diff --git a/ClangTidyCheck.h b/ClangTidyCheck.h
index 17e9df9..656a2f0 100644
--- a/ClangTidyCheck.h
+++ b/ClangTidyCheck.h
@@ -184,13 +184,13 @@ class ClangTidyCheck : public ast_matchers::MatchFinder::MatchCallback {
     /// integral type ``T``.
     ///
     /// Reads the option with the check-local name \p LocalName from the
-    /// ``CheckOptions``. If the corresponding key is not present, return
-    /// ``std::nullopt``.
+    /// ``CheckOptions``. If the corresponding key is not present,
+    ///  return ``std::nullopt``.
     ///
     /// If the corresponding key can't be parsed as a ``T``, emit a
     /// diagnostic and return ``std::nullopt``.
     template <typename T>
-    std::enable_if_t<std::is_integral<T>::value, std::optional<T>>
+    std::enable_if_t<std::is_integral_v<T>, std::optional<T>>
     get(StringRef LocalName) const {
       if (std::optional<StringRef> Value = get(LocalName)) {
         T Result{};
@@ -201,6 +201,31 @@ class ClangTidyCheck : public ast_matchers::MatchFinder::MatchCallback {
       return std::nullopt;
     }
 
+    /// Read a named option from the ``Context`` and parse it as an
+    /// integral type ``T``.
+    ///
+    /// Reads the option with the check-local name \p LocalName from the
+    /// ``CheckOptions``. If the corresponding key is `none`, `null`,
+    /// `-1` or empty, return ``std::nullopt``. If the corresponding
+    /// key is not present, return \p Default.
+    ///
+    /// If the corresponding key can't be parsed as a ``T``, emit a
+    /// diagnostic and return \p Default.
+    template <typename T>
+    std::enable_if_t<std::is_integral_v<T>, std::optional<T>>
+    get(StringRef LocalName, std::optional<T> Default) const {
+      if (std::optional<StringRef> Value = get(LocalName)) {
+        if (Value == "" || Value == "none" || Value == "null" ||
+            (std::is_unsigned_v<T> && Value == "-1"))
+          return std::nullopt;
+        T Result{};
+        if (!StringRef(*Value).getAsInteger(10, Result))
+          return Result;
+        diagnoseBadIntegerOption(NamePrefix + LocalName, *Value);
+      }
+      return Default;
+    }
+
     /// Read a named option from the ``Context`` and parse it as an
     /// integral type ``T``.
     ///
@@ -211,8 +236,8 @@ class ClangTidyCheck : public ast_matchers::MatchFinder::MatchCallback {
     /// If the corresponding key can't be parsed as a ``T``, emit a
     /// diagnostic and return \p Default.
     template <typename T>
-    std::enable_if_t<std::is_integral<T>::value, T> get(StringRef LocalName,
-                                                        T Default) const {
+    std::enable_if_t<std::is_integral_v<T>, T> get(StringRef LocalName,
+                                                   T Default) const {
       return get<T>(LocalName).value_or(Default);
     }
 
@@ -227,7 +252,7 @@ class ClangTidyCheck : public ast_matchers::MatchFinder::MatchCallback {
     /// If the corresponding key can't be parsed as a ``T``, emit a
     /// diagnostic and return ``std::nullopt``.
     template <typename T>
-    std::enable_if_t<std::is_integral<T>::value, std::optional<T>>
+    std::enable_if_t<std::is_integral_v<T>, std::optional<T>>
     getLocalOrGlobal(StringRef LocalName) const {
       std::optional<StringRef> ValueOr = get(LocalName);
       bool IsGlobal = false;
@@ -245,6 +270,39 @@ class ClangTidyCheck : public ast_matchers::MatchFinder::MatchCallback {
       return std::nullopt;
     }
 
