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.
This disallows building a facet type that contains another facet type
with non-extend constraints in it. Which in turn prevents the
possibility of introducing a different `.Self` into a facet type.
Eval can still insert a facet type with non-extend constraints, as we
only prevent it for `where` being written into the facet type. There is
a TODO in handle_where.cpp for this and some tests in
toolchain/check/testdata/facet/nested_facet_types_from_eval.carbon
Move the existing derived->base conversion earlier in
`PerformBuiltinConversion`, into the block that handles qualifier
conversions. This allows, for example, converting from `partial Derived`
to `partial Base` -- see the tests in
`toolchain/check/testdata/class/inheritance/derived_to_base.carbon`.
This test was assuming that we'd allow qualified lookup in rewrite
constraints, but that is not in agreement with the design. The design
says that the LHS of a rewrite must be a member access designator like
`.Member`.
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>
Implements proposal #7016: `self` moves from the deduced implicit list
(`fn F[self: Self]()`) to the front of the explicit list. Its type may
be written explicitly (`fn F(self: Self)`) or omitted, in which case it
defaults to `Self` (`fn F(self)`, `fn F(ref self)`); `self` in the
implicit list is rejected.
Throughout checking, `self` is modeled as the first explicit parameter.
Because a method is just a function whose first parameter is `self`, it
can also be called as an ordinary function with the receiver passed
explicitly (`Type.M(obj, ...)`), not only as `obj.M(...)`. A new
`SemIR::CallArgParamPatterns` helper chooses the parameters matched
against the explicit arguments, excluding a leading `self` only when it
is supplied as a method-call receiver; arity checking, conversion, and
generic deduction use it. The resulting SemIR and lowering are
unchanged: `self` is still `call_param0`, and witnesses, thunks, and
vtables are unaffected.
An omitted `self` type is parsed as a `SelfBindingPattern` node with no
type expression; checking synthesizes the `Self` type so it behaves
exactly like `self: Self`. However, the exact spelling used must match
between a forward declaration and a definition, following #3763's rules
around declaration matching.
Generated functions, thunks, and C++ interop import/export build `self`
as the first explicit parameter, and the `self`-type override (e.g.
Derived->Base for a virtual override) applies to the explicit `self`.
Placement is validated by new diagnostics: `SelfInImplicitParamList`,
`SelfNotFirstParam`, and `SelfOutsideParamList`. The benchmark source
generator and the documentation adopt the `(self)` shorthand; the
prelude, the examples, and the test data are migrated in the following
commits.
Assisted-by: Claude Code with Claude Opus 4.7
---------
Co-authored-by: josh11b <15258583+josh11b@users.noreply.github.com>
We exposed `Core.IntLiteral()`, `Core.FloatLiteral()`,
`Core.CharLiteral()`, and `Core.Bool()` as functions as a workaround,
because we had no way to provide the type names without parentheses that
the design requests. But now we can do so, by using an alias. Switch all
of these over from being functions to simply being names of the
corresponding types.
Assisted-by: Gemini via Antigravity
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.
Implement support for floating-point <-> integer type conversions as
described in #820 and #845, extended to support `unsafe as` conversions
for the conversions that can't be expressed as either implicit
conversions or `as` conversions.
One tricky part here is conversions from floating-point literals to
integer types. Such literals may have both a very large mantissa and a
corresponding somewhat large negative exponent, and still produce a
result that is in the range of values that a small integer type can
represent. In order to support that while avoiding building very large
2^N or 10^N constants in general, we first compute a conservative
approximation of the number of bits necessary to represent the integer
result, with an early exit if the number is either definitely too large
or definitely zero. The remaining cases have a reasonable bound on the
size of integer necessary to compute the base^exponent multiplicand.
Assisted-by: Gemini via Antigravity
Update the orphan rule to require a name to be defined within, or by,
the same scope as the impl declaration. Since libraries can not be
nested, this also enforces the old rule, but rejects more impl
declarations. In particular, it rejects an impl declaration in a generic
context which would have no way to provide a value for the generic
bindings it inherited from its enclosing scope, making the impl
unusable.
Discussed in open discussion
[2026-05-04](https://docs.google.com/document/d/1mjllGO3ZCL4qGt9uJHUtcxKoHAGEY7Y999ie4EtBWB8/edit?tab=t.3ifnhz83n73d#heading=h.p45zfugbmdih).
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`.
Instead of requiring just one to have a designator, require each one.
