When impl lookup results in an `ImplWitness`, either directly or later
through `LookupImplWitness` evaluating to an `ImplWitness` inside some
specific, it represents a dependency on the eval blocks of the
`ImplDecl` that the `ImplWitness` comes from. The `ImplWitness` contains
a `SpecificId` of the `ImplDecl`, and the constants in the witness table
must be viewed through that `SpecificId`. The constants may depend on
the declaration or the definition block of the `ImplDecl`'s specific, so
any use of the witness table from `ImplWitness` requires the specific
from the `ImplWitness` to be fully resolved: both the decl and
definition blocks.
The specific declaration block is always resolved immediately when
forming a specific id, so there's nothing to do there. And things are
simple when the `ImplWitness` returned from impl lookup is concrete. We
would simply resolve the specific definition directly in the evaluation
of `LookupImplWitness`.
But when the `ImplWitness` is symbolic, meaning there's a dependency on
generic parameters in its referenced specific, then we have a dependency
on resolving the specific definition in the `ImplWitness` for every
specific that gets applied to the `ImplWitness`, eventually resulting in
a concrete specific.
Previously we attempted to do this by representing a dependency edge
from the eval block containing the `ImplWitness` instruction to the
definition block of the specific inside the `ImplWitness`. We
represented this dependency edge with the `RequireSpecificDefinition`
instruction.
The challenge with the `RequireSpecificDefinition` instruction was
ensuring it always landed in the _same eval block_ as the one holding
the symbolic `ImplWitness`. Ultimately, we've found a way to do this
without the `RequireSpecificDefinition`. The witness table is accessed
through `ImplWitnessAccess`, so we resolve the specific definition
before each access to the witness table. If the definition is already
resolved, this just costs a lookup of the Specific from the value store.
We document the other things we tried, which don't work or were too
complex, below.
In PR #6236, we added the `RequireSpecificDefinition` instruction in the
eval of `LookupImplWitness`, but this is too late. If impl lookup
resolved to a symbolic `LookupImplWitness`, the `LookupImplWitness` is
added some eval block. Later, we form specifics and re-evaluate that
eval block, and the `LookupImplWitness` can evaluate to an
`ImplWitness`. Adding the `RequireSpecificDefinition` instruction at
this point inserts the instruction into whatever generic's eval block
happens to be on the top of the generic stack, not the eval block of the
generic we are building a specific for. And indeed we can't add
instructions to a generic's eval block later like this, as it would be
missing from specifics that were already resolved for the generic. This
incorrect insertion shows up as a crash in eval at the CHECK introduced
but commented out in [eval.cpp in
#7981](https://github.com/carbon-language/carbon-lang/blob/56d9bbc40add1e9263f2f9b2555c3a27292d1725/toolchain/check/eval.cpp#L3507-L3512).
This is covered by the
`require_specific_impl_definition_through_specific_instantiation.carbon`
test.
We tried moving the insertion of `RequireSpecificDefinition` to be
earlier - at the point where the `LookupImplWitness` is constructed, in
the `LookupImplWitness()` function, instead of inside evaluation. This
seemed like a straightforwardly correct answer, as the eval block that
contains the `LookupImplWitness` will then also contain the
`RequireSpecificDefinition`. However, this can cause us to lose the
`RequireSpecificDefinition` entirely. Because it's a separate
instruction, not an operand of `LookupImplWitness`, it does not get
treated as a dependency of the witness. When we do an impl lookup inside
an `alias`, we build a generic for the alias and then discard it. This
discards the eval block containing the `LookupImplWitness`. Then, in an
enclosing generic, we refer to the constructed `AliasDecl` instruction,
which pulls all its dependent operands into the enclosing eval block.
This pulls in the `LookupImplWitness` into the enclosing eval block, but
it does not preserve the `RequireSpecificDefinition`. This is covered by
the
`require_specific_impl_definition_from_lookup_impl_witness_in_class_definition.carbon`
test.
We tried having `ImplWitness` evaluation resolve the specific definition
of the specific `ImplDecl` it refers to. This seems like the simplest
approach by far as we should always be working with the correct eval
block and nothing can get lost. However it does not work because of the
recursive nature of `ImplWitness`. The `ImplWitness` instruction appears
in the declaration of an `ImplDecl`, and the `ImplWitness` holds a
`SpecificId` for that same `ImplDecl`. When building a specific
`ImplDecl`, we evaluate the `ImplWitness` in the `ImplDecl`'s
declaration block which then immediately resolves the specific
definition before the declaration is finished. This leads to missing
instructions in the specific definition. In short, this puts the
dependency edge to the `ImplDecl`'s specific inside the `ImplDecl`
itself, which is problematic.