+    /// Read a named option from the ``Context`` and parse it as an
+    /// integral type ``T``.
+    ///
+    /// Reads the option with the check-local name \p LocalName from local or
+    /// global ``CheckOptions``. Gets local option first. If local is not
+    /// present, falls back to get global option. If global option is not
+    /// present either, return \p Default. If the value value was found
+    /// and equals ``none``, ``null``, ``-1`` or empty, return ``std::nullopt``.
+    ///
+    /// If the corresponding key can't be parsed as a ``T``, emit a
+    /// diagnostic and return \p Default.
+    template <typename T>
+    std::enable_if_t<std::is_integral_v<T>, std::optional<T>>
+    getLocalOrGlobal(StringRef LocalName, std::optional<T> Default) const {
+      std::optional<StringRef> ValueOr = get(LocalName);
+      bool IsGlobal = false;
+      if (!ValueOr) {
+        IsGlobal = true;
+        ValueOr = getLocalOrGlobal(LocalName);
+        if (!ValueOr)
+          return Default;
+      }
+      T Result{};
+      if (ValueOr == "" || ValueOr == "none" || ValueOr == "null" ||
+          (std::is_unsigned_v<T> && ValueOr == "-1"))
+        return std::nullopt;
+      if (!StringRef(*ValueOr).getAsInteger(10, Result))
+        return Result;
+      diagnoseBadIntegerOption(
+          IsGlobal ? Twine(LocalName) : NamePrefix + LocalName, *ValueOr);
+      return Default;
+    }
+
     /// Read a named option from the ``Context`` and parse it as an
     /// integral type ``T``.
     ///
@@ -256,7 +314,7 @@ class ClangTidyCheck : public ast_matchers::MatchFinder::MatchCallback {
     /// If the corresponding key can't be parsed as a ``T``, emit a
     /// diagnostic and return \p Default.
     template <typename T>
-    std::enable_if_t<std::is_integral<T>::value, T>
+    std::enable_if_t<std::is_integral_v<T>, T>
     getLocalOrGlobal(StringRef LocalName, T Default) const {
       return getLocalOrGlobal<T>(LocalName).value_or(Default);
     }
@@ -274,7 +332,7 @@ class ClangTidyCheck : public ast_matchers::MatchFinder::MatchCallback {
     /// \ref clang::tidy::OptionEnumMapping must be specialized for ``T`` to
     /// supply the mapping required to convert between ``T`` and a string.
     template <typename T>
-    std::enable_if_t<std::is_enum<T>::value, std::optional<T>>
+    std::enable_if_t<std::is_enum_v<T>, std::optional<T>>
     get(StringRef LocalName, bool IgnoreCase = false) const {
       if (std::optional<int64_t> ValueOr =
               getEnumInt(LocalName, typeEraseMapping<T>(), false, IgnoreCase))
@@ -286,8 +344,8 @@ class ClangTidyCheck : public ast_matchers::MatchFinder::MatchCallback {
     /// enum type ``T``.
     ///
     /// Reads the option with the check-local name \p LocalName from the
-    /// ``CheckOptions``. If the corresponding key is not present, return
-    /// \p Default.
+    /// ``CheckOptions``. If the corresponding key is not present,
+    /// return \p Default.
     ///
     /// If the corresponding key can't be parsed as a ``T``, emit a
     /// diagnostic and return \p Default.
@@ -295,8 +353,8 @@ class ClangTidyCheck : public ast_matchers::MatchFinder::MatchCallback {
     /// \ref clang::tidy::OptionEnumMapping must be specialized for ``T`` to
     /// supply the mapping required to convert between ``T`` and a string.
     template <typename T>
-    std::enable_if_t<std::is_enum<T>::value, T>
-    get(StringRef LocalName, T Default, bool IgnoreCase = false) const {
+    std::enable_if_t<std::is_enum_v<T>, T> get(StringRef LocalName, T Default,
+                                               bool IgnoreCase = false) const {
       return get<T>(LocalName, IgnoreCase).value_or(Default);
     }
 
