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Add basic caller-side support for default values in check (#7800)

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Modifies the arity check to include a lower-bound for arguments.
Adds logic to pattern matching to supply default arguments for
missing parameters.
This commit is contained in:
Lucile Rose Nihlen
2026-09-22 22:07:35 +00:00
committed by GitHub
parent 795729bb4a
commit 53b7cfbaba
8 changed files with 508 additions and 159 deletions
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toolchain/check/call.cpp
+23 -10
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@@ -42,9 +42,13 @@ enum class EntityKind : uint8_t {
} // namespace
// Resolves the callee expression in a call to a specific callee, or diagnoses
// if no specific callee can be identified. This verifies the arity of the
// callee and determines any compile-time arguments, but doesn't check that the
// runtime arguments are convertible to the parameter types.
// if no specific callee can be identified. This determines any compile-time
// arguments, but doesn't check that the runtime arguments are convertible to
// the parameter types. It also verifies that the number of arguments is within
// the range [callee_arity - arity_lower_bound_margin, callee_arity]. This
// allows arity matching when the callee has default arguments for some
// subpatterns. In all other cases supply the default value `0` for exact arity
// checking.
//
// `self_id` and `arg_ids` are the self argument and explicit arguments in the
// call.
@@ -56,14 +60,21 @@ static auto ResolveCalleeInCall(Context& context, SemIR::LocId loc_id,
EntityKind entity_kind_for_diagnostic,
SemIR::SpecificId enclosing_specific_id,
SemIR::InstId self_id,
llvm::ArrayRef<SemIR::InstId> arg_ids)
llvm::ArrayRef<SemIR::InstId> arg_ids,
int32_t arity_lower_bound_margin = 0)
-> std::optional<SemIR::SpecificId> {
// Check that the arity matches the explicit arguments.
// Check that the arity exactly matches or is the upper bound of the explicit
// arguments.
auto param_patterns =
context.inst_blocks().GetOrEmpty(entity.param_patterns_id);
size_t expected_args_size =
param_patterns.size() - (self_id.has_value() ? 1 : 0);
if (arg_ids.size() != expected_args_size) {
CARBON_CHECK(static_cast<size_t>(arity_lower_bound_margin) <=
expected_args_size);
size_t size_lower_bound =
expected_args_size - static_cast<size_t>(arity_lower_bound_margin);
if (arg_ids.size() < size_lower_bound ||
arg_ids.size() > expected_args_size) {
CARBON_DIAGNOSTIC(CallArgCountMismatch, Error,
"{0} argument{0:s} passed to "
"{1:=0:function|=1:generic class|=2:generic "
@@ -219,11 +230,13 @@ auto PerformCallToFunction(Context& context, SemIR::LocId loc_id,
llvm::ArrayRef<SemIR::InstId> arg_ids,
bool is_desugared) -> SemIR::InstId {
// If the callee is a generic function, determine the generic argument values
// for the call.
// for the call. Also check the arity of the function against the arguments,
// with allowance for default argument values.
const auto& function = context.functions().Get(callee_function.function_id);
auto callee_specific_id = ResolveCalleeInCall(
context, loc_id, context.functions().Get(callee_function.function_id),
EntityKind::Function, callee_function.enclosing_specific_id,
callee_function.self_id, arg_ids);
context, loc_id, function, EntityKind::Function,
callee_function.enclosing_specific_id, callee_function.self_id, arg_ids,
function.default_value_arity);
if (!callee_specific_id) {
return SemIR::ErrorInst::InstId;
}