We tried wrapping `ImplWitness` in another instruction,
`ImplWitnessUse`. Inside the `ImplDecl` declaration there is still
`ImplWitness`, but then in the definition there is `ImplWitnessUse` and
that is what is returned from the evaluation of `LookupImplWitness`. The
`ImplWitnessUse` is an `ImplWitness` plus it ensures the specific
referred to by the witness has its definition resolved. However this
breaks constant comparisons, as we get different witnesses inside an
impl versus outside.
The first iteration of this PR's solution had us insert the
`RequireSpecificDefinition` into the eval block when we sniffed a
`LookupImplWitness` instruction, however that missed cases where impl
lookup immediately resolved to a symbolic `ImplWitness`, which is why we
now sniff for the `ImplWitness` in the eval block. This is covered by
the
`require_specific_impl_definition_from_symbolic_impl_in_class_definition.carbon`
test.
We also originally made a mistake of not inserting
`RequireSpecificDefinition` when inside the impl definition that the
`ImplWitness` refers to. But we can form specifics ImplWitness values
through function signatures, and these must add the dependency edge on
that specific ImplDecl definition. This is covered by the
`require_specific_impl_definition_from_inside_impl_definition.carbon`
test.
Finally, we did have a working solution. It was to sniff instructions
added to the eval block of a generic, and when an `ImplWitness` is added
to the eval block (it is implied that it is symbolic), also add a
`RequireSpecificDefinition` to that eval block immediately. We also
resolved the definition of a specific referred to by `ImplWitness` when
`LookupImplWitness` evaluates to `ImplWitness` to cover the concrete
witness case. This complicated the construction of the eval block
immensely, however. It caused a situation where adding one inst to the
eval block actually adds two, which we needed to avoid when importing.
And it required inst-kind specific behaviour in the very general
construction of an eval block, completely outside of eval itself.
A `where` expression can have symbolic references to `.Self` inside it,
but those references do not represent symbolic instructions that should
be part of an enclosing generic eval block. They are internal details of
the facet type, and as such they are PeriodSelfSymbolic, not Symbolic.
The WhereExpr evaluation is careful to produce a Symbolic constant value
only if it has symbolic dependencies on the LHS of the `where`, which
avoids leaking the symbolic nature of `.Self` into he facet type's
constant value.
But until now, those PeriodSelfSymbolic insts could still leak into the
enclosing eval block if they ended up in an operand of a Call
expression. A compile-time Call expr evaluates to a TemplateSymbolic
phase constant if it's not concrete, which includes PeriodSelfSymbolic,
because we don't want to evaluate the Call expr until the `.Self` gets
replaced during identify. But that means the Call constant value, and
its operands including PeriodSelfSymbolic constants, all end up in the
eval block. We fix this by making Call evaluate to a PeriodSelfSymbolic
phase if its input phase is PeriodSelfSymbolic. This keeps the RHS of
the `where` expression self-contained. If the facet type is concrete,
then it doesn't add any instructions to the enclosing eval block (which
may not exist at all in a non-generic context). Regardless, when we
identify the facet type and replace `.Self`, the dependent Call
expression will be rebuilt as well and it will evaluate as appropriate.
We also enclose the `where` expression in its own generic scope. This
means that instructions which are not part of the facet type do not end
up in an eval block. They may be symbolic instructions, and they will
not get updated by a specific when it's applied the enclosing generic
anymore. But since they are not part of the facet type their
substitution is not required.
The new test had an incorrectly elided SpecificImplFunction instruction
in the resulting semir, as SubstPeriodSelf was using the location of the
input canonical instructions as the location for the results which
resulted in an instruction without a location. We fix that by using
`loc_id_` in the subst rebuild.
Formatting now saw the initialization of a value from an `eval fn` call
to a function in a witness table, so it needed to be taught to look
through ImplWitnessAssociatedConstant (which is what we find in the
witness table).
A number of stores have been added to File without updating
CollectMemUsage. Add all the stores that were missed, ordering
everything by the order the fields appear in the class. Also include the
filename_ string, which requires a new overload of Collect, since
strings are like vectors of chars.
This test generates an infinite recursion between Carbon and C++ making
a new type at each step through the recursion, producing an infinite
number of types. We improve the test in a few ways:
- Remove direct dependencies on min_prelude parts, we should just depend
on a single min_prelude, and not `import Core` explicitly.
- Remove a dependency on `i32` so we rely on less prelude.
- Remove the use of pointers, which currently introduce a dependency on
`Optional`, so we rely on less prelude. Instead use a generic `Wrap(T)`
type that we nest repeatedly to generate types.
- Add some comments and expand function names to help explain the
behaviour being tested
Now the test just depends on the convert.carbon prelude, which makes it
much simpler when running under a debugger.
