carbon-lang/toolchain/semantics/semantics_parse_tree_handler.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/semantics/semantics_parse_tree_handler.h"

#include "common/vlog.h"
#include "llvm/Support/PrettyStackTrace.h"
#include "toolchain/lexer/token_kind.h"
#include "toolchain/lexer/tokenized_buffer.h"
#include "toolchain/parser/parse_node_kind.h"
#include "toolchain/semantics/semantics_builtin_kind.h"
#include "toolchain/semantics/semantics_node.h"

namespace Carbon {

class SemanticsParseTreeHandler::PrettyStackTraceNodeStack
    : public llvm::PrettyStackTraceEntry {
 public:
  explicit PrettyStackTraceNodeStack(const SemanticsParseTreeHandler* handler)
      : handler_(handler) {}
  ~PrettyStackTraceNodeStack() override = default;

  auto print(llvm::raw_ostream& output) const -> void override {
    output << "node_stack_:\n";
    for (int i = 0; i < static_cast<int>(handler_->node_stack_.size()); ++i) {
      const auto& entry = handler_->node_stack_[i];
      output << "\t" << i << ".\t"
             << handler_->parse_tree_->node_kind(entry.parse_node);
      if (entry.result_id.is_valid()) {
        output << " -> " << entry.result_id;
      }
      output << "\n";
    }
  }

 private:
  const SemanticsParseTreeHandler* handler_;
};

class SemanticsParseTreeHandler::PrettyStackTraceNodeBlockStack
    : public llvm::PrettyStackTraceEntry {
 public:
  explicit PrettyStackTraceNodeBlockStack(
      const SemanticsParseTreeHandler* handler)
      : handler_(handler) {}
  ~PrettyStackTraceNodeBlockStack() override = default;

  auto print(llvm::raw_ostream& output) const -> void override {
    output << "node_block_stack_:\n";
    for (int i = 0; i < static_cast<int>(handler_->node_block_stack_.size());
         ++i) {
      const auto& entry = handler_->node_block_stack_[i];
      output << "\t" << i << ".\t" << entry << "\n";
    }
  }

 private:
  const SemanticsParseTreeHandler* handler_;
};

auto SemanticsParseTreeHandler::Build() -> void {
  PrettyStackTraceNodeStack pretty_node_stack(this);
  PrettyStackTraceNodeBlockStack pretty_node_block_stack(this);

  // Add a block for the ParseTree.
  node_block_stack_.push_back(semantics_->AddNodeBlock());

  for (auto parse_node : parse_tree_->postorder()) {
    switch (auto parse_kind = parse_tree_->node_kind(parse_node)) {
#define CARBON_PARSE_NODE_KIND(Name) \
  case ParseNodeKind::Name(): {      \
    Handle##Name(parse_node);        \
    break;                           \
  }
#include "toolchain/parser/parse_node_kind.def"
    }
  }
}

auto SemanticsParseTreeHandler::AddNode(SemanticsNode node) -> SemanticsNodeId {
  CARBON_VLOG() << "AddNode " << node_block_stack_.back() << ": " << node
                << "\n";
  return semantics_->AddNode(node_block_stack_.back(), node);
}

auto SemanticsParseTreeHandler::Push(ParseTree::Node parse_node) -> void {
  CARBON_VLOG() << "Push " << node_stack_.size() << ": "
                << parse_tree_->node_kind(parse_node) << "\n";
  CARBON_CHECK(node_stack_.size() < (1 << 20))
      << "Excessive stack size: likely infinite loop";
  node_stack_.push_back({parse_node, SemanticsNodeId::MakeInvalid()});
}

auto SemanticsParseTreeHandler::Push(ParseTree::Node parse_node,
                                     SemanticsNode node) -> void {
  CARBON_VLOG() << "Push " << node_stack_.size() << ": "
                << parse_tree_->node_kind(parse_node) << " -> " << node.kind()
                << "\n";
  CARBON_CHECK(node_stack_.size() < (1 << 20))
      << "Excessive stack size: likely infinite loop";
  auto node_id = AddNode(node);
  node_stack_.push_back({parse_node, node_id});
}

auto SemanticsParseTreeHandler::Push(ParseTree::Node parse_node,
                                     SemanticsNodeId node_id) -> void {
  CARBON_VLOG() << "Push " << node_stack_.size() << ": "
                << parse_tree_->node_kind(parse_node) << " -> " << node_id
                << "\n";
  CARBON_CHECK(node_stack_.size() < (1 << 20))
      << "Excessive stack size: likely infinite loop";
  node_stack_.push_back({parse_node, node_id});
}

