In #7436 we stopped substituting `.Self` when collecting witnesses out
of a facet type. While this was correct, it did not capture all the
cases that need to avoid substituting `.Self`. And it poisoned the
`IdentifiedFacetType` cache by not replacing `.Self` but storing the
result in the cache. This led to incoherent behaviour, where the result
of an impl lookup would change depending on which ones had been done
previously.
Now we use a flag to track for each `.Self` if we're currently
type-checking inside the scope where it was introduced in a facet type.
While inside that scope, identify should not replace the `.Self`. Any
use of it should remain as-is since we don't yet know what value will
replace it. We call this state "frozen" since it should not be modified
by identify. This requires a substitution step when we leave the scope
that introduced the `.Self`, to remove the flag. The flag is set in the
`EntityName` of the `SymbolicBinding`, and is part of the canonical
value, since `.Self` can become part of types, which are constants, and
the flag needs to follow it for correct behaviour.
We also have to ensure the flag is the same when doing comparison with
constants from inside a facet type and constants from outside. For
instance in `(Z where .Z1 = ()) where .Z2 = .Z1`, when we arrive at the
second `.Z1` its `.Self` will be frozen, while the `.Z1 = ()` contains a
non-frozen `.Self`. So we add the frozen flag to the first when storing
it in `where_stack` in order to compare the constant values of the two
`.Z1`.
The `WhereExpr` requirement inst kinds now have an `InstConstantKind` of
`AlwaysUnique` instead of `Never`. This allows us to add them to the
usual InstBlocks, and in an `eval fn` body they have a constant value,
so eval does not fail when trying to call that function. We have to be
careful to not consider `AlwaysUnique` as being actually concrete
though, since their constant value erases `.Self`-dependence. This
allows us to stop special casing them when thawing the requirements
block in a `WhereExpr`, and we can just thaw each `InstId` in the block
in a straightforward manner.
We add the new flag to the instruction's fingerprint and name in
formatted semir.
This adds SemIR structs and implements building `observe` lists, as well
as naming, formatting, and importing `observe` declarations.
---------
Co-authored-by: Dana Jansens <danakj@orodu.net>
This performs `.Self` substitution in a single step, for the whole facet
type, instead of doing it individually for each constraint visited in
the top-level facet type. Then we don't need to track state to avoid
subst in constraints that come from other named constraints.
The semir changes are because we now generate a whole other FacetType
from the substitution.
The bulk of this change is changing most pattern insts to be `Always`
rather than `AlwaysUnique` constants, so that they can be wrapped in
`SpecificConstant`s to perform substitution. That then lets thunking
rely much more on `SpecificConstant` wrappers instead of deep-copying
the inst tree with modified types.
This approach to thunking should scale better, particularly as things
like form generics make function signatures more complex, because we can
leverage the existing support for constant evaluation and substitution.
Unfortunately, applying this approach to binding patterns will require
more work; see the TODO near the top of `thunk.cpp` for details.
---------
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Fix import logic to make all imported packages be children of the
`NameScopeId::Package` scope. Previously, indirectly-imported packages
would end up as children of their importing package's scope, which
resulted in them not being treated as packages at all, and in particular
not being fingerprinted as packages.
Fixing that caused a failure in the fingerprinting logic as we started
to encounter packages with no correspoding import scopes. Instead of
looking for import scopes, use a simpler mechanism to map packages to
their package names, and clean up.
Unfortunately the latter change churns all the fingerprints again :(
Hopefully this is the last time for a while.
When we import from another library in the same package, its entities
end up with our library as their parent scope, resulting in cross-file
fingerprint mismatches. Instead, only include the library ID when
fingerprinting either a package-private entity or an `ImportIRId` that
refers to a particular `SemIR::File`.
Fixes link failures when referencing a symbol involving a fingerprint
from a different package.
Previously we included the `Namespace`'s `import_id` as part of its
fingerprint, which caused local and imported namespaces to get different
fingerprints. We now store the `import_id` on the `NameScope` instead of
on the `Namespace` inst to avoid this problem.
Also, when we reach a package-level `NameScopeId`, consistently
fingerprint it as a (package name, library name) pair. Previously the
fingerprinting depended on whether it was imported or not, as an
imported `NameScopeId` had a parent scope (the current package). We need
to include the library name here so that private entities with the same
name in different libraries have different fingerprints.