Drop dependencies on the prelude so it can be debugged with no prelude
import if needed. Ensure the return type of MakeC is used in C++ since
it's part of the imported function signature.
The values in `IdentifiedFacetType` may contain `IdentifiedWitness`
instructions, and those insts need to be either converted to
`LookupImplWitness` and evaluated as such, or substituted by the user of
the `IdentifiedFacetType` with witnesses of its own.
This changes the API so that the user must go through a method doing one
of those two things to get to the underlying values in the
`IdentifiedFacetType`, unless they explcitly request to bypass them.
Then we split extend impls requirements out into their own set so that
the user can determine what is being extended _after_ evaluation or
substitution of `IdentifiedWitness` insts. This is critical because we
can not dedupe SpecificInterfaces until after that takes places, as
demonstrated by the test fixed by this PR.
`IdentifiedFacetType` is a concept that is only used by check. It does
not appear in the semir output, unlike `DeclaredFacetType`s.
`IdentifiedFacetType` is used in check to collapse named constraints
together, building a single structure of requirements from a
`DeclaredFacetType` and any referenced named constraints. This is used
for operations like impl lookup, and building `FacetValue`s.
The outputs of `IdentifiedFacetType` are now in an intermediate state,
where they contain `IdentifiedWitness`es, and need to be processed
before they are used. We'd like to build that into the API of
`IdentifiedFacetType` so that their use is more robust. But the
`IdentifiedWitnesses` need to be replaced by subst, which is a part of
check, so we need to move `IdentifiedFacetType` to check in order to
build the type on top of subst.
Update tests for observe equivalence chains to cover more cases and to
better test the things they meant to. The design is clarified to explain
that in an `interface` the types in an equivalence chain must all be
related to that interface except for one.
This is based on #7484 with some followup changes by me.
Co-authored by: ozguronsoy@gmail.com
We were explicitly marking the specifics of `require` decls as
`identified` when creating them during identify. But the require may
contain calls to other generics internally. And forming the specific for
the `require` can also form new specifics for those calls, if they
depend on `Self`. The resulting specific can have `IdentifiedWitness`
instructions in its arguments, in accesses or FacetValues, etc. Or they
may appear in the decl block as it's resolved. So it's very important
that the specifics be marked `identified`, as those witnesses may only
appear in `identified` specifics. This allows the new
`access_through_nested_specific_in_named_constraint.carbon` test to
succeed without any poisoning errors.
SemIR formatting is changed so that `identified` specifics are more
clearly differentiated where they are used, so that we can see if
`identified` specifics are misused outside of identifying.
Now that we construct more `identified` specifics, we also need to
ensure we remove the `identified` state from specifics that come out of
`EvaluateIdentifiedWitnesses` and `SubstIdentifiedWitnesses`. To do that
we add a new callback method on `SubstInstCallbacks` that we use to
build specifics during subst. Then during those operations, we drop the
`identified` flag from any specific that we form, because we know that
we have also removed any `IdentifiedWitness` instructions because:
- We replace them all from arguments during subst.
- We CHECK that we're not in the middle of identifying before starting
the subst.
However now an `IdentifiedFacetType` is not fully deduped, because it
may contain a non-identified specific that comes from a
`DeclaredFacetType` along with an identified specific that comes from a
named constraint, where they have the same arguments. That results in
the `IdentifiedFacetType` having two specific interfaces when it really
only refers to one. The
`fail_todo_impl_as_constraint_duplicates_interface.carbon` test
demonstrates this, and that we then diagnose an `impl` as invalid since
we find more than one specific interface being extended. To fix this we
need to dedupe and count specific interfaces _after_
substituting/evaluating away the IdentifiedWitnesses. This is left to
future work.
If we perform impl lookup during identify by resolving a specific, we
can run into IdentifiedWitnesses in a FacetValue. If the witness is the
only one in the FacetValue we may use it as a final witness, which is
not correct. IdentifiedWitness is not a final witness.
To test this, we add a test that places an IdentifiedWitness into a
FacetValue and then uses that facet value to get an associated constant.
If treated as a final witness, we try to do a lookup where the query
self contains the IdentifiedWitness and we crash coming across it in the
TypeIterator. We should never come across an IdentifiedWitness in an
impl lookup query.
The test also shows a case that should work but does not because of
`impl_lookup_no_symbolic_final_lookups`. We set
`impl_lookup_no_symbolic_final_lookups` while collecting witnesses to
avoid cycles in impl lookup. This test fails because of that. It
prevents us from forming a correct specific for the class `C` by
creating a specific where `C.C1` is a symbolic value. Later we try to
form the specific again, where we would see a concrete value for `C.C1`,
but the specific already exists, so we can't get to the concrete value.
