We were emitting a superclass constraint for each connected component
of derived same-type constraints within an equivalence class, when in
fact we only need one superclass constraint for the entire equivalence
class.
As we've done with all of the other kinds of constraints, keep track
of all of the layout constraints on the equivalence class. Use the
normal mechanism to diagnose conflicts between different layout
constraints, warn about duplicate layout constraints, etc.
As we've been doing with other kinds of constraints, track *all* of
the requirement sources for deriving same-type constraints within the
equivalence class, then remove self-derived constraints at the end.
There is no checking for duplicated same-type constraints yet.
Move the storage for the protocols to which a particular potential
archetype conforms into EquivalenceClass, so that it is more easily
shared. More importantly, keep track of *all* of the constraint
sources that produced a particular conformance requirement, so we can
revisit them later, which provides a number of improvements:
* We can drop self-derived requirements at the end, once we've
established all of the equivalence classes
* We diagnose redundant conformance requirements, e.g., "T: Sequence"
is redundant if "T: Collection" is already specified.
* We can choose the best path when forming the conformance access
path.
Our handling of nested types was scattered in several places, and
(worse) correct computation of archetype anchors required us to
"explode" out all of the potential archetypes for every associated
type with the given name to ensure that we get the right one.
Make nested type construction somewhat more lazy: if asked for a
nested type for a specific associated type, just create the nested
type for that associated type (instead of *all* of them). If asked for
a nested type by name, either return the one we already have or create
the one that's most likely to be the archetype anchor. Overall, this
should result in many fewer potential archetypes being constructed.
This hack is papering over other issues in the generic signature
builder, where canonicalizing an existing generic signature---in which
we already know the specific associated type declarations---could
introduce "inferred" requirements, breaking the resulting requirement
signatures by producing too-short paths. By delaying same-type
requirements, we make this case less likely.
The correct solution is to eliminate
PotentialArchtype::getNestedType()'s injection of an inferred
requirement, but doing so requires a bit more surgery.
If a requirement is made redundant due to another requirement that was
inferred from the signature of a generic declaration, don't diagnose
the former as redundant. The user has likely written the requirement
explicitly for clarity purposes (e.g., to emphasize the Hashable
requirement on a function that takes a Set<T>). Removing the
requirement to silence the warning would make the code less clear.
This eliminates all of the annoying, spurious warnings from the build
of the overlays.
The ad hoc substitution functions here were really odd; use
SubstitutionMap directly, and pass it through to
GenericSignatureBuilder::addRequirement().
The stored dependent types in ProtocolRequirement elements within
requirement sources were incorrect for requirements created from the
requirement signature of another protocol, because we picked up the
already-substituted subject type. Thread the optional substitution map
through addRequirement(Requirement) as well, so we maintain the
original spelling of the stored dependent type.
This is a temporary fix; we should be able to recover the stored
dependent types from the potential archetypes in the requirement
source, so that we don't need to specify them explicitly at
construction time.
For a protocol requirement element within a requirement source, track
both the protocol in which the requirement was introduced as well as
the dependent type (relative to that protocol) on which the
requirement was introduced. This information is important when
reconstructing the path from a requirement-as-written to the location
of a desired protocol conformance.
Start reshuffling RequirementSource to store more information about
requirements in protocols. As a small step, track the source locations
for requirements written within the protocols themselves.
Note: there's a QoI regression here where we get duplicated
diagnostics (due to multiple generic signature builders being built
from a bad signature).
The use of floating sources allows us to carry through the protocol
information (i.e., "in which protocol do we look for this
information?") without immediately forming a new
RequirementSource. Yet more NFC refactoring for protocol-requirement
sources to carry more pertinent information.
This got reverted because it made our non-deterministic deserialization
crasher come up more often. Re-applying this patch to test the theory
that @jrose-apple's fix addressed the issue.
Centralize the checking of a superclass constraint against a
same-type-to-concrete constraint. Additionally, produce a warning if
the superclass constraint is satisfied but is made redundant by an
existing same-type constraint.
Use the same infrastructure we have for same-type-to-concrete
constraints to check superclass constraints. Specifically,
* Track all superclass constraints; never "update" a requirement source
* Remove self-derived superclass constraints
* Pick the best superclass constraint within each connected component
of an equivalence class and use that for requirement generation.
* Diagnose conflicting superclass requirements during finalization
* Diagnose redundant superclass requirements (during finalization)
Introduce an operation on RequirementSource to determine whether a
constraint with such a source, when it lands on a given potential
archetype, is "self-derived": e.g., the final constraint is derived
from the original constraint. Remove such constraints from the system
during finalization, because otherwise they would make the original
constraint redundant.
Fixes rdar://problem/30478915, although we still need to apply this
same logic to other kinds of constraints in the system.
Use TrailingObjects to help us efficiently store the root potential
archetype within requirement sources, so we can reconstruct the
complete path from the point where a requirement was created to the
potential archetype it affects.
The test changes are because we are now dumping the root potential
archetype as part of -debug-generic-signatures.
Whenever we create a (root) requirement source, associate it with the
potential archetype on which the requirement is written. This lets us
follow a requirement source from the (stated or implied) requirement on
the root potential archetype to the effective requirement on the
resulting potential archetype.
Introduce FloatingRequirementSource for the cases where we need to
state what the root source is, but don't yet have a potential
archetype to attach it to. These get internally resolved to
RequirementSources as soon as possible.
Most clients that will be considering same-type-to-concrete
constraints will need to look at all of the constraints within the
equivalence class together. Store the same-type-to-concrete
constraints on the EquivalenceClass itself, which fits this use case
better, and should reduce the storage requirements by making potential
archetypes two pointers smaller. NFC