@@ -314,7 +372,7 @@ class ClangTidyCheck : public ast_matchers::MatchFinder::MatchCallback {
     /// \ref clang::tidy::OptionEnumMapping must be specialized for ``T`` to
     /// supply the mapping required to convert between ``T`` and a string.
     template <typename T>
-    std::enable_if_t<std::is_enum<T>::value, std::optional<T>>
+    std::enable_if_t<std::is_enum_v<T>, std::optional<T>>
     getLocalOrGlobal(StringRef LocalName, bool IgnoreCase = false) const {
       if (std::optional<int64_t> ValueOr =
               getEnumInt(LocalName, typeEraseMapping<T>(), true, IgnoreCase))
@@ -336,7 +394,7 @@ class ClangTidyCheck : public ast_matchers::MatchFinder::MatchCallback {
     /// \ref clang::tidy::OptionEnumMapping must be specialized for ``T`` to
     /// supply the mapping required to convert between ``T`` and a string.
     template <typename T>
-    std::enable_if_t<std::is_enum<T>::value, T>
+    std::enable_if_t<std::is_enum_v<T>, T>
     getLocalOrGlobal(StringRef LocalName, T Default,
                      bool IgnoreCase = false) const {
       return getLocalOrGlobal<T>(LocalName, IgnoreCase).value_or(Default);
@@ -350,19 +408,32 @@ class ClangTidyCheck : public ast_matchers::MatchFinder::MatchCallback {
     /// Stores an option with the check-local name \p LocalName with
     /// integer value \p Value to \p Options.
     template <typename T>
-    std::enable_if_t<std::is_integral<T>::value>
+    std::enable_if_t<std::is_integral_v<T>>
     store(ClangTidyOptions::OptionMap &Options, StringRef LocalName,
           T Value) const {
       storeInt(Options, LocalName, Value);
     }
 
+    /// Stores an option with the check-local name \p LocalName with
+    /// integer value \p Value to \p Options. If the value is empty
+    /// stores ``
+    template <typename T>
+    std::enable_if_t<std::is_integral_v<T>>
+    store(ClangTidyOptions::OptionMap &Options, StringRef LocalName,
+          std::optional<T> Value) const {
+      if (Value)
+        storeInt(Options, LocalName, *Value);
+      else
+        store(Options, LocalName, "none");
+    }
+
     /// Stores an option with the check-local name \p LocalName as the string
     /// representation of the Enum \p Value to \p Options.
     ///
     /// \ref clang::tidy::OptionEnumMapping must be specialized for ``T`` to
     /// supply the mapping required to convert between ``T`` and a string.
     template <typename T>
-    std::enable_if_t<std::is_enum<T>::value>
+    std::enable_if_t<std::is_enum_v<T>>
     store(ClangTidyOptions::OptionMap &Options, StringRef LocalName,
           T Value) const {
       ArrayRef<std::pair<T, StringRef>> Mapping =
@@ -383,7 +454,7 @@ class ClangTidyCheck : public ast_matchers::MatchFinder::MatchCallback {
                                       bool CheckGlobal, bool IgnoreCase) const;
 
     template <typename T>
-    std::enable_if_t<std::is_enum<T>::value, std::vector<NameAndValue>>
+    std::enable_if_t<std::is_enum_v<T>, std::vector<NameAndValue>>
     typeEraseMapping() const {
       ArrayRef<std::pair<T, StringRef>> Mapping =
           OptionEnumMapping<T>::getEnumMapping();
diff --git a/ClangTidyDiagnosticConsumer.h b/ClangTidyDiagnosticConsumer.h
index 15f1b67..9280eb1 100644
--- a/ClangTidyDiagnosticConsumer.h
+++ b/ClangTidyDiagnosticConsumer.h
@@ -70,7 +70,8 @@ class ClangTidyContext {
 public:
   /// Initializes \c ClangTidyContext instance.
   ClangTidyContext(std::unique_ptr<ClangTidyOptionsProvider> OptionsProvider,
-                   bool AllowEnablingAnalyzerAlphaCheckers = false);
+                   bool AllowEnablingAnalyzerAlphaCheckers = false,
+                   bool EnableModuleHeadersParsing = false);
   /// Sets the DiagnosticsEngine that diag() will emit diagnostics to.
   // FIXME: this is required initialization, and should be a constructor param.
   // Fix the context -> diag engine -> consumer -> context initialization cycle.
@@ -86,10 +87,10 @@ class ClangTidyContext {
   /// tablegen'd diagnostic IDs.
   /// FIXME: Figure out a way to manage ID spaces.
   DiagnosticBuilder diag(StringRef CheckName, SourceLocation Loc,
-                         StringRef Message,
+                         StringRef Description,
                          DiagnosticIDs::Level Level = DiagnosticIDs::Warning);
 
