Eager child attributes in excluded modules

Summary:
Some modules imported at the application level, could be importing modules whose parent is listed in the eager list. The attributes added to the (eager) parent would then be lazy attributes. This is undesirable for the purposes of having whole packages flagged as eager.

For example, doing `import torch.distributed.fsdp` from a non-eager module, adds `fsdp` as a lazy attribute to `torch.distributed` (even when `torch.*` is in the "eager list"). This produces a problem with a PyTorch subsystem that walks all objects inside all the `torch` namespace. This in turn triggers imports and eventually import cycles. This diff prevents adding lazy attributes pointing to children submodules on modules that are flagged as eager.

This is the traceback for the example: P834477377

Reviewed By: cxxxs

Differential Revision: D49647778

fbshipit-source-id: d475bc18964533f2ca810fa3417874c4b9de9752

Lib/test/lazyimports/parent_eager_import.py

@@ -0,0 +1,12 @@
+import self
+if not self._lazy_imports:
+    self.skipTest("Test relevant only when running with lazy imports enabled")
+
+import importlib
+
+importlib.set_lazy_imports(excluding=["test.lazyimports.data.metasyntactic.foo.bar"])
+
+import test.lazyimports.data.metasyntactic.foo.bar as bar
+import test.lazyimports.data.metasyntactic.foo.bar.baz
+
+self.assertFalse(importlib.is_lazy_import(bar.__dict__, "baz"))

Python/import.c

@@ -1648,6 +1648,7 @@ add_lazy_modules(PyThreadState *tstate, PyObject *builtins, PyObject *name)
         }
         Py_DECREF(lazy_submodules);
     }
+    PyObject *filter = tstate->interp->eager_imports;
     while (1) {
         Py_ssize_t dot = PyUnicode_FindChar(name, '.', 0, PyUnicode_GET_LENGTH(name), -1);
         if (dot < 0) {
@@ -1657,6 +1658,11 @@ add_lazy_modules(PyThreadState *tstate, PyObject *builtins, PyObject *name)
         if (parent == NULL) {
             goto error;
         }
+        if (filter != NULL && PySequence_Contains(filter, parent)) {
+            ret = 0; /* If the direct parent is eager, load eagerly */
+            goto end;
+        }
+        filter = NULL;
         Py_XDECREF(child);
         child = PyUnicode_Substring(name, dot + 1, PyUnicode_GET_LENGTH(name));
         if (child == NULL) {