You can't write `(type where A == B) & (type where C == .Self)` because
`A == B` has no designator. If the two facet types are combined into a
single `where` syntactically, their meaning does not change, and what we
allow should not change either. That is, `type where A == B and C ==
.Self` should be rejected since `A == B` does not contain a designator.
The design is also updated to make this clear.
The `unused` modifier is rejected on parameters of a function
declaration, but the check only covered the explicit parameter list, so
an implicit parameter (such as self or a compile-time binding) could
carry unused without a definition. Check the implicit parameter list
too.
The code changes and the test updates are split into two commits for
easier review.
Assisted-by: Claude Code with Claude Opus 4.7
---------
Co-authored-by: Christopher Di Bella <cjdb.ns@gmail.com>
We've talked about adding the title to the filename several times over
the years and it seems really valuable. This requires us to compute a
"slug" for the title spelling that can be part of the filename.
Beyond that, we crossed 7000 recently, and so it seems likely that we
will need to add digits sooner rather than later here, so this goes
ahead and moves us to 6 digits so we don't have to adjust again for a
reasonable length of time.
To implement this and ensure we can sustain it going forward this adds a
tool to our pre-commit that validates (and corrects if needed) the
filename.
In order to update everything and keep links working, there are a _lot_
of changes, but the most interesting for direct review are in
`proposals/scripts`.
Assisted-by: Antigravity with Gemini
---------
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
When forming the constant value of a `where` expression, don't consider
it to be `.Self`-dependent if the dependence only comes from the RHS of
the `where`. More generally, ignore `.Self` dependence when evaluating a
facet type unless it comes from an extended interface or named
constraint. While we can get other kinds of constraint from the
left-hand side of a `where`, such constraints must either come from the
right-hand side of other `where` expressions or be extend constraints.
This fixes a crash in lowering caused by a concrete function containing
a `.Self`-symbolic `where` constant.
Assisted-by: Gemini via Antigravity
When performing deduction for a call to a generic function, we would
previously convert runtime arguments to match the parameter type, then
throw away the result. Instead, track whether deduction needs the value
of the argument, which will be the case only within compile-time
contexts such as generic bindings and types of instructions, and only
perform conversions during deduction for those contexts.
Fixes miscompiles when passing an argument requiring a runtime
conversion with side-effects to a generic function, where previously the
side-effects would have happened twice! (Once from deduction and once
from the real call argument conversion.)
Assisted-by: Gemini via Antigravity
In handle_let_and_var.cpp, field initializers are now handled like
regular `var` initializers, by calling `LocalPatternMatch`.
In pattern_match.cpp, `FieldDecl`s with initializers are handled by
storing a value in `SemIR::File::field_initializers()`. This is a new
map where the keys are `FieldDecl` `InstId`s and the map values are
`InstId`s representing the initializer value.
In convert.cpp, `ConvertStructToStructOrClass` now has a `get_default`
function parameter that callers can use to provide a field default.
`ConvertStructToClass` uses this to provide a default from field
initializers.
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.
When a class extends an interface, referring to a member name of the
interface as an unqualified name should refer to the class's
corresponding associated entity value, not to the associated entity
itself. Similarly, in an `impl`, unqualified names of associated
entities should refer to the `impl`'s corresponding value for that
entity.
To support this, we treat `impl`s as `extend`ing their implemented facet
type, and we make lookups into an extended facet type use the `Self`
type of the extending `impl` or `class` if lookup finds an associated
entity. We already did the latter if the extending entity was an
interface; this extends the existing support for these other cases.
While this can only happen when some other error is taking place, we
should handle it gracefully and report a concrete (but unmatchable)
value in the type structure instead of CHECK-failing.
Class vars are still restricted to simple `name: type` bindings, not
full patterns. This is now handled in the check phase instead of during
parsing.
This is in preparation for supporting `static var`.
When an outer type defines an `extend` relationship to an inner type, we
require that inner type to be complete so that we can know that name
lookup can search both scopes as soon as the outer type is complete.
When doing name lookup, we require the type in which we are looking to
be complete. Then, we recursively add extended scopes, but then also
require each of them to be complete again, which inserts
RequireCompleteType instructions into the block doing lookup.
While these new instructions may differ in terms of their specifics,
they are redundant since we already required the type to be complete,
and specifics can not change the completeness of a type. They are also
problematic because a named constraint or interface can extend a scope
with a symbolic specific, by using `Self` as an argument. This inserts a
symbolic instruction into the block doing name lookup, even though that
block may not be generic.
A nested designator like `.(X.X1).(Y.Y1)` results in nested
ImplWitnessAccess instructions, which can produce cycles in the
toolchain easily when replacing `.Self`.