-  DiagnosticBuilder diag(StringRef CheckName, StringRef Message,
+  DiagnosticBuilder diag(StringRef CheckName, StringRef Description,
                          DiagnosticIDs::Level Level = DiagnosticIDs::Warning);
 
   DiagnosticBuilder diag(const tooling::Diagnostic &Error);
@@ -198,6 +199,12 @@ class ClangTidyContext {
     return AllowEnablingAnalyzerAlphaCheckers;
   }
 
+  // This method determines whether preprocessor-level module header parsing is
+  // enabled using the `--experimental-enable-module-headers-parsing` option.
+  bool canEnableModuleHeadersParsing() const {
+    return EnableModuleHeadersParsing;
+  }
+
   void setSelfContainedDiags(bool Value) { SelfContainedDiags = Value; }
 
   bool areDiagsSelfContained() const { return SelfContainedDiags; }
@@ -205,11 +212,11 @@ class ClangTidyContext {
   using DiagLevelAndFormatString = std::pair<DiagnosticIDs::Level, std::string>;
   DiagLevelAndFormatString getDiagLevelAndFormatString(unsigned DiagnosticID,
                                                        SourceLocation Loc) {
-    return DiagLevelAndFormatString(
+    return {
         static_cast<DiagnosticIDs::Level>(
             DiagEngine->getDiagnosticLevel(DiagnosticID, Loc)),
         std::string(
-            DiagEngine->getDiagnosticIDs()->getDescription(DiagnosticID)));
+            DiagEngine->getDiagnosticIDs()->getDescription(DiagnosticID))};
   }
 
   void setOptionsCollector(llvm::StringSet<> *Collector) {
@@ -221,7 +228,7 @@ class ClangTidyContext {
   // Writes to Stats.
   friend class ClangTidyDiagnosticConsumer;
 
-  DiagnosticsEngine *DiagEngine;
+  DiagnosticsEngine *DiagEngine = nullptr;
   std::unique_ptr<ClangTidyOptionsProvider> OptionsProvider;
 
   std::string CurrentFile;
@@ -241,12 +248,13 @@ class ClangTidyContext {
 
   llvm::DenseMap<unsigned, std::string> CheckNamesByDiagnosticID;
 
-  bool Profile;
+  bool Profile = false;
   std::string ProfilePrefix;
 
   bool AllowEnablingAnalyzerAlphaCheckers;
+  bool EnableModuleHeadersParsing;
 
-  bool SelfContainedDiags;
+  bool SelfContainedDiags = false;
 
   NoLintDirectiveHandler NoLintHandler;
   llvm::StringSet<> *OptionsCollector = nullptr;
@@ -305,9 +313,9 @@ class ClangTidyDiagnosticConsumer : public DiagnosticConsumer {
   bool EnableNolintBlocks;
   std::vector<ClangTidyError> Errors;
   std::unique_ptr<llvm::Regex> HeaderFilter;
-  bool LastErrorRelatesToUserCode;
-  bool LastErrorPassesLineFilter;
-  bool LastErrorWasIgnored;
+  bool LastErrorRelatesToUserCode = false;
+  bool LastErrorPassesLineFilter = false;
+  bool LastErrorWasIgnored = false;
 };
 
 } // end namespace tidy
diff --git a/ClangTidyModule.h b/ClangTidyModule.h
index 0e55c1e..28f5433 100644
--- a/ClangTidyModule.h
+++ b/ClangTidyModule.h
@@ -70,7 +70,7 @@ class ClangTidyCheckFactories {
   std::vector<std::unique_ptr<ClangTidyCheck>>
   createChecksForLanguage(ClangTidyContext *Context) const;
 
-  typedef llvm::StringMap<CheckFactory> FactoryMap;
+  using FactoryMap = llvm::StringMap<CheckFactory>;
   FactoryMap::const_iterator begin() const { return Factories.begin(); }
   FactoryMap::const_iterator end() const { return Factories.end(); }
   bool empty() const { return Factories.empty(); }
diff --git a/ClangTidyModuleRegistry.h b/ClangTidyModuleRegistry.h
index 30ffe18..78d914b 100644
--- a/ClangTidyModuleRegistry.h
+++ b/ClangTidyModuleRegistry.h
@@ -14,7 +14,7 @@
 
 namespace clang::tidy {
 
-typedef llvm::Registry<ClangTidyModule> ClangTidyModuleRegistry;
+using ClangTidyModuleRegistry = llvm::Registry<ClangTidyModule>;
 
