//===----------------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
///
///  \file This file implements a clang-tidy tool.
///
///  This tool uses the Clang Tooling infrastructure, see
///    https://clang.llvm.org/docs/HowToSetupToolingForLLVM.html
///  for details on setting it up with LLVM source tree.
///
//===----------------------------------------------------------------------===//

#include "ClangTidyMain.h"
#include "../ClangTidy.h"
#include "../ClangTidyForceLinker.h" // IWYU pragma: keep
#include "../GlobList.h"
#include "../utils/OptionsUtils.h"
#include "clang/Tooling/CommonOptionsParser.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/InitLLVM.h"
#include "llvm/Support/PluginLoader.h" // IWYU pragma: keep
#include "llvm/Support/Process.h"
#include "llvm/Support/Signals.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/Support/WithColor.h"
#include "llvm/TargetParser/Host.h"
#include <optional>

using namespace clang::tooling;
using namespace llvm;

static cl::desc desc(StringRef Description) { return {Description.ltrim()}; }

static cl::OptionCategory ClangTidyCategory("clang-tidy options");

static cl::extrahelp CommonHelp(CommonOptionsParser::HelpMessage);
static cl::extrahelp ClangTidyParameterFileHelp(R"(
Parameters files:
  A large number of options or source files can be passed as parameter files
  by use '@parameter-file' in the command line.
)");
static cl::extrahelp ClangTidyHelp(R"(
Configuration files:
  clang-tidy attempts to read configuration for each source file from a
  .clang-tidy file located in the closest parent directory of the source
  file. The .clang-tidy file is specified in YAML format. If any configuration
  options have a corresponding command-line option, command-line option takes
  precedence.

  The following configuration options may be used in a .clang-tidy file:

  CheckOptions                 - List of key-value pairs defining check-specific
                                 options. Example:
                                   CheckOptions:
                                     some-check.SomeOption: 'some value'
  Checks                       - Same as '--checks'. Additionally, the list of
                                 globs can be specified as a list instead of a
                                 string.
  CustomChecks                 - Array of user defined checks based on
                                 Clang-Query syntax.
  ExcludeHeaderFilterRegex     - Same as '--exclude-header-filter'.
  ExtraArgs                    - Same as '--extra-arg'.
  ExtraArgsBefore              - Same as '--extra-arg-before'.
  FormatStyle                  - Same as '--format-style'.
  HeaderFileExtensions         - File extensions to consider to determine if a
                                 given diagnostic is located in a header file.
  HeaderFilterRegex            - Same as '--header-filter'.
  ImplementationFileExtensions - File extensions to consider to determine if a
                                 given diagnostic is located in an
                                 implementation file.
  InheritParentConfig          - If this option is true in a config file, the
                                 configuration file in the parent directory
                                 (if any exists) will be taken and the current
                                 config file will be applied on top of the
                                 parent one.
  RemovedArgs                  - Same as '--removed-arg'.
  SystemHeaders                - Same as '--system-headers'.
  UseColor                     - Same as '--use-color'.
  User                         - Specifies the name or e-mail of the user
                                 running clang-tidy. This option is used, for
                                 example, to place the correct user name in
                                 TODO() comments in the relevant check.
  WarningsAsErrors             - Same as '--warnings-as-errors'.

  The effective configuration can be inspected using --dump-config:

    $ clang-tidy --dump-config
    ---
    Checks:                       '-*,some-check'
    WarningsAsErrors:             ''
    HeaderFileExtensions:         ['', 'h','hh','hpp','hxx']
    ImplementationFileExtensions: ['c','cc','cpp','cxx']
    HeaderFilterRegex:            '.*'
    FormatStyle:                  none
    InheritParentConfig:          true
    User:                         user
    CheckOptions:
      some-check.SomeOption: 'some value'
    ...

