As I'm looking at splitting value type setting out, this is to make it a
bit easier to see what's part of each type. Note, I expect
`ValueStoreTypes` to remain because of the `StringRef` logic it does --
I'm giving that its own file.
In a facet type constraint, you can write `where .Self impls T` for any
facet type `T`, or the constant `type`. It is possible to write `type`
in different ways though, with a `NameRef` instruction appearing on the
RHS instead of `TypeType`. In this case, the canonical constant value's
instruction will still be `TypeType`, so make eval look at the canonical
instruction to see this.
Add a test with an `alias Type = type` which hits this case.
After this change, we only will accept and find one of the following on
the RHS of `impls`:
- `TypeType`
- A facet type
- An error, if the source code had something else there, which will
already be diagnosed. Tested by `fail_right_of_impls_non_type.carbon`
and `fail_right_of_impls_non_facet_type.carbon`.
So we handle these three cases, and drop the implicit handling of other
things which will never appear there.
`AddImportedInstruction` was turning errors in an instruction into a
Runtime constant value instead of an Error, which led to crashes when
importing an instruction that had an error inside it somewhere.
Fixes#5726
The `IsPeriodSelf` function is problematic, as it's possible for a
FacetType to contain multiple `.Self` bindings which refer to different
selves, when one FacetType is nested within another: `I where .Self.J =
(K where .Self impls type)`.
The `WhereExpr` instruction contains the instruction of the `.Self` of
that `where` clause, which is what `IsPeriodSelf` is looking for, so we
can compare with its constant value instead.
When building a FacetType from an existing FacetType, don't diagnose
rewrite constraints that are compatible with the existing FacetType.
To do this, we consider two RHS as identical[1] if they have the same
constant value after substituting from available rewrite constraints in
the being-constructed FacetType, since the syntactic representation of
the RHS is lost during eval.
[1]
https://docs.google.com/document/d/1Yt-i5AmF76LSvD4TrWRIAE_92kii6j5yFiW-S7ahzlg/edit?tab=t.0#heading=h.qti4vn50zwy
Uses of `ConstantValueStore::GetConstantInstId` or
`ConstantValueStore::GetInstId` in eval indicate that the code expects a
constant value. Instead of just ending up with `None` in strange places,
diagnose this and convert to an `ErrorInst` when expectations are not
met.
We add `RequireConstantValue` to pair with `GetConstantValue`, and
rename `GetConstantValueIgnoringPeriodSelf` to
`RequireConstantValueIgnoringPeriodSelf` since the former would just be
unused.
Adds a test where a runtime value ends up in the RHS of a rewrite
constraint, where a constant value is expected. This issue was uncovered
by a fuzzer.
---------
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
Given a facet type: `(Z where .X = .Y) where .X =.Y`
The rewrite constraints in the inner facet type are each an
`ImplWitnessAccess` into a witness for the self of type `Z` (which is
the facet type before the `where`). The rewrite constraints in the outer
facet type are each an `ImplWitnessAccess` for the self of type `Z where
.X = .Y`, which is a different self facet type.
This means when deduping in canonicalization, the first `.X` and the
second `.X` are different instructions, and different constant values,
so they both remain in the rewrite constraints, incorrectly. Then if the
outer `.X` is allowed to evaluate to a value from its facet type, it
finds `.Y` resulting in `.Y = .Y` which is also incorrect.
Because of the failure to dedupe the first facet type, that is also
diagnosed as two different assignments to the same `.X`. To resolve
that, we introduce `CompareFacetTypeConstraintValues()` compare values
in facet type constraints, and treat accesses to the same associated
constant in the same facet value as `equivalent` even when through
different witnesses. This allows us to dedupe the two `.X = .Y` rules
into one in the combined facet type.
Given a different facet type: `(Z where .X = ()) where .X = {}`. Here we
want to diagnose that `.X` has been assigned two different values. To do
so, we need to see that the two `.X` values are the same, and we use
`CompareFacetTypeConstraintValues()` to do this comparison. Then we see
two rewrite rules for the same LHS, and we can diagnose that.