The rules in early impls are stored with frozen `.Self`. However when
forming a specific, we can perform an impl lookup query against a facet
type written outside of the current facet type, which means any `.Self`
in that facet type will _not_ be frozen. In order to compare a witness
from early impls with the non-frozen requirement, we need to thaw what
we get out of the early impls.
However there are also cases where we are doing a lookup against
requirements that are part of the current facet type, so the
requirements are frozen.
Rather than picking one, and having to thaw all impl lookup queries, for
example, we store the frozen and thawed copy of the early impls rule so
that we can satisfy lookup queries that involve either.
We allow using `InstId` as a `LocId` for diagnostics, which works great
in `handle_*` functions, where we are working with non-canonical insts.
And convert and pattern matching often are given non-canonical insts,
which they can use, or pull apart to find some other inst, and use those
as a location for diagnostics. However these operations can also be
called with canonical insts, which have no location. In that case if we
need to diagnose an error, it ends up not being attached to any code at
all. Since we always have a `LocId` somewhere up the call stack, pass it
along and in these places that handle canonical instructions too, use
`GetInstLocationOrFallback()` to get a valid location for diagnostics.
This is also similar to what eval does with its fallback `LocId`.
The result is that many diagnostics now have a location where they had
none before. It also means some insts don't get `<elided>` in formatted
semir for not having a location at all and thus not being in range.
When the LHS is not a type, or the RHS is not a facet type, that is the
most important error to give, so prioritize that. Only fall back to the
"no .Self present" when the types are correct.
This was especially confusing when the RHS _did_ contain a `.Self` but
was not a facet type.
Add TypeExpr::SetError, as the lack of this was the main reason for the
bad error checking ordering, as setting multiple fields was awkward when
an error was found.
This handles the common case where there is a `context` variable or
method available in scope.
Users can't provide this alias in their own config files since the
`dump` command does not yet exist when user configs are parsed.
An accidental copy would cause an extra save/restore. This is meant as
an RAII object to denote a save for a given scope. Also disallow move so
we don't need to add branches to the dtor.
Instead of only looking for rewrite constraints in the declared facet
type, identify the facet type and collect rewrite constraints from named
constraints as well. This allows rewrites in a named constraint to be
found such as `T: N, U: T.X` where `N` is a named constraint that does
`extend require impls Z where .X = ...`. The type of `U` will be
whatever is specified in the rewrite of `.X` inside `N`.
Note this removes some more uses of SubstPeriodSelf from outside of
identify, which is a progression, as identifying is meant to be the way
to substitute `.Self` generally.
This allows you to `dump` the SpecificInterface directly instead of
having to dump its components always, for the common cases where we have
a SpecificInterface rather than a SpecificInterfaceId.
It looks like:
```
interface: interface50000000: {name: name0, parent_scope: name_scope0, require_impls_block_id: require_block_empty, core_interface: Copy} `Copy`
- specific_id: specific<none>
```
Instead of only getting rewrite/equality requirements from the declared
facet type, impl lookup now uses the full IdentifiedFacetType of the
query's constraint to get rewrite/equality requirements from named
constraints as well.
SpecificStore::HasError can return false when the specific ID is None,
which avoids having to check the ID in the caller. This is similar to
the GetArgsOrEmpty() helper.
Normally ImplSelfWitness would be replaced in an impl decl by the time
we are constructing the witness table. If it was part of an access to an
associated constant, rewrite constraint resolution would have replaced
that access with the value assigned to the associated constant already.
But we can use `.Self` in places where it converts and forms a
FacetValue, which preserves the ImplSelfWitness in the witness block of
the FacetValue. In that case, we want to replace it with the impl's
ImplWitness before we put it into the witness table.
This is a followup fix for
https://github.com/carbon-language/carbon-lang/pull/7930 which
introduces the CARBON_FATAL incorrectly, now that we know how to run
into it.
Add some tests that cover these situations, including one that tries to
access using the FacetValue and its witness, which fails, as a TODO
test.
Rewrites in `extend requires` are used to set the witness table values
of the impl. Rewrites in non-extend `requires` are treated as same-type
constraints and must be true at the point of the impl definition.
When identifying a facet type, defer evaluation of LookupImplWitnesses
by redirecting them to evaluate into IdentifiedWitness. Then the caller
of identify will need to substitute the IdentifiedWitnesses, either with
witnesses of their own, or with LookupImplWitness to cause a lookup
operation.
This allows:
- An `impl as` on a named constraint can subst the witnesses in
designators from the named constraint with a witness to the impl itself.
