[clang-tidy] Fix DanglingHandleCheck for the correct conversion operation between basic_string and basic_string_view.

[sbenza]

Summary

Fix DanglingHandleCheck to handle the final implementation of std::string and std::string_view.
These use a conversion operator instead of a conversion constructor.

[hokein]

LGTM

clang-tidy/bugprone/DanglingHandleCheck.cpp

 namespace tidy {
 namespace bugprone {
 
 namespace {
 
 ast_matchers::internal::BindableMatcher<Stmt>
 handleFrom(const ast_matchers::internal::Matcher<RecordDecl> &IsAHandle,
            const ast_matchers::internal::Matcher<Expr> &Arg) {
-  return cxxConstructExpr(hasDeclaration(cxxMethodDecl(ofClass(IsAHandle))),
-                          hasArgument(0, Arg));
+  return expr(
+      anyOf(cxxConstructExpr(hasDeclaration(cxxMethodDecl(ofClass(IsAHandle))),
+                             hasArgument(0, Arg)),
+            cxxMemberCallExpr(hasType(cxxRecordDecl(IsAHandle)),
+                              callee(memberExpr(member(cxxConversionDecl()))),
+                              on(Arg))));
 }
 
 ast_matchers::internal::Matcher<Stmt> handleFromTemporaryValue(
     const ast_matchers::internal::Matcher<RecordDecl> &IsAHandle) {
   // If a ternary operator returns a temporary value, then both branches hold a
   // temporary value. If one of them is not a temporary then it must be copied
   // into one to satisfy the type of the operator.
   const auto TemporaryTernary =

test/clang-tidy/bugprone-dangling-handle.cpp

 template <typename Key, typename Value>
 class map {
  public:
   using value_type = pair<Key, Value>;
   value_type& operator[](const Key& key);
   value_type& operator[](Key&& key);
 };
 
+class basic_string_view;
+
 class basic_string {
  public:
   basic_string();
   basic_string(const char*);
+
+  operator basic_string_view() const noexcept;
+
   ~basic_string();
 };
 
 typedef basic_string string;
 
 class basic_string_view {
  public:
   basic_string_view(const char*);
-  basic_string_view(const basic_string&);
 };
 
 typedef basic_string_view string_view;
 
 }  // namespace std
 
 namespace llvm {