 } // namespace clang::tidy
 
diff --git a/ClangTidyOptions.h b/ClangTidyOptions.h
index b3b7143..e7636cb 100644
--- a/ClangTidyOptions.h
+++ b/ClangTidyOptions.h
@@ -30,7 +30,7 @@ struct FileFilter {
   std::string Name;
 
   /// LineRange is a pair<start, end> (inclusive).
-  typedef std::pair<unsigned, unsigned> LineRange;
+  using LineRange = std::pair<unsigned int, unsigned int>;
 
   /// A list of line ranges in this file, for which we show warnings.
   std::vector<LineRange> LineRanges;
@@ -118,13 +118,13 @@ struct ClangTidyOptions {
     /// files to disambiguate local vs global value from different levels.
     unsigned Priority = 0;
   };
-  typedef std::pair<std::string, std::string> StringPair;
-  typedef llvm::StringMap<ClangTidyValue> OptionMap;
+  using StringPair = std::pair<std::string, std::string>;
+  using OptionMap = llvm::StringMap<ClangTidyValue>;
 
   /// Key-value mapping used to store check-specific options.
   OptionMap CheckOptions;
 
-  typedef std::vector<std::string> ArgList;
+  using ArgList = std::vector<std::string>;
 
   /// Add extra compilation arguments to the end of the list.
   std::optional<ArgList> ExtraArgs;
@@ -165,7 +165,7 @@ class ClangTidyOptionsProvider {
   ///       commandline option is specified, clang-tidy will ignore the
   ///       configuration file.
   ///    * '-checks' commandline option.
-  typedef std::pair<ClangTidyOptions, std::string> OptionsSource;
+  using OptionsSource = std::pair<ClangTidyOptions, std::string>;
 
   /// Returns an ordered vector of OptionsSources, in order of increasing
   /// priority.
@@ -199,9 +199,7 @@ class FileOptionsBaseProvider : public DefaultOptionsProvider {
 protected:
   // A pair of configuration file base name and a function parsing
   // configuration from text in the corresponding format.
-  typedef std::pair<std::string, std::function<llvm::ErrorOr<ClangTidyOptions>(
-                                     llvm::MemoryBufferRef)>>
-      ConfigFileHandler;
+  using ConfigFileHandler = std::pair<std::string, std::function<llvm::ErrorOr<ClangTidyOptions> (llvm::MemoryBufferRef)>>;
 
   /// Configuration file handlers listed in the order of priority.
   ///
@@ -220,7 +218,7 @@ class FileOptionsBaseProvider : public DefaultOptionsProvider {
   ///
   /// With the order of handlers shown above, the ".my-tidy-config" file would
   /// take precedence over ".clang-tidy" if both reside in the same directory.
-  typedef std::vector<ConfigFileHandler> ConfigFileHandlers;
+  using ConfigFileHandlers = std::vector<ConfigFileHandler>;
 
   FileOptionsBaseProvider(ClangTidyGlobalOptions GlobalOptions,
                           ClangTidyOptions DefaultOptions,
@@ -232,7 +230,6 @@ class FileOptionsBaseProvider : public DefaultOptionsProvider {
                           ClangTidyOptions OverrideOptions,
                           ConfigFileHandlers ConfigHandlers);
 
-protected:
   void addRawFileOptions(llvm::StringRef AbsolutePath,
                          std::vector<OptionsSource> &CurOptions);
 
diff --git a/FileExtensionsSet.h b/FileExtensionsSet.h
index 417b1b6..7ca4e6e 100644
--- a/FileExtensionsSet.h
+++ b/FileExtensionsSet.h
@@ -13,7 +13,7 @@
 #include "llvm/ADT/StringRef.h"
 
 namespace clang::tidy {
-typedef llvm::SmallSet<llvm::StringRef, 5> FileExtensionsSet;
+using FileExtensionsSet = llvm::SmallSet<llvm::StringRef, 5>;
 } // namespace clang::tidy
 
 #endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_FILE_EXTENSIONS_SET_H