We compute the canonical type by first simplifying the type term, and
then checking if it is a concrete type. If there's no concrete type,
we convert the simplified term back to an interface type and return
that; otherwise, we canonicalize any structural sub-components of
the concrete type that contain interface types, and so on.
Due to a quirk of how the existing declaration checker works, we also
need to handle "purely concrete" member types, eg if I have a
signature `<T where T == Foo>`, and we're asked to canonicalize the
type `T.[P:A]` where Foo : A.
This comes up because we can derive the signature `<T where T == Foo>`
from a generic signature like `<T where T : P>`; adding the
concrete requirement 'T == Foo' renders 'T : P' redundant. We then
want to take interface types written against the original signature
and canonicalize them with respect to the derived signature.
The problem is that `T.[P:A]` is not a valid term in the rewrite system
for `<T where T == Foo>`, since we do not have the requirement T : P.
A more principled solution would build a substitution map when
building a derived generic signature that adds new requirements;
interface types would first be substituted before being canonicalized
in the new signature.
For now, we handle this with a two-step process; we split a term up
into a longest valid prefix, which must resolve to a concrete type,
and the remaining suffix, which we use to perform a concrete
substitution using subst().
This becomes a utility that maps the requirement's types into the
generic environment if needed before calling out to the new
Requirement::isSatisfied().
The new approach is to not look at RequirementSources at all. Instead,
we exhaustively enumerate all conformance access paths, beginning
from the root conformance requirements in the signature, then doing
all conformance requirements from those protocols' requirement
signatures, and so on.
We enumerate conformance access paths in breadth first order by
length until we find the one we want. The results are memoized.
This fixes a regression with another change I'm working on. The
test case does not fail with this PR alone, but I'm adding it now
anyway.
Doing this when computing a canonical signature didn't really
make sense because canonical signatures are not canonicalized
any more strongly _with respect to the builder_; they just
canonicalize their requirement types.
Instead, let's do these checks after creating the signature in
computeGenericSignature().
The old behavior had another undesirable property; since the
canonicalization was done by registerGenericSignatureBuilder(),
we would always build a new GSB from scratch for every
signature we compute.
The new location also means we do these checks for protocol
requirement signatures as well. This flags an existing fixed
crasher where we still emit bogus same-type requirements in
the requirement signature, so I moved this test back into
an unfixed state.
Previously we would look for a derived source before an explicit one,
on account of the explicit one possibly being redundant. However, the
presence of 'self-derived' sources meant that we had to call
getMinimalConformanceSource() to ensure the derived sources
were actually usable and would not produce an infinite conformance
access path.
I'd like to remove getMinimalConformanceSource() now that we have
an alternate algorithm to identify redundant explicit requirements.
Instead, we can handle the explicit case first, by checking for a
conformance requirement in the generic signature -- its presence
means it was not redundant, by construction.
Then once we handle that case, we know we're going to use a derived
source, and finding the shortest one seems to be good enough.
This fixes the IRGen crash in https://bugs.swift.org/browse/SR-11153;
the requirement signatures in that test still have unnecessary
same-type requirements printed, so I added a separate RUN: line
for those, and it's marked as known-failing with 'not %FileCheck'.
A new implementation from "first principles". The idea is that
for a given conformance, we either have an explicit source
which forms the root of the requirement path, or a derived
source, which we 'factor' into a parent type/parent protocol
pair, and a requirement signature requirement.
We recursively compute the conformance access path of the
parent type and parent protocol, and append the path element
for the requirement.
This fixes a long-standing crasher, and eliminates two hacks,
the 'usesRequirementSource' flag in RequirementSource, and
the 'HadAnyRedundantConstraints' flag in GenericSignatureBuilder.
Fixes https://bugs.swift.org/browse/SR-7371 / rdar://problem/39239511
This simplifies fixing the master-next build. Upstream LLVM already
has a copy of this function, so on master-next we only need to delete
the Swift copy, reducing the potential for merge conflicts.
Motivation: `GenericSignatureImpl::getCanonicalSignature` crashes for
`GenericSignature` with underlying `nullptr`. This led to verbose workarounds
when computing `CanGenericSignature` from `GenericSignature`.
Solution: `GenericSignature::getCanonicalSignature` is a wrapper around
`GenericSignatureImpl::getCanonicalSignature` that returns the canonical
signature, or `nullptr` if the underlying pointer is `nullptr`.
Rewrite all verbose workarounds using `GenericSignature::getCanonicalSignature`.
ProtocolConformanceRef already has an invalid state. Drop all of the
uses of Optional<ProtocolConformanceRef> and just use
ProtocolConformanceRef::forInvalid() to represent it. Mechanically
translate all of the callers and callsites to use this new
representation.
Structurally prevent a number of common anti-patterns involving generic
signatures by separating the interface into GenericSignature and the
implementation into GenericSignatureBase. In particular, this allows
the comparison operators to be deleted which forces callers to
canonicalize the signature or ask to compare pointers explicitly.
This memoizes the result, which is fine for all callers; the only
exception is open existential types where each new open existential
now explicitly gets a unique generic environment, allocated by
calling GenericEnvironment::getIncomplete().
When a request for an abstract generic signature contains noncanonical
types, first compute the abstract generic signature for the
canonicalized types, then map back to the provided generic
parameters. Clients of this request generally work in canonical types
already, but it's a small win.
Introduce a request to form an abstract generic signature given a
base signature, additional generic parameters, and additional
requirements. It is meant to provide a caching layer in front of the
generic signature builder.
Switch one direct client of the generic signature builder over to this
mechanism, the formation of a generic signature for an existential
type.
Opaque result type archetypes can involve type variables, which
then get introduced into GenericSignatureBuilders and the
generated GenericSignatures. Allocate them in the proper arena
So we don’t end up with use-after-free errors.
Fixes rdar://problem/50309503.
When substituting type parameters to compute a canonical type within a
given generic context, also handle the case where the type parameter is
directly known to be a concrete type. The type checker won’t do this, but
SourceKit does.
Fixes a regression in SourceKit/DocSupport/doc_stdlib.swift.