We enable evaluating `ImplWitnessAccess` on `.Self` to pull a value from
rewrite constraints in a facet type so that we can see that we are not
incorrect evaluating the LHS of rewrite constraints and producing
cycles. By doing so, also enable generic code to see and use concrete
values in associated constants in facet types.
The `BitAnd` operation combines two `FacetTypeInfo` structures by
concatenating their lists, but did not apply the current specific to the
instructions in the `FacetTypeInfo` as it forgot to go through
`GetContantFacetTypeInfo`.
`WhereExpr` handling duplicates a lot of the logic in
`GetConstantFacetTypeInfo` by calling `GetConstantValue` on things,
instead of calling `GetConstantFacetTypeInfo` on the `FacetTypeInfo` it
constructs. This meant it also needed to call `GetConstantFacetTypeInfo`
on the base facet type, and on any `impls`-requirement facet types
before merging their values together into a single `FacetTypeInfo`.
Instead, make `WhereExpr` more like `BitAnd`, and have it concatenate
things together as-is to construct a `FacetTypeInfo`. Then call
`GetConstantFacetTypeInfo` to canonicalize it and return a constant
value referring to it.
In `GetConstantFacetTypeInfo` we fix a crasher by propagating errors
inserted into the `FacetTypeInfo` out to the `Phase` so that the
resulting instruction depending on the `FacetTypeInfo` is not resolved
to a constant value with errors inside it. A test is added for this,
which was crashing on import of the `FacetType` with an error within
from the imported `impl` decl.
This refactoring gives us three benefits:
* There's now only a single place that does
`ResolveRewriteConstraintsAndCanonicalize`, which is inside
`GetConstantFacetTypeInfo`. This makes the inputs/behaviour of
`ResolveRewriteConstraintsAndCanonicalize` more consistent.
* There's now only a single place that updates the instructions in
`FacetTypeInfo` constraints with new constant values, so that changes
that rely on observing and interacting with that code only need to be
written in a single place. This will avoid duplicating logic in
https://github.com/carbon-language/carbon-lang/pull/5644.
* This will make it easier to move `WhereExpr` handling to a
`EvalConstantInst` function, as it no longer directly depends on
`GetConstantValue()` from `eval.cpp`.
This preserves the constant values of the arguments to the thunk, which
is important if the thunk requires conversion of an `IntLiteral` to some
other type. This should become unnecessary once we have form support,
but avoiding the indirection through a thunk function seems valuable
even once that support is in place.
To support this, track whether a function is a thunk on the Function
object, and if so, what the callee of the thunk is. This information is
also included in formatted SemIR when dumping the thunk.
Add a facet type rewrite constraint resolution step that is run every
time a facet type is constructed, in line with the design here:
https://docs.carbon-lang.dev/docs/design/generics/appendix-rewrite-constraints.html#rewrite-constraint-resolution
The resolution has multiple steps, and this PR implements the first of
them, finding and diagnosing any duplicate rewrites to the same
associated constant.
We already diagnosed this for impl construction, now we do so for all
facet types, which includes the one used for impl construction, so this
diagnostic is a superset of the previous.
Also fix substitution into constants to provide a source location. This
matters if the result of substitution ends up being part of a generic
eval block.
---------
Co-authored-by: Dana Jansens <danakj@orodu.net>
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
I was thinking about these after #5526, was wondering how others will
feel about this kind of approach:
- Adding a helper to `TypeEnum` to get the table construction.
- In what were previously `Make` functions, return the element instead
of returning the table.
- By returning the element, no more need to pass in a nullptr (now have
a concrete instance).
I think this is a mild simplification, but maybe worth it.
Note, would appreciate it if there are thoughts on how to provide a
boilerplate `Invalid` implementation (maybe it'd be fine to just return
`nullptr` and cause a crash that way, but I was hesitant to do that).