This lets us stop eliding it in textual semir tests with dump ranges.
Previously it would always get elided, even though it was part of the
range being dumped, and was referred to by other instructions in the
dump range.
Since each `.Self` is unique (can change its type if not its value) in a
facet type, having each one distinct by location also aids
understanding.
A `where` expression nested inside a `T impls X` constraint makes
`.Self` ambiguous on the right-hand side of the `where` if `T` is
anything other than `.Self`. After the `where`, the value of a `.Self`
could be `T` or could be the value of `.Self` before the `impls`
constraint: the so-called top-level value of `.Self`.
Implicit use of `.Self` in designators is always allowed, and they are
bound (and replaced by a reference) to the inner-most possible value of
`.Self`. On the right-hand side of the nested `where` above, they have
the value `T as X`.
`.Self impls ...` is also always allowed, since it acts more as a
keyword here, and it always refers to the inner-most possible value of
`.Self`.
Any other explicit use of `.Self` is diagnosed when ambiguous, in any
kind of constraint. This is done in the handling of `WhereExpr` since it
has enough context to allow `.Self impls` (which is an explicit use)
while disallowing other explicit uses. And because it has non-canonical
instructions to work with, so it is able to diagnose errors with precise
locations.
Since `.Self` is no longer going to be marked with depth modifiers, the
eval of `WhereExpr` does not need an input facet value instruction
representing `.Self` to compare with, as they are now going to all be
equivalent. So revert it back to just looking for the `PeriodSelf` name
id, through a shared helper being introduced as `IsPeriodSelf`. And drop
the period self InstId from the `WhereExpr` instruction. This causes
most of the formatted SemIR changes.
Move helpers for working with and replacing `.Self` to their own file,
out of the `facet_type.h` header/cpp files. These are working with
`.Self` facet values more than facet types, though `.Self` is a name
that only exists inside the scope of a facet type.
This allows `T impls X` constraints to function, since they must contain
some reference to `.Self` in order to be valid. This should be
sufficient to support the interfaces we need for for loops over C++
range-for-compatible types.
We replace `.Self` in the following places:
- In a require decl, as we have a specific self facet to replace it with
from the declaration, either a user-specified facet or the symbolic
`Self`.
- When identifying a facet type, as we have a specific self that we are
identifying the facet type with. That self gets used for all `.Self`
references.
- Implicit `.Self` references on the RHS of an `impls` constraint when
building a facet type. The `.Self` references there no longer refer to
the top level self facet, so replace them with the facet that we now
know they refer to, which is found on the LHS of the `where` before the
`impls`.
- Rewrite constraints in impl lookup when validating them and comparing
them with constants from witnesses, which come from identifying a facet
type.
- Rewrite constraints in ImplWitnessAccess eval when comparing them with
constants from witnesses, which come from identifying a facet type.
Substitution is done through `SubstPeriodSelf`. It handles replacing
`.Self` and `.Self as type`, for a replacement facet that is either of
type FacetType or TypeType.
Eval currently diagnoses some ambiguous `.Self` references when doing
substitution of `.Self` but this is the incorrect place to do it, so
there are TODOs about moving this to name lookup. To support these
diagnostics there's some additional complexity in `SubstPeriodSelf` that
can go away once the TODOs are addressed, such as asking the caller if
they want to replace each `.Self`, in order for it to report a
diagnostic.
There are a number of follow-up work items here:
- Some TODO tests.
- Remove `SymbolicBindingType` since its intention was to support
`.Self` but we don't need it with this approach.
- Replace `.Self` in rewrite constraints of require decls.
- Replace `.Self` in rewrite constraints of impl as when constructing
the witness table.
- Reject explicit `.Self` in name lookup when it would be ambiguous.
- Officially disallow `.Self.A = B` in rewrite constraints in the design
docs, so that we don't have the case where `.A` is allowed but `.Self.A`
is not due to ambiguity.
EvalOrAddInst has to create a non-canonical instruction for evaluating a
few typed insts, such as LookupImplWitness which uses an InstId to
provide a location for diagnostics.
