modernize-replace-auto-ptr

This check replaces the uses of the deprecated class std::auto_ptr by std::unique_ptr (introduced in C++11). The transfer of ownership, done by the copy-constructor and the assignment operator, is changed to match std::unique_ptr usage by using explicit calls to std::move().

Migration example:

-void take_ownership_fn(std::auto_ptr<int> int_ptr);
+void take_ownership_fn(std::unique_ptr<int> int_ptr);

 void f(int x) {
-  std::auto_ptr<int> a(new int(x));
-  std::auto_ptr<int> b;
+  std::unique_ptr<int> a(new int(x));
+  std::unique_ptr<int> b;

-  b = a;
-  take_ownership_fn(b);
+  b = std::move(a);
+  take_ownership_fn(std::move(b));
 }

Since std::move() is a library function declared in <utility> it may be necessary to add this include. The check will add the include directive when necessary.

Known Limitations

• If headers modification is not activated or if a header is not allowed to be changed this check will produce broken code (compilation error), where the headers' code will stay unchanged while the code using them will be changed.
• Client code that declares a reference to an std::auto_ptr coming from code that can't be migrated (such as a header coming from a 3^rd party library) will produce a compilation error after migration. This is because the type of the reference will be changed to std::unique_ptr but the type returned by the library won't change, binding a reference to std::unique_ptr from an std::auto_ptr. This pattern doesn't make much sense and usually std::auto_ptr are stored by value (otherwise what is the point in using them instead of a reference or a pointer?).

 // <3rd-party header...>
 std::auto_ptr<int> get_value();
 const std::auto_ptr<int> & get_ref();

 // <calling code (with migration)...>
-std::auto_ptr<int> a(get_value());
+std::unique_ptr<int> a(get_value()); // ok, unique_ptr constructed from auto_ptr

-const std::auto_ptr<int> & p = get_ptr();
+const std::unique_ptr<int> & p = get_ptr(); // won't compile

• Non-instantiated templates aren't modified.

template <typename X>
void f() {
    std::auto_ptr<X> p;
}

// only 'f<int>()' (or similar) will trigger the replacement.

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