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Improve type substitution in ExportFunctionSpecializationToCpp (#7495)

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Instead of manually creating a map from symbolic types to concrete
types, create a Specific and look up parameter types via that Specific.

This allows C++ to call a Carbon function like `fn F[T: type](unused t:
T*) {}`. See generic_pointer.carbon.
This commit is contained in:
Nicholas Bishop
2026-07-13 21:11:31 +00:00
committed by GitHub
parent b6179ecbbb
commit 3d71858386
5 changed files with 66 additions and 51 deletions
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toolchain/check/cpp/export.cpp
+25 -30
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@@ -15,7 +15,9 @@
#include "toolchain/check/cpp/import.h"
#include "toolchain/check/cpp/location.h"
#include "toolchain/check/cpp/type_mapping.h"
#include "toolchain/check/facet_type.h"
#include "toolchain/check/function.h"
#include "toolchain/check/generic.h"
#include "toolchain/check/import_ref.h"
#include "toolchain/check/name_lookup.h"
#include "toolchain/check/pattern.h"
@@ -288,10 +290,14 @@ namespace {
struct FunctionInfo {
struct Param {
Param(Context& context, SemIR::InstId param_inst_id)
: type_id(ExtractScrutineeType(
: pattern_inst_id(param_inst_id),
type_id(ExtractScrutineeType(
context.sem_ir(), context.insts().Get(param_inst_id).type_id())),
kind(GetParamPatternKind(context, param_inst_id)) {}
// The parameter's pattern type.
SemIR::InstId pattern_inst_id;
// Type of the parameter's scrutinee.
SemIR::TypeId type_id;
@@ -810,9 +816,11 @@ auto ExportFunctionSpecializationToCpp(
// between specializations.
std::string extra_name;
// Create a mapping from Carbon generic parameters to the
// corresponding C++ type in `template_args`.
Map<SemIR::InstId, SemIR::TypeId> symbolic_to_actual;
// Map the `clang::TemplateArgument`s into Carbon types suitable for
// passing into `MakeSpecific`.
//
// Also initialize `extra_name`.
llvm::SmallVector<SemIR::InstId> specific_arg_ids;
for (auto [binding_inst_id, clang_template_arg] :
llvm::zip(bindings, template_args)) {
auto type_expr =
@@ -825,37 +833,24 @@ auto ExportFunctionSpecializationToCpp(
return false;
}
auto binding_const_inst_id =
context.constant_values().GetConstantInstId(binding_inst_id);
symbolic_to_actual.Insert(binding_const_inst_id, type_expr.type_id);
// TODO: this generates a pretty ugly name.
extra_name += std::string(llvm::formatv("{}", type_expr.inst_id));
auto binding_const_inst_id =
context.constant_values().GetConstantInstId(binding_inst_id);
specific_arg_ids.push_back(ConvertToValueOfType(
context, loc_id, type_expr.inst_id,
context.insts().Get(binding_const_inst_id).type_id()));
}
// Replace symbolic explicit parameters with a concrete Carbon type.
//
// This will only handle simple cases like `x: T`, and not things like
// `x: T*`. Ultimately what we should be doing here is producing a Specific
// for the generic function. See `fail_todo_generic_pointer.carbon`.
// Create a specific, and use that to convert from parameters with
// symbolic types to concrete types.
auto specific_id = MakeSpecific(context, loc_id, target.function.generic_id,
specific_arg_ids);
for (auto& param : target.explicit_params) {
auto param_type_inst_id = context.types().GetTypeInstId(param.type_id);
SemIR::InstId symbolic_inst_id = SemIR::InstId::None;
if (auto symbolic_binding =
context.insts().TryGetAs<SemIR::SymbolicBinding>(
param_type_inst_id)) {
symbolic_inst_id = param_type_inst_id;
} else if (auto facet_access_type =
context.insts().TryGetAs<SemIR::FacetAccessType>(
param_type_inst_id)) {
symbolic_inst_id = facet_access_type->facet_value_inst_id;
}
if (symbolic_inst_id.has_value()) {
if (auto lookup = symbolic_to_actual.Lookup(symbolic_inst_id)) {
param.type_id = lookup.value();
}
}
param.type_id =
GetScrutineeTypeInSpecific(context, param.pattern_inst_id, specific_id);
}
// TODO: handle generic return type.