client API: deprecate qthelper.hpp

It's a WTF that we have something as specific in the API. It could be
argued that we should provide helpers for other language and GUI toolkit
combinations. Obviously that's not going to scale, and it's somewhat
likely that it will bitrot. The rest is said in the API changelog.

DOCS/client-api-changes.rst

@@ -55,6 +55,12 @@ API changes
             mpv_opengl_cb_report_flip => mpv_render_context_report_swap
             mpv_opengl_cb_uninit_gl => mpv_render_context_free
           The VO opengl-cb is also renamed to "libmpv".
+        - deprecate the qthelper.hpp header file. This provided some C++ helper
+          utility functions for Qt with use of libmpv. There is no reason to
+          keep this in the mpv git repository, nor to make it part of the libmpv
+          API. If you're using this header, you can safely copy it into your
+          project - it uses only libmpv public API. Alternatively, it could be
+          maintained in a separate repository by interested parties.
  1.27   - make opengl-cb the default VO. This causes a subtle behavior change
           if the API user called mpv_opengl_cb_init_gl(), but does not set
           the "vo" option. Before, it would still have used another VO (like

libmpv/qthelper.hpp

@@ -13,6 +13,15 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#ifndef MPV_CLIENT_API_QTHELPER_H_
+#define MPV_CLIENT_API_QTHELPER_H_
+
+#include <mpv/client.h>
+
+#if !MPV_ENABLE_DEPRECATED
+#error "This helper is deprecated. Copy it into your project instead."
+#else
+
 /**
  * Note: these helpers are provided for convenience for C++/Qt applications.
  * This is based on the public API in client.h, and it does not encode any
@@ -21,9 +30,6 @@
  * for other languages.
  */
 
-#ifndef MPV_CLIENT_API_QTHELPER_H_
-#define MPV_CLIENT_API_QTHELPER_H_
-
 #include <cstring>
 
 #include <QVariant>
@@ -33,8 +39,6 @@
 #include <QSharedPointer>
 #include <QMetaType>
 
-#include <mpv/client.h>
-
 namespace mpv {
 namespace qt {
 
@@ -377,4 +381,6 @@ static inline QVariant command(mpv_handle *ctx, const QVariant &args)
 
 Q_DECLARE_METATYPE(mpv::qt::ErrorReturn)
 
+#endif /* else #if MPV_ENABLE_DEPRECATED */
+
 #endif