// 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/function.h"

#include "toolchain/check/merge.h"
#include "toolchain/sem_ir/ids.h"

namespace Carbon::Check {

auto CheckFunctionTypeMatches(Context& context,
                              const SemIR::Function& new_function,
                              const SemIR::Function& prev_function,
                              SemIR::SpecificId prev_specific_id,
                              bool check_syntax) -> bool {
  // TODO: When check_syntax is false, the functions should be allowed to have
  // different signatures as long as we can synthesize a suitable thunk. i.e.,
  // when there's an implicit conversion from the original parameter types to
  // the overriding parameter types, and from the overriding return type to the
  // original return type.
  // Also, build that thunk.
  if (!CheckRedeclParamsMatch(context, DeclParams(new_function),
                              DeclParams(prev_function), prev_specific_id,
                              check_syntax)) {
    return false;
  }

  // TODO: Pass a specific ID for `prev_function` instead of substitutions and
  // use it here.
  auto new_return_type_id =
      new_function.GetDeclaredReturnType(context.sem_ir());
  auto prev_return_type_id =
      prev_function.GetDeclaredReturnType(context.sem_ir(), prev_specific_id);
  if (new_return_type_id == SemIR::ErrorInst::SingletonTypeId ||
      prev_return_type_id == SemIR::ErrorInst::SingletonTypeId) {
    return false;
  }
  if (!context.types().AreEqualAcrossDeclarations(new_return_type_id,
                                                  prev_return_type_id)) {
    CARBON_DIAGNOSTIC(
        FunctionRedeclReturnTypeDiffers, Error,
        "function redeclaration differs because return type is {0}",
        SemIR::TypeId);
    CARBON_DIAGNOSTIC(
        FunctionRedeclReturnTypeDiffersNoReturn, Error,
        "function redeclaration differs because no return type is provided");
    auto diag =
        new_return_type_id.has_value()
            ? context.emitter().Build(new_function.latest_decl_id(),
                                      FunctionRedeclReturnTypeDiffers,
                                      new_return_type_id)
            : context.emitter().Build(new_function.latest_decl_id(),
                                      FunctionRedeclReturnTypeDiffersNoReturn);
    if (prev_return_type_id.has_value()) {
      CARBON_DIAGNOSTIC(FunctionRedeclReturnTypePrevious, Note,
                        "previously declared with return type {0}",
                        SemIR::TypeId);
      diag.Note(prev_function.latest_decl_id(),
                FunctionRedeclReturnTypePrevious, prev_return_type_id);
    } else {
      CARBON_DIAGNOSTIC(FunctionRedeclReturnTypePreviousNoReturn, Note,
                        "previously declared with no return type");
      diag.Note(prev_function.latest_decl_id(),
                FunctionRedeclReturnTypePreviousNoReturn);
    }
    diag.Emit();
    return false;
  }

  return true;
}

auto CheckFunctionReturnType(Context& context, SemIR::LocId loc_id,
                             SemIR::Function& function,
                             SemIR::SpecificId specific_id)
    -> SemIR::ReturnTypeInfo {
  auto return_info = SemIR::ReturnTypeInfo::ForFunction(context.sem_ir(),
                                                        function, specific_id);

  // If we couldn't determine the return information due to the return type
  // being incomplete, try to complete it now.
  if (return_info.init_repr.kind == SemIR::InitRepr::Incomplete) {
    auto diagnose_incomplete_return_type = [&] {
      CARBON_DIAGNOSTIC(IncompleteTypeInFunctionReturnType, Error,
                        "function returns incomplete type {0}", SemIR::TypeId);
      return context.emitter().Build(loc_id, IncompleteTypeInFunctionReturnType,
                                     return_info.type_id);
    };
    auto diagnose_abstract_return_type = [&] {
      CARBON_DIAGNOSTIC(AbstractTypeInFunctionReturnType, Error,
                        "function returns abstract type {0}", SemIR::TypeId);
      return context.emitter().Build(loc_id, AbstractTypeInFunctionReturnType,
                                     return_info.type_id);
    };

    // TODO: Consider suppressing the diagnostic if we've already diagnosed a
    // definition or call to this function.
    if (context.RequireConcreteType(return_info.type_id, loc_id,
                                    diagnose_incomplete_return_type,
                                    diagnose_abstract_return_type)) {
      return_info = SemIR::ReturnTypeInfo::ForFunction(context.sem_ir(),
                                                       function, specific_id);
    }
  }

  return return_info;
}

}  // namespace Carbon::Check