carbon-lang/toolchain/parse/handle_pattern_list.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/parse/context.h"
#include "toolchain/parse/handle.h"

namespace Carbon::Parse {

// Handles PatternListElementAs(Tuple|Explicit|Implicit).
static auto HandlePatternListElement(Context& context, StateKind pattern_state,
                                     StateKind finish_state_kind) -> void {
  auto state = context.PopState();

  context.PushStateForPattern(finish_state_kind, state.in_var_pattern,
                              state.in_unused_pattern,
                              state.in_field_shorthand_pattern,
                              state.binding_context, state.ambient_precedence);

  // For patterns inside of list elements we normally check for a default value.
  // Parsing a struct designator is special case as that also is looking for a
  // required `=` sign, so we handle looking for an optional default value in
  // that state.
  if (pattern_state != StateKind::StructPatternFieldAfterDesignator) {
    context.PushStateForPattern(
        StateKind::PatternListElementCheckForDefaultValue, state.in_var_pattern,
        state.in_unused_pattern, state.in_field_shorthand_pattern,
        state.binding_context, state.ambient_precedence);
  }

  context.PushStateForPattern(pattern_state, state.in_var_pattern,
                              state.in_unused_pattern,
                              state.in_field_shorthand_pattern,
                              state.binding_context, state.ambient_precedence);
}

auto HandlePatternListElementAsTuple(Context& context) -> void {
  HandlePatternListElement(context, StateKind::Pattern,
                           StateKind::PatternListElementFinishAsTuple);
}

auto HandlePatternListElementAsStruct(Context& context) -> void {
  switch (context.PositionKind()) {
    case Lex::TokenKind::Period:
      HandlePatternListElement(context,
                               StateKind::StructPatternFieldAfterDesignator,
                               StateKind::PatternListElementFinishAsStruct);
      context.PushState(StateKind::PeriodAsStruct);
      break;
    case Lex::TokenKind::Underscore:
      // If this ends up as part of a binding pattern, it will look like a
      // shorthand pattern such as `{_: i32}`.
      // Set flag on state which will be popped in HandlePatternListElement.
      context.state_stack().back().in_field_shorthand_pattern = true;
      HandlePatternListElement(context, StateKind::StructPatternUnderscore,
                               StateKind::PatternListElementFinishAsStruct);
      break;
    default:
      // Set flag on state which will be popped in HandlePatternListElement.
      context.state_stack().back().in_field_shorthand_pattern = true;
      HandlePatternListElement(context, StateKind::Pattern,
                               StateKind::PatternListElementFinishAsStruct);
      break;
  }
}

auto HandlePatternListElementAsExplicit(Context& context) -> void {
  HandlePatternListElement(context, StateKind::Pattern,
                           StateKind::PatternListElementFinishAsExplicit);
}

auto HandlePatternListElementAsImplicit(Context& context) -> void {
  HandlePatternListElement(context, StateKind::Pattern,
                           StateKind::PatternListElementFinishAsImplicit);
}

auto HandleStructPatternDesignatedFieldFinish(Context& context) -> void {
  auto state = context.PopState();
  context.AddNode(NodeKind::StructPatternDesignatedField, state.token,
                  state.has_error);
}

auto HandleStructPatternFieldAfterDesignator(Context& context) -> void {
  auto state = context.PopState();

  auto skip_to_recovery_position = [&](bool add_invalid_parse) {
    auto recovery_pos =
        context.FindNextOf({Lex::TokenKind::Equal, Lex::TokenKind::Comma,
                            Lex::TokenKind::CloseCurlyBrace});

    if (add_invalid_parse) {
      if (context.tokens().GetKind(*recovery_pos) != Lex::TokenKind::Equal) {
        context.AddInvalidParse(*context.position());
      }
    }
    context.SkipTo(*recovery_pos);
  };

  if (state.has_error) {
    // recover from error returned when parsing designator
    skip_to_recovery_position(/*add_invalid_parse=*/false);
  }

  if (!context.PositionIs(Lex::TokenKind::Equal)) {
    if (!state.has_error) {
      state.has_error = true;

      CARBON_DIAGNOSTIC(ExpectedStructPatternDesignatedField, Error,
                        "expected `= value` after `.field`");
      context.emitter().Emit(*context.position(),
                             ExpectedStructPatternDesignatedField);
    }
    skip_to_recovery_position(/*add_invalid_parse=*/true);

    if (context.PositionIs(Lex::TokenKind::Comma) ||
        context.PositionIs(Lex::TokenKind::CloseCurlyBrace)) {
      context.PushState(state, StateKind::StructPatternDesignatedFieldFinish);
      return;
    }
  }

  state.token = context.ConsumeChecked(Lex::TokenKind::Equal);