)");

const char DefaultChecks[] = // Enable these checks by default:
    "clang-diagnostic-*";    //   * compiler diagnostics

static cl::opt<std::string> Checks("checks", desc(R"(
Comma-separated list of globs with optional '-'
prefix. Globs are processed in order of
appearance in the list. Globs without '-'
prefix add checks with matching names to the
set, globs with the '-' prefix remove checks
with matching names from the set of enabled
checks. This option's value is appended to the
value of the 'Checks' option in .clang-tidy
file, if any.
)"),
                                   cl::init(""), cl::cat(ClangTidyCategory));

static cl::opt<std::string> WarningsAsErrors("warnings-as-errors", desc(R"(
Upgrades warnings to errors. Same format as
'-checks'.
This option's value is appended to the value of
the 'WarningsAsErrors' option in .clang-tidy
file, if any.
)"),
                                             cl::init(""),
                                             cl::cat(ClangTidyCategory));

static cl::opt<std::string> HeaderFilter("header-filter", desc(R"(
Regular expression matching the names of the
headers to output diagnostics from. The default
value is '.*', i.e. diagnostics from all non-system
headers are displayed by default. Diagnostics
from the main file of each translation unit are
always displayed.
Can be used together with -line-filter.
This option overrides the 'HeaderFilterRegex'
option in .clang-tidy file, if any.
)"),
                                         cl::init(".*"),
                                         cl::cat(ClangTidyCategory));

static cl::opt<std::string> ExcludeHeaderFilter("exclude-header-filter",
                                                desc(R"(
Regular expression matching the names of the
headers to exclude diagnostics from. Diagnostics
from the main file of each translation unit are
always displayed.
Must be used together with --header-filter.
Can be used together with -line-filter.
This option overrides the 'ExcludeHeaderFilterRegex'
option in .clang-tidy file, if any.
)"),
                                                cl::init(""),
                                                cl::cat(ClangTidyCategory));

static cl::opt<bool> SystemHeaders("system-headers", desc(R"(
Display the errors from system headers.
This option overrides the 'SystemHeaders' option
in .clang-tidy file, if any.
)"),
                                   cl::init(false), cl::cat(ClangTidyCategory));

static cl::opt<std::string> LineFilter("line-filter", desc(R"(
List of files and line ranges to output diagnostics from.
The range is inclusive on both ends. Can be used together
with -header-filter. The format of the list is a JSON
array of objects. For example:

  [
    {"name":"file1.cpp","lines":[[1,3],[5,7]]},
    {"name":"file2.h"}
  ]

This will output diagnostics from 'file1.cpp' only for
the line ranges [1,3] and [5,7], as well as all from the
entire 'file2.h'.
)"),
                                       cl::init(""),
                                       cl::cat(ClangTidyCategory));

static cl::opt<bool> Fix("fix", desc(R"(
Apply suggested fixes. Without -fix-errors
clang-tidy will bail out if any compilation
errors were found.
)"),
                         cl::init(false), cl::cat(ClangTidyCategory));

static cl::opt<bool> FixErrors("fix-errors", desc(R"(
Apply suggested fixes even if compilation
errors were found. If compiler errors have
attached fix-its, clang-tidy will apply them as
well.
)"),
                               cl::init(false), cl::cat(ClangTidyCategory));

static cl::opt<bool> FixNotes("fix-notes", desc(R"(
If a warning has no fix, but a single fix can
be found through an associated diagnostic note,
apply the fix.
Specifying this flag will implicitly enable the
'--fix' flag.
)"),
                              cl::init(false), cl::cat(ClangTidyCategory));

static cl::opt<std::string> FormatStyle("format-style", desc(R"(
Style for formatting code around applied fixes:
  - 'none' (default) turns off formatting
  - 'file' (literally 'file', not a placeholder)
    uses .clang-format file in the closest parent
    directory
  - '{ <json> }' specifies options inline, e.g.
    -format-style='{BasedOnStyle: llvm, IndentWidth: 8}'
  - 'llvm', 'google', 'webkit', 'mozilla'
See clang-format documentation for the up-to-date
information about formatting styles and options.
This option overrides the 'FormatStyle` option in
.clang-tidy file, if any.
)"),
                                        cl::init("none"),
                                        cl::cat(ClangTidyCategory));