This prevents them from looking for and finding some other overlapping
impl. (This PR)
- Impl lookup to collect rewrite/equality requirements from all named
constraints and then use the impls it has already found to evaluate any
designators in those requirements instead of performing impl lookup
again (creating a cycle). (Done in
https://github.com/carbon-language/carbon-lang/pull/7944)
- Similarly, an `impl as` can collect impls and equality requirements
from all named constraints and verify them correctly by replacing
witnesses that should refer to the impl with the correct witness instead
of performing a lookup and finding an overlapping impl. (Done in
https://github.com/carbon-language/carbon-lang/pull/7937)
- ImplWitnessAccess to be able to find rewrites from a named constraint,
not just from the initial DeclaredFacetType. (TBD)
To do this we need to introduce the concept of "identified" specifics.
In order to identify a facet type, we must construct a specific for each
require decl in a named constraint. These specifics will have
IdentifiedWitnesses inside them, but their args would otherwise match a
specific for the require decl constructed in another context. To avoid
polluting the canonical specific namespace, we introduce a second
namespace of specifics that are "identified" since they are created by
identifying.
As we have introduced a new global state that modifies eval behaviour,
we must disable that state when resolving a specific (as per
https://github.com/carbon-language/carbon-lang/pull/7923). But inside an
"identified" specific, we preserve the behaviour so that the witnesses
modified by identify (through SubstPeriodSelf or through evaluating a
require specific) have their evaluation deferred.
Sets a variable to a new value, saving a copy of that new value. Then
CHECKs that the variable is still set to that new value before restoring
the original value over top of it. This is meant to catch data loss
where the variable holds some change that would be overwritten by the
restore. In particular, this would catch bad bracketing of sets and
restores.
We plumb through the ID so that we can later see if a requirement was in
the IdentifiedFacetType, and potentially grab a final witness from the
witness source if it's a FacetValue.
Instead of plumbing through the IdentifiedFacetTypeId, collect all the
requirements up front, and the final witnesses if they exist.
We want to do this because in future work we will need to subst/evaluate
the outputs of IdentifiedFacetType to use it since it will contain
IdentifiedWitnesses, and we'd like to do that once up front instead of
multiple places. That is more efficient and ensures less time/code with
access to the intermediate state of the IdentifiedFacetTypeId.
This statically ensures that identify always works with a constant
value, in the most restrictive way possible (ensuring it's a type not
just a constant).
We plumb the IdentifiedFacetTypeId through instead of identifying the
constraint twice, even though the second one should result in a cache
hit, as this makes things more clear and explicit.
Also a few other smaller cleanups and comments around forming the facet
type and identifying it, that I am trying to pull out of a much larger
change to identifying, so as to reduce noise there.
We set the `declaring_impl_decls` state to modify the evaluation of
LookupImplWitness instructions formed inside an `impl as` decl's
constraint. However while checking that constraint, we may form other
specifics through calls to generic classes, etc. Specifics are canonical
and are keyed by their arguments and the generic ID. This means every
time we see the same arguments for a specific, we must produce the same
instructions. The `declaring_impl_decls` state can break that, causing
instructions inside the specific to be formed in a way they wouldn't at
another time.
To fix this, remove the effect of `declaring_impl_decls` while resolving
a specific. This keeps the specific's evaluation consistent so that the
key truly represents the canonical specific for its arguments.
This doesn't break anything. Existing LookupImplWitnesses (such as in a
class decl) are not guaranteed to point to an `impl as` when they are
modified by a specific. It is designators in the `impl as` constraint
that are guaranteed as such. Designators in an `extend require impls`
statement in a named constraint will be pointed to the `impl as` through
another mechanism in a followup, which will make the
`impl_as_named_constraint.carbon` test pass again.
We perform the same canonicalization as in LookupImplWitness, which
makes the output of eval more consistent across witness types, and
enables more straightforward constant comparisons between them when
needed.
This allows us to collect rewrites from named constraints and use them
to initialize the witness table for an `impl as` statement.
Only rewrites from extend constraints are tracked, as other constraints
should turn into equality constraints, as they don't modify the witness
table.
When an LLM tool is used to prototype a change, one of the major tasks
it must undertake is validating filetest output changes. This skill
helps to ground that validation in some best practices and explain what
sorts of changes should or should not be expected, and how to judge
STDOUT vs STDERR changes.
Assisted-by: Opus 5
When there's a wildcard in a path, git treats the path as matching
exactly, unless the path also ends in a wildcard. So
`toolchain/*/testdata` only matches the testdata directory names,
whereas `toolchain/*/testdata/*` matches all the files under them.
The type `type` is now a `FacetType` inst with no constraints. This
brings the model implemented in the toolchain into better alignment with
the language design. The `SemIR::TypeType` struct remains as a scope for
holding the `TypeInstId`, `ConstantId`, and `TypeId` constants, but is
not an `InstKind` anymore.
