carbon-lang/toolchain/check/class.cpp

// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#include "toolchain/check/class.h"

#include "toolchain/check/context.h"
#include "toolchain/check/convert.h"
#include "toolchain/check/cpp/export.h"
#include "toolchain/check/eval.h"
#include "toolchain/check/function.h"
#include "toolchain/check/generic.h"
#include "toolchain/check/impl.h"
#include "toolchain/check/import_ref.h"
#include "toolchain/check/inst.h"
#include "toolchain/check/name_lookup.h"
#include "toolchain/check/pattern.h"
#include "toolchain/check/pattern_match.h"
#include "toolchain/check/thunk.h"
#include "toolchain/check/type.h"
#include "toolchain/diagnostics/format_providers.h"
#include "toolchain/parse/node_ids.h"
#include "toolchain/sem_ir/builtin_function_kind.h"
#include "toolchain/sem_ir/function.h"
#include "toolchain/sem_ir/ids.h"
#include "toolchain/sem_ir/typed_insts.h"

namespace Carbon::Check {

auto SetClassSelfType(Context& context, SemIR::ClassId class_id) -> void {
  auto& class_info = context.classes().Get(class_id);
  auto specific_id = context.generics().GetSelfSpecific(class_info.generic_id);
  class_info.self_type_id = GetClassType(context, class_id, specific_id);
}

auto StartClassDefinition(Context& context, SemIR::Class& class_info,
                          SemIR::InstId definition_id) -> void {
  // Track that this declaration is the definition.
  CARBON_CHECK(!class_info.has_definition_started());
  class_info.definition_id = definition_id;
  class_info.scope_id = context.name_scopes().Add(
      definition_id, SemIR::NameId::None, class_info.parent_scope_id);

  // Introduce `Self`.
  auto self_type_inst_id =
      context.types().GetTypeInstId(class_info.self_type_id);
  context.name_scopes().AddRequiredName(
      class_info.scope_id, SemIR::NameId::SelfType, self_type_inst_id);
  context.name_scopes()
      .Get(class_info.scope_id)
      .set_self_type_id(self_type_inst_id);
}

// Checks that the specified finished adapter definition is valid and builds and
// returns a corresponding complete type witness instruction.
static auto CheckCompleteAdapterClassType(
    Context& context, Parse::NodeId node_id, SemIR::ClassId class_id,
    llvm::ArrayRef<SemIR::InstId> field_decls,
    llvm::ArrayRef<SemIR::InstId> body) -> SemIR::InstId {
  const auto& class_info = context.classes().Get(class_id);
  if (class_info.base_id.has_value()) {
    CARBON_DIAGNOSTIC(AdaptWithBase, Error, "adapter with base class");
    CARBON_DIAGNOSTIC(AdaptWithBaseHere, Note, "`base` declaration is here");
    context.emitter()
        .Build(class_info.adapt_id, AdaptWithBase)
        .Note(class_info.base_id, AdaptWithBaseHere)
        .Emit();
    return SemIR::ErrorInst::InstId;
  }

  if (!field_decls.empty()) {
    CARBON_DIAGNOSTIC(AdaptWithFields, Error, "adapter with fields");
    CARBON_DIAGNOSTIC(AdaptWithFieldHere, Note,
                      "first field declaration is here");
    context.emitter()
        .Build(class_info.adapt_id, AdaptWithFields)
        .Note(field_decls.front(), AdaptWithFieldHere)
        .Emit();
    return SemIR::ErrorInst::InstId;
  }

  for (auto inst_id : body) {
    if (auto function_decl =
            context.insts().TryGetAs<SemIR::FunctionDecl>(inst_id)) {
      auto& function = context.functions().Get(function_decl->function_id);
      if (function.virtual_modifier ==
          SemIR::Function::VirtualModifier::Virtual) {
        CARBON_DIAGNOSTIC(AdaptWithVirtual, Error,
                          "adapter with virtual function");
        CARBON_DIAGNOSTIC(AdaptWithVirtualHere, Note,
                          "first virtual function declaration is here");
        context.emitter()
            .Build(class_info.adapt_id, AdaptWithVirtual)
            .Note(inst_id, AdaptWithVirtualHere)
            .Emit();
        return SemIR::ErrorInst::InstId;
      }
    }
  }