Previously we walked the global variables defined by the current file
and emitted an LLVM global variable definition for each of them. Now
instead, when emitting a constant reference to a global variable, we
emit an LLVM global variable declaration, and we then subsequently walk
the global variables defined by the current file and convert each of
them from a declaration to a definition.
In order to make import of names of global variables work, add support
for import of `var`, as well as support for importing `tuple_access` and
`tuple_pattern` in the case where the `var` has a tuple pattern in its
declaration. Also treat `bind_name`s that are reference bindings to
`var`s as having the same constant reference value as their `var` so
that we can properly import and lower them.
---------
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
Co-authored-by: Carbon Infra Bot <carbon-external-infra@google.com>
Tinkering with #5517, splitting out this suggestion to try to avoid
delaying merge. I figured out what I was missing on the variadiac
expansion. :)
(and also realized the struct could probably be a function)
Move the operation of resolving the specific decl block from
`GetConstantValue()` to `TryEvalTypedInst()`, with is now happening
after replacing the fields of the instruction with new constant values,
but before running the evaluation of the instruction. Since imported
instructions are not evaluated, this avoids resolving the specific decl
block from imported instructions, resolving a TODO in
`AddImportedConstant()`. Now `AddImportedConstant()` can replace
constant values in its fields without having to worry about that
operation resolving any specific decl blocks.
We get to add a new TODO however, to explain why we still need a special
case in resolving specific decl blocks for handling `Impl` construction.
The witness table contains instructions with specifics referring to the
generic self of the impl declaration. But the table must be constructed
before the impl's generic is finished, in order to make the instructions
dependent for the generic. But then resolving the specific decl block
can't be done when the instructions are created and evaluated, as that
requires a finished generic.
---------
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
- Track the `VarPattern` instruction on the `VarStorage` instruction so
that it's available for name mangling.
- Mangle global variables based on the first binding name within their
pattern.
- Give global variables external rather than internal linkage, except if
they have no bindings whatsoever in their pattern.
- To support lowering references to bindings nested within a global var,
such as for `var (x: i32, b: i32)`, add some basic initial support for
reference constant expressions. Treat a global `var` as a reference
constant, and treat an aggregate access into a reference constant as a
reference constant.
I'm trying to make the offsetting a little easier to understand, and
also get a better `requires` structure on calls. The second is for an
attempt to refactor the `Formatter` API, but also changing the `InstId`
`derived_from` requires seems helpful for clarity on what's really
happening.
InstValueKind is really just wrapping HasTypeIdMember. Rather than
exposing this as an enum, expose it as a bool since it better reflects
what's going on.
In eval.cpp, AddImportedConstant should never be called on an untyped
instruction.
In FormatInstLhs, we can also depend on whether InstNamer has assigned a
name in order to decide whether to print an instruction. This should
avoid some divergence with CollectNamesInBlock.
We also discussed restoring InstValueKind::Untyped, but that's mainly
motivated by the formatter, and the InstNamer approach gives a more
localized implementation.
#5445 updates to bazel 8.2.1, this does more updates (including to
buildifier, which does autofixes like the `sh_test` loads in the other
PR).
Note I'm using the latest available clang-format wheel. That's not
really something I expect people to have installed, but should mostly be
consistent. I'm specifically skipping clang-format 18 because it had
some broad regressions, and 19 got really confused by a `requires` on a
trailing return. Using the latest seemed probably okay since most people
won't see the difference. Do note that trailing returns in macros,
https://github.com/llvm/llvm-project/issues/47664, seems to be cropping
up again as an issue.
Instead of building an eval block as a separate pass at the end of a
generic, build the eval block incrementally.
The larger change here is that asking for the type or constant value of
an instruction now always returns an unattached type or constant value,
in order to preserve the behavior that we previously achieved by doing
the rewrite to attached types and constant values at the end of handling
the generic.