First, when constructing a facet type like `V:! Z where .Z1 impls (Y
where .Y1 = U)` we substitute replace `.Self` in the nested facet type,
and in this case we replace `.Self` with `.Z1` which contains a `.Self`
of its own. This was coming from us being lazy about replacing `.Self`
in an `impl as` declaration, such as `impl C as Z where .Z1 = .Self`.
The self type is known there, so we can more eagerly replace `.Self` as
we do in a `require impls` declaration. Then the replacement for `.Self`
never comes with a `.Self` that needs to also be replaced. Any resulting
`.Self` would always be the top-level one.
Second, when evaluating ImplWitnessAccess, we were replacing .Self in
the LHS of rewrite constraints, but the `.Self` may itself have a type
that contains rewrite constraints. If one of those rewrite constraints
has nested ImplWitnessAccess instructions, we evaluate the new
ImplWitnessAccess, which again finds rewrite constraints to replace
`.Self` in, and we repeat forever. For this one we just stop replacing
.Self in the LHS of rewrite constraints. Since they are always against
.Self, we can always look in the access facet's type for a value.
While fixing ImplWitness access, also correct the lookup to search
through the types of nested ImplWitnessAccess instructions to find a
rewrite value, since it may find it at any level up to the eventual
`.Self`.
---------
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Any non-extend require decls must be satisfied when the impl definition
starts, but they are not checked. We only check for require decls in the
target interface being impld.
Implement the alias rules from proposal #5389, wherein an alias is
permitted so long as the target has a constant value. While that
proposal is not yet accepted, this seems like a reasonable basis for
further iteration, and will be useful for the examples we're currently
pursuing.
We were treating ImplWitnessAccess as a concrete type, but that is
incorrect if its accessing a symbolic type value. This results in
concrete impl lookup queries failing to match a generic impl that is
built with a symbolic ImplWitnessAccess in its type structure, when the
query does not have the equivalent ImplWitnessAccess in its own type
structure.
We need to look in the top level facet being accessed through
ImplWitnessAccess for witnesses, such as in `T:! Z where .Z1 impls Y`
where `T` provides the witness for `T.Z1 as Y`. But we also need to look
in the facet type of the ImplWitnessAccess for witnesses, such as in
`T:! Z` for `interface Z { let Z1:! Y }`, where `T.Z1` provides the
witness for `T.Z1 as Y`.
To support that we give TypeIterator an iteration step for
ImplWitnessAccess before recursing into it, like we do for FacetValue.
While doing this, we make TypeIterator more recursive, by making less
special casing around the step from one inst into the next. Instead of
eagerly finding a SymbolicType, we consistently recurse back into the
big switch statement and have it decide the next iteration step. This
allows it to recurse into instructions like ImplWitnessAccess and
FacetValue in a consistent manner.
Fixes mangling collisions when two thunks with the same name (eg, `Op`)
are created in the same context, which in turn would lead to LLVM
verifier failures and miscompiles.
To support this, add a new value store to track a little more
information about thunks beyond what's in the `Function`.
Avoid crashing on the fact that block scopes have no related InstId. So
we can't push the InstId of the current scope in the ImplIntroducer
node, as it can be None. Instead we have to find the parent InstId when
we're building the ImplDecl, because the ImplDecl has a node at the top
of the scope stack for the DeclNameStack.
Impls are allowed in sequential (non-declarative) scopes (functions,
blocks), but [redeclarations are not
allowed](https://github.com/carbon-language/carbon-lang/blob/db24042fe56d22275aa801696e2f8f5c4171e35b/proposals/p3763.md?plain=1#L279).
We now diagnose these redecls as invalid.
An `impl` decl in an impl file can refer only to things defined in the
api file, without the orphan rule rejecting it. If they are in different
scopes (such as one being in a class and one not), then they are treated
as separate `impl` decls. But if they have the same type structure, then
they fully overlap which is an error unless they are in a match_first
block.
This catches the overlap when two `impl` decls are in the same library
but are split between the api and the impl file of the library.
Previously we only diagnosed if they were in the same _file_ but now we
diagnose if they are in the same _library_.
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 enables thunking to work when the function has `ref` parameters,
without jumping through hoops to add `ref` tags in the desugared
function body.
This also renames `is_operator_syntax` to `is_desugared`, which is more
general and more accurate.
See
[here](https://docs.google.com/document/d/1rWcueFwIfZox6GKVGxiUG4cBzjrZ6djXiIDGyJDtrE4/edit?tab=t.0)
for the design doc.
