[clang-tools-extra] [clang-tidy][C++20] Add support for Initialization Forwarding in structs and Nested Objects within modernize-use-emplace (PR #131969)

[Baranov Victor via cfe-commits]

================
@@ -332,19 +376,42 @@ void UseEmplaceCheck::check(const MatchFinder::MatchResult &Result) {
   }();
 
   assert(Call && "No call matched");
-  assert((CtorCall || MakeCall) && "No push_back parameter matched");
+  assert((CtorCall || MakeCall || AggInitCall) &&
+         "No push_back parameter matched");
 
   if (IgnoreImplicitConstructors && CtorCall && CtorCall->getNumArgs() >= 1 &&
       CtorCall->getArg(0)->getSourceRange() == CtorCall->getSourceRange())
     return;
 
+  if (IgnoreImplicitConstructors && AggInitCall &&
+      AggInitCall->getNumInits() >= 1 &&
+      AggInitCall->getInit(0)->getSourceRange() ==
+          AggInitCall->getSourceRange())
+    return;
+
+  if (getLangOpts().LangStd >= LangStandard::lang_cxx20 && AggInitCall) {
+    for (const auto *Init : AggInitCall->inits()) {
+      if (const auto *InnerConstructorExpr = unwrapToConstructorExpr(Init)) {
+        // consume all args if it's an empty constructor call so that we can ->
+        // T{} -> emplace_back()
+        if (InnerConstructorExpr && InnerConstructorExpr->getNumArgs() == 0) {
----------------
vbvictor wrote:

```suggestion
        if (InnerConstructorExpr->getNumArgs() == 0) {
```
No need to check that `InnerConstructorExpr` is not null here because it's done in previous `if`

https://github.com/llvm/llvm-project/pull/131969