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Dana Jansens
f51c075f8b
Point symbolic witnesses into `.Self` written inside an impl decl at the impl that is being declared. This is tricky because the impl does not yet exist. So we use a new instruction `ImplSelfWitness` which _will_ be replaced by the `ImplWitness` once it becomes available. The `ImplSelfWitness` acts like a symbolic witness, except it does not perform lookup, since we know which impl we will get a witness from. This prevents us from finding other impls when performing lookups into `.Self` in an impl decl, which produces incorrect/incoherent results.
101 lines
4.8 KiB
C++
101 lines
4.8 KiB
C++
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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#ifndef CARBON_TOOLCHAIN_CHECK_IMPL_LOOKUP_H_
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#define CARBON_TOOLCHAIN_CHECK_IMPL_LOOKUP_H_
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#include <variant>
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#include "toolchain/check/context.h"
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#include "toolchain/sem_ir/identified_facet_type.h"
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#include "toolchain/sem_ir/ids.h"
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#include "toolchain/sem_ir/inst.h"
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#include "toolchain/sem_ir/typed_insts.h"
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namespace Carbon::Check {
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// Looks up the witnesses to use for a type value or facet value, and a facet
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// type naming a set of interfaces required to be implemented for that type, as
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// well as possible constraints on those interfaces.
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//
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// N.B. In the future, `TypeType` will become a facet type, at which point type
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// values will also be facet values.
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//
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// The return value is one of:
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// - An InstBlockId value, containing an `ImplWitness` instruction for each
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// required interface in the `query_facet_type_const_id`. This verifies the
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// facet type is satisfied for the type in `type_const_id`, and provides a
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// witness for accessing the impl of each interface.
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//
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// - `InstBlockId::None`, indicating lookup failed for at least one required
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// interface in the `query_facet_type_const_id`. The facet type is not
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// satisfied for the type in `type_const_id`. This represents lookup failure,
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// but is not an error, so no diagnostic is emitted.
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//
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// - An error value, indicating the program is invalid and a diagonstic has been
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// produced, either in this function or before.
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auto LookupImplWitness(Context& context, SemIR::LocId loc_id,
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SemIR::ConstantId query_self_const_id,
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SemIR::ConstantId query_facet_type_const_id,
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bool diagnose = true) -> SemIR::InstBlockIdOrError;
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// Construct witnesses for a `facet_value` from the facet type of a `.Self`.
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//
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// This does not actually perform lookup, but constructs witnesses anyways, so
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// can't be used in most cases. This is specifically for the case where we are
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// replacing `.Self` with another facet. Since it is replacing `.Self` we know
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// that it implements the facet type of the `.Self`. So we can construct
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// witnesses for the interfaces in that facet type.
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auto MakeWitnessesForPeriodSelfTypeWithoutLookup(Context& context,
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SemIR::LocId loc_id,
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SemIR::ConstantId facet_value,
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SemIR::ConstantId period_self)
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-> SemIR::InstBlockIdOrError;
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// Returns whether the query matches against the given impl. This is like a
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// `LookupImplWitness` operation but for a single interface, and against only
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// the single impl.
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auto LookupMatchesImpl(Context& context, SemIR::LocId loc_id,
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SemIR::ConstantId query_self_const_id,
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SemIR::SpecificInterface query_specific_interface,
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SemIR::ImplId target_impl_id) -> bool;
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// Given a self facet, returns the canonical query self for a LookupImplWitness
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// instruction. The canonicalization looks through `FacetValue` and makes a
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// canonical form for `facet` and `facet as type`.
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//
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// If the input self facet is a `FacetValue` that is looked through, it can be
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// returned in `out_facet_value`, in order to preserve its facet type and
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// witnesses.
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auto GetCanonicalQuerySelfForLookupImplWitness(
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Context& context, SemIR::ConstantId self,
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SemIR::InstId* out_facet_value = nullptr) -> SemIR::ConstantId;
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// The kind of impl lookup being performed by a call to
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// `EvalLookupSingleFinalWitness`.
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enum class EvalImplLookupMode {
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// This is a regular impl lookup performed during check. If we produce a final
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// witness value that uses a specializable impl, the query will be poisoned so
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// that we will recheck it at the end of the compilation.
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Normal,
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// This is a re-check of a poisoned lookup being performed at the end of a
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// file. This disables any caching of lookup results for this query and redoes
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// the impl lookup.
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RecheckPoisonedLookup,
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};
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// Looks for a final witness for an impl lookup query consisting of a self (type
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// or facet) and a single interface. This is for eval to execute lookup via the
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// `LookupImplWitness` instruction. Since this query is re-evaluated against
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// specifics, it provides monomorphization of the impl lookup, which allows for
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// finding specializations.
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auto EvalLookupSingleFinalWitness(Context& context, SemIR::LocId loc_id,
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SemIR::LookupImplWitness eval_query,
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SemIR::InstId self_facet_value_inst_id,
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EvalImplLookupMode mode) -> SemIR::ConstantId;
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} // namespace Carbon::Check
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#endif // CARBON_TOOLCHAIN_CHECK_IMPL_LOOKUP_H_
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