  // The object representation of the adapter is the object representation
  // of the adapted type.
  auto adapted_type_id =
      class_info.GetAdaptedType(context.sem_ir(), SemIR::SpecificId::None);
  auto object_repr_id = context.types().GetObjectRepr(adapted_type_id);

  return AddInst<SemIR::CompleteTypeWitness>(
      context, node_id,
      {.type_id = GetSingletonType(context, SemIR::WitnessType::TypeInstId),
       // TODO: Use InstId from the adapt declaration.
       .object_repr_type_inst_id =
           context.types().GetTypeInstId(object_repr_id)});
}

static auto AddStructTypeFields(
    Context& context,
    llvm::SmallVector<SemIR::StructTypeField>& struct_type_fields,
    llvm::ArrayRef<SemIR::InstId> field_decls) -> SemIR::StructTypeFieldsId {
  for (auto field_decl_id : field_decls) {
    auto field_decl = context.insts().GetAs<SemIR::FieldDecl>(field_decl_id);
    auto& field = context.fields().Get(field_decl.field_id);
    field.index =
        SemIR::ElementIndex{static_cast<int>(struct_type_fields.size())};
    if (field_decl.type_id == SemIR::ErrorInst::TypeId) {
      struct_type_fields.push_back(
          {.name_id = field.name_id,
           .type_inst_id = SemIR::ErrorInst::TypeInstId});
      continue;
    }
    auto unbound_element_type =
        context.sem_ir().types().GetAs<SemIR::UnboundElementType>(
            field_decl.type_id);
    struct_type_fields.push_back(
        {.name_id = field.name_id,
         .type_inst_id = unbound_element_type.element_type_inst_id});
  }
  auto fields_id =
      context.struct_type_fields().AddCanonical(struct_type_fields);
  return fields_id;
}

// Result of comparing a virtual function in a base class with a potential
// overrider in a derived class.
enum class OverrideMatchResult : uint8_t {
  // The functions match.
  Match,
  // The potential overrider is not marked `override`.
  NotAnOverride,
  // The names do not match.
  NameMismatch,
  // The arity (number of explicit parameters) does not match.
  ArityMismatch,
};

// Compares a virtual function in a base class with a potential overrider in a
// derived class.
static auto CompareVirtualWithOverrider(const SemIR::Function& base_fn,
                                        const SemIR::Function& derived_fn)
    -> OverrideMatchResult {
  if (derived_fn.virtual_modifier !=
      SemIR::FunctionFields::VirtualModifier::Override) {
    return OverrideMatchResult::NotAnOverride;
  }
  if (derived_fn.name_id != base_fn.name_id) {
    return OverrideMatchResult::NameMismatch;
  }
  if (derived_fn.call_param_ranges.explicit_size() !=
      base_fn.call_param_ranges.explicit_size()) {
    return OverrideMatchResult::ArityMismatch;
  }
  // TODO: We should check more thoroughly for compatibility between the two
  // functions here, so that we can determine which function is being overridden
  // if the base function is in a C++ overload set.
  return OverrideMatchResult::Match;
}

// Builds and returns a vtable for the current class. Assumes that the virtual
// functions for the class are listed as the top element of the `vtable_stack`.
static auto BuildVtable(Context& context, Parse::ClassDefinitionId node_id,
                        SemIR::ClassId class_id,
                        std::optional<SemIR::ClassType> base_class_type,
                        llvm::ArrayRef<SemIR::InstId> vtable_contents)
    -> SemIR::VtableId {
  auto base_vtable_id = SemIR::VtableId::None;
  auto base_class_specific_id = SemIR::SpecificId::None;