auto SemanticsParseTreeHandler::Pop(ParseNodeKind pop_parse_kind) -> void {
  auto back = node_stack_.pop_back_val();
  auto parse_kind = parse_tree_->node_kind(back.parse_node);
  CARBON_VLOG() << "Pop " << node_stack_.size() << ": " << pop_parse_kind
                << "\n";
  CARBON_CHECK(parse_kind == pop_parse_kind)
      << "Expected " << pop_parse_kind << ", found " << parse_kind;
  CARBON_CHECK(!back.result_id.is_valid())
      << "Expected no result ID on " << parse_kind << ", was "
      << back.result_id;
}

auto SemanticsParseTreeHandler::PopWithResult() -> SemanticsNodeId {
  auto back = node_stack_.pop_back_val();
  auto node_id = back.result_id;
  CARBON_VLOG() << "Pop " << node_stack_.size() << ": any ("
                << parse_tree_->node_kind(back.parse_node) << ") -> " << node_id
                << "\n";
  CARBON_CHECK(node_id.is_valid())
      << "Invalid PopWithResult on " << parse_tree_->node_kind(back.parse_node);
  return node_id;
}

auto SemanticsParseTreeHandler::PopWithResult(ParseNodeKind pop_parse_kind)
    -> SemanticsNodeId {
  auto back = node_stack_.pop_back_val();
  auto parse_kind = parse_tree_->node_kind(back.parse_node);
  auto node_id = back.result_id;
  CARBON_VLOG() << "Pop " << node_stack_.size() << ": " << pop_parse_kind
                << ") -> " << node_id << "\n";
  CARBON_CHECK(parse_kind == pop_parse_kind)
      << "Expected " << pop_parse_kind << ", found " << parse_kind;
  CARBON_CHECK(node_id.is_valid())
      << "Invalid PopWithResult with " << parse_kind;
  return node_id;
}

auto SemanticsParseTreeHandler::PopWithResultIf(ParseNodeKind pop_parse_kind)
    -> std::optional<SemanticsNodeId> {
  auto parse_kind = parse_tree_->node_kind(node_stack_.back().parse_node);
  if (parse_kind != pop_parse_kind) {
    return std::nullopt;
  }

  auto back = node_stack_.pop_back_val();
  auto node_id = back.result_id;
  CARBON_VLOG() << "Pop " << node_stack_.size() << ": " << pop_parse_kind
                << ") -> " << node_id << "\n";
  CARBON_CHECK(node_id.is_valid())
      << "Invalid PopWithResult with " << parse_kind;
  return node_id;
}

auto SemanticsParseTreeHandler::TryTypeConversion(ParseTree::Node parse_node,
                                                  SemanticsNodeId lhs_id,
                                                  SemanticsNodeId rhs_id,
                                                  bool /*can_convert_lhs*/)
    -> SemanticsNodeId {
  auto block = node_block_stack_.back();
  auto lhs_type = semantics_->GetType(block, lhs_id);
  auto rhs_type = semantics_->GetType(block, rhs_id);
  // TODO: This should attempt a type conversion, but there's not enough
  // implemented to do that right now.
  if (lhs_type != rhs_type) {
    auto invalid_type = SemanticsNodeId::MakeBuiltinReference(
        SemanticsBuiltinKind::InvalidType());
    if (lhs_type != invalid_type && rhs_type != invalid_type) {
      // TODO: This is a poor diagnostic, and should be expanded.
      CARBON_DIAGNOSTIC(TypeMismatch, Error, "Type mismatch");
      emitter_->Emit(parse_tree_->node_token(parse_node), TypeMismatch);
    }
    return invalid_type;
  }
  return lhs_type;
}

auto SemanticsParseTreeHandler::AddIdentifier(ParseTree::Node decl_node)
    -> SemanticsIdentifierId {
  CARBON_CHECK(parse_tree_->node_kind(decl_node) ==
               ParseNodeKind::DeclaredName())
      << parse_tree_->node_kind(decl_node);
  auto text = parse_tree_->GetNodeText(decl_node);
  return semantics_->AddIdentifier(text);
}

auto SemanticsParseTreeHandler::HandleBreakStatement(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleBreakStatementStart(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleCallExpression(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleCallExpressionComma(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleCallExpressionStart(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleCodeBlock(ParseTree::Node /*parse_node*/)
    -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleCodeBlockStart(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleContinueStatement(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleContinueStatementStart(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleDeclaredName(ParseTree::Node parse_node)
    -> void {
  // The parent is responsible for binding the name.
  Push(parse_node);
}

