carbon-lang/toolchain/parse/handle_let.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/diagnostics/diagnostic.h"
#include "toolchain/diagnostics/format_providers.h"
#include "toolchain/lex/token_kind.h"
#include "toolchain/parse/context.h"
#include "toolchain/parse/handle.h"
#include "toolchain/parse/node_kind.h"

namespace Carbon::Parse {

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

  // These will start at the `let`.
  context.PushState(state, StateKind::LetFinishAsRegular);
  context.PushState(state, StateKind::LetAfterPatternAsRegular);

  context.PushStateForPattern(StateKind::Pattern, /*in_var_pattern=*/false,
                              /*in_unused_pattern=*/false,
                              /*in_field_shorthand_pattern=*/false,
                              BindingContext::ExplicitParam,
                              PrecedenceGroup::ForTopLevelPattern());
}

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

  // Parse the associated constant pattern: identifier : type. The binding is a
  // checked generic by context, so no phase keyword is used.
  auto identifier = context.ConsumeIf(Lex::TokenKind::Identifier);
  if (!identifier) {
    auto kind = context.PositionKind();
    if (kind == Lex::TokenKind::Generic || kind == Lex::TokenKind::Runtime ||
        kind == Lex::TokenKind::Template) {
      // Diagnose a phase keyword specifically, rather than reporting a missing
      // associated constant name.
      CARBON_DIAGNOSTIC(
          PhaseKeywordInAssociatedConstant, Error,
          "phase keyword is not allowed on an associated constant");
      context.emitter().Emit(*context.position(),
                             PhaseKeywordInAssociatedConstant);
      state.has_error = true;
    } else {
      // A word that can't be a name, followed by the `:`, was most likely
      // meant as the name, and is what the message is about. Otherwise the
      // name is missing, and goes after `let`.
      bool recover_as_raw =
          kind.is_word() &&
          context.PositionKind(Lookahead::NextToken) == Lex::TokenKind::Colon;
      CARBON_DIAGNOSTIC(
          ExpectedAssociatedConstantIdentifier, Error,
          "expected identifier in associated constant declaration"
          "{0:; prefix reserved word with `r#` to form a valid identifier|}",
          Diagnostics::BoolAsSelect);
      context.emitter().Emit(recover_as_raw ? DiagnosticLoc(*context.position())
                                            : context.PointAfterPreviousToken(),
                             ExpectedAssociatedConstantIdentifier,
                             recover_as_raw);
      if (recover_as_raw) {
        identifier = context.tokens().AddPostLexingRecoveryTokenAsIdentifier(
            context.Consume());
      } else {
        state.has_error = true;
      }
    }
  }

  auto colon = context.ConsumeIf(Lex::TokenKind::Colon);
  if (identifier && !colon) {
    CARBON_DIAGNOSTIC(ExpectedAssociatedConstantColon, Error,
                      "expected `:` in associated constant declaration");
    context.emitter().Emit(context.PointAfterPreviousToken(),
                           ExpectedAssociatedConstantColon);
    state.has_error = true;
  }

  if (!identifier || !colon) {
    auto end_token = context.SkipPastLikelyEnd(*(context.position() - 1));
    context.AddNode(NodeKind::AssociatedConstantDecl, end_token,
                    /*has_error=*/true);
    state.has_error = true;
    return;
  }

  context.AddLeafNode(NodeKind::IdentifierNameNotBeforeSignature, *identifier);
  state.token = *colon;
  context.PushState(state, StateKind::LetFinishAsAssociatedConstant);
  context.PushState(state, StateKind::LetAfterPatternAsAssociatedConstant);
  context.PushState(StateKind::Expr);
}

static auto HandleLetAfterPattern(Context& context, NodeKind init_kind)
    -> void {
  auto state = context.PopState();

  if (state.has_error) {
    if (auto after_pattern =
            context.FindNextOf({Lex::TokenKind::Equal, Lex::TokenKind::Semi})) {
      context.SkipTo(*after_pattern);
    }
  }

  if (auto equals = context.ConsumeIf(Lex::TokenKind::Equal)) {
    context.AddLeafNode(init_kind, *equals);
    context.PushState(StateKind::Expr);
  }
}

auto HandleLetAfterPatternAsRegular(Context& context) -> void {
  HandleLetAfterPattern(context, NodeKind::LetInitializer);
}

auto HandleLetAfterPatternAsAssociatedConstant(Context& context) -> void {
  auto state = context.PopState();
  context.AddNode(NodeKind::AssociatedConstantNameAndType, state.token,
                  state.has_error);
  context.PushState(state);
  HandleLetAfterPattern(context, NodeKind::AssociatedConstantInitializer);
}

static auto HandleLetFinish(Context& context, NodeKind node_kind) -> void {
  auto state = context.PopState();

  auto end_token = state.token;
  if (context.PositionIs(Lex::TokenKind::Semi)) {
    end_token = context.Consume();
  } else {
    context.DiagnoseExpectedDeclSemi(Lex::TokenKind::Let);
    state.has_error = true;
    end_token = context.SkipPastLikelyEnd(state.token);
  }
  context.AddNode(node_kind, end_token, state.has_error);
}

auto HandleLetFinishAsRegular(Context& context) -> void {
  HandleLetFinish(context, NodeKind::LetDecl);
}

auto HandleLetFinishAsAssociatedConstant(Context& context) -> void {
  HandleLetFinish(context, NodeKind::AssociatedConstantDecl);
}

}  // namespace Carbon::Parse