The instruction does act somewhat like a witness, saying that an impl
does exist for a lookup, but the instruction more concretely represents
an impl lookup - since that is done when it is evaluated.
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>
When transforming instructions with symbolic constant values into the
eval block, we previously special-cased `bind_symbolic_name` (and
`symbolic_binding_pattern`) because they are places where symbolicness
is introduced, rather than propagated from operands, and just copied
them into the eval block. However, `bind_symbolic_name` can be dependent
on other symbolic constants, because it can have a type that is
dependent. In this case, the copy in the eval block would not have its
type properly adjusted to refer to the type within the eval block.
Fix this by performing substitution into `bind_symbolic_name` rather
than copying it directly, and instead, detect cases where substitution
determined that the instruction was unchanged despite having a symbolic
constant value, and force it to be rebuilt in that case.
I've not found any way that the previous behavior actually caused
problems, or affected the observable behavior of the toolchain. The type
of these instructions in the eval block doesn't make much difference to
anything because they get immediately replaced by their corresponding
argument values when we run the eval block. But this came up and caused
some test output churn when I was making a different change, and it
seems like a fix to our representation even if it's not changing
behavior, so I'm splitting it out so it can be handled separately.
When a generic function declaration was encountered for the second or
more time, we would FinishGenericRedecl() for the function decl, but
this just popped the generic region stack and moved on.
The issue with that is when the stack entry is gone, we lose the
symbolic constants from that declaration, and are unable to rewrite them
to point to the actual generic. This left us with a function declaration
with abstract symbolic values that were not useful, and in a function
call we use the declaration attached to the definition, which would be a
declaration with broken symbolic values. Then the function would be
uncallable since deduce would be unable to determine argument types
without the generic bindings.
This resolves the issue for functions, as well as ensuring the correct
generic id from a previous declaration is used for other generic entity
types that have redeclarations.
When a function declaration is qualified, such as defining a class
method outside the class body, we need only the function declaration to
contribute to its generic region stack. The code was collecting constant
values from all qualifier segments together incorrectly.
So when we PushNameQualifierScope(), we also drop the current generic
region stack and rewrite its constant values by calling
FinishGenericRedecl(), and open a new stack entry for the next part of
the qualified declaration.
If a generic declaration somehow has more dependent instruction than a
previous declaration, it would add new instructions to its eval block
with indices beyond the elements in the actual declaration eval block,
since we only store the block from the first declaration found. To avoid
this we plumb through that we are in a redeclaration, and terminate with
an ICE instead of adding new instructions to crash on later.
Fixes#5136.
When the parameter is a deduced symbolic FacetValue, refering to a
BindSymbolicName, and the argument is a concrete FacetValue that would
match the FacetType requirements on the BindSymbolicName's type, we
currently do not deduce that the argument matches the parameter.
The argument is not _converted_ to the parameter type because they are
both FacetValues of the same FacetType type. However they are also not
equal constant values so the argument is not saved as a deduced match
for the parameter.
In order to accept the FacetValue, we need to consider them as
`deduce_through`, which attempts to deduce each of the fields in the
argument FacetValue against the fields in the parameter FacetValue.
This deduces that the argument's concrete type matches the symbolic
BindSymbolicName and its witnesses are the same.
Since the parameter is a FacetValue, its argument is not the type that
needs to be recorded as the deduced type for the binding. The
BindSymbolicName inside the parameter is the place that we need to find
the deduced type for the binding. So simply walking into the FacetValue
gets us to that position, where we eventually record the deduced
argument type as being the concrete type from the original argument
FacetValue.
Similarly, when determining what interfaces are satisfied by a
FacetValue for deduce, we want to use the full type available in the
FacetValue rather than just those from its FacetType. Determining
availability of interfaces here is equivalent to converting, and we want
converting a FacetValue to always work on the full available type info.
Only API access (member lookup) is restricted by a FacetValue to the
interfaces provided by its FacetType type.
