Use FacetAccessType when converting to a value of type FacetType #4925
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danakj
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When attempting to convert to a value of type FacetType, and the source
value is a FacetAccessType, then if the type of the underlying
FacetValue is the same as the target, we can use the FacetValue there
as the conversion output.
If the type of the FacetValue differs, then we still want to do impl
lookup with the FacetValue to see if it matches with the target
FacetType, but that is still a TODO.
This allows a generic function with a value whose type is constrained
by a FacetType (thus the value's type is a FacetAccessType), to call
other functions with the value as an argument when it is constrained
by the same FacetType:
```
fn F[T:! FacetType](x: T);
fn G[T:! FacetType](x: T) { F(x); }
```
It is also an optimization to avoid impl lookup where we've already done
it to produce the FacetAccessType.
Adds a bunch of new tests with values of types which are constrained by
a facet type (or "facet value value" for short), with some more tests
that currently fail and should be made to pass.
danakj
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zygoloid
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Feb 11, 2025
toolchain/check/convert.cpp
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| @@ -991,7 +991,24 @@ static auto PerformBuiltinConversion(Context& context, SemIR::LocId loc_id, | |||
| } | |||
|
|
|||
| if (sem_ir.types().Is<SemIR::FacetType>(target.type_id)) { | |||
| if (sem_ir.types().Is<SemIR::FacetType>(value_type_id)) { | |||
| auto lookup_inst = value_id; | |||
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We'd usually call this lookup_inst_id instead to indicate that it's an InstId not an Inst.
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Right, done. Thanks for the review!
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When attempting to convert to a value of type FacetType, and the source value is a FacetAccessType, then if the type of the underlying FacetValue is the same as the target, we can use the FacetValue there as the conversion output.
If the type of the FacetValue differs, then we still want to do impl lookup with the FacetValue to see if it matches with the target FacetType, but that is still a TODO.
This allows a generic function with a value whose type is constrained by a FacetType (thus the value's type is a FacetAccessType), to call other functions with the value as an argument when it is constrained by the same FacetType:
It is also an optimization to avoid impl lookup where we've already done it to produce the FacetAccessType.
Adds a bunch of new tests with values of types which are constrained by a facet type (or "facet value value" for short), with some more tests that currently fail and should be made to pass.