static cl::opt<bool> ListChecks("list-checks", desc(R"(
List all enabled checks and exit. Use with
-checks=* to list all available checks.
)"),
                                cl::init(false), cl::cat(ClangTidyCategory));

static cl::opt<bool> ExplainConfig("explain-config", desc(R"(
For each enabled check explains, where it is
enabled, i.e. in clang-tidy binary, command
line or a specific configuration file.
)"),
                                   cl::init(false), cl::cat(ClangTidyCategory));

static cl::opt<std::string> Config("config", desc(R"(
Specifies a configuration in YAML/JSON format:
  -config="{Checks: '*',
            CheckOptions: {x: y}}"
When the value is empty, clang-tidy will
attempt to find a file named .clang-tidy for
each source file in its parent directories.
)"),
                                   cl::init(""), cl::cat(ClangTidyCategory));

static cl::opt<std::string> ConfigFile("config-file", desc(R"(
Specify the path of .clang-tidy or custom config file:
 e.g. --config-file=/some/path/myTidyConfigFile
This option internally works exactly the same way as
 --config option after reading specified config file.
Use either --config-file or --config, not both.
)"),
                                       cl::init(""),
                                       cl::cat(ClangTidyCategory));

static cl::opt<bool> DumpConfig("dump-config", desc(R"(
Dumps configuration in the YAML format to
stdout. This option can be used along with a
file name (and '--' if the file is outside of a
project with configured compilation database).
The configuration used for this file will be
printed.
Use along with -checks=* to include
configuration of all checks.
)"),
                                cl::init(false), cl::cat(ClangTidyCategory));

static cl::opt<bool> EnableCheckProfile("enable-check-profile", desc(R"(
Enable per-check timing profiles, and print a
report to stderr.
)"),
                                        cl::init(false),
                                        cl::cat(ClangTidyCategory));

static cl::opt<std::string> StoreCheckProfile("store-check-profile", desc(R"(
By default reports are printed in tabulated
format to stderr. When this option is passed,
these per-TU profiles are instead stored as JSON.
)"),
                                              cl::value_desc("prefix"),
                                              cl::cat(ClangTidyCategory));

/// This option allows enabling the experimental alpha checkers from the static
/// analyzer. This option is set to false and not visible in help, because it is
/// highly not recommended for users.
static cl::opt<bool>
    AllowEnablingAnalyzerAlphaCheckers("allow-enabling-analyzer-alpha-checkers",
                                       cl::init(false), cl::Hidden,
                                       cl::cat(ClangTidyCategory));

static cl::opt<bool> EnableModuleHeadersParsing("enable-module-headers-parsing",
                                                desc(R"(
Enables preprocessor-level module header parsing
for C++20 and above, empowering specific checks
to detect macro definitions within modules. This
feature may cause performance and parsing issues
and is therefore considered experimental.
)"),
                                                cl::init(false),
                                                cl::cat(ClangTidyCategory));

static cl::opt<std::string> ExportFixes("export-fixes", desc(R"(
YAML file to store suggested fixes in. The
stored fixes can be applied to the input source
code with clang-apply-replacements.
)"),
                                        cl::value_desc("filename"),
                                        cl::cat(ClangTidyCategory));

static cl::opt<bool> Quiet("quiet", desc(R"(
Run clang-tidy in quiet mode. This suppresses
printing statistics about ignored warnings and
warnings treated as errors if the respective
options are specified.
)"),
                           cl::init(false), cl::cat(ClangTidyCategory));

static cl::opt<std::string> VfsOverlay("vfsoverlay", desc(R"(
Overlay the virtual filesystem described by file
over the real file system.
)"),
                                       cl::value_desc("filename"),
                                       cl::cat(ClangTidyCategory));