This also incidentally fixes some subtle issues where attached types and
constant values would leak out into check and cause it to get confused
about differences between attached and unattached values. Check should
no longer see attached values except where it explicitly asks for them.
---------
Co-authored-by: Dana Jansens <danakj@orodu.net>
Remove calls to `InstStore::GetLocId()` to build a LocId from an InstId
now that they can be constructed directly from the InstId. Most uses of
LocId are just plumbing, so this does not affect them. However places
that want to look inside the LocId do not want to work with the InstId
form. In these places, introduce `InstStore::GetResolvedLocId()` which
converts a LocId (or an InstId as an optimization) into a LocId which is
not backed by an InstId. These locations can be printed (they have a
line and column when they are a NodeId), they can have flags added to
them (`ToImplicit`, `ToTokenOnly`), they can be converted to an
underlying ImportIRInstId, or they may be `None`.
`Dump()` is made to print a resolved location instead of printing the
InstId in the location, since (at least in my experience) the resolved
location is what is interesting in debugging, and this saves manual
`MakeInstId` steps in the debugger every time a location is of interest.
The LocId constructor from InstId is made `explicit` to add clarity to
function calls passing an `inst_id` now directly instead of calling
`context.insts().GetLocId(inst_id)`. To avoid needing to construct
`SemIR::LocId(...)` explicitly in all cases though, the diagnostics code
in Check uses `DiagnosticLocId` as its template parameter which accepts
InstId as well and does the construction of LocId from it.
Because LocId now requires an explicit construction from InstId, any
callers to `AddInst()` functions will have to explicitly convert to
LocId if they had an InstId, but not if they pass a NodeId. To make this
difference clear to callers, we `requires` that the input type can be
converted to LocId. This ensures that passing an InstId results in an
error at the callsite where the InstId is passed, instead of generating
a compiler error when trying to construct `LocIdAndInst` inside
`AddInst()`, which is less clear about what went wrong and doesn't seem
entirely intentional.
---------
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
Provide builtins for compound assignments instead of defining them in
the prelude as a use of a binary operator and an assignment. This allows
us to lower compound assignment directly to LLVM operations instead of
producing a function call. In the short term this also allows us to
define a type-generic compound assignment in the prelude.
Instead of evaluating a non-parameterized class or interface to a
constant with `SpecificId::None`, use the self specific for that class
or interface, which will not be `None` if there is an enclosing generic.
These constant instructions are all TypeInstId already in their type,
and this makes their names match.
Change the name of MakeSingletonInstId as well and update its comment.
We frequently want to operate on singletons. Per discussion, drop
`Singleton` to make the code shorter.
This started off as wanting to write `inst_id.is_error()`, but the
dependency relationship between ids.h and singleton_insts.h would
require some kind of delayed evaluation to allow the implementation to
remain in headers (which I suspect is helpful to have for inlining). I
could have added something like `IsErrorInst`, forward declared in ids.h
and defined in singleton_insts.h (which would always be included by
typed_insts.h), but the template approach felt like a decent balance
between (a) removing the boilerplate `::SingletonInstId`, (b)
understandability, (c) still visually mirroring if we immediately return
a singleton, and (d) flexibility for more than just `ErrorInst`. But TBH
I'd probably still have written `is_error()` if it didn't require
addressing the cross-header cycle.
Then I tried `SemIR::InstId::Is<SemIR::ErrorInst>`, which generally
worked with types but generated the complaint that it didn't shorten
*all* singleton uses. So pulling back on `::Is`, and instead just
dropping `Singleton`.
This is part of a broader plan to have noop destructor functions for
trivial destruction.
Note this emits a SemIR call (`%no_op: init %empty_tuple.type = call
%NoOp.ref() [concrete = constants.%empty_tuple]`), but not LLVM IR. My
thought was this was probably okay, since even though it'll be a little
spammy with destructor calls, the flipside is there'll probably already
be a fair amount for the name reference, and this at least shows when
the call is injected (and discarded).