auto SemanticsParseTreeHandler::HandleDesignatedName(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleDesignatorExpression(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleEmptyDeclaration(
    ParseTree::Node parse_node) -> void {
  // Empty declarations have no actions associated, but we still balance the
  // tree.
  Push(parse_node);
}

auto SemanticsParseTreeHandler::HandleExpressionStatement(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleFileEnd(ParseTree::Node /*parse_node*/)
    -> void {
  CARBON_CHECK(node_block_stack_.size() == 1) << node_block_stack_.size();
}

auto SemanticsParseTreeHandler::HandleForHeader(ParseTree::Node /*parse_node*/)
    -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleForHeaderStart(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleForIn(ParseTree::Node /*parse_node*/)
    -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleForStatement(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleFunctionDeclaration(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleFunctionDefinition(
    ParseTree::Node parse_node) -> void {
  // Merges code block children up under the FunctionDefinitionStart.
  while (parse_tree_->node_kind(node_stack_.back().parse_node) !=
         ParseNodeKind::FunctionDefinitionStart()) {
    node_stack_.pop_back();
  }
  Pop(ParseNodeKind::FunctionDefinitionStart());
  node_block_stack_.pop_back();
  Push(parse_node);
}

auto SemanticsParseTreeHandler::HandleFunctionDefinitionStart(
    ParseTree::Node parse_node) -> void {
  Pop(ParseNodeKind::ParameterList());
  auto name_node = node_stack_.back().parse_node;
  auto name = AddIdentifier(name_node);
  node_stack_.pop_back();
  auto fn_node = node_stack_.back().parse_node;
  Pop(ParseNodeKind::FunctionIntroducer());

  auto decl_id = AddNode(SemanticsNode::MakeFunctionDeclaration(fn_node));
  // TODO: Propagate the type of the function.
  AddNode(SemanticsNode::MakeBindName(name_node, SemanticsNodeId::MakeInvalid(),
                                      name, decl_id));
  auto block_id = semantics_->AddNodeBlock();
  AddNode(SemanticsNode::MakeFunctionDefinition(parse_node, decl_id, block_id));
  node_block_stack_.push_back(block_id);
  Push(parse_node);
}

auto SemanticsParseTreeHandler::HandleFunctionIntroducer(
    ParseTree::Node parse_node) -> void {
  // No action, just a bracketing node.
  Push(parse_node);
}

auto SemanticsParseTreeHandler::HandleIfCondition(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleIfConditionStart(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleIfStatement(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleIfStatementElse(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleInfixOperator(ParseTree::Node parse_node)
    -> void {
  auto rhs_id = PopWithResult();
  auto lhs_id = PopWithResult();
  SemanticsNodeId result_type =
      TryTypeConversion(parse_node, lhs_id, rhs_id, /*can_convert_lhs=*/true);

  // Figure out the operator for the token.
  auto token = parse_tree_->node_token(parse_node);
  switch (auto token_kind = tokens_->GetKind(token)) {
    case TokenKind::Plus():
      Push(parse_node, SemanticsNode::MakeBinaryOperatorAdd(
                           parse_node, result_type, lhs_id, rhs_id));
      break;
    default:
      CARBON_FATAL() << "Unrecognized token kind: " << token_kind.name();
  }
}

auto SemanticsParseTreeHandler::HandleInterfaceBody(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleInterfaceBodyStart(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleInterfaceDefinition(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleLiteral(ParseTree::Node parse_node)
    -> void {
  auto token = parse_tree_->node_token(parse_node);
  switch (auto token_kind = tokens_->GetKind(token)) {
    case TokenKind::IntegerLiteral(): {
      auto id =
          semantics_->AddIntegerLiteral(tokens_->GetIntegerLiteral(token));
      Push(parse_node, SemanticsNode::MakeIntegerLiteral(parse_node, id));
      break;
    }
    case TokenKind::RealLiteral(): {
      // TODO: Add storage of the Real literal.
      Push(parse_node, SemanticsNode::MakeRealLiteral(parse_node));
      break;
    }
    case TokenKind::IntegerTypeLiteral(): {
      auto text = tokens_->GetTokenText(token);
      CARBON_CHECK(text == "i32") << "Currently only i32 is allowed";
      Push(parse_node, SemanticsNodeId::MakeBuiltinReference(
                           SemanticsBuiltinKind::IntegerType()));
      break;
    }
    default:
      CARBON_FATAL() << "Unhandled kind: " << token_kind.name();
  }
}