The `TypeType` inst looks a lot like singletons, but there are many
`FacetType` insts so it doesn't quite fit that model. So we put it
alongside singletons with a fixed inst id but refer to it as a more
general "builtin" inst that is not a singleton.
`Namespace::PackageInstId` is similar, and we group it with `TypeType`
conceptually as another builtin instruction with a fixed id.
No conversion is needed anymore to use a `type` as a facet, since types
also have a `FacetType` type. This simplifies and removes a number of
helpers and branches throughout the code.
The `TypeType` inst is now part of the constant store, so we end up
printing it in the constants block in every test. But it's also named
`type` rather than `%type` to preserve the majority of existing
formatting behaviour, though this does look different from other
constants.
Assisted-by: Opus 5 was used to generate a first draft and validate the
refactoring. Though nearly everything non-trivial the tool wrote has
been modified or rewritten.
Add rules to not overwrite git/jj history without asking, since this
destroys the reviewer's view of things. And some information on dealing
with stacks of commits within a single bookmark/PR.
Prek can make fixes for whatever caused a failure, and then pass when
you run it again, even though the user didn't change anything, and that
is now explained.
Assisted-by: Opus 5
We were passing a SpecificInterfaceId which just makes code have to do a
lookup to get the actual SpecificInterface. The caller already has the
SpecificInterface, so plumb that around.
SpecificInterfaceId really only exists when we need to stick a
SpecificInterface into an instruction as an operand.
Use a single `SemIR::Function` per `Core` interface method, whether it's
generated locally or imported. This prevents generating duplicate
functions, which lead to different types when the witness appears in a
`FacetValue` as part of a specific for a class.
We use a `CanonicalValueStore` of `GeneratedFunction` objects that allow
finding an existing FunctionId for a `Generated` special function before
(re-)generating it. Mangling for `Generated` functions is also moved to
use the values from the `GeneratedFunction`'s canonicalization key, so
that we have a consistent source of truth for the unique ID of a
`Generated` function across all files.
New tests are in
`toolchain/check/testdata/impl/custom_witness/destroy.carbon`.
Some `google-` prefixed rules have been renamed to rules without the
prefix. The `google-` prefix still remains as an alias to these new
rules. Since we turn on the `google-` prefix rules and use those in
NOLINT expressions, disable the new aliased names. Otherwise we have to
put both names in NOLINT expressions.
This is a style choice we often agree with, and call out in code review.
But there are many cases where we do want to split apart nested ifs,
such as when working with LLVM apis like `dyn_cast`:
```
if (auto* thing = dyn_cast<Thing>(other)) {
if (thing->foo()) {
...
}
}
```
Or we may have TODOs or other comments in the scope of the outer if,
which the tidy check ignores.
Since this doesn't lead to bugs, we disable the check and leave this to
reviews and authors for their discretion.
The hashing code is generic over the type of the value being given to
sizeof() so ideally this warning would not happen at all, but it does.
Possibly because the value is the return of an overload set, so it's not
obvious that it's the templated type. One of those overloads returns
`const void*` but change that to an integer does not remove the warning
still.
Clang is synthesizing a cast when using an enum value from a template
parameter, and then clang-tidy is finding and reporting that cast.
Upstream bug: https://github.com/llvm/llvm-project/issues/222793
clang-tidy 24 warns on C-style variadics, and we don't need to use one
here anymore. Instead of a function call with an argument list, use a
concept to determine if a type can be list initialized.
This check allows styles that we don't use so it's not really useful for
enforcing our style guide. And prevents the use of `_1` or similar in
destructuring declarations where want to use `_` for multiple variables,
such as `auto [_1, _2, foo] = bar()`.
The warning wants all classes inherited as CRTP base classes to hide all
their constrcuctors and friend all uses of them. We use CRTP quite a lot
and across different components of the toolchain, which would make
maintaining friend lists frustrating.
The StringRef represents a bounded region of a string, but using data()
drops the end bound, and makes LLVM construct a new StringRef starting
in the same position and going until a nul terminator. If this worked
correctly before, it was because the StringRef was always pointing to a
full `std::string` or the tail of one.
While we do adhere to its expectations most of the time, we don't
always. This is a low value check, and it's a stylistic choice to use
`#if defined(...)` when paired with `#elif defined(...)`.
Avoid CHECK failure when performing member access on a runtime type
value. We will just fail to find the CanonicalFacetOrTypeValue and then
fail lookup.
We use multiple inheritance extensively, such as with our
EntityWithParamsBase subclasses. But we don't do this for
vtables/virtual, we do it for composing fields.