---------
Co-authored-by: Chandler Carruth <chandlerc@gmail.com>
Use TypeInstId in many more places where the instruction is required
to/known to always be a type value. This should be a somewhat exhaustive
set of places, as it covers all instructions given to
GetTypeIdFromTypeInstId().
The things of interest here are:
- Singleton instructions are always of type TypeType, so they are now
TypeInstIds.
- ErrorInst::SingletonInstId gets upcast to be an InstId because it's
sometimes used to define the type of a variable (as in `auto inst_id =
SemIR::ErrorInst::SingletonInstId;` that may hold other InstIds.
- Parse nodes don't really know about TypeInstId, so NodeStack::Push
needs to do some special casing to avoid CHECK failures when given a
TypeInstId but expecting an InstId. We leave a TODO behind here because
the nodes which are being pushed a TypeInstId should probably be taught
to expect that, but such a change is a bit tricky, so too much for this
PR.
This allows us to import the table for a given impl only once, while we
can import many ImplWitness instructions with different specifics for a
generic impl.
For example in convert_facet_value_to_narrowed_facet_type.carbon we see
that a single witness table is imported for the BitAnd interface, with
multiple witnesses (for different specifics) imported and sharing the
same table.
The ImplWitnessTable now contains a back-link to the Impl the witness is
for, allowing inst namer to name that interface in the textual semir,
and allowing the interface to be found when debugging from a witness.
---------
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
TypeInstId is an InstId whose constant value has a type of TypeType.
This includes:
- Type value instructions, the `ClassType` or `IntLiteralType`
instructions.
- Constraint value instructions, which are the `FacetType` and
`TypeType` instructions, each of which also have type TypeType.
TypeInstId encodes in the type system that it is safe to convert the
instruction's value to a TypeId, and CHECKs at construction that this
invariant is maintained.
---------
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
In preparation for shifting from `TypeId`s potentially representing
attached types to always representing unattached types, using
[terminology suggested on
Discord](https://discord.com/channels/655572317891461132/963846118964350976/1359286326779973712).
This change causes us to track slightly more type spelling information
through SemIR.
One change that has significant impact on the SemIR output is that we
now build a `struct_type` instruction in each class representing the
types of the fields, including the spelling used for those types. This
is now no longer always identical to the corresponding canonical
`struct_type` for the object representation, so it's built separately
and owned by the class.
Also remove `TypeBlock` support entirely, as its only use was
representing `TupleType`s, which now use an `InstBlock`.
This follows the pattern used elsewhere, and allows facet types in eval
blocks to directly reference their operands instead of doing so
indirectly via a `ConstantId` attached to the generic. This prepares us
for making `ConstantId`s always be unattached.
In passing, add a stringified version of the `InstId` to diagnostics in
a couple of places where it seems useful.
Use that instead of `AddInstInNoBlock` to get the value of an
instruction when evaluation might depend on the `InstId` but only the
`ConstantId` of the instruction is desired by the consumer.
For each kind of instruction, specify whether its constant evaluation
needs an `InstId` or not. If it does, ensure that all constant
evaluation of that instruction provides one. Otherwise, allow calling
into the evaluator without providing an `InstId`.
This allows us to reliably use the `InstId` in evaluation steps that
either need a location or need to look at the original operands of the
instruction prior to evaluation, and also to support `TryEvalInst` calls
safely for instructions whose evaluation does not need an `InstId`.
Reduce usage of `GetConstantInSpecific` to a single caller in constant
evaluation, with a TODO to remove that.
This gets us closer to being able to fully perform type-checking against
abstract types instead of types anchored within a particular generic.
Trust that import_ref produces constants that are already in their
evaluated form. We still do one pass over the operands to map them into
their canonical constant values. Even that is mostly unnecessary, but
there are a few instructions produced by importing that still need it
for now.