auto SemanticsParseTreeHandler::HandleNameReference(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandlePackageApi(ParseTree::Node /*parse_node*/)
    -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandlePackageDirective(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandlePackageImpl(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandlePackageIntroducer(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandlePackageLibrary(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleParameterList(ParseTree::Node parse_node)
    -> void {
  // TODO: This should transform into a usable parameter list. For now
  // it's unused and only stored so that node counts match.
  Pop(ParseNodeKind::ParameterListStart());
  Push(parse_node);
}

auto SemanticsParseTreeHandler::HandleParameterListComma(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleParameterListStart(
    ParseTree::Node parse_node) -> void {
  // TODO: See HandleParameterList.
  Push(parse_node);
}

auto SemanticsParseTreeHandler::HandleParenExpression(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleParenExpressionOrTupleLiteralStart(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandlePatternBinding(ParseTree::Node parse_node)
    -> void {
  // Allocate storage.
  auto type = node_stack_.pop_back_val();
  CARBON_CHECK(type.result_id.is_valid());
  auto storage_id =
      AddNode(SemanticsNode::MakeVarStorage(parse_node, type.result_id));

  // Get the name.
  auto name_node = node_stack_.pop_back_val().parse_node;
  auto name_id = AddIdentifier(name_node);

  // Bind the name to storage.
  AddNode(SemanticsNode::MakeBindName(name_node, type.result_id, name_id,
                                      storage_id));

  // If this node's result is used, it'll be for the storage address, so provide
  // that.
  Push(parse_node, storage_id);
}

auto SemanticsParseTreeHandler::HandlePostfixOperator(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandlePrefixOperator(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleReturnStatement(
    ParseTree::Node parse_node) -> void {
  if (parse_tree_->node_kind(node_stack_.back().parse_node) ==
      ParseNodeKind::ReturnStatementStart()) {
    Pop(ParseNodeKind::ReturnStatementStart());
    Push(parse_node, SemanticsNode::MakeReturn(parse_node));
  } else {
    auto arg = PopWithResult();
    auto arg_type = semantics_->GetType(node_block_stack_.back(), arg);
    Pop(ParseNodeKind::ReturnStatementStart());
    Push(parse_node,
         SemanticsNode::MakeReturnExpression(parse_node, arg_type, arg));
  }
}

auto SemanticsParseTreeHandler::HandleReturnStatementStart(
    ParseTree::Node parse_node) -> void {
  // No action, just a bracketing node.
  Push(parse_node);
}

auto SemanticsParseTreeHandler::HandleReturnType(ParseTree::Node /*parse_node*/)
    -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleStructComma(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleStructFieldDesignator(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleStructFieldType(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleStructFieldUnknown(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleStructFieldValue(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleStructLiteral(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleStructLiteralOrStructTypeLiteralStart(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleStructTypeLiteral(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleTupleLiteral(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleTupleLiteralComma(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleVariableDeclaration(
    ParseTree::Node parse_node) -> void {
  auto init_id = PopWithResultIf(ParseNodeKind::VariableInitializer());
  auto storage_id = PopWithResult(ParseNodeKind::PatternBinding());
  if (init_id) {
    auto storage_type = TryTypeConversion(parse_node, storage_id, *init_id,
                                          /*can_convert_lhs=*/false);
    AddNode(SemanticsNode::MakeAssign(parse_node, storage_type, storage_id,
                                      *init_id));
  }
  Pop(ParseNodeKind::VariableIntroducer());
  Push(parse_node, storage_id);
}

auto SemanticsParseTreeHandler::HandleVariableIntroducer(
    ParseTree::Node parse_node) -> void {
  // No action, just a bracketing node.
  Push(parse_node);
}

auto SemanticsParseTreeHandler::HandleVariableInitializer(
    ParseTree::Node parse_node) -> void {
  // The child is the expression; propagate it for the parent.
  Push(parse_node, PopWithResult());
}

auto SemanticsParseTreeHandler::HandleWhileCondition(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleWhileConditionStart(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleWhileStatement(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleAddress(ParseTree::Node /*parse_node*/)
    -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleSelfType(ParseTree::Node /*parse_node*/)
    -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleDeducedParameterList(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleSelfDeducedParameter(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}

auto SemanticsParseTreeHandler::HandleDeducedParameterListStart(
    ParseTree::Node /*parse_node*/) -> void {
  CARBON_FATAL() << "TODO";
}
}  // namespace Carbon