---------
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
When performing a call through an impl witness, the callee that we
type-check against is the function in the interface, so we form a
specific for that callee. However, once the impl witness access
resolves, the eventual callee is a different function -- the function in
the impl -- so this would cause us to form a `SpecificFunction` where
the callee is one function but the specific refers to a different
function.
Address this by adding another instruction, `SpecificImplFunction`, that
takes a function in an impl and a specific for the corresponding
function in the interface, and computes and returns a `SpecificFunction`
referring to the corresponding specific function in the impl, or returns
a direct reference to the function in the `impl` if it's not a generic
function.
This flows out of #5084 and trying to reduce UnsafeMake use. It turns
out imports and namespaces were using unexpected node kinds (previously
ImportIntroducer instead of ImportDecl, for example). This fixes and
adds validation.
I was uncertain about whether to just remove the is_convertible check,
since I don't see it as motivating creation of a conversion between
NodeIdOneOf types. So I've just left a TODO for now.
According to approved syntax at
https://github.com/carbon-language/carbon-lang/blob/trunk/proposals/p3848.md#syntax-defined,
`fn F[]` without explicit parameters should be valid. This makes it
work, then adds some validation to prevent `class C[]` in check.
Note that for `fn`, positional parameters are a TODO -- but this allows
me to test validation in `fn destroy[]` which is rejected, not just a
TODO.
When converting to a facet there are three different failure modes:
1. You provided a non-type value. Only types can convert to facets. So
we tell you that we found a non-type value.
2. You provided a facet type (which has type TypeType) which does not
have witnesses for the the target facet's type. So we tell you that the
type `T` implements `X` but needs to implement `Y`.
2. You provided a (non-facet-type) concrete type (of type TypeType)
which does not implement the target facet's type (which is a FacetType).
So we tell you that we need the type to implement the FacetType but it
does not.
3. You provided a FacetAccessType (which is of type TypeType also, but
we special case this), whose underlying FacetType is not compatible with
the target facet's type. So we tell you that we need the type to
implement `X` but found a FacetAccessType `T` which implements `Y`.
Closes#5027
This changes the SemIR of invalid redeclarations, because previously
they lacked a name. We've avoided this in diagnostics so it doesn't
otherwise come up, but I plan to use it for more easily validating
redeclarations.
Currently this test fails with trying to access a comptime function with
runtime values:
```
fn F() {
let a: J = {} as J;
let b: J = {} as J;
// CHECK:STDERR: fail_bit_and_values_no_impl.carbon:[[@LINE+7]]:3: error: non-constant call to compile-time-only function [NonConstantCallToCompTimeOnlyFunction]
// CHECK:STDERR: a & b;
// CHECK:STDERR: ^~~~~
// CHECK:STDERR: core/prelude/operators/bitwise.carbon:96:3: note: compile-time-only function declared here [CompTimeOnlyFunctionHere]
// CHECK:STDERR: fn Op[self: Self](other: Self) -> Self = "type.and";
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
a & b;
}
```
The issue is that the BitAnd impl for facet types is matching on any
value of any type:
```
impl forall [T:! type] T as BitAnd
```
What we really want is for it to match on facet types (which are type
values), which is written as:
```
impl type as BitAnd
```
After this change, the error makes more sense in the above test:
```
fn F() {
let a: J = {} as J;
let b: J = {} as J;
// CHECK:STDERR: fail_bit_and_values_no_impl.carbon:[[@LINE+4]]:3: error: cannot access member of interface `Core.BitAnd` in type `J` that does not implement that interface [MissingImplInMemberAccess]
// CHECK:STDERR: a & b;
// CHECK:STDERR: ^~~~~
// CHECK:STDERR:
a & b;
}
```
This required allowing incomplete facet types where previously
completeness was required. Once we support named constraints, we will
need a way to consistently go from an interface to a facet type witness
index without requiring the interface to be complete in these cases.
---------
Co-authored-by: Josh L <josh11b@users.noreply.github.com>
When deduction has to substitute binding parameters into further generic
parameters, we do conversion of the argument to the substituted type.
Then we replace the argument instruction id with that Converted
instruction. This causes a redundant specific to be created for the
Converted instruction which is not needed. What we want is the specific
for its constant value.