Factor out logic to evaluate `EntityNameId` instead of duplicating it
between `BindSymbolicName` and `SymbolicBindingPattern`. Remove support
in `SymbolicBindingPattern` for evaluating a pattern to the constant
value of the corresponding binding, which doesn't really make any sense
given that patterns don't generally evaluate to the value that they
matched.
This results in the handling for `SymbolicBindingPattern` being simply
the default handling for an always-constant instruction, so remove the
special case for it entirely and change its constant kind to `Always`.
It's not entirely clear that it makes sense for `SymbolicBindingPattern`
to be treated as a constant when other patterns aren't, but we seem to
be relying on this in various places, so leave it as a constant for now.
Changing it to never be constant will be a smaller change now -- it just
requires changing the `constant_kind`.
The IR changes in the tests are fairly widespread, but mechanical, and
there are two kinds of things changing:
- `symbolic_binding_pattern`s in specifics now evaluate to
`symbolic_binding_pattern`s, not to the argument values. This means in a
few cases we end up with additional `symbolic_binding_pattern`
constants.
- We evaluate the type operand of `symbolic_binding_pattern` now, so an
error in the type will now properly be propagated into an error in the
pattern's constant value.
This builds on #5212 which is adding ArgAndKind. This further modifies
CARBON_KIND_SWITCH support so that we can use it with ArgAndKind in
addition to Inst. That creates a quirk where it's easier if ArgAndKind
provides `kind` as an accessor instead of a data member, so I'm just
switching it to a class.
#5171 ran into an issue where the wrong kind was associated with an arg
(`auto arg1 = RefineOperand(context, loc_id, arg0_kind,
action.arg1());`). This PR is trying to reduce risk of similar errors by
replaced `ArgKinds()` with instead an `ArgAndKind` structure and
corresponding accessors.
A couple things I considered and discarded were:
- Adding `CARBON_KIND_SWITCH` support (in this PR -- see #5216).
- The particular way that `ForCase` works would need to change, and I
was hesitant to do that here.
- But this is why I did add `As` to `ArgAndKind`, because it had me
thinking in that direction.
- Trying to make wrapper functions like `MutateArgs(callback_fn);`. This
kind of approach gets a little messy due to some of the conditional
passes, and in particular the reverse-iteration done for `PopOperand` in
subst.cpp
- Making something like `args_and_kinds() -> std::array<ArgAndKind, 2>`.
There's one spot where iteration is already set up as a loop, but for
others it felt a little convoluted with less gain than
`MutateArgs`-style things.
I'm not sure if there's a better way to set up the table generators, I
might keep tinkering with those for ideas.
Given the namespacing of `Diagnostics` in #5173, now we can use
`DiagnosticEmitter` for phase-specific emitters. This is consistent with
how we do `Context`, and also check had started this with
`DiagnosticBuilder` in anticipation of the namespacing.
Also renames `Emitter::DiagnosticBuilder` to `Emitter::Builder` for
consistency with other `Diagnostics` entities.
In check, I'm still splitting `DiagnosticEmitterBase` and
`DiagnosticEmitter` just to keep the emitter definition separate from
the context.
Also cleans up some incorrect check diagnostic emitter dependencies in
lower.
What this really does is avoids shadowing names, so that we can
comfortable have things like `Check::DiagnosticEmitter` or
`Check::DiagnosticLoc` without shadowing being a concern.
Note, down this path I'm also thinking about:
- Renaming misc DiagnosticConsumer/DiagnosticEmitter classes, possibly
just to DiagnosticConsumer/DiagnosticEmitter (so
`Check::DiagnosticEmitter` instead of `SemIRLocDiagnosticEmitter`).
- Dropping `Diagnostic` from `Emitter::DiagnosticBuilder`.
- But not for `Check::DiagnosticBuilder`, because `Check::Builder` would
be ambiguous.
- Renaming diagnostics/diagnostic_* to drop "diagnostic".