static cl::opt<bool> UseColor("use-color", desc(R"(
Use colors in diagnostics. If not set, colors
will be used if the terminal connected to
standard output supports colors.
This option overrides the 'UseColor' option in
.clang-tidy file, if any.
)"),
                              cl::init(false), cl::cat(ClangTidyCategory));

static cl::opt<bool> VerifyConfig("verify-config", desc(R"(
Check the config files to ensure each check and
option is recognized without running any checks.
)"),
                                  cl::init(false), cl::cat(ClangTidyCategory));

static cl::opt<bool> AllowNoChecks("allow-no-checks", desc(R"(
Allow empty enabled checks. This suppresses
the "no checks enabled" error when disabling
all of the checks.
)"),
                                   cl::init(false), cl::cat(ClangTidyCategory));

static cl::opt<bool> ExperimentalCustomChecks("experimental-custom-checks",
                                              desc(R"(
Enable experimental clang-query based
custom checks.
see https://clang.llvm.org/extra/clang-tidy/QueryBasedCustomChecks.html.
)"),
                                              cl::init(false),
                                              cl::cat(ClangTidyCategory));

static cl::list<std::string> RemovedArgs("removed-arg", desc(R"(
List of arguments to remove from the command
line sent to the compiler. Please note that
removing arguments might change the semantic
of the analyzed code, possibly leading to
compiler errors, false positives or
false negatives. This option is applied 
before --extra-arg and --extra-arg-before)"),
                                         cl::cat(ClangTidyCategory));

namespace clang::tidy {

static void printStats(const ClangTidyStats &Stats) {
  if (Stats.errorsIgnored()) {
    llvm::errs() << "Suppressed " << Stats.errorsIgnored() << " warnings (";
    StringRef Separator = "";
    if (Stats.ErrorsIgnoredNonUserCode) {
      llvm::errs() << Stats.ErrorsIgnoredNonUserCode << " in non-user code";
      Separator = ", ";
    }
    if (Stats.ErrorsIgnoredLineFilter) {
      llvm::errs() << Separator << Stats.ErrorsIgnoredLineFilter
                   << " due to line filter";
      Separator = ", ";
    }
    if (Stats.ErrorsIgnoredNOLINT) {
      llvm::errs() << Separator << Stats.ErrorsIgnoredNOLINT << " NOLINT";
      Separator = ", ";
    }
    if (Stats.ErrorsIgnoredCheckFilter)
      llvm::errs() << Separator << Stats.ErrorsIgnoredCheckFilter
                   << " with check filters";
    llvm::errs() << ").\n";
    if (Stats.ErrorsIgnoredNonUserCode)
      llvm::errs() << "Use -header-filter=.* or leave it as default to display "
                      "errors from all non-system headers. Use -system-headers "
                      "to display errors from system headers as well.\n";
  }
}

static std::unique_ptr<ClangTidyOptionsProvider>
createOptionsProvider(llvm::IntrusiveRefCntPtr<vfs::FileSystem> FS) {
  ClangTidyGlobalOptions GlobalOptions;
  if (const std::error_code Err = parseLineFilter(LineFilter, GlobalOptions)) {
    llvm::errs() << "Invalid LineFilter: " << Err.message() << "\n\nUsage:\n";
    llvm::cl::PrintHelpMessage(/*Hidden=*/false, /*Categorized=*/true);
    return nullptr;
  }

  ClangTidyOptions DefaultOptions;
  DefaultOptions.Checks = DefaultChecks;
  DefaultOptions.WarningsAsErrors = "";
  DefaultOptions.HeaderFilterRegex = HeaderFilter;
  DefaultOptions.ExcludeHeaderFilterRegex = ExcludeHeaderFilter;
  DefaultOptions.SystemHeaders = SystemHeaders;
  DefaultOptions.FormatStyle = FormatStyle;
  DefaultOptions.User = llvm::sys::Process::GetEnv("USER");
  // USERNAME is used on Windows.
  if (!DefaultOptions.User)
    DefaultOptions.User = llvm::sys::Process::GetEnv("USERNAME");