  // Get some base class/type/specific info.
  if (base_class_type) {
    auto& base_class_info = context.classes().Get(base_class_type->class_id);
    auto base_vtable_decl_inst_id = base_class_info.vtable_decl_id;
    if (base_vtable_decl_inst_id.has_value()) {
      LoadImportRef(context, base_vtable_decl_inst_id);
      auto canonical_base_vtable_inst_id =
          context.constant_values().GetConstantInstId(base_vtable_decl_inst_id);
      const auto& base_vtable_decl_inst =
          context.insts().GetAs<SemIR::VtableDecl>(
              canonical_base_vtable_inst_id);
      base_vtable_id = base_vtable_decl_inst.vtable_id;
      base_class_specific_id = base_class_type->specific_id;
    }
  }

  const auto& class_info = context.classes().Get(class_id);
  auto class_generic_id = class_info.generic_id;

  // Wrap vtable entries in SpecificFunctions as needed/in generic classes.
  auto build_specific_function =
      [&](SemIR::InstId fn_decl_id) -> SemIR::InstId {
    if (!class_generic_id.has_value()) {
      return fn_decl_id;
    }
    const auto& fn_decl =
        context.insts().GetAs<SemIR::FunctionDecl>(fn_decl_id);
    const auto& function = context.functions().Get(fn_decl.function_id);
    return GetOrAddInst<SemIR::SpecificFunction>(
        context, node_id,
        {.type_id =
             GetSingletonType(context, SemIR::SpecificFunctionType::TypeInstId),
         .callee_id = fn_decl_id,
         .specific_id =
             context.generics().GetSelfSpecific(function.generic_id)});
  };

  llvm::SmallVector<SemIR::InstId> vtable;
  Set<SemIR::FunctionId, 16> implemented_impls;
  bool carbon_native_vtable = true;

  // Add vtable entries from the base class, updating them to point to a derived
  // class overrider if there is one.
  if (base_vtable_id.has_value()) {
    const auto& base_vtable = context.vtables().Get(base_vtable_id);
    carbon_native_vtable = base_vtable.carbon_native_vtable;
    auto base_vtable_inst_block =
        context.inst_blocks().Get(base_vtable.virtual_functions_id);
    // TODO: Avoid quadratic search. Perhaps build a map from `NameId` to the
    // elements of the top of `vtable_stack`.
    for (auto base_vtable_entry_id : base_vtable_inst_block) {
      if (!base_vtable_entry_id.has_value()) {
        // Foreign vtables may have holes in them for information that we don't
        // use. Just skip those entries.
        CARBON_CHECK(
            !context.vtables().Get(base_vtable_id).carbon_native_vtable);
        vtable.push_back(SemIR::InstId::None);
        continue;
      }

      auto [derived_vtable_entry_id, derived_vtable_entry_const_id, fn_id,
            specific_id] =
          DecomposeVirtualFunction(context.sem_ir(), base_vtable_entry_id,
                                   base_class_specific_id);
      const auto& fn = context.sem_ir().functions().Get(fn_id);
      const auto* i = llvm::find_if(
          vtable_contents, [&](SemIR::InstId override_fn_decl_id) -> bool {
            const auto& override_fn = context.functions().Get(
                context.insts()
                    .GetAs<SemIR::FunctionDecl>(override_fn_decl_id)
                    .function_id);
            return CompareVirtualWithOverrider(fn, override_fn) ==
                   OverrideMatchResult::Match;
          });
      if (i != vtable_contents.end()) {
        auto override_fn_id =
            context.insts().GetAs<SemIR::FunctionDecl>(*i).function_id;
        implemented_impls.Insert(override_fn_id);