[Discussion about SemIRLoc ->
DiagnosticLoc](https://discord.com/channels/655572317891461132/655578254970716160/1353771570463768698)
reminded me of this (in particular the older [Check::DiagnosticBuilder
discussion](https://discord.com/channels/655572317891461132/655578254970716160/1344363562608627763)),
but I'd only do that rename if there's matching consensus about a path
forward where we keep SemIRLoc, and in a way that it's only ever used
for diagnostics (the divergence from which is at the root of current
LocId discussion).
I'm trying to keep that separate from a namespace addition for clarity.
Add a new instruction called ImplSymbolicWitness which represents a
search for an impl declaration given a self type and an interface to
find implemented for the self type. The self type is stored as a
constant instruction id, rather than as a ConstantId, as instructions
don't currently support holding ConstantId. The interface is stored as a
SpecificInterface but we can't fit all of it directly into the
instruction. So we add a new id to refer to the SpecificInterface as
follows.
Add a new SpecificInterfaceId which indexes into a canonical value store
on SemIR::File. This tracks all `SpecificInterface`s stored in an
instruction - specifically the ImplSymbolicWitness instruction.
The SpecificInterface on Impl is still stored there as a value, not as
an id, and no id is eagerly constructed for it. We wait until an id is
needed to make one. Since they are canonical, a new id is only create
when a new SpecificInterface value is seen.
When doing impl lookup, and the query is not concrete, and the impl is
not effectively final, the query needs to consider future impls that may
specialize either the self type or the constaint to make a more precise
match and replace the found impl declaration. Instead of returning the
ImplWitness instruction from the found impl, we generate a
ImplSymbolicWitness instruction, storing the query so that it can be
replayed later. This instruction is added to the generic eval block and
thus will be re-evaluated later with a SpecificId that may make the
query more concrete. When evaluating the instruction and replaying the
query, the lookup has the same conditions and if it does not decide to
use the found impl concretely, then the same instruction is returned
from eval, leaving it as symbolic.
--- Impl lookup changes ---
Impl lookup gets a little more interesting now. It continues to look in
the facet value for a witness if the self type is a facet value. Then
falls back to looking for an impl declaration. This step is no longer
done directly. Instead, we construct a ImplSymbolicWitness instruction
and evaluate it immediately for each interface that are in the query
facet type.
The ImplSymbolicWitness instruction, when evaluated, calls back to the
impl lookup code, with a query specific interface. There we resume back
into the same code path as from before, finding a witness in an impl
declaration. But we may return "found a non-final impl" instead of a
concrete witness. If eval receives this back, it evaluates to the
current ImplSymbolicWitness instruction as the resulting constant value.
To pass lookup failures back through eval, a result of InstId::None from
the second step of impl lookup will result in a non-constant value,
which is used as a signal back up the stack to the original impl lookup
function that the lookup failed. Using a non-constant value here would
break evaluation of the generic eval block if impl lookup could fail
there, however we know it will not since we only leave behind an
ImplSymbolicWitness instruction in the eval block if we found at least
one matching impl already, and we just want to look for a better match
with a more specific query.
We must take care to not store a reference into any value store across
computation in impl lookup, since impl lookup can recurse into itself
invalidate those stores. That includes the SpecificInterface obtained
from a SpecificInterfaceId, which impl lookup also inserts into the
store.
--- The long tail ---
Adding a new instruction and a new id type requires a myriad of changes
to support them:
We add Dump() support for SpecificInterfaceId. And fix a crash in Dump
for SpecificId::None. We also add MakeSpecificInterfaceId() for dumping
arbitrary ids.
The type of ImplSymbolicWitness is a new singleton builtin type
instruction called WitnessSymbolicType (like WitnessType is the type for
an ImplWitness).
Both ImplSymbolicWitness and WitnessSymbolicType are given `Value` as
their expression category as they are builtin constant values. And
BuildInfo() in TypeCompleter is taught about them both, returning a
`ValueRepr::Copy`.
WitnessSymbolicType is added to the set of SingletonInstKinds, so that
it can have a singleton instrution id as a static member.