So when we replace the argument instruction id, replace it with the
instruction from the constant value of the converted argument.
This was raised in [discord
#toolchain](https://discord.com/channels/655572317891461132/655578254970716160/1349067541070217306).
This makes inline and out-of-line functions produce the same type.
I was looking at this and wasn't sure if it was deliberate. It seems
desirable to reuse the type when possible, since it's probably cheaper
too.
A query facet type may contain multiple required interfaces, in which
case impl lookup should return an ImplWitness for an impl that is used
for each interface in the query. We bundle these together into an
instruction block and return that from impl lookup. The witnesses are in
the same order as the interfaces in the
`CompleteFacetType::required_interfaces`. This allows walking the
`required_interfaces` to find an interface to give an index that can
also be used to grab a witness from this set, or from FacetValue.
FacetValue now has an InstBlockId for the set of witnesses of the
FacetType, instead of a single ImplWitness instruction id.
FacetAccessWitness includes the index of the witness (determined from
the position in `required_interfaces`) of the witness it's accessing
from the FacetType.
The
toolchain/check/testdata/facet/no_prelude/fail_todo_call_combined_impl_witness.carbon
test demonstrates the fix in the resulting SemIR. We can see the calls
to methods on a multi-interface FacetType result in a FacetAccessWitness
with an index of the correct interface, and this results in a witness
that leads to the correct impl's function.
There is a TODO in member access, where it does not have a
`CompleteFacetType` yet, so it uses the index in
`FacetTypeInfo::impls_constraints` instead, but this can be incorrect in
the presence of named constraints, which when completed can add more
interfaces to the `CompleteFacetType` and which are sorted into an
arbitrary order with the rest there.
---------
Co-authored-by: josh11b <15258583+josh11b@users.noreply.github.com>
During SemIR, when identifying a specific in a specific context, we'd
have to either look through a specific or through a bound method.
Canonicalize which one to look through first, by having the BoundMethod
created around a SpecificFunction instead.
This changes a lot of check tests.
TODO: As the SemIr does not currently allow removal (access to insts()
is intentionally const), the bound instruction created prior to finding
the specific is not removed from the instructions.
Options: (1) leave as is, (2) add a way to remove the previous bound,
(3) rethink how/when the BoundMethod inst is created.
Implements the rule:
> For compound member access `a.(b)` where `b` names a _non-instance_
member of an interface `I`:
> * `a` is implicitly converted to `I`
> * let `T` be the result of symbolically evaluating the converted
expression
> * `impl` lookup is performed for `T as I`.
>
> Instance binding is never performed.
See
https://docs.carbon-lang.dev/docs/design/expressions/member_access.html#impl-lookup-for-compound-member-access.
Before this PR, non-instance members were treated as instance members.
---------
Co-authored-by: Josh L <josh11b@users.noreply.github.com>
- Explicitly document that `*Param` and `*ParamPattern` insts represent
`Call` parameters.
- Stop wrapping compile-time parameter patterns in `ValueParamPattern`
insts (because they aren't `Call` parameters).
- Document how `MatchContext::results_` relates to the `Call`
parameters, and be more consistent about when it's written to.
- Remove `RuntimeParamIndex::Unknown`: we no longer need to distinguish
"this `Param`'s runtime index is unknown" from "this `Param` isn't a
runtime param", because we no longer use `Param`s at all in the latter
case.
- Rename `RuntimeParamIndex` to `CallParamIndex`.
As a side effect of removing the `ValueParamPattern` insts, this fixes a
minor diagnostic bug where `NoteInitializingParam` didn't identify the
specific parameter that led to a deduction failure, because it expects
generic parameters to only be represented by `SymbolicBindingPattern`s,
but before this change they could be wrapped in `ValueParamPattern`s.
TODO to resolve whether it should conditionally say "object of"
depending on the category
---------
Co-authored-by: Josh L <josh11b@users.noreply.github.com>
Doing so results in TODOs in the resulting semir, since we don't handle
combining the facet types together properly or doing lookup into them.
