gh-158140: Resolve lazily imported sibling submodules independently

Author: pablogsal

Include/internal/pycore_import.h

@@ -40,6 +40,9 @@ PyAPI_FUNC(PyObject *) _PyImport_LoadLazyImportTstate(
 // Bind a pending child on module before removing its registration. Return a
 // new reference, NULL without an exception if absent, or NULL on error.
 // Set recheck_dict if a concurrent lookup may have already bound the child.
+extern PyObject *_PyImport_LoadLazySubmodule(PyThreadState *tstate, PyObject *name);
+extern PyObject *_PyImport_GetLazySubmodules(PyThreadState *, PyObject *);
+extern int _PyImport_ClearLazySubmodules(PyThreadState *, PyObject *);
 extern PyObject * _PyImport_TryLoadLazySubmodule(
     PyObject *module, PyObject *attr_name, int *recheck_dict);
 extern PyObject * _PyImport_LazyImportModuleLevelObject(

Include/internal/pycore_interp_structs.h

@@ -356,9 +356,12 @@ struct _import_state {
     // lazily imported. This value is only for debugging/introspection
     // purposes and is not used by the runtime.
     PyObject *lazy_modules;
-    // A dict mapping package names to a set of submodule names that
-    // may need to be imported when an attribute is missing on the package.
+    // A dict mapping package names to dicts of pending child names.
+    // Values are declarations, True for completed imports, or False for
+    // optional from-import attributes.
     PyObject *lazy_pending_submodules;
+    // Cached imports may need to replace a published lazy binding.
+    int has_lazy_submodules;
 #ifdef Py_GIL_DISABLED
     PyMutex lazy_mutex;
 #endif

Include/internal/pycore_lazyimportobject.h

@@ -18,6 +18,9 @@ PyAPI_FUNC(PyObject *) _PyLazyImport_New(
     struct _PyInterpreterFrame *frame, PyObject *builtins,
     PyObject *name, PyObject *fromlist);
 
+extern int _PyLazyImport_IsSubmodule(PyObject *op);
+extern int _PyLazyImport_IsStrictSubmodule(PyObject *op);
+
 extern int _PyLazyImport_IsResolving(PyThreadState *tstate, PyObject *op);
 
 // Resolve a placeholder and replace its binding if it is unchanged or holds
@@ -27,6 +30,11 @@ PyAPI_FUNC(PyObject *) _PyLazyImport_Reify(
     PyThreadState *tstate, PyObject *placeholder,
     PyObject *name, PyObject *ns);
 
+// Optional module lookups preserve from-import and __getattr__ fallbacks.
+extern PyObject *_PyLazyImport_ReifyOptional(
+    PyThreadState *tstate, PyObject *placeholder,
+    PyObject *name, PyObject *ns);
+
 #ifdef __cplusplus
 }
 #endif