This produces a warning on every use of CARBON_KIND() with clang 24.
I tried putting NOLINT comments into the macro on the else to no avail.
It seems that comments are stripped from the macro output when it's
performing the check.
We already require {} on every if/else (outside of these weird macro
cases) so this doesn't seem like a problem to disable.
The float.carbon conversions for int->float, uint->float and
float->float were using various workarounds through extra indirections
in order to avoid the impls overlapping. Now we can write them all as
`impl From as ImplicitAs(Float(To))`, which makes them all appear to
overlap, though any given type will only match at most one of them. We
use `match_first` to give them an ordering regardless so that they are
allowed to overlap in type structure.
The SDK returned by `xcrun --show-sdk-path` does not always match the
SDK
that is used by clang under homebrew, because homebrew has its own
configurations per target that specify an SDK path to `-isysroot`. And
on
Darwin, the `-isysroot` flag supercedes the `--sysroot` flag entirely
when
present.
To override homebrew, and ensure we use the SDK we expect to be using
from
`xcrun`, specify `-isysroot` ourselves on the command line, both when
finding
the include paths and when building.
The compiler ends up taking a dependency on a JSON file at the root of
the
SDK as well, so add that to our allowlist of non-hermetic files,
along-side
the SDK include paths.
There's no way for the user to override and disable the disk cache once
a path is specified in our current version of bazel. Later versions
would allow the user to specify `--nodisk-cache`. If the user really
wants a disk cache anyway, they can specify as such in their
`user.bazelrc` file.
The declarations in a `match_first` must always be in the same file as
the first owning declaration, in order to maintain a consistent view of
impl lookup across all files.
We propose a principle that it's always possible to inline the import of
a library from within the same package without changing the meaning of
or diagnostics applied to the code. This is similar to the textual
inlining of an `#include` statement in C++, but is slightly less
general. Cross-package imports place the imported names inside the name
scope of the package, so inlining those necessarily changes the paths
for name lookup.
---------
Co-authored-by: josh11b <15258583+josh11b@users.noreply.github.com>
Co-authored-by: Carbon Infra Bot <carbon-external-infra@google.com>
When implementing a named constraint, like `impl as N`, any accesses
through `Self` in the named constraint need to get the value of the
associated constant from the impl's witness table. This isn't possible
immediately, since the impl does not even exist until the declaration is
complete. We use the same model as for accesses found directly in the
impl declaration, but applied to the point where accesses in the named
constraint are substituted during identify to point at the impl's self
type. To get there, we need LookupImplWitness instructions in the named
constraint, when re-evaluated during construction of their enclosing
specific, to evaluate to ImplSelfWitness when they are a reference to
the type and interface being implemented.
This reduces object sizes which is desirable for linking speed.
zygoloid did some analysis to determine if any of our code requires RTTI
for `dynamic_cast` here:
https://github.com/carbon-language/carbon-lang/pull/7532#discussion_r3611196721:
> The only thing I found is that libc++ requires dynamic_cast in order
for std::print to correctly write Unicode to terminals on Windows
We use `llvm::print` functionality, not `std::print`, so this doesn't
affect our toolchain.
Note that libc++ and libc++abi are built with RTTI enabled. It is
explicitly allowed to use different compiler flags when building these
libraries even though they share some headers with users of the
libraries, so this does not cause ODR violations.
In Convert, we require the source value's type to be compete so that we
can look for `base` classes and `adapt` relationships. However these can
only be present in a `ClassType`, so we only need `ClassType`s to be
complete.
Reduce the requirement in Convert to not complete types that are not a
`ClassType`, and which can not contain a `ClassType` as part of their
class.
Ideally we would only _only_ require the `ClassType` itself to be
complete, and only if we're looking for a base or adapt. However lower
depends on us completing all Convert source types that contain a class.
This seems to suggest we're lacking checks for complete types somewhere
else and Convert is making up for it. A TODO has been added. The
`toolchain/driver/testdata/compile/optimize/optimize_debug.carbon` test
is an example that CHECKs due to failing to verify the LLVM module if we
do not compute the complete type of all class-containing types in
Convert.
The critical step this PR is doing is to stop trying to complete a
`FacetType` when converting from a facet. This avoids trying to complete
a named constraint when converting `Self` inside that named constraint.
Doing so causes a cycle when the conversion of `Self` is performed in
eval of an `extend require` decl, since requiring the named constraint
to be complete re-evaluates the `extend require` decl again. A test is
added that crashed in an infinite loop before this change.
It also depends on #7584, which was intended to be an optimization but
is now load bearing. Because converting `Self` leaves an impl lookup
inst behind, and if that inst is re-evaluated inside impl lookup (by
forming a specific of a `require` decl through identify) then we have a
similar cycle.