  ClangTidyOptions OverrideOptions;
  if (Checks.getNumOccurrences() > 0)
    OverrideOptions.Checks = Checks;
  if (WarningsAsErrors.getNumOccurrences() > 0)
    OverrideOptions.WarningsAsErrors = WarningsAsErrors;
  if (HeaderFilter.getNumOccurrences() > 0)
    OverrideOptions.HeaderFilterRegex = HeaderFilter;
  if (ExcludeHeaderFilter.getNumOccurrences() > 0)
    OverrideOptions.ExcludeHeaderFilterRegex = ExcludeHeaderFilter;
  if (SystemHeaders.getNumOccurrences() > 0)
    OverrideOptions.SystemHeaders = SystemHeaders;
  if (FormatStyle.getNumOccurrences() > 0)
    OverrideOptions.FormatStyle = FormatStyle;
  if (UseColor.getNumOccurrences() > 0)
    OverrideOptions.UseColor = UseColor;
  if (RemovedArgs.getNumOccurrences() > 0)
    OverrideOptions.RemovedArgs = RemovedArgs;

  auto LoadConfig =
      [&](StringRef Configuration,
          StringRef Source) -> std::unique_ptr<ClangTidyOptionsProvider> {
    llvm::ErrorOr<ClangTidyOptions> ParsedConfig =
        parseConfiguration(MemoryBufferRef(Configuration, Source));
    if (ParsedConfig)
      return std::make_unique<ConfigOptionsProvider>(
          std::move(GlobalOptions),
          ClangTidyOptions::getDefaults().merge(DefaultOptions, 0),
          std::move(*ParsedConfig), std::move(OverrideOptions), std::move(FS));
    llvm::errs() << "Error: invalid configuration specified.\n"
                 << ParsedConfig.getError().message() << "\n";
    return nullptr;
  };

  if (ConfigFile.getNumOccurrences() > 0) {
    if (Config.getNumOccurrences() > 0) {
      llvm::errs() << "Error: --config-file and --config are "
                      "mutually exclusive. Specify only one.\n";
      return nullptr;
    }

    llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> Text =
        llvm::MemoryBuffer::getFile(ConfigFile);
    if (const std::error_code EC = Text.getError()) {
      llvm::errs() << "Error: can't read config-file '" << ConfigFile
                   << "': " << EC.message() << "\n";
      return nullptr;
    }

    return LoadConfig((*Text)->getBuffer(), ConfigFile);
  }

  if (Config.getNumOccurrences() > 0)
    return LoadConfig(Config, "<command-line-config>");

  return std::make_unique<FileOptionsProvider>(
      std::move(GlobalOptions), std::move(DefaultOptions),
      std::move(OverrideOptions), std::move(FS));
}

static llvm::IntrusiveRefCntPtr<vfs::FileSystem>
getVfsFromFile(const std::string &OverlayFile, vfs::FileSystem &BaseFS) {
  llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> Buffer =
      BaseFS.getBufferForFile(OverlayFile);
  if (!Buffer) {
    llvm::errs() << "Can't load virtual filesystem overlay file '"
                 << OverlayFile << "': " << Buffer.getError().message()
                 << ".\n";
    return nullptr;
  }

  IntrusiveRefCntPtr<vfs::FileSystem> FS = vfs::getVFSFromYAML(
      std::move(Buffer.get()), /*DiagHandler*/ nullptr, OverlayFile);
  if (!FS) {
    llvm::errs() << "Error: invalid virtual filesystem overlay file '"
                 << OverlayFile << "'.\n";
    return nullptr;
  }
  return FS;
}

static StringRef closest(StringRef Value, const StringSet<> &Allowed) {
  unsigned MaxEdit = 5U;
  StringRef Closest;
  for (auto Item : Allowed.keys()) {
    const unsigned Cur = Value.edit_distance_insensitive(Item, true, MaxEdit);
    if (Cur < MaxEdit) {
      Closest = Item;
      MaxEdit = Cur;
    }
  }
  return Closest;
}

