//===--- UnusedReturnValueCheck.cpp - clang-tidy---------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "UnusedReturnValueCheck.h"
#include "../utils/OptionsUtils.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"

using namespace clang::ast_matchers;
using namespace clang::ast_matchers::internal;

namespace clang {
namespace tidy {
namespace bugprone {

namespace {

// Matches functions that are instantiated from a class template member function
// matching InnerMatcher. Functions not instantiated from a class template
// member function are matched directly with InnerMatcher.
AST_MATCHER_P(FunctionDecl, isInstantiatedFrom, Matcher<FunctionDecl>,
              InnerMatcher) {
  FunctionDecl *InstantiatedFrom = Node.getInstantiatedFromMemberFunction();
  return InnerMatcher.matches(InstantiatedFrom ? *InstantiatedFrom : Node,
                              Finder, Builder);
}

} // namespace

UnusedReturnValueCheck::UnusedReturnValueCheck(llvm::StringRef Name,
                                               ClangTidyContext *Context)
    : ClangTidyCheck(Name, Context),
      CheckedFunctions(Options.get("CheckedFunctions",
                                   "::std::async;"
                                   "::std::launder;"
                                   "::std::remove;"
                                   "::std::remove_if;"
                                   "::std::unique;"
                                   "::std::unique_ptr::release;"
                                   "::std::basic_string::empty;"
                                   "::std::vector::empty")) {}

void UnusedReturnValueCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
  Options.store(Opts, "CheckedFunctions", CheckedFunctions);
}

void UnusedReturnValueCheck::registerMatchers(MatchFinder *Finder) {
  auto FunVec = utils::options::parseStringList(CheckedFunctions);
  auto MatchedCallExpr = expr(ignoringImplicit(ignoringParenImpCasts(
      callExpr(callee(functionDecl(
                   // Don't match void overloads of checked functions.
                   unless(returns(voidType())),
                   isInstantiatedFrom(hasAnyName(
                       std::vector<StringRef>(FunVec.begin(), FunVec.end()))))))
          .bind("match"))));

  auto UnusedInCompoundStmt =
      compoundStmt(forEach(MatchedCallExpr),
                   // The checker can't currently differentiate between the
                   // return statement and other statements inside GNU statement
                   // expressions, so disable the checker inside them to avoid
                   // false positives.
                   unless(hasParent(stmtExpr())));
  auto UnusedInIfStmt =
      ifStmt(eachOf(hasThen(MatchedCallExpr), hasElse(MatchedCallExpr)));
  auto UnusedInWhileStmt = whileStmt(hasBody(MatchedCallExpr));
  auto UnusedInDoStmt = doStmt(hasBody(MatchedCallExpr));
  auto UnusedInForStmt =
      forStmt(eachOf(hasLoopInit(MatchedCallExpr),
                     hasIncrement(MatchedCallExpr), hasBody(MatchedCallExpr)));
  auto UnusedInRangeForStmt = cxxForRangeStmt(hasBody(MatchedCallExpr));
  auto UnusedInCaseStmt = switchCase(forEach(MatchedCallExpr));

  Finder->addMatcher(
      stmt(anyOf(UnusedInCompoundStmt, UnusedInIfStmt, UnusedInWhileStmt,
                 UnusedInDoStmt, UnusedInForStmt, UnusedInRangeForStmt,
                 UnusedInCaseStmt)),
      this);
}

void UnusedReturnValueCheck::check(const MatchFinder::MatchResult &Result) {
  if (const auto *Matched = Result.Nodes.getNodeAs<CallExpr>("match")) {
    diag(Matched->getBeginLoc(),
         "the value returned by this function should be used")
        << Matched->getSourceRange();
    diag(Matched->getBeginLoc(),
         "cast the expression to void to silence this warning",
         DiagnosticIDs::Note);
  }
}

} // namespace bugprone
} // namespace tidy
} // namespace clang