There's a test added demonstrating this, which will be made to work in
followups.
---------
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
Replace the large and growing `TryEvalInstInContext` function with one
function per kind. While we still have special-case handling for a small
number of instruction kinds, most instructions are now handled either
fully automatically or use a common codepath that evaluates the
instruction operands and then performs an eval-context-independent
evaluation of the instruction.
To support this, `InstConstantKind` is expanded to describe more
fine-grained details about how each kind of instruction interacts with
constant evaluation. Also, the operand kinds of instructions become
slightly more fine-grained: we now distinguish between operands that
describe the destination of an initializing expression (`DestInstId`)
from other `InstId` operands, because `DestInstId` operands need
different treatment during constant evaluation. In particular, an
initializing expression can have a constant value even if its
destination is non-constant or has not yet been set, because evaluation
of an initializing expression doesn't include the store to the
destination.
Some minor test changes:
- We now more consistently propagate errors into the results of constant
evaluation, so more instructions that depend on errors have a constant
value of `<error>`.
- Diagnostic location for invalid array types now point at the whole
array type rather than the array index expression, because
`EvalConstantinst` doesn't have access to the original expression.
- Diagnostic for failed `RequireCompleteType` doesn't print the original
type any more because `EvalConstantInst` doesn't have access to the
original expression.
As a follow-up, some of this -- in particular, the `EvalConstantInst`
overloads -- will be moved to a separate file, in an effort to split the
overall constant evaluation machinery apart from the logic to evaluate
each individual kind of instruction.
An imported generic has bindings which are of type ImportRefLoaded, and
if they come from another package, they have no entity name attached to
them.
Since a binding name is always a constant-time value, we can get the
constant value instruction for the imported instruction to get a
canonical non-imported instruction. And that one will have a local
`NameId`.
---------
Co-authored-by: josh11b <15258583+josh11b@users.noreply.github.com>
Make facet types complete like other types. This means that in the body
of an interface, the type of `Self` is incomplete. This involved fixing
an issue where eval of a specific_id that was already canonical was not
resolving the specific declaration, which could occur as part of
substituting into a facet type.
---------
Co-authored-by: Josh L <josh11b@users.noreply.github.com>
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Co-authored-by: Dana Jansens <danakj@orodu.net>
Emit diagnostics for a function declared in a non-owning library, that
is not redeclared (or defined) in the owning library.
---------
Co-authored-by: jonmeow <jperkins@google.com>
In line with the proposal in #4682, this changes the array syntax to be
array(T, N). `array` is a builtin keyword which must be followed by
parens containing two expressions and a separating comma.
The array type expression is still fully builtin, it does not forward to
a Core.Array library type yet. It merely adds the `ArrayType`
instruction, as was done with the previous syntax.
Followup work will change the instruction to reference to Core.Array,
once the library type exists and can be used directly.
---------
Co-authored-by: zygoloid <richard@metafoo.co.uk>
Parameter lists need substantially different treatment than tuple
patterns in other contexts, so this change splits them into separate
parse node kinds.
---------
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
* Add `RequireCompleteFacetType` and `ResolveFacetTypeImplWitness` to
`check::Context`. Goal was to move code from `impl.cpp` (mostly) without
functional changes.
* Complete type information is cached with the facet type, and is stored
in a `complete_facet_types()` table.
* Main functional change is to diagnose attempts to use a rewrite
constraint on an associated function. Some existing diagnostics have
been updated.
* Remove `check::Context::RequireDefinedType`:
* For class types, use `RequireCompleteType`
* For facet types, use `RequireCompleteFacetType`
* Introduce a `SemIR::SpecificInterface` to hold an interface and
specific id pair.
* Keep the specific interface ids in the impl object.
* Avoid some extra copies in `Dump` functions.
* Future work missing from this PR:
* Resolving for member access or actions that require impl lookup.
* Resolving rewrites constraints that refer to non-concrete values.
* Any support for adding implied constraints that result from a `where`
clause (though TODOs have been added).