static constexpr StringLiteral VerifyConfigWarningEnd = " [-verify-config]\n";

static bool verifyChecks(const StringSet<> &AllChecks, StringRef CheckGlob,
                         StringRef Source) {
  const GlobList Globs(CheckGlob);
  bool AnyInvalid = false;
  for (const auto &Item : Globs.getItems()) {
    if (Item.Text.starts_with("clang-diagnostic"))
      continue;
    if (llvm::none_of(AllChecks.keys(),
                      [&Item](StringRef S) { return Item.Regex.match(S); })) {
      AnyInvalid = true;
      if (Item.Text.contains('*'))
        llvm::WithColor::warning(llvm::errs(), Source)
            << "check glob '" << Item.Text << "' doesn't match any known check"
            << VerifyConfigWarningEnd;
      else {
        llvm::raw_ostream &Output =
            llvm::WithColor::warning(llvm::errs(), Source)
            << "unknown check '" << Item.Text << '\'';
        const llvm::StringRef Closest = closest(Item.Text, AllChecks);
        if (!Closest.empty())
          Output << "; did you mean '" << Closest << '\'';
        Output << VerifyConfigWarningEnd;
      }
    }
  }
  return AnyInvalid;
}

static bool verifyFileExtensions(
    const std::vector<std::string> &HeaderFileExtensions,
    const std::vector<std::string> &ImplementationFileExtensions,
    StringRef Source) {
  bool AnyInvalid = false;
  for (const auto &HeaderExtension : HeaderFileExtensions) {
    for (const auto &ImplementationExtension : ImplementationFileExtensions) {
      if (HeaderExtension == ImplementationExtension) {
        AnyInvalid = true;
        auto &Output = llvm::WithColor::warning(llvm::errs(), Source)
                       << "HeaderFileExtension '" << HeaderExtension << '\''
                       << " is the same as ImplementationFileExtension '"
                       << ImplementationExtension << '\'';
        Output << VerifyConfigWarningEnd;
      }
    }
  }
  return AnyInvalid;
}

static bool verifyOptions(const llvm::StringSet<> &ValidOptions,
                          const ClangTidyOptions::OptionMap &OptionMap,
                          StringRef Source) {
  bool AnyInvalid = false;
  for (auto Key : OptionMap.keys()) {
    if (ValidOptions.contains(Key))
      continue;
    AnyInvalid = true;
    auto &Output = llvm::WithColor::warning(llvm::errs(), Source)
                   << "unknown check option '" << Key << '\'';
    const llvm::StringRef Closest = closest(Key, ValidOptions);
    if (!Closest.empty())
      Output << "; did you mean '" << Closest << '\'';
    Output << VerifyConfigWarningEnd;
  }
  return AnyInvalid;
}

static SmallString<256> makeAbsolute(llvm::StringRef Input) {
  if (Input.empty())
    return {};
  SmallString<256> AbsolutePath(Input);
  if (const std::error_code EC = llvm::sys::fs::make_absolute(AbsolutePath)) {
    llvm::errs() << "Can't make absolute path from " << Input << ": "
                 << EC.message() << "\n";
  }
  return AbsolutePath;
}

static llvm::IntrusiveRefCntPtr<vfs::OverlayFileSystem> createBaseFS() {
  llvm::IntrusiveRefCntPtr<vfs::OverlayFileSystem> BaseFS(
      new vfs::OverlayFileSystem(vfs::getRealFileSystem()));

  if (!VfsOverlay.empty()) {
    IntrusiveRefCntPtr<vfs::FileSystem> VfsFromFile =
        getVfsFromFile(VfsOverlay, *BaseFS);
    if (!VfsFromFile)
      return nullptr;
    BaseFS->pushOverlay(std::move(VfsFromFile));
  }
  return BaseFS;
}

int clangTidyMain(int argc, const char **argv) {
  const llvm::InitLLVM X(argc, argv);
  SmallVector<const char *> Args{argv, argv + argc};

