MNT: move the PyOS_InputHook call up a loop level

If we have returned from the input hook then there is something to read in the
stdin so read it out to the new line before calling the input hook again.

Author: tacaswell

Doc/c-api/veryhigh.rst

@@ -151,8 +151,7 @@ the same library that the Python runtime is using.
    event loops, as done in :file:`Modules/_tkinter.c` in the
    Python source code.
 
-   This function should block until stdin is readable but may return
-   early.
+   This function should block until stdin is readable.
 
    .. versionchanged:: 3.12
       This function is only called from the

Parser/myreadline.c

@@ -38,7 +38,7 @@ int (*PyOS_InputHook)(void) = NULL;
    except if _PyOS_InterruptOccurred() returns true. */
 
 static int
-my_fgets(PyThreadState* tstate, char *buf, int len, FILE *fp, int n)
+my_fgets(PyThreadState* tstate, char *buf, int len, FILE *fp)
 {
 #ifdef MS_WINDOWS
     HANDLE handle;
@@ -53,12 +53,6 @@ my_fgets(PyThreadState* tstate, char *buf, int len, FILE *fp, int n)
 #endif
 
     while (1) {
-        if (PyOS_InputHook != NULL && n == 0 &&
-            // GH-104668: See PyOS_ReadlineFunctionPointer's comment below...
-            _Py_IsMainInterpreter(tstate->interp))
-        {
-            (void)(PyOS_InputHook)();
-        }
 
         errno = 0;
         clearerr(fp);
@@ -313,6 +307,13 @@ PyOS_StdioReadline(FILE *sys_stdin, FILE *sys_stdout, const char *prompt)
     }
     fflush(stderr);
 
+    if (PyOS_InputHook != NULL &&
+        // GH-104668: See PyOS_ReadlineFunctionPointer's comment below...
+        _Py_IsMainInterpreter(tstate->interp))
+    {
+      (void)(PyOS_InputHook)();
+    }
+
     n = 0;
     p = NULL;
     do {
@@ -333,7 +334,7 @@ PyOS_StdioReadline(FILE *sys_stdin, FILE *sys_stdout, const char *prompt)
             return NULL;
         }
         p = pr;
-        int err = my_fgets(tstate, p + n, (int)incr, sys_stdin, n);
+        int err = my_fgets(tstate, p + n, (int)incr, sys_stdin);
         if (err == 1) {
             // Interrupt
             PyMem_RawFree(p);