  context.PushState(state, StateKind::StructPatternDesignatedFieldFinish);
  context.PushStateForPattern(StateKind::Pattern, state.in_var_pattern,
                              state.in_unused_pattern,
                              state.in_field_shorthand_pattern,
                              state.binding_context, state.ambient_precedence);
}

auto HandleStructPatternUnderscore(Context& context) -> void {
  auto state = context.PopState();

  if (context.PositionKind(Lookahead::NextToken)
          .is_binding_pattern_operator()) {
    context.PushStateForPattern(
        StateKind::BindingPattern, state.in_var_pattern,
        state.in_unused_pattern, state.in_field_shorthand_pattern,
        state.binding_context, state.ambient_precedence);

    return;
  }

  auto underscore = context.ConsumeChecked(Lex::TokenKind::Underscore);

  bool is_last = context.PositionIs(Lex::TokenKind::CloseCurlyBrace);

  if (!is_last) {
    CARBON_DIAGNOSTIC(
        ExpectedCloseAfterUnderscore, Error,
        "unexpected token `{0}` after `_` in struct pattern, expected `}`",
        Lex::TokenKind);
    context.emitter().Emit(*context.position(), ExpectedCloseAfterUnderscore,
                           context.PositionKind());
    state.has_error = true;
  }

  context.AddNode(NodeKind::UnderscoreName, underscore, state.has_error);

  if (state.has_error) {
    context.ReturnErrorOnState();
  }
}

auto HandlePatternListElementCheckForDefaultValue(Context& context) -> void {
  auto state = context.PopState();

  if (state.has_error) {
    context.ReturnErrorOnState();
  }

  // Check for the optional `=` indicating a default value.
  auto equals_token = context.ConsumeIf(Lex::TokenKind::Equal);
  if (!equals_token) {
    return;
  }

  state.token = *equals_token;
  state.kind = StateKind::PatternListElementFinishDefaultValue;
  context.PushState(state);

  // Check for the underscore `_` indicating the default value is unspecified.
  auto underscore = context.ConsumeIf(Lex::TokenKind::Underscore);
  if (underscore) {
    context.AddLeafNode(NodeKind::DefaultValueUnspecified, *underscore);
    return;
  }

  // No underscore, we parse this as a normal expression.
  context.PushStateForExpr(state.ambient_precedence);
}

auto HandlePatternListElementFinishDefaultValue(Context& context) -> void {
  auto state = context.PopState();

  // Propagate any expr parsing errors upwards to initiate error recovery
  // at the pattern list level.
  if (state.has_error) {
    context.ReturnErrorOnState();
  }

  context.AddNode(NodeKind::DefaultValuePattern, state.token, state.has_error);
}

// Handles PatternListElementFinishAs(Tuple|Struct|Explicit|Implicit).
static auto HandlePatternListElementFinish(Context& context,
                                           Lex::TokenKind close_token,
                                           StateKind param_state_kind) -> void {
  auto state = context.PopState();

  if (state.has_error) {
    context.ReturnErrorOnState();
  }

  auto list_token_kind = context.ConsumeListToken(NodeKind::PatternListComma,
                                                  close_token, state.has_error);

  // If we have a comma, the parent is now a tuple pattern not a parenthesized
  // pattern.
  if (list_token_kind != Context::ListTokenKind::Close &&
      param_state_kind == StateKind::PatternListElementAsTuple) {
    auto parent_state = context.PopState();
    CARBON_CHECK(parent_state.kind == StateKind::PatternListFinishAsTuple ||
                 parent_state.kind == StateKind::PatternListFinishAsParen);
    context.PushState(parent_state, StateKind::PatternListFinishAsTuple);
  }

  if (list_token_kind == Context::ListTokenKind::Comma) {
    context.PushStateForPattern(
        param_state_kind, state.in_var_pattern, state.in_unused_pattern,
        /*in_field_shorthand_pattern=*/false, state.binding_context,
        state.ambient_precedence);
  }
}

auto HandlePatternListElementFinishAsTuple(Context& context) -> void {
  HandlePatternListElementFinish(context, Lex::TokenKind::CloseParen,
                                 StateKind::PatternListElementAsTuple);
}

auto HandlePatternListElementFinishAsStruct(Context& context) -> void {
  HandlePatternListElementFinish(context, Lex::TokenKind::CloseCurlyBrace,
                                 StateKind::PatternListElementAsStruct);
}

auto HandlePatternListElementFinishAsExplicit(Context& context) -> void {
  HandlePatternListElementFinish(context, Lex::TokenKind::CloseParen,
                                 StateKind::PatternListElementAsExplicit);
}

auto HandlePatternListElementFinishAsImplicit(Context& context) -> void {
  HandlePatternListElementFinish(context, Lex::TokenKind::CloseSquareBracket,
                                 StateKind::PatternListElementAsImplicit);
}