Pass `-fno-exceptions` when building the toolchain. We do not use
exceptions, so we do not have any try/catch in main, so uncaught
exceptions just unwind and exit. They do not hit our signal handler and
we do not print the stack trace.
Instead of adding a try/catch in main, and redirecting that, we can
build with `-fno-exceptions`. This turns any throw into an `abort()`.
And indeed with that flag, the following code crashes and prints a stack
trace:
```cpp
std::variant<int, bool> a = {1};
std::get<bool>(a);
```
Note that libc++ and libc++abi need to be built with exceptions enabled.
It is explicitly allowed to use different compiler flags when building
these libraries even though they share some headers with users of the
libraries, so this does not cause ODR violations.
Fixes#5225
During impl lookup, for each (generic) impl candidate, we form a
specific for that impl by deducing its generic arguments. Then we
compare the query interface against the impl's specific interface. That
comparison needs the deduced arguments applied to the impl's specific
interface. Previously we were doing this by getting the impl's
constraint facet type with the impl's specific applied (via
`GetConstantValueInSpecific()`) and then identifying that facet type
with the impl's deduced self.
Identify is a fairly expensive operation. It runs subst, trying to
replace `.Self` references. It walks named constraints. It collects
require declarations. We're looking at making it do _more_ in the future
too, including rewrite constraint resolution and collecting rewrite and
same-type constraints. For this reason we have a cache to make it cheap
on the second run, but it's still a very heavyweight operation to
involve in impl lookup, when all we want is to apply the impl's specific
to its target interface.
We almost have all the information we need to avoid the identification
step. We have the impl's specific after deduction. And we have the
SpecificInterface that the impl is targeting in the `Impl` struct. When
we form the specific for the impl itself, we resolve the declaration
block and form new constant values for all instructions in there, but
that does not cover the SpecificInterface that we're storing in the
`Impl` struct. So we add a new instruction to the impl's eval block,
which will be symbolic when the impl is generic and the target interface
depends on a generic parameter. And we store the `InstId` in the `Impl`
struct. This allows us to gets its constant value later with the impl's
specific applied. From that constant value we can then pull out the
SpecificInterface that the impl is targeting.
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.
This makes SubstPeriodSelf more generally useful, with one less gotcha.
Previously calling it with a facet type would just do nothing.
This is possible now because we
- Have SubstOperandsSkipType to make use of
- Have banned constructs which introduce ambiguous .Self, so we don't
need to try avoid finding undesired .Self insts in facet types in other
positions (like in specifics).
As a follow up to #7546 (and see the discussion there), verify our
assumptions that you can't have an object of type facet where the facet
is not symbolic, and then need to find a Destroy witness for the object.
This is in addition to finding a `where` on the RHS of another `where`.
Since a generic binding introduces `.Self`, any `where` expression that
isn't part of a facet type modifying the binding itself would introduce
an ambiguous `.Self`.
Add virtual parse nodes for let, var, and form bindings, which goes
before the type. This allows us to track if `where` appears in the
binding's type. We only need to look for an invalid `where` if any
appeared in the type. We combine these three nodes together into a
single node kind, which requires us to remove the name from it as a
child. We move it up to the Pattern node again, and rename the
PatternStart nodes to PatternTypeStart as they are now located in the
middle of the Pattern nodes, just before the type.
And we only need to thaw `.Self` in generic bindings. Non-generic
bindings can only have `.Self` through a `where` expression, since the
name is not provided otherwise to non-generic bindings. And `where`
expressions thaw their `.Self` independently. So the binding only needs
to thaw a `.Self` that it introduced, which is only for generic
bindings.
Require rewrite and same-type constraints that do not depend on `.Self`
to be satisfied when a facet type is identified, since those constraints
may not be found later.
For a symbolic value with a type being a facet, we need to find a
witness either from the facet's type or from an impl. Custom witness is
for producing a concrete final witness, but there is no such witness in
this case. We should fail to find a witness, and defer to impl lookup to
find the Destroy witness.
Currently it tries to find a witness from the facet type, but it ignores
named constraints, which means it's incomplete at best. But there's no
value in trying to say that the value is trivially destroyable, when it
has a type that impls Destroy. It may not be trivial, and we can't
actually make a witness for it while symbolic.
We checked that requirements inside the impl-as target interface were
satisfied. But we also need to check that requirements coming from the
constraint facet type, or named constraints that it targets, are
satisfied.
I wanted to move it to check but there'd still be an
IdentifiedFacetTypeId and we keep all Ids in sem_ir. So leaving it in
sem_ir, but moving it to its own file. This more clearly separates
DeclaredFacetTypes and IdentifiedFacetTypes.
Dana Jansens