But the output of the function is a ConstantId. We do not have access to
the non-canonical InstId after the function returns. But if the constant
value was symbolic, it was being attached to the inst, and the inst
would be added to the eval block of the enclosing generic. This
needlessly added semir for a symbolic value.
The ConstantId returned by EvalOrAddInst can be used immediately, such
as to evaluate an ImplWitnessAccess. In that case, the final evaluated
result is all we need to keep in semir.
If the ConstantId needs to be replaced by specifics, it is only as part
of some other instruction, since ConstantIds themselves are not modified
by specifics, instructions are. In that case, the canonical instruction
in the constant value would have been added to some other (now symbolic)
instruction, which would be replaced by a specific.
This has no functional change, but it reduces runtime overhead and semir
output for LookupImplWitness and ImplWitnessAccess.
This is a step toward removing the index from `InitForm`, so that equal
form values always have equal representations.
---------
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
Currently each interface has a `Self` facet internally that becomes a
binding to every entity inside the interface: associated constants,
functions, and require decls. Each of these has to be independently
generic as a result. This makes is challenging in extended name lookup
to move into an extended scope of an interface, as we have a specific
for the interface, but the names within require a different specific
that includes a `Self` facet value.
We generalize this relationship by adding a second generic to Interface,
called `generic_with_self`. When we want to work with entities inside
the interface, we move from the interface-without-specific to the
interface-with-self specific by adding a Self to the specific. This is
done independently of any particular entity inside the Interface, as
those entities are now all members of the interface-with-self generic.
Associated constants no longer need a generic of their own, as they do
not have separate generic bindings. Functions retain a generic, but if
the function has no generic arguments, it will have no bindings of its
own now.
Require decls retain a generic so that their specific can be
instantiated separately from the interface. Requiring the interface to
be complete does not require the types in a require decl to be complete
unless it is modified by `extend`. So we allow them to be completed
later by keeping them in a separate generic.
Named constraints look like interfaces and gain the additional inner
generic-with-self, with the same relationship to require decls.
This removes the need for name lookup to perform Substitution of a Self
facet into the extended scope instruction. Instead, the
`SpecificConstant` instruction inserted by a `require` decl is part of
the interface-with-self generic. When looking through a FacetType for
extended scopes, for each interface, we push the scope with the specific
for the interface-with-self. Then the constant value of the
`SpecificConstant` is correctly modified by the provided self
automatically through applying that specific.
This gets us a step closer toward resolving TODOs in member access
around facets, by making the lookup into a facet value a "lookup in
base" operation instead of a "lookup in type of base". However the base
given to find scopes in still remains the facet type of the facet, which
is still a TODO.
Then we can simplify the "lookup in type of base" case a bit, with a
single code path doing the name lookup step. But we keep a TODO where if
the type of base is a facet, we change the lookup target to be the facet
type of the facet instead.
This is toward having name lookup into an interface that is extending a
named constraint work correctly with a `Self` in its specific. To
perform that name lookup, we will need to tell name lookup what is the
base, so that it can replace `Self` with the base. This change gets us
in a position where we can correctly provide the base in the `T.F()`
(lookup in facet) and `t.F()` (lookup in type of facet) correctly and
straightforwardly.
We provide a marginally improved diagnostic when looking into a facet
with an incomplete facet type, which will move into
AppendLookupScopesForConstant once we are looking into the facet
directly instead of its type.
The key changes are:
- Function output parameters are now prefixed with `out`, and more
consistently formatted as named parameters.
- Function and inst output arguments are now written as part of the inst
form, rather than as one of the inst arguments.
As a drive-by fix, this also changes `Temporary::storage_id` from
`DestInstId` to `InstId`, because it doesn't represent an output
parameter of the `Temporary` inst itself.
See the review of
[#6532](https://github.com/carbon-language/carbon-lang/pull/6532) and
[this Discord
discussion](https://discord.com/channels/655572317891461132/999638000126394370/1458268977020141589)
for additional background.
Also clarify and enforce that `ConversionTarget::init_id` is used only
as storage for in-place initialization, and correspondingly rename it to
`storage_id`.
Not all functions have a return slot, and once we have composite forms,
functions will be able to have any number of return slots. Obtaining a
unique return slot for a function only makes sense in `returned var`
handling.
