A lot of the fixes here are adjustments to compensate in the
fulfillment and metadata-path subsystems for the recent pack
substitutions representation change. I think these adjustments
really make the case for why the change was the right one to make:
the code was clearly not considering the possibility of packs
in these positions, and the need to handle packs makes everything
work out much more cleanly.
There's still some work that needs to happen around type packs;
in particular, we're not caching them or fulfilling them as a
whole, and we do have the setup to do that properly now.
Nested archetypes are represented by their base archetype kinds (primary,
opened, or opaque type) with an interface type that is a nested type,
as represented by a DependentMemberType. This provides a more uniform
representation of archetypes throughout the frontend.
A PackExpansionType is the interface type of the explicit expansion of a
corresponding set of variadic generic parameters.
Pack expansions are spelled as single-element tuples with a single variadic
component in most contexts except functions where they are allowed to appear without parentheses to match normal variadic declaration syntax.
```
func expand<T...>(_ xs: T...) -> (T...)
~~~~ ~~~~~~
```
A pack expansion type comes equipped with a pattern type spelled before
the ellipses - `T` in the examples above. This pattern type is the subject
of the expansion of the pack that is tripped when its variadic generic
parameter is substituted for a `PackType`.
A pack type looks a lot like a tuple in the surface language, except there
is no way for the user to spell a pack. Pack types are created by the solver
when it encounters an apply of a variadic generic function, as in
```
func print<T...>(_ xs: T...) {}
// Creates a pack type <String, Int, String>
print("Macs say Hello in", 42, " different languages")
```
Pack types substituted into the variadic generic arguments of a
PackExpansionType "trip" the pack expansion and cause it to produce a
new pack type with the pack expansion pattern applied.
```
typealias Foo<T...> = (T?...)
Foo<Int, String, Int> // Forces expansion to (Int?, String?, Int?)
```
The new type, called ExistentialType, is not yet used in type resolution.
Later, existential types written with `any` will resolve to this type, and
bare protocol names will resolve to this type depending on context.
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.
Context archetypes and opened existential archetypes differ in a number of details, and this simplifies the overlapping storage of the kind-specific fields. This should be NFC; for now, this doesn't change the interface of ArchetypeType, but should allow some refinements of how the special handling of certain archetypes are handled.
We need to search the type metadata of superclass bounds to handle signatures like:
class K<T> {}
$@convention(witness_method: A2) <τ_0_0><τ_1_0 where τ_0_0 : K<τ_1_0>, τ_1_0 : C> (@in_guaranteed τ_0_0) -> ()
rdar://46173958
SR-9305
This silences the instances of the warning from Visual Studio about not all
codepaths returning a value. This makes the output more readable and less
likely to lose useful warnings. NFC.
Certain uses of protocols only formally need the requirement
signature, not any of the method requirements. This results in IRGen
seeing a protocol where none of the members have been validated except
the associated types. Account for this by allowing ProtocolInfo to
only contain the layout for the base protocols and associated types,
if requested.
Note that this relies on the layout of a witness table always putting
the "requirement signature part" at the front, or at least at offsets
that aren't affected by function requirements.
rdar://problem/43260117
Most of the work of this patch is just propagating metadata states
throughout the system, especially local-type-data caching and
metadata-path resolution. It took a few design revisions to get both
DynamicMetadataRequest and MetadataResponse to a shape that felt
right and seemed to make everything easier.
The design is laid out pretty clearly (I hope) in the comments on
DynamicMetadataRequest and MetadataResponse, so I'm not going to
belabor it again here. Instead, I'll list out the work that's still
outstanding:
- I'm sure there are places we're asking for complete metadata where
we could be asking for something weaker.
- I need to actually test the runtime behavior to verify that it's
breaking the cycles it's supposed to, instead of just not regressing
anything else.
- I need to add something to the runtime to actually force all the
generic arguments of a generic type to be complete before reporting
completion. I think we can get away with this for now because all
existing types construct themselves completely on the first request,
but there might be a race condition there if another asks for the
type argument, gets an abstract metadata, and constructs a type with
it without ever needing it to be completed.
