[clang-tools-extra] [clang-tidy] filter check options by enabled checks in '--dump-config' (PR #147142)

[Victor Chernyakin via cfe-commits]

================
@@ -503,6 +503,21 @@ getCheckNames(const ClangTidyOptions &Options,
   return Factory.getCheckNames();
 }
 
+void filterCheckOptions(ClangTidyOptions &Options,
+                        const std::vector<std::string> &EnabledChecks) {
+  StringSet<> EnabledChecksSet(llvm::from_range, EnabledChecks);
+  ClangTidyOptions::OptionMap FilteredOptions;
+  for (const auto &[OptionName, Value] : Options.CheckOptions) {
+    const size_t CheckNameEndPos = OptionName.find('.');
+    if (CheckNameEndPos == StringRef::npos)
+      continue;
+    const StringRef CheckName = OptionName.substr(0, CheckNameEndPos);
+    if (EnabledChecksSet.contains(CheckName))
+      FilteredOptions[OptionName] = Value;
+  }
+  Options.CheckOptions = std::move(FilteredOptions);
+}
----------------
localspook wrote:

Instead of building up a new `OptionMap` and then overwriting `Options.CheckOptions`, could we avoid allocations by directly erasing the elements we don't want to keep from `Options.CheckOptions`? Something like this (not tested):
```diff
void filterCheckOptions(ClangTidyOptions &Options,
                        const std::vector<std::string> &EnabledChecks) {
  StringSet<> EnabledChecksSet(llvm::from_range, EnabledChecks);
-  ClangTidyOptions::OptionMap FilteredOptions;
-  for (const auto &[OptionName, Value] : Options.CheckOptions) {
+ for (auto I = Options.CheckOptions.begin(), E = Options.CheckOptions.end(); I != E; ++I) {
+ const auto &[OptionName, Value] = *I;
   const size_t CheckNameEndPos = OptionName.find('.');
    if (CheckNameEndPos == StringRef::npos)
      continue;
    const StringRef CheckName = OptionName.substr(0, CheckNameEndPos);
-    if (EnabledChecksSet.contains(CheckName))
-      FilteredOptions[OptionName] = Value;
+    if (!EnabledChecksSet.contains(CheckName))
+      Options.CheckOptions.erase(I);
  }
-  Options.CheckOptions = std::move(FilteredOptions);
}
```

https://github.com/llvm/llvm-project/pull/147142