  // expand parameters file to argc and argv.
  llvm::BumpPtrAllocator Alloc;
  llvm::cl::TokenizerCallback Tokenizer =
      llvm::Triple(llvm::sys::getProcessTriple()).isOSWindows()
          ? llvm::cl::TokenizeWindowsCommandLine
          : llvm::cl::TokenizeGNUCommandLine;
  llvm::cl::ExpansionContext ECtx(Alloc, Tokenizer);
  if (llvm::Error Err = ECtx.expandResponseFiles(Args)) {
    llvm::WithColor::error() << llvm::toString(std::move(Err)) << "\n";
    return 1;
  }
  argc = static_cast<int>(Args.size());
  argv = Args.data();

  // Enable help for -load option, if plugins are enabled.
  if (cl::Option *LoadOpt = cl::getRegisteredOptions().lookup("load"))
    LoadOpt->addCategory(ClangTidyCategory);

  llvm::Expected<CommonOptionsParser> OptionsParser =
      CommonOptionsParser::create(argc, argv, ClangTidyCategory,
                                  cl::ZeroOrMore);
  if (!OptionsParser) {
    llvm::WithColor::error() << llvm::toString(OptionsParser.takeError());
    return 1;
  }

  const llvm::IntrusiveRefCntPtr<vfs::OverlayFileSystem> BaseFS =
      createBaseFS();
  if (!BaseFS)
    return 1;

  auto OwningOptionsProvider = createOptionsProvider(BaseFS);
  auto *OptionsProvider = OwningOptionsProvider.get();
  if (!OptionsProvider)
    return 1;

  const SmallString<256> ProfilePrefix = makeAbsolute(StoreCheckProfile);

  StringRef FileName("dummy");
  auto PathList = OptionsParser->getSourcePathList();
  if (!PathList.empty())
    FileName = PathList.front();

  const SmallString<256> FilePath = makeAbsolute(FileName);
  ClangTidyOptions EffectiveOptions = OptionsProvider->getOptions(FilePath);

  const std::vector<std::string> EnabledChecks =
      getCheckNames(EffectiveOptions, AllowEnablingAnalyzerAlphaCheckers,
                    ExperimentalCustomChecks);

  if (ExplainConfig) {
    // FIXME: Show other ClangTidyOptions' fields, like ExtraArg.
    std::vector<clang::tidy::ClangTidyOptionsProvider::OptionsSource>
        RawOptions = OptionsProvider->getRawOptions(FilePath);
    for (const std::string &Check : EnabledChecks) {
      for (const auto &[Opts, Source] : llvm::reverse(RawOptions)) {
        if (Opts.Checks && GlobList(*Opts.Checks).contains(Check)) {
          llvm::outs() << "'" << Check << "' is enabled in the " << Source
                       << ".\n";
          break;
        }
      }
    }
    return 0;
  }

  if (ListChecks) {
    if (EnabledChecks.empty() && !AllowNoChecks) {
      llvm::errs() << "No checks enabled.\n";
      return 1;
    }
    llvm::outs() << "Enabled checks:";
    for (const auto &CheckName : EnabledChecks)
      llvm::outs() << "\n    " << CheckName;
    llvm::outs() << "\n\n";
    return 0;
  }

  if (DumpConfig) {
    EffectiveOptions.CheckOptions =
        getCheckOptions(EffectiveOptions, AllowEnablingAnalyzerAlphaCheckers,
                        ExperimentalCustomChecks);
    ClangTidyOptions OptionsToDump =
        ClangTidyOptions::getDefaults().merge(EffectiveOptions, 0);
    filterCheckOptions(OptionsToDump, EnabledChecks);
    llvm::outs() << configurationAsText(OptionsToDump) << "\n";
    return 0;
  }

