If we failed to construct a rewrite system for a protocol, either because
the Knuth-Bendix algorithm failed or because of a request cycle while
resolving requirements, we would end up in a situation where the resulting
rewrite system didn't include all conformance requirements and associated
types, so name lookup would find declarations whose interface types are
not valid type parameters.
Fix this by propagating failure better and just doing nothing in
getReducedTypeParameter().
Fixes rdar://147277543.
The concrete nesting limit, which defaults to 30, catches
things like A == G<A>. However, with something like
A == (A, A), you end up with an exponential problem size
before you hit the limit.
Add two new limits.
The first is the total size of the concrete type, counting
all leaves, which defaults to 4000. It can be set with the
-requirement-machine-max-concrete-size= frontend flag.
The second avoids an assertion in addTypeDifference() which
can be hit if a certain counter overflows before any other
limit is breached. This also defaults to 4000 and can be set
with the -requirement-machine-max-type-differences= frontend flag.
We already need to track the inverses separate from the members in a
ProtocolCompositionType, since inverses aren't real types. Thus, the
only purpose being served by InverseType is to be eliminated by
RequirementLowering when it appears in a conformance requirement.
Instead, we introduce separate type InverseRequirement just to keep
track of which inverses we encounter to facilitate cancelling-out
defaults and ensuring that the inverses are respected after running
the RequirementMachine.
We want `T.A == U.B` to imply `shape(T) == shape(U)` if T (and thus U)
is a parameter pack.
To do this, we introduce some new rewrite rules:
1) For each associated type symbol `[P:A]`, a rule `([P:A].[shape] => [P:A])`.
2) For each non-pack generic parameter `τ_d_i`, a rule `τ_d_i.[shape] => [shape]`.
Now consider a rewrite rule `(τ_d_i.[P:A] => τ_D_I.[Q:B])`. The left-hand
side overlaps with the rule `([P:A].[shape] => [shape])` on the term
`τ_d_i.[P:A].[shape]`. Resolving the overlap gives us a new rule
t_d_i.[shape] => T_D_I.[shape]
If T is a term corresponding to some type parameter, we say that `T.[shape]` is
a shape term. If `T'.[shape]` is a reduced term, we say that T' is the reduced
shape of T.
Recall that shape requirements are represented as rules of the form:
τ_d_i.[shape] => τ_D_I.[shape]
Now, the rules of the first kind reduce our shape term `T.[shape]` to
`τ_d_i.[shape]`, where `τ_d_i` is the root generic parameter of T.
If `τ_d_i` is not a pack, a rule of the second kind reduces it to `[shape]`,
so the reduced shape of a non-pack parameter T is the empty term.
Otherwise, if `τ_d_i` is a pack, `τ_d_i.[shape]` might reduce to `τ_D_I.[shape]`
via a shape requirement. In this case, `τ_D_I` is the reduced shape of T.
Fixes rdar://problem/101813873.
This basically undoes 3da6fe9c0d, which in hindsight was wrong.
There were no other usages of TypeArrayView anywhere else except for
GenericSignature::getGenericParams(), and it was almost never what
you want, so callers had to convert back and forth to an ArrayRef.
Remove it.
We had two notions of canonical types, one is the structural property
where it doesn't contain sugared types, the other one where it does
not contain reducible type parameters with respect to a generic
signature.
Rename the second one to a 'reduced type'.
The Requirement Machine operates on canonical types internally and erases
sugared types appearing in generic requirements as a result.
For trivial cases like Array<T> vs [T], we can use the existing
TypeBase::reconstituteSugar() utility to produce a more aesthetically-pleasing
generic signature.
The final step in minimization is building Requirements and
ProtocolTypeAliases from the minimal Rules in the RewriteSystem.
Move this to a new file and refactor it a bit to handle
Requirements and ProtocolTypeAliases more consistently.
The RequirementSignature generalizes the old ArrayRef<Requirement>
which stores the minimal requirements that a conforming type's
witnesses must satisfy, to also record the protocol typealiases
defined in the protocol.
Now that we can detect protocol typealias rules, collect and keep
track of them so that they can be recorded in protocol requirement
signatures.
For now, this is all NFC since nothing introduces such rules into
the rewrite system, except for invalid requirements which are
diagnosed anyway.
- Rename StepLimit to MaxRuleCount, DepthLimit to MaxRuleLength
- Rename command line flags to -requirement-machine-max-rule-{count,length}=
- Check limits outside of PropertyMap::buildPropertyMap()
- Simplify the logic in RequirementMachine::computeCompletion()
When minimizing a generic signature, we only care about loops
where the basepoint is a generic parameter symbol.
When minimizing protocol requirement signatures in a connected
component, we only care about loops where the basepoint is a
protocol symbol or associated type symbol whose protocol is
part of the connected component.
All other loops can be discarded since they do not encode
redundancies that are relevant to us.
We assert when building a rewrite system for an existing generic
signature, or in AbstractGenericSignatureRequest, where there is no
source location.
In RequirementSignatureRequest and InferredGenericSignatureRequest
we now produce a diagnostic.
This is a source-level error, not an invariant violation. Instead, plumb
a new hadError() flag, which in the future will assert if no diagnostic
was produced.
We would skip recording a conformance access path if the subject
type canonicalized to a concrete type, but this was incorrect.
The correct formulation is to use the _canonical anchor_ and not
the canonical type as the caching key; that is, we always want it
to be a type parameter, even if it is fixed to a concrete type,
because type parameters fixed to concrete types can appear in
the middle of conformance access paths, as the example in the
radar demonstrates.
Fixes rdar://problem/83687967.
This was manifesting as module interfaces printing generic parameters
as `τ_0_0` in some cases.
Note that the GSB has the same bug, so this test case will fail with
-requirement-machine=off. I don't plan on fixing the bug in the GSB
unless we need to.
Fixes rdar://problem/78977127.