The main changes here are:
- Introducing `InitForm` and `RefForm` to represent initializing and
reference forms (the two return forms currently supported by the
parser).
- Introducing the `FormType` singleton inst to represent their type
(i.e. `Core.Form`).
- Emitting an inst representing a function's declared return form as
part of handling the function signature.
The return form inst is currently ignored. Subsequent PRs will expose it
in `SemIR::Function` and use it to determine the form of call
expressions.
Pursuant to recent decisions on #6124, switch `Destroy` to use a
`CustomWitness` for its implementation. Right now this is manufacturing
no-op implementation functions on each lookup, which obviously isn't
ideal but is intended as a first pass. I'm mostly trying to find the
right balance between updating the approach to reflect new decisions,
while still breaking apart work in a way.
The `CoreInterface` logic is intended to build on `CoreIdentifier`
support. We have a number of additional interfaces that require
specialized logic, and that'll extend pretty far with C++ interop, so it
seemed easiest to have a generic function for it. That's what's
replacing the logic inside C++ interop that was doing string comparisons
(which could have already been moved to `CoreIdentifier`, I just missed
it in my first pass).
This adds `CustomWitness` support because the `Destroy` witnesses can be
imported cross-file. `CustomWitness` was previously only used for C++
types, which don't yet support import, which is why that wasn't
previously an issue. The addition of `query_specific_interface_id` is
similarly needed in order to get correct sorting of witness blocks when
imported.
This PR also removes builtin constraint logic (note this is in a
separate commit to help review; it's not a separate PR because it's
difficult to split apart without tests breaking). This had been made
generic with the expectation that destroy, copy, move, and conversions
would all need related support. Under the new decision, we are not going
to do blanket impls and will instead just manufacture a `CustomWitness`
for everything.
A lot of SemIR fingerprints change, but that's probably because the
addition of `Destroy` on core classes is yielding structural changes.
Instead of naming the root namespace `package` (because it's accessed by
the `package` keyword), change it to use the current package name. Note,
buried in the checksum changes,
`toolchain/check/testdata/package_expr/fail_not_found.carbon`:
```
- // CHECK:STDERR: fail_not_found.carbon:[[@LINE+4]]:16: error: member name `x` not found in `package` [MemberNameNotFoundInInstScope]
+ // CHECK:STDERR: fail_not_found.carbon:[[@LINE+4]]:16: error: member name `x` not found in `Main` [MemberNameNotFoundInInstScope]
```
for:
```
// CHECK:STDERR: var y: i32 = package.x;
// CHECK:STDERR: ^~~~~~~~~
```
I'll leave it to you if you prefer this; the alternative I see is to
just rename `IsCorePackage` to `IsImportedCorePackage`, and/or change it
to a helper that takes a `Context` and does the right thing with
`parse_tree` (which, I need for `Destroy`-related reasons and was my
default approach).
This is a prerequisite for support for interop with C++ template names.
No behavior change here, except that it sadly changes the fingerprinting
for a lot of tests.
Give TupleLiteral and StructLiteral a constant value, if their contents
have constant values. Their constant values are TupleValue and
StructValue respectively. This supports their ability to convert to a
constant type (or facet type).
This way when deduce finds a TupleLiteral as the argument to a
_symbolic_ facet type, it can also find a constant value to use for that
argument. This allows deduction to move onto step two, where it can
substitute into the symbolic parameter from previous deduced arguments,
and then perform the conversion from the TupleValue to the desired facet
type.
Allow `PerformBuiltinConversion()` to convert from a canonical
TupleValue or StructValue to `type` instead of only from literals. Then,
also support conversion from a symbolic binding of type TupleType or
StructType to `type`.
The SymbolicBindingType refers to the type value that will be
substituted in for the BindSymbolicName, but holds onto the EntityNameId
from the BindSymbolicName instead of (or in addition to, for now) the
instruction.
The EntityNameId will be used to look in the ScopeStack to find the
witnesses either from the BindSymbolicName instruction, or other
instructions that specify `impls` constraints against the EntityName.
This will allow us to have the `T` in `I(T)` resolve to a `.Self`
reference in the type so that we get type equality with the binding's
type: `T:! I(.Self)`.