        // TODO: When the base class is a C++ class, we could have multiple
        // potential functions to override. Check against each of them rather
        // than trying to override them all.
        auto override_or_thunk_id =
            BuildThunk(context, fn_id, specific_id, class_info.self_type_id, *i,
                       /*defer_definition=*/true);
        if (override_or_thunk_id != SemIR::ErrorInst::InstId) {
          auto override_or_thunk_fn_id =
              context.insts()
                  .GetAs<SemIR::FunctionDecl>(override_or_thunk_id)
                  .function_id;
          auto& override_or_thunk_fn =
              context.functions().Get(override_or_thunk_fn_id);
          derived_vtable_entry_id =
              build_specific_function(override_or_thunk_id);
          override_or_thunk_fn.virtual_index = vtable.size();
          CARBON_CHECK(override_or_thunk_fn.virtual_index == fn.virtual_index);
        }
      } else if (auto base_vtable_specific_function =
                     context.insts().TryGetAs<SemIR::SpecificFunction>(
                         derived_vtable_entry_id)) {
        if (derived_vtable_entry_const_id.is_symbolic()) {
          // Create a new instruction here that is otherwise identical to
          // `derived_vtable_entry_id` but is dependent within the derived
          // class. This ensures we can `GetConstantValueInSpecific` for it
          // with the derived class's specific (when forming further derived
          // classes, lowering the vtable, etc).
          derived_vtable_entry_id = GetOrAddInst<SemIR::SpecificFunction>(
              context, node_id,
              {.type_id = GetSingletonType(
                   context, SemIR::SpecificFunctionType::TypeInstId),
               .callee_id = base_vtable_specific_function->callee_id,
               .specific_id = base_vtable_specific_function->specific_id});
        }
      }
      vtable.push_back(derived_vtable_entry_id);
    }
  }

  // Add any remaining virtual functions from the derived class to the vtable,
  // and diagnose any `override fn`s that didn't override anything.
  for (auto inst_id : vtable_contents) {
    auto fn_decl = context.insts().GetAs<SemIR::FunctionDecl>(inst_id);
    auto& fn = context.functions().Get(fn_decl.function_id);
    if (fn.virtual_modifier !=
        SemIR::FunctionFields::VirtualModifier::Override) {
      fn.virtual_index = vtable.size();
      vtable.push_back(build_specific_function(inst_id));
    } else if (!implemented_impls.Lookup(fn_decl.function_id)) {
      CARBON_DIAGNOSTIC(OverrideWithoutVirtualInBase, Error,
                        "override without compatible virtual in base class");
      CARBON_DIAGNOSTIC(OverrideCandidateArityMismatch, Note,
                        "base class function has {2:more|fewer} parameters "
                        "({0} vs {1} excluding `self`)",
                        Diagnostics::IntAsSelect, Diagnostics::IntAsSelect,
                        Diagnostics::BoolAsSelect);
      auto builder = context.emitter().Build(SemIR::LocId(inst_id),
                                             OverrideWithoutVirtualInBase);
      if (base_vtable_id.has_value()) {
        const auto& base_vtable = context.vtables().Get(base_vtable_id);
        auto base_vtable_inst_block =
            context.inst_blocks().Get(base_vtable.virtual_functions_id);
        for (auto base_vtable_entry_id : base_vtable_inst_block) {
          if (!base_vtable_entry_id.has_value()) {
            continue;
          }
          auto [derived_vtable_entry_id, derived_vtable_entry_const_id, fn_id,
                specific_id] =
              DecomposeVirtualFunction(context.sem_ir(), base_vtable_entry_id,
                                       base_class_specific_id);
          const auto& base_fn = context.sem_ir().functions().Get(fn_id);
          switch (CompareVirtualWithOverrider(base_fn, fn)) {
            case OverrideMatchResult::ArityMismatch:
              builder.Note(base_fn.first_owning_decl_id,
                           OverrideCandidateArityMismatch,
                           base_fn.call_param_ranges.explicit_size() - 1,
                           fn.call_param_ranges.explicit_size() - 1,
                           base_fn.call_param_ranges.explicit_size() >
                               fn.call_param_ranges.explicit_size());
              break;
            case OverrideMatchResult::NameMismatch:
              // TODO: If the name is similar enough and the overrider otherwise
              // matches, emit a note about the potential misspelling.
              break;
            case OverrideMatchResult::Match:
              CARBON_FATAL("Unexpectedly found a matching overrider");
            case OverrideMatchResult::NotAnOverride:
              CARBON_FATAL("Should only consider `override fn`s here");
          }
        }
      }
      builder.Emit();
    }
  }

  return context.vtables().Add(
      {{.class_id = class_id,
        .virtual_functions_id = context.inst_blocks().Add(vtable),
        .carbon_native_vtable = carbon_native_vtable}});
}