---------
Co-authored-by: Josh L <josh11b@users.noreply.github.com>
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Co-authored-by: Dana Jansens <danakj@orodu.net>
In order to have the name available for diagnostics, we now always set
`NameId` in `NameContext` and put `poisoning_loc_id` as part of the
union with `resolved_inst_id` instead (since we never need both).
Treat template bindings as introducing template phase, and propagate it
in the same way we propagate the checked generic phase.
Rename "symbolic" to "checked symbolic" to make room for "template
symbolic". Also rename "phase" to "dependence".
Currently it returns false which just ends typechecking. Instead handle
the error state later and avoid firing overlapping diagnostics in
'extend impl as'.
---------
Co-authored-by: josh11b <15258583+josh11b@users.noreply.github.com>
Change parse tree from `template (T:! type)` to `(template T):! type`,
so that we have information about whether a binding is a template
binding available when forming the representation of the binding
pattern. This incidentally fixes a bug that we would accept `template
addr A:! B` instead of the intended `addr template A:! B`.
Track whether a symbolic binding is a template binding on the
`EntityName` object. I'm borrowing a bit from the `CompileTimeBindIndex`
for this in order to avoid making `EntityName`s larger. Longer-term, we
should think about using a different representation for symbolic
bindings, to avoid including these fields in all `EntityName`s, but
that's out of scope for this change.
So far, template bindings are treated as having the same phase as
checked bindings, but that will change in a future PR.
When a function has a generic FacetType parameter, it can depend on
other FacetTypes bound as earlier parameters. To deduce the FacetValue,
we need to know the impl to attach to it, which requires knowing the
full type signature of the generic FacetType parameter. To do this,
after deducing other arguments to determine the value of non-generic
FacetType parameters, we substitute them sequentially into later
symbolic parameters to get their full facet types, then converts the
arguments to those full facet types to get the FacetValue. For example:
```
fn F(T: type, U: Interface(T));
```
Here the `T` binding is deduced to the be the caller's argument type.
But the Interface(T) can not be properly deduced to a FacetValue in the
first pass, and it will just be the caller's argument type directly.
After the first deduce pass, we will substitute the deduced T binding
into Interface(T), at which point the argument type can and will be
converted to a matching FacetValue as long as an impl can be found.
Closes#4868
This is based on PRs #4881 and #4863
---------
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Functions with positional parameters omit any implicit or explicit
parameter lists. This causes them to not have a pattern block, which
crashes if there is a return type that needs to add to the pattern
block.
Add a test covering this and handle it by having the ReturnTypeId
handler peek at the node stack and conditionally add the missing pattern
block. To do so it looks to see if the previous node is a
`IdentifierNameNotBeforeParams` which implies it was not expecting a
pattern (since there are no params) and thus the pattern block was not
added to the stack.
Note that lambdas also allow functions to omit an identifier, which will
need a pattern block on the stack for implicit parameters, explicit
parameters or a return type, without seeing any IdentifierName-like
parse nodes. To handle this, we will need to look for additional nodes
in the future and add the missing pattern block to the stack - possibly
for the FunctionInitializer, but the parse support needs to be created
for lambdas first.
AsCompatible changes a source instruction's type to a compatible type,
so it also needs its constant value to take on the compatible type.
Otherwise the type of the instruction and its constant value will
differ, which makes moving to the constant value into a lossy
transformation.
Part of #4868
For an expression such as `(Type as Interface).AssocFn()`, track the
`Self` type `Type` in the result of the member access so that it's
available when checking the function call.
This introduces a new kind of type, `ImplFunctionType`, that represents
the type of a function that is expected within an impl, modeled as the
type of the function within the interface plus a value to use as `Self`.
Calls to values of this type behave like calls to the underlying
function except that the `Self` parameter is pre-bound to the self type
from the facet.
In order to support this, fix an issue where the imported list of
generic bindings lost their association with their enclosing generic.
This adds a little complexity to `import_ref`, including a new recursive
cycle that I intend to address in a follow-up PR.
---------
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
Richard Smith
Dana Jansens
josh11bandJosh L
Alina Sbirlea
Geoff RomerandRichard Smith
Boaz Brickner