Lower's BuildTypeForInst() is taught to make an empty struct for
WitnessSymbolicType, similar to WitnessType.
Instruction formatter (FormatterImpl) grows support for printing a
SpecificInterfaceId so that it can print both arguments of
ImplSymbolicWitness on the RHS when printing the SemIR instruction. To
print a SpecificInterfaceId, it prints both the interface id and the
specific id (if there is one). For example, for a query on a generic
interface `Z` with one parameter, the RHS includes the query, interface,
and specific:
```
%Z.impl_symbolic_witness: <symbolic witness> = impl_symbolic_witness %U, @Z, @Z(%U.as_type) [symbolic]
```
IdKind is extended to include SpecificInterfaceId.
InstFingerprinter is taught to look through SpecificInterfaceId and use
the interface and specific ids in the fingerprint.
InstNamer is taught about SpecificInterfaceId, counting the interfaces
when building an index. It is also tought about ImplSymbolicWitness,
using the name of the interface within and the `.impl_symbolic_witness`
suffix. For example, here the LHS is named after the interface in the
query:
```
%Z.impl_symbolic_witness: <symbolic witness> = impl_symbolic_witness %U, @Z, @Z(%U.as_type) [symbolic]
```
StringifyTypeExpr is taught about WitnessSymbolicType, which uses its IR
name since it's a singleton. And about ImplSymbolicWitness which uses
its constant value. The handling of ImplWitnessAccess also needed to be
adjusted, since it assumed that ImplWitnessAccess::witness_id would
always be a FacetAccessWitness, but it can now also be an
ImplSymbolicWitness. (It seems that the witness_id is also assigned
ImplWitness instructions, but those ImplWitnessAccess instructions don't
ever seem to get stringified in a diagnostic at this time.) At the
moment the ImplWitnessAccess with a symbolic witness is just stringified
as "<symbolic>", such as in:
```
x.carbon:1:2: error: cannot implicitly convert value of type `()` to `<symbolic>` [ConversionFailure]
let a: C(D).(Z.X) = ();
^~
```
There is a TODO left behind to include more information there.
The TypeStructure builder is made to handle WitnessSymbolicType and
WitnessType. These come up now in deduce where a generic impl will have
a ImplSymbolicWitness in a FacetValue for a generic self type. The query
may have a concrete ImplWitness in the same position. Since deduce tries
to deduce through the FacetValue, it tries to convert ImplWitness to
ImplSymbolicWitness, tries to do an impl lookup for `impl ImplWitness as
ImplicitAs(ImplSymbolicWitness)` and causes us to build type structures
with each of these.
Subst is updated to handle pushing and popping SpecificInterfaceId.
Without this, when finishing a generic's eval block, we would walk into
the ImplSymbolicWitness instruction, and its arguments, and fail to
recurse down into the SpecificInterfaceId. Then any specifics inside
would be left as "orphaned" without any generic id attached to them, and
we would never update the instructions in the SpecificInterface's
instructions (inside its own SpecificId) with new constant values when
evaluating the generic eval block against a specific. To do this we push
the specific_id inside the SpecificInterface, and when popping we pop
the specific_id then construct a new canonical SpecificInterface with it
and return that id.
We add support for importing ImplSymbolicWitness by importing its self
constant instruction and specific interface id. However we also had to
add import support for SpecificImplFunction, which can now appear in the
generic eval block for a generic impl declaration, and thus must be
imported with the declaration. This is done very similarly to
SpecificFunction, except the `type_id` is a singleton value.
---------
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
This prevents conversion from an InstId which is its base class, and
documents that this is invalid in the code.
Also expand the comment on the AbsoluteInstBlockId, which I had locally
but seem to have not saved and included in #5141.
---------
Co-authored-by: josh11b <15258583+josh11b@users.noreply.github.com>
Jon Ross-Perkins
Dana Jansens
Geoff RomerandRichard Smith
Thomas Köppe
Boaz Brickner