gh-124872: Change PyContext_WatchCallback to take PyObject

The PyContext struct is not intended to be public, and users of the
API don't need anything more specific than PyObject.  Also see
gh-78943.

Author: rhansen

Doc/c-api/contextvars.rst

@@ -127,7 +127,7 @@ Context object management functions:
 
    .. versionadded:: 3.14
 
-.. c:type:: int (*PyContext_WatchCallback)(PyContextEvent event, PyContext* ctx)
+.. c:type:: int (*PyContext_WatchCallback)(PyContextEvent event, PyObject* ctx)
 
    Type of a context object watcher callback function.
    If *event* is ``Py_CONTEXT_EVENT_ENTER``, then the callback is invoked

Include/cpython/context.h

@@ -41,7 +41,7 @@ typedef enum {
  * if the callback returns with an exception set, it must return -1. Otherwise
  * it should return 0
  */
-typedef int (*PyContext_WatchCallback)(PyContextEvent, PyContext *);
+typedef int (*PyContext_WatchCallback)(PyContextEvent, PyObject *);
 
 /*
  * Register a per-interpreter callback that will be invoked for context object

Modules/_testcapi/watchers.c

@@ -630,7 +630,7 @@ static int num_context_object_enter_events[NUM_CONTEXT_WATCHERS] = {0, 0};
 static int num_context_object_exit_events[NUM_CONTEXT_WATCHERS] = {0, 0};
 
 static int
-handle_context_watcher_event(int which_watcher, PyContextEvent event, PyContext *ctx) {
+handle_context_watcher_event(int which_watcher, PyContextEvent event, PyObject *ctx) {
     if (event == Py_CONTEXT_EVENT_ENTER) {
         num_context_object_enter_events[which_watcher]++;
     }
@@ -644,22 +644,22 @@ handle_context_watcher_event(int which_watcher, PyContextEvent event, PyContext
 }
 
 static int
-first_context_watcher_callback(PyContextEvent event, PyContext *ctx) {
+first_context_watcher_callback(PyContextEvent event, PyObject *ctx) {
     return handle_context_watcher_event(0, event, ctx);
 }
 
 static int
-second_context_watcher_callback(PyContextEvent event, PyContext *ctx) {
+second_context_watcher_callback(PyContextEvent event, PyObject *ctx) {
     return handle_context_watcher_event(1, event, ctx);
 }
 
 static int
-noop_context_event_handler(PyContextEvent event, PyContext *ctx) {
+noop_context_event_handler(PyContextEvent event, PyObject *ctx) {
     return 0;
 }
 
 static int
-error_context_event_handler(PyContextEvent event, PyContext *ctx) {
+error_context_event_handler(PyContextEvent event, PyObject *ctx) {
     PyErr_SetString(PyExc_RuntimeError, "boom!");
     return -1;
 }

Python/context.c

@@ -124,7 +124,7 @@ static void notify_context_watchers(PyContextEvent event, PyContext *ctx, PyThre
         if (bits & 1) {
             PyContext_WatchCallback cb = interp->context_watchers[i];
             assert(cb != NULL);
-            if (cb(event, ctx) < 0) {
+            if (cb(event, (PyObject *)ctx) < 0) {
                 PyErr_FormatUnraisable(
                     "Exception ignored in %s watcher callback for %R",
                     context_event_name(event), ctx);