// Handles PatternListAs(Tuple|Struct|Explicit|Implicit).
static auto HandlePatternList(Context& context, NodeKind node_kind,
                              Lex::TokenKind open_token_kind,
                              Lex::TokenKind close_token_kind,
                              StateKind param_state,
                              StateKind finish_state_empty,
                              StateKind finish_state_nonempty) -> void {
  auto state = context.PopState();

  if (state.in_field_shorthand_pattern) {
    if (node_kind == NodeKind::TuplePatternStart) {
      CARBON_DIAGNOSTIC(NestedTuplePatternInStructPatternShortField, Error,
                        "Tuple pattern in shorthand struct pattern field. Use "
                        "`.field = (...)` instead");
      context.emitter().Emit(*context.position(),
                             NestedTuplePatternInStructPatternShortField);

      context.ReturnErrorOnState();
    } else if (node_kind == NodeKind::StructPatternStart) {
      CARBON_DIAGNOSTIC(NestedStructPatternStructPatternShortField, Error,
                        "Struct pattern in shorthand struct pattern field. Use "
                        "`.field = {{...}` instead");
      context.emitter().Emit(*context.position(),
                             NestedStructPatternStructPatternShortField);

      context.ReturnErrorOnState();
    }
  }

  auto open_token = context.ConsumeChecked(open_token_kind);
  bool empty = context.PositionIs(close_token_kind);

  context.PushStateForPattern(
      empty ? finish_state_empty : finish_state_nonempty, state.in_var_pattern,
      state.in_unused_pattern, state.in_field_shorthand_pattern,
      state.binding_context, state.ambient_precedence);
  context.AddLeafNode(node_kind, open_token);

  if (!empty) {
    context.PushStateForPattern(
        param_state, state.in_var_pattern, state.in_unused_pattern,
        state.in_field_shorthand_pattern, state.binding_context,
        PrecedenceGroup::ForTopLevelExpr());
  }
}

auto HandlePatternListAsTuple(Context& context) -> void {
  // If the list is nonempty, use PatternListFinishAsParen as the parent. This
  // will be replaced by PatternListFinishAsTuple if we see a comma.
  HandlePatternList(
      context, NodeKind::TuplePatternStart, Lex::TokenKind::OpenParen,
      Lex::TokenKind::CloseParen, StateKind::PatternListElementAsTuple,
      StateKind::PatternListFinishAsTuple, StateKind::PatternListFinishAsParen);
}

auto HandlePatternListAsStruct(Context& context) -> void {
  HandlePatternList(
      context, NodeKind::StructPatternStart, Lex::TokenKind::OpenCurlyBrace,
      Lex::TokenKind::CloseCurlyBrace, StateKind::PatternListElementAsStruct,
      StateKind::PatternListFinishAsStruct,
      StateKind::PatternListFinishAsStruct);
}

auto HandlePatternListAsExplicit(Context& context) -> void {
  HandlePatternList(context, NodeKind::ExplicitParamListStart,
                    Lex::TokenKind::OpenParen, Lex::TokenKind::CloseParen,
                    StateKind::PatternListElementAsExplicit,
                    StateKind::PatternListFinishAsExplicit,
                    StateKind::PatternListFinishAsExplicit);
}

auto HandlePatternListAsImplicit(Context& context) -> void {
  HandlePatternList(context, NodeKind::ImplicitParamListStart,
                    Lex::TokenKind::OpenSquareBracket,
                    Lex::TokenKind::CloseSquareBracket,
                    StateKind::PatternListElementAsImplicit,
                    StateKind::PatternListFinishAsImplicit,
                    StateKind::PatternListFinishAsImplicit);
}

// Handles PatternListFinishAs(Paren|Tuple|Explicit|Implicit).
static auto HandlePatternListFinish(Context& context, NodeKind node_kind,
                                    Lex::TokenKind token_kind) -> void {
  auto state = context.PopState();

  context.AddNode(node_kind, context.ConsumeChecked(token_kind),
                  state.has_error);
}

auto HandlePatternListFinishAsParen(Context& context) -> void {
  HandlePatternListFinish(context, NodeKind::ParenPattern,
                          Lex::TokenKind::CloseParen);
}

auto HandlePatternListFinishAsTuple(Context& context) -> void {
  HandlePatternListFinish(context, NodeKind::TuplePattern,
                          Lex::TokenKind::CloseParen);
}

auto HandlePatternListFinishAsStruct(Context& context) -> void {
  HandlePatternListFinish(context, NodeKind::StructPattern,
                          Lex::TokenKind::CloseCurlyBrace);
}

auto HandlePatternListFinishAsExplicit(Context& context) -> void {
  HandlePatternListFinish(context, NodeKind::ExplicitParamList,
                          Lex::TokenKind::CloseParen);
}

auto HandlePatternListFinishAsImplicit(Context& context) -> void {
  HandlePatternListFinish(context, NodeKind::ImplicitParamList,
                          Lex::TokenKind::CloseSquareBracket);
}

}  // namespace Carbon::Parse