// Checks that the specified finished class definition is valid and builds and
// returns a corresponding complete type witness instruction.
static auto CheckCompleteClassType(
    Context& context, Parse::ClassDefinitionId node_id, SemIR::ClassId class_id,
    llvm::ArrayRef<SemIR::InstId> field_decls,
    llvm::ArrayRef<SemIR::InstId> vtable_contents,
    llvm::ArrayRef<SemIR::InstId> body) -> SemIR::InstId {
  auto& class_info = context.classes().Get(class_id);
  if (class_info.adapt_id.has_value()) {
    return CheckCompleteAdapterClassType(context, node_id, class_id,
                                         field_decls, body);
  }

  bool defining_vptr = class_info.is_dynamic;
  auto base_type_id =
      class_info.GetBaseType(context.sem_ir(), SemIR::SpecificId::None);
  // TODO: Use InstId from base declaration.
  auto base_type_inst_id = context.types().GetTypeInstId(base_type_id);
  std::optional<SemIR::ClassType> base_class_type;
  if (base_type_id.has_value()) {
    // TODO: If the base class is template dependent, we will need to decide
    // whether to add a vptr as part of instantiation.
    base_class_type = context.types().TryGetAs<SemIR::ClassType>(base_type_id);
    if (base_class_type &&
        context.classes().Get(base_class_type->class_id).is_dynamic) {
      defining_vptr = false;
    }
  }

  llvm::SmallVector<SemIR::StructTypeField> struct_type_fields;
  struct_type_fields.reserve(defining_vptr + class_info.base_id.has_value() +
                             field_decls.size());
  if (defining_vptr) {
    struct_type_fields.push_back(
        {.name_id = SemIR::NameId::Vptr,
         .type_inst_id = context.types().GetTypeInstId(
             GetPointerType(context, SemIR::VtableType::TypeInstId))});
  }
  if (base_type_id.has_value()) {
    auto base_decl = context.insts().GetAs<SemIR::BaseDecl>(class_info.base_id);
    base_decl.index =
        SemIR::ElementIndex{static_cast<int>(struct_type_fields.size())};
    ReplaceInstPreservingConstantValue(context, class_info.base_id, base_decl);
    struct_type_fields.push_back(
        {.name_id = SemIR::NameId::Base, .type_inst_id = base_type_inst_id});
  }

  if (class_info.is_dynamic) {
    auto vtable_id = BuildVtable(context, node_id, class_id, base_class_type,
                                 vtable_contents);
    auto vptr_type_id = GetPointerType(context, SemIR::VtableType::TypeInstId);
    class_info.vtable_decl_id = AddInst<SemIR::VtableDecl>(
        context, node_id, {.type_id = vptr_type_id, .vtable_id = vtable_id});
  }

  auto struct_type_id = GetStructType(
      context, AddStructTypeFields(context, struct_type_fields, field_decls));

  return AddInst<SemIR::CompleteTypeWitness>(
      context, node_id,
      {.type_id = GetSingletonType(context, SemIR::WitnessType::TypeInstId),
       .object_repr_type_inst_id =
           context.types().GetTypeInstId(struct_type_id)});
}

auto ComputeClassObjectRepr(Context& context, Parse::ClassDefinitionId node_id,
                            SemIR::ClassId class_id,
                            llvm::ArrayRef<SemIR::InstId> field_decls,
                            llvm::ArrayRef<SemIR::InstId> vtable_contents,
                            llvm::ArrayRef<SemIR::InstId> body) -> void {
  auto complete_type_witness_id = CheckCompleteClassType(
      context, node_id, class_id, field_decls, vtable_contents, body);
  auto& class_info = context.classes().Get(class_id);
  class_info.complete_type_witness_id = complete_type_witness_id;
}

auto InNonStaticFieldDecl(Context& context) -> bool {
  return context.full_pattern_stack().IsCurrentKindClassScopeVarDecl() &&
         !context.decl_introducer_state_stack()
              .innermost()
              .modifier_set.HasAnyOf(KeywordModifierSet::Static);
}

auto InStaticClassScopeVar(Context& context) -> bool {
  return context.full_pattern_stack().IsCurrentKindClassScopeVarDecl() &&
         context.decl_introducer_state_stack()
             .innermost()
             .modifier_set.HasAnyOf(KeywordModifierSet::Static);
}

}  // namespace Carbon::Check