This is in support of a goal of changing the blanket `destroy` impl to
use (roughly):
```
private fn CanAggregateDestroy() -> type = "type.can_aggregate_destroy";
// Handles aggregate type destruction.
impl forall [AggregateDestroyT:! CanAggregateDestroy()] AggregateDestroyT as Destroy {
fn Op[addr self: Self*]() = "type.aggregate_destroy";
}
```
That isn't done here because there's still other issues that migrating
raises. What this *does* do is add the builtin functions, and in
particular, support to `FacetTypeInfo` to make `CanAggregateDestroy`
work.
The "special requirement" approach in `FacetTypeInfo` allows us to
support restricting a blanket impl under the current approach of impls.
Maybe we'll find a cleaner approach that can work in the future, but
this fits into the current model by propagating similar to other
requirements. I'm using an enum mask because we have a number of similar
things to add (e.g. copy, move) but I'm not sure we need a full vector.
A few alternatives considered were:
- Supporting syntax more like `where .Self impls
TypeCanAggregateDestroy(.Self, SupportedInterface,
UnsupportedInterface)`. I think it'd be a little cleaner, but requires
better compile-time evaluation in order to assess the type of the call.
Right now it's expected to be a `FacetType` too early to make this work,
and I was concerned about pouring too much more time down this route.
- Providing an actual interface, in particular doing name lookup back
into `Core.` for an interface. This would've added name lookup overhead,
and the question of whether an `impl` exists.
- Generating an interface. This avoids the name lookup, but would still
raise the question of whether an `impl` should also be generated. Work
I've previously done generating interfaces for class destruction also
feels complex to both write and understand (an unfortunate issue).
- Still modeling as an `ImplsConstraint`, for example by defining a
special `InterfaceId::CanAggregateDestroy = -2` similar to what we do on
other ids. I was hesitant because of how this expands the number of
modes of `InterfaceId`, and things for consuming code to watch out for,
for what feels like a relatively niche set of use-cases that are only
interface-like.
---------
Co-authored-by: Dana Jansens <danakj@orodu.net>
When returning a value from a function whose return type has a by-copy
initializing representation, perform initialization like we do when the
return type has an in-place initializing representation. This makes our
SemIR representation more uniform, as the return expression will now
always be an initializing expression rather than a value expression, but
more importantly it means that attempts to return a non-copyable type by
value now fail, even if the type has a by-copy initializing
representation.
This catches a bunch of places where we were returning a value of an
unconstrained template parameter `T:! type`, which we were incorrectly
allowing because we didn't notice it was not copyable. Unfortunately
this then requires quite a few test updates.
Like #6034, this exposes a lowering issue where lowering crashes when
attempting to lower a specific copy operation for certain types; a
couple more tests are temporarily disabled here. An upcoming PR
dependent on this one will fix the issue and re-enable those tests.
If it's just `TypeType` then the `BindSymbolicName` appears directly in
type positions, but if it is replaced with another facet value, then we
would need to insert a `FacetAccessType` around it. By giving it a
`FacetType` type, like other `BindSymbolicName`s we make it consistent
and avoid having to introduce extra instructions.
This uses each vector's size as a barrier between lists, to eliminate
the possibility of incidental collisions between entries of different
lists. This is the same as is done inside `AddBlock`.
We add a virtual node (`CompileTimeBindingPatternStart`) as the first
child of `CompileTimeBindingPattern` which holds the identifier
underneath it, so that it is checked just before the type expression of
the `CompileTimeBindingPattern`. When we reach this virtual node during
check, we add `.Self` as a name in the current scope, and when we reach
`CompileTimeBindingPattern` we remove it from scope, which ensures it's
present during only the checking of the type expression for the compile
time pattern.
At the moment the `.Self` has a different type (it's a `TypeType`) than
other `.Self` in the facet type (which are a single `FacetType`), but
the intention is to immediately substitute it out of the facet type
entirely, replacing it with a reference to the compile time binding (a
`BindSymbolicName`) itself. A TODO has been added for this.
---------
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
Dana Jansens
Özgür T. ÖnsoyandDana Jansens
Geoff RomerandRichard Smith
