint on the potential archetype
against which it was written, and ensure that the requirement sources
for such same-type constraints stay with the potential archetypes on
which they were described. This is similar to the way we track
same-type constraints among potential archetypes.
Use this information to canonicalize same-type-to-concrete constraints
appropriately. For each connected component within an equivalence
class of potential archetypes, select the best requirement source to
the concrete type, or substitute in an abstract requirement source if
none exists. This approach ensures that components that would be
equivalent to that concrete type anyway get a derived source, while
components that get the concrete-type equivalence by being tied to
another
To get here, we also needed to change the notion of the archetype
anchor so that potential archetypes with no same-type constraints
directly in their path are preferred over potential archetypes that do
have a same-type constraint in their path. Otherwise, the anchor might
be something that is always concrete and is, therefore, not terribly
interesting.
Fixes the new case that popped up in rdar://problem/30478915.
Generic typealiases are entirely broken as archetypes, but some things
mostly worked with them before introducing ResolvedType, so let's
restore that behaviour.
This adds the concept of an "unresolved type" and a "resolved type",
where the latter involves stripping away any typealias archetype layers
from the former, to get to the "true" potential archetype or concrete
type that something refers to.
Unify the handling of the "inheritance" clauses of a generic type
parameter, associated type, or protocol, walking them in a
TypeRepr-preserving manner and adding requirements as they are
discovered. This sets the stage for providing better source-location
information [*].
This eliminates a redundant-but-different code path for protocol
"inheritance" clauses, which was using
ProtocolDecl::getInheritedProtocols() rather than looking at the
actual TypeReprs, and unifies the logic with that of associated types
and type parameters. This eliminates a near-DRY violation, sets us up
for simplifying the "inherited protocols" part of ProtocolDecl, and
sets us up better for the soon-to-be-proposed
class C { }
protocol P: C { }
[*] We still drop it, but now we have a FIXME!
Reimplement the RequirementSource class, which captures how
a particular requirement is satisfied by a generic signature. The
primary goal of this rework is to keep the complete path one follows
in a generic signature to get from some explicit requirement in the
generic signature to some derived requirement or type, e.g.,
1) Start at an explicit requirement "C: Collection"
2) Go to the inherited protocol Sequence,
3) Get the "Iterator" associated type
4) Get its conformance to "IteratorProtocol"
5) Get the "Element" associated type
We don't currently capture all of the information we want in the path,
but the basic structure is there, and should also allow us to capture
more source-location information, find the "optimal" path, etc. There are
are a number of potential uses:
* IRGen could eventually use this to dig out the witness tables and
type metadata it needs, instead of using its own fulfillment
strategy
* SubstitutionMap could use this to lookup conformances, rather than
it's egregious hacks
* The canonical generic signature builder could use this to lookup
conformances as needed, e.g., for the recursive-conformances case.
... and probably more simplifications, once we get this right.
This essentially undoes the implementation in 51da51dfc0, which
implicitly did a substitution of the Self type in a protocol's
requirement signature by threading around the replacement PA. This is
brittle because every part of the code needs to take and pass around the
argument. By preemptively substituting, the whole requirement is in the
right form from the time it enters `addRequirement`.
The infrastructure here also allows simplifying some code.