- Non-generic resilient types need to be switched over to an IRGen
pattern that supports initialization suspension.
- We should probably space out the MetadataStates so that there's some
space between Abstract and Complete.
- The runtime just calmly sits there, never making progress and
permanently blocking any waiting threads, if you actually form an
unresolvable metadata dependency cycle. It is possible to set up such
a thing in a way that Sema can't diagnose, and we should detect it at
runtime. I've set up some infrastructure so that it should be
straightforward to diagnose this, but I haven't actually implemented
the diagnostic yet.
- It's not clear to me that swift_checkMetadataState is really cheap
enough that it doesn't make sense to use a cache for type-fulfilled
metadata in associated type access functions. Fortunately this is not
ABI-affecting, so we can evaluate it anytime.
- Type layout really seems like a lot of code now that we sometimes
need to call swift_checkMetadataState for generic arguments. Maybe
we can have the runtime do this by marking low bits or something, so
that a TypeLayoutRef is actually either (1) a TypeLayout, (2) a known
layout-complete metadata, or (3) a metadata of unknown state. We could
do that later with a flag, but we'll need to at least future-proof by
allowing the runtime functions to return a MetadataDependency.
A concrete conformance may involve conditional conformances, which are witness
tables that we can access from the original conformance's one. We need to track
metadata and be able to follow it in a metadata path.
The list of directly inherited protocols of a ProtocolDecl is already
encoded in the requirement signature, as conformance constraints where
the subject is Self. Gather the list from there rather than separately
computing/storing the list of "inherited protocols".
not have access to their type arguments at runtime. Use this to
fix the emission of native thunks for imported ObjC-generic
initializers, since they may need to perform bridging.
For now, pseudo-genericity is all-or-nothing, but we may want to
make it apply only to certain type arguments.
Also, clean up some code that was using dead mangling nodes.
We prevent the generic parameters to an ObjC generic from being used in an extension method at the sema level, and we don't want the polymorphic convention to try to generate independent parameters since that would break the method convention. Trick the polymorphic convention by producing "impossible" fulfillments for the generic parameters derivable from an ObjC generic method's self type.
...even if the 'self' type is generic. Additionally, Objective-C generic
types cannot be used as a source of type metadata, because Objective-C
generics are erased at runtime by default. (This may need to change.)
With these two changes, we now pass type metadata explicitly when we need
to, and /don't/ try to pass it to Objective-C methods that would have
needed it if they were Swift methods.
fulfillments, because we don't actually fill them in.
This is a minimal, temporary, speculative fix for the failure
described in rdar://25069637, for which I unfortunately do not have
a minimal test case and which I have been unable to duplicate in
my own testing due to various language restrictions that I hope
to lift given the better (but temporarily reverted) fix.
"minimal" is defined as the set of requirements that would be
passed to a function with the type's generic signature that
takes the thick metadata of the parent type as its only argument.
There are several interesting new features here.
The first is that, when emitting a SILFunction, we're now able to
cache type data according to the full dominance structure of the
original function. For example, if we ask for type metadata, and
we've already computed it in a dominating position, we're now able
to re-use that value; previously, we were limited to only doing this
if the value was from the entry block or the LLVM basic block
matched exactly. Since this tracks the SIL dominance relationship,
things in IRGen which add their own control flow must be careful
to suppress caching within blocks that may not dominate the
fallthrough; this mechanism is currently very crude, but could be
made to allow a limited amount of caching within the
conditionally-executed blocks.
This query is done using a proper dominator tree analysis, even at -O0.
I do not expect that we will frequently need to actually build the
tree, and I expect that the code-size benefits of doing a real
analysis will be significant, especially as we move towards making
more metadata lazily computed.
The second feature is that this adds support for "abstract"
cache entries, which indicate that we know how to derive the metadata
but haven't actually done so. This code isn't yet tested, but
it's going to be the basis of making a lot of things much lazier.
