[clang-tidy] llvm-twine-local ignores parameters

[njames93]

Summary

Ignore paramater declarations of type ::llvm::Twine, These don't suffer the same use after free risks as local twines.

[aaron.ballman]

LGTM!

clang-tools-extra/clang-tidy/llvm/TwineLocalCheck.cpp

 using namespace clang::ast_matchers;
 
 namespace clang {
 namespace tidy {
 namespace llvm_check {
 
 void TwineLocalCheck::registerMatchers(MatchFinder *Finder) {
   auto TwineType =
-      qualType(hasDeclaration(recordDecl(hasName("::llvm::Twine"))));
-  Finder->addMatcher(varDecl(hasType(TwineType)).bind("variable"), this);
+      qualType(hasDeclaration(cxxRecordDecl(hasName("::llvm::Twine"))));
+  Finder->addMatcher(
+      varDecl(unless(parmVarDecl()), hasType(TwineType)).bind("variable"),
+      this);
 }
 
 void TwineLocalCheck::check(const MatchFinder::MatchResult &Result) {
   const auto *VD = Result.Nodes.getNodeAs<VarDecl>("variable");
   auto Diag = diag(VD->getLocation(),
                    "twine variables are prone to use-after-free bugs");
 
   // If this VarDecl has an initializer try to fix it.

clang-tools-extra/test/clang-tidy/checkers/llvm-twine-local.cpp

 // RUN: %check_clang_tidy %s llvm-twine-local %t
 
 namespace llvm {
 class Twine {
 public:
   Twine(const char *);
   Twine(int);
   Twine();
   Twine &operator+(const Twine &);
 };
 }
 
 using namespace llvm;
 
 void foo(const Twine &x);
+void bar(Twine x);
 
 static Twine Moo = Twine("bark") + "bah";
 // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: twine variables are prone to use-after-free bugs
 // CHECK-MESSAGES: note: FIX-IT applied suggested code changes
 // CHECK-FIXES: static std::string Moo = (Twine("bark") + "bah").str();
 
 int main() {
   const Twine t = Twine("a") + "b" + Twine(42);