This also removes the default value of the `result_type_inst_id`
parameter of `HandleAction`, moves it before the action in the parameter
list, and documents it. This solves two problems:
- The default made it easy to forget, leading to unnecessary
`TypeOfInst` instructions.
- When it was present, putting it after the fairly "bulky" action
argument tended to make the callsite harder to read.
This makes rewrites of a constraint that requires a generic `I(Self)`
work. The `Self` there is replaced in the identified facet type by the
impl-as self type. But the rewrite is for the interface `.I(.Self)`, so
they don't match. Once `.Self` is replaced with the impl-as self type,
then they match and the rewrite is applied.
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.
We were not copying named constraints in the base facet type over to the
result of the WhereExpr eval.
Add tests that cover this by doing `impl as Constraint where ...` with
rewrite contraints either in the impl-as or in the named constraint.
When the interface is generic, these tests fail (as TODOs). When the
impl is used in impl lookup, we crash (with TODOs in the tests).
Part of #6991.
- A function with a return declaration always has exactly one
`ReturnSlotPattern`, representing the whole return declaration (whereas
previously that was omitted for value and reference returns).
- The `ReturnSlotPattern` always has a subpattern with the same form.
`OutParamPattern` already plays that role for initializing forms, and
`TuplePattern` will play that role for tuple forms. This change
introduces `ValueReturnPattern` and `RefReturnPattern` to represent
value and reference return forms.
- As before, the `ReturnSlotPattern` has a corresponding `ReturnSlot`
that represents the output that is initialized by a `return` statement.
Its structure parallels the structure of the `ReturnSlotPattern`, so we
need `ValueReturn` and `RefReturn` insts that correspond to
`ValueReturnPattern` and `RefReturnPattern`.
This is a step toward supporting generic return forms, where the
`ReturnSlotPattern`'s subpattern may be an action: this change ensures
that evaluating the action for a specific form produces the same SemIR
as if the form were concrete to begin with. More speculatively, this
should simplify the implementation of `return` statements with compound
return forms.
---------
Co-authored-by: Chandler Carruth <chandlerc@gmail.com>
This makes them part of the identified facet type, and we can see the
constraints as part of stringify and format output.
But this does not do enough to make them useful yet: Any `T impls X`
constraint must contain a reference to `.Self` somewhere. And `.Self`
references do not get substituted, so neither `T(.Self) impls X` and `T
impls X(.Self)` will match against an incoming facet value derived from
an `impl T(U) as X` or `impl T as X(U)`, since `U` and `.Self` are never
the same thing until `.Self` can be substituted.
Now that impl lookup runs into facet values containing `.Self` (a
symbolic binding), such as in `C(.Self)`, we were crashing assuming the
type of `.Self` is a FacetType, but it can be `type` in the case of
`type where C(.Self) impls...`. Instead, use an empty facet type for the
type of `.Self` so it is always a facet. This assists with substituting
other facets into it, without having to insert an extra FacetAccessType.
`MakePeriodSelfFacetValue()` now enforces this requirement.
---------
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
The type must be complete to look for a witness for Destroy. Do this
check through type completion rather than just checking to see if the
ClassInfo says the definition is closed, since completing the type has
side effects (resolves the self specific definition).
Then look for whether the class is abstract through the CompleteTypeInfo
instead of just looking at the inheritance type on ClassInfo, like type
completion does.
Last, FacetTypes are trivially destroyed just like TypeType.
Fix some situations where we'd drop the storage argument when building
an in-place initializing expression. We now guarantee that an expression
with the in-place initializing category always has a storage argument.
This is only fixing the decision about *whether* to produce a witness.
Implementation of the witness is still a TODO, though where a body is
generated, it should also precisely reflect where one _needs_ to be
generated.
Note the tests:
- toolchain/lower/testdata/function/generic/import_core_witness.carbon
- toolchain/lower/testdata/function/generic/import_unused_def.carbon
These tests can probably be produced _without_ Core.Destroy, but I found
the essence of them while trying to build //examples with Core.Destroy
and a simpler minimization wasn't striking me.
Assisted-by: Google Antigravity with Gemini
---------
Co-authored-by: jonmeow <jperkins@google.com>
This will be used for const-evaling functions. Splitting into a separate
commit since it touches a lot of test files, and a couple fail_todo
tests are no longer failing.
Dana Jansens
Geoff Romer
Nicholas Bishop
Chandler Carruthandjosh11b
Jon Ross-Perkinsandjonmeow