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

[Baranov Victor 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);
+}
----------------
vbvictor wrote:

The question is can we both iterate over `llvm::StringMap` and erase elements from it. For `std::unordered_map::erase` we [can](https://en.cppreference.com/w/cpp/container/unordered_map/erase), but I don't know for sure about `llvm::StringMap::erase`. Even if it could like `std::unordered_map::erase`, it still takes some manual management of iterators that I don't like:
```cpp
    std::unordered_map<int, std::string> c =
    {
        {1, "one"}, {2, "two"}, {3, "three"},
        {4, "four"}, {5, "five"}, {6, "six"}
    };
    // erase all odd numbers from c
    for (auto it = c.begin(); it != c.end();)
    {
        if (it->first % 2 != 0)
            it = c.erase(it);
        else
            ++it;
    }
```
My code is not in a hot path by any means and the number of check options is relatively small, so I'd keep readability over little performance gain.

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