Ultimately this is to support the disambiguation of protocol requirements when printing stubs. This allows us to disambiguate the case where two modules declare a nominal type, and when that type appears in a protocol requirement. In such a case, we now fully qualify the types involved.
Fixing this also appears to now be consistently printing module qualification in many more places, hence the updates to the IDE/SourceKit tests.
rdar://72830118
Under non-editor mode, the fixit for inserting protocol stubs is associated with a note
pointing to the missing protocol member declaration which could stay in a separate file from
the conforming type, leading to the behavior of rdar://51534405. This change checks if
the fixit is in a separate file and issues another note to carry the fixit if so.
rdar://51534405
We don't allow things like
extension Type: P where Param: P {}
extension Type: P where Param: Q {}
or
extension Type: P where Param == Int {}
extension Type: P where Param == Float {}
or
extension Type: P where Param: P {}
extension Type: P where Param == SomethingThatIsntP {}
and the default error message "redundant conformance" message doesn't convey
this very well.
Fixes rdar://problem/36262409.
When an extension introduces a conformance that already exists, the
type checker will reject the conformance and then ignore it. In cases
where the original conformance is in the same module as the type or
protocol (but the new, redundant conformance is in some other module),
downgrade this error to a warning. This helps with library-evolution
cases where a library omitted a particular conformance for one of its
own types/protocols in a previous version, then introduces it in a new
version.
The specific driver for this is the conformance of String to
Collection, which affects source compatibility. Fixes
rdar://problem/31104415.
This reverts part of #4038 which made the compiler consider it to be an `Explicit` conformance, breaking source code that was accepted in Swift 3.0 which declared a raw type as well as explicit conformance to `RawRepresentable` (reported as rdar://problem/30386658). While I'm here, a couple of spot fixes:
- Ensure an enum's raw value exprs are type-checked before checking conformances of any of its extensions, since the RawRepresentable conformance derivation will blow up if the raw value exprs haven't been checked. Fixes an order dependency issue if `extension Foo: RawRepresentable {}` gets checked before `enum Foo: Int { ... }`.
- Don't display the custom `enum_declares_rawrep_with_raw_type` diagnostic if the source location for the enum's inheritance clause is invalid, so that we don't emit a dislocated diagnostic.
One minor revision: this lifts the proposed restriction against
overriding a non-open method with an open one. On reflection,
that was inconsistent with the existing rule permitting non-public
methods to be overridden with public ones. The restriction on
subclassing a non-open class with an open class remains, and is
in fact consistent with the existing access rule.
Instead of requiring the user to disambiguate where an implied
protocol conformance goes---which they really, really don't care
about---just pick an arbitrary-but-deterministic location for the
conformance, which corresponds to the file unit in which the witness
table will be emitted. Fixes rdar://problem/21538899.
Swift SVN r30168
Inference of type witnesses for associated types was previously
implemented as part of value witness matching in the constraint
solver. This led to a number of serious problems, including:
- Recursion problems with the solver hunting for a type witness,
which triggers more attemts to match value witnesses...
- Arbitrarily crummy attempts to break the recursion causing
type-check failures in fun places.
- Ordering dependencies abound: different results depending on which
value witnesses were satisfied first, failures because of the order
in which we attempted to infer type witnesses, etc.
This new implementation of type witness inference uses a separate pass
that occurs whenever we're looking for any type witness, and solves
all of the type witnesses within a given conformance
simultaneously. We still look at potential value witnesses to infer
type witnesses, but we match them structurally, without invoking the
constraint solver.
There are a few caveats to this implementation:
* We're not currently able to infer type witnesses from value
witnesses that are global operators, so some tricks involving global
operators (*cough* ~> *cough*) might require some manually-specified
type witnesses. Note that the standard library doesn't include any
such cases.
* Yes, it's another kind of solver. At simple one, fortunately.
On the other hand, this implementation should be a big step forward:
* It's far more predictable, order-invariant, and non-recursive.
* The diagnostics for failures to infer type witnesses have
improved.
Fixes rdar://problem/20598513.
Swift SVN r27616
(Note that this registry isn't fully enabled yet; it's built so that
we can test it, but has not yet taken over the primary task of
managing conformances from the existing system).
The conformance registry tracks all of the protocols to which a
particular nominal type conforms, including those for which
conformance was explicitly specified, implied by other explicit
conformances, inherited from a superclass, or synthesized by the
implementation.
The conformance registry is a lazily-built data structure designed for
multi-file support (which has been a problematic area for protocol
conformances). It allows one to query for the conformances of a type
to a particular protocol, enumerate all protocols to which a type
conforms, and enumerate all of the conformances that are associated
with a particular declaration context (important to eliminate
duplicated witness tables).
The conformance registry diagnoses conflicts and ambiguities among
different conformances of the same type to the same protocol. There
are three common cases where we'll see a diagnostic:
1) Redundant explicit conformance of a type to a protocol:
protocol P { }
struct X : P { }
extension X : P { } // error: redundant explicit conformance
2) Explicit conformance to a protocol that collides with an inherited
conformance:
protocol P { }
class Super : P { }
class Sub : Super, P { } // error: redundant explicit conformance
3) Ambiguous placement of an implied conformance:
protocol P1 { }
protocol P2 : P1 { }
protocol P3 : P1 { }
struct Y { }
extension Y : P2 { }
extension Y : P3 { } // error: ambiguous implied conformance to 'P1'
This happens when two different explicit conformances (here, P2 and
P3) placed on different declarations (e.g., two extensions, or the
original definition and other extension) both imply the same
conformance (P1), and neither of the explicit conformances imply
each other. We require the user to explicitly specify the ambiguous
conformance to break the ambiguity and associate the witness table
with a specific context.
Swift SVN r26067
