Add a support for clang tidy to import another configurations files from .clang-tidy

[ykfre]

Summary

add ConfigurationsFilesToImport option - to make it possible to import another configurations files from .clang-tidy, So there will be no need
to duplicate anymore the configuration file among projects, and it will be possible to just point the configuration file to some config in a share.

[JDevlieghere]

Please upload the diff with full context. This would also need a test.

[LegalizeAdulthood]

Please upload a full context diff so that the changes can be properly viewed. Thanks.

[LegalizeAdulthood]

No action taken, removing myself as a reviewer

clang-tools-extra/clang-tidy/ClangTidyOptions.h

   /// Output warnings from system headers matching \c HeaderFilterRegex.
   llvm::Optional<bool> SystemHeaders;
 
+  /// Clang tidy configurations files to import.
+  llvm::Optional<std::vector<std::string>> ConfigurationsFilesToImport;
+
   /// Format code around applied fixes with clang-format using this
   /// style.
   ///

clang-tools-extra/clang-tidy/ClangTidyOptions.cpp

     IO.mapOptional("CheckOptions", NOpts->Options);
     IO.mapOptional("ExtraArgs", Options.ExtraArgs);
     IO.mapOptional("ExtraArgsBefore", Options.ExtraArgsBefore);
+    IO.mapOptional("ConfigurationsFilesToImport", Options.ConfigurationsFilesToImport);
   }
 };
 

 }
 
 llvm::ErrorOr<ClangTidyOptions> parseConfiguration(StringRef Config) {
-  llvm::yaml::Input Input(Config);
-  ClangTidyOptions Options;
-  Input >> Options;
-  if (Input.error())
-    return Input.error();
-  return Options;
+  ClangTidyOptions Options;
+  llvm::yaml::Input Input(Config);
+
+  Input >> Options;
+  if (Input.error())
+    return Input.error();
+  if (!Options.ConfigurationsFilesToImport.hasValue()) {
+    return Options;
+  }
+  for (const auto& file : *Options.ConfigurationsFilesToImport)
+  {
+    llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> Text = llvm::MemoryBuffer::getFile(file);
+        if (std::error_code EC = Text.getError()) {
+            llvm::errs() << "Can't read " << file << ": " << EC.message()
+                << "\n";
+            return EC;
+        }
+    Config = Text->get()->getBuffer();
+    auto ReturnedOptions = parseConfiguration(Config);
+    if (ReturnedOptions)
+    {
+      Options = ReturnedOptions->mergeWith(Options);
+    }
+    else {
+      return ReturnedOptions;
+    }
+  }
+  return Options;
 }
 
 std::string configurationAsText(const ClangTidyOptions &Options) {

clang-tools-extra/docs/clang-tidy/index.rst

   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. If any configuration options have a corresponding command-line
+    file. This file can also imports configuration from another configuration file,
+    using ConfigurationsFilesToImport option.
+    If any configuration options have a corresponding command-line
     option, command-line option takes precedence. The effective
     configuration can be inspected using -dump-config:
 

       Checks:          '-*,some-check'
       WarningsAsErrors: ''
       HeaderFilterRegex: ''
+      ConfigurationsFilesToImport: ['yaml1FilePath', 'yaml2FilePath']
       FormatStyle:     none
       User:            user
       CheckOptions: