fix comment

Author: HerrCai0907

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

@@ -290,15 +290,14 @@ ClangTidyOptions &ClangTidyOptions::mergeWith(const ClangTidyOptions &Other,
   overrideValue(UseColor, Other.UseColor);
   mergeVectors(ExtraArgs, Other.ExtraArgs);
   mergeVectors(ExtraArgsBefore, Other.ExtraArgsBefore);
-
+  // FIXME: how to handle duplicate names check?
+  mergeVectors(CustomChecks, Other.CustomChecks);
   for (const auto &KeyValue : Other.CheckOptions) {
     CheckOptions.insert_or_assign(
         KeyValue.getKey(),
         ClangTidyValue(KeyValue.getValue().Value,
                        KeyValue.getValue().Priority + Order));
   }
-  mergeVectors(CustomChecks, Other.CustomChecks);
-
   return *this;
 }
 

clang-tools-extra/clang-tidy/custom/CustomTidyModule.cpp

@@ -16,8 +16,8 @@ class CustomModule : public ClangTidyModule {
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {}
 };
 
-// FIXME: could be clearer to add parameter of addCheckFactories to pass
-// Options?
+// We need to register the checks more flexibly than builtin modules. The checks
+// will changed dynamically when switching to different source file.
 extern void registerCustomChecks(ClangTidyOptions const &Options,
                                  ClangTidyCheckFactories &Factories) {
   static llvm::SmallSet<llvm::SmallString<32>, 8> CustomCheckNames{};