  if (VerifyConfig) {
    const std::vector<ClangTidyOptionsProvider::OptionsSource> RawOptions =
        OptionsProvider->getRawOptions(FileName);
    const ChecksAndOptions Valid = getAllChecksAndOptions(
        AllowEnablingAnalyzerAlphaCheckers, ExperimentalCustomChecks);
    bool AnyInvalid = false;
    for (const auto &[Opts, Source] : RawOptions) {
      if (Opts.Checks)
        AnyInvalid |= verifyChecks(Valid.Checks, *Opts.Checks, Source);
      if (Opts.HeaderFileExtensions && Opts.ImplementationFileExtensions)
        AnyInvalid |=
            verifyFileExtensions(*Opts.HeaderFileExtensions,
                                 *Opts.ImplementationFileExtensions, Source);
      AnyInvalid |= verifyOptions(Valid.Options, Opts.CheckOptions, Source);
    }
    if (AnyInvalid)
      return 1;
    llvm::outs() << "No config errors detected.\n";
    return 0;
  }

  if (EnabledChecks.empty()) {
    if (AllowNoChecks) {
      llvm::outs() << "No checks enabled.\n";
      return 0;
    }
    llvm::errs() << "Error: no checks enabled.\n";
    llvm::cl::PrintHelpMessage(/*Hidden=*/false, /*Categorized=*/true);
    return 1;
  }

  if (PathList.empty()) {
    llvm::errs() << "Error: no input files specified.\n";
    llvm::cl::PrintHelpMessage(/*Hidden=*/false, /*Categorized=*/true);
    return 1;
  }

  llvm::InitializeAllTargetInfos();
  llvm::InitializeAllTargetMCs();
  llvm::InitializeAllAsmParsers();

  ClangTidyContext Context(
      std::move(OwningOptionsProvider), AllowEnablingAnalyzerAlphaCheckers,
      EnableModuleHeadersParsing, ExperimentalCustomChecks);
  std::vector<ClangTidyError> Errors =
      runClangTidy(Context, OptionsParser->getCompilations(), PathList, BaseFS,
                   FixNotes, EnableCheckProfile, ProfilePrefix, Quiet);
  const bool FoundErrors = llvm::any_of(Errors, [](const ClangTidyError &E) {
    return E.DiagLevel == ClangTidyError::Error;
  });

  // --fix-errors and --fix-notes imply --fix.
  const FixBehaviour Behaviour = FixNotes             ? FB_FixNotes
                                 : (Fix || FixErrors) ? FB_Fix
                                                      : FB_NoFix;

  const bool DisableFixes = FoundErrors && !FixErrors;

  unsigned WErrorCount = 0;

  handleErrors(Errors, Context, DisableFixes ? FB_NoFix : Behaviour,
               WErrorCount, BaseFS);

  if (!ExportFixes.empty() && !Errors.empty()) {
    std::error_code EC;
    llvm::raw_fd_ostream OS(ExportFixes, EC, llvm::sys::fs::OF_None);
    if (EC) {
      llvm::errs() << "Error opening output file: " << EC.message() << '\n';
      return 1;
    }
    exportReplacements(FilePath.str(), Errors, OS);
  }

  if (!Quiet) {
    printStats(Context.getStats());
    if (DisableFixes && Behaviour != FB_NoFix)
      llvm::errs()
          << "Found compiler errors, but -fix-errors was not specified.\n"
             "Fixes have NOT been applied.\n\n";
  }

  if (WErrorCount) {
    if (!Quiet) {
      const StringRef Plural = WErrorCount == 1 ? "" : "s";
      llvm::errs() << WErrorCount << " warning" << Plural << " treated as error"
                   << Plural << "\n";
    }
    return 1;
  }

  if (FoundErrors) {
    // TODO: Figure out when zero exit code should be used with -fix-errors:
    //   a. when a fix has been applied for an error
    //   b. when a fix has been applied for all errors
    //   c. some other condition.
    // For now always returning zero when -fix-errors is used.
    if (FixErrors)
      return 0;
    if (!Quiet)
      llvm::errs() << "Found compiler error(s).\n";
    return 1;
  }

  return 0;
}

} // namespace clang::tidy
