bpo-45395: Make custom frozen modules additions instead of replacements. (gh-28778)

Currently custom modules (the array set on PyImport_FrozenModules) replace all the frozen stdlib modules. That can be problematic and is unlikely to be what the user wants. This change treats the custom frozen modules as additions instead. They take precedence over all other frozen modules except for those needed to bootstrap the import system. If the "code" field of an entry in the custom array is NULL then that frozen module is treated as disabled, which allows a custom entry to disable a frozen stdlib module.

This change allows us to get rid of is_essential_frozen_module() and simplifies the logic for which frozen modules should be ignored.

https://bugs.python.org/issue45395

1 files changed, 12 insertions, 7 deletions

diff --git a/Python/frozen.c b/Python/frozen.c
index 499b3b9..15baa97 100644
--- a/Python/frozen.c
+++ b/Python/frozen.c
@@ -63,14 +63,15 @@
 
 /* Note that a negative size indicates a package. */
 
-static const struct _frozen _PyImport_FrozenModules[] = {
-    /* import system */
+static const struct _frozen bootstrap_modules[] = {
     {"_frozen_importlib", _Py_M__importlib__bootstrap,
         (int)sizeof(_Py_M__importlib__bootstrap)},
     {"_frozen_importlib_external", _Py_M__importlib__bootstrap_external,
         (int)sizeof(_Py_M__importlib__bootstrap_external)},
     {"zipimport", _Py_M__zipimport, (int)sizeof(_Py_M__zipimport)},
-
+    {0, 0, 0} /* bootstrap sentinel */
+};
+static const struct _frozen stdlib_modules[] = {
     /* stdlib - startup, without site (python -S) */
     {"abc", _Py_M__abc, (int)sizeof(_Py_M__abc)},
     {"codecs", _Py_M__codecs, (int)sizeof(_Py_M__codecs)},
@@ -87,8 +88,9 @@ static const struct _frozen _PyImport_FrozenModules[] = {
     {"os", _Py_M__os, (int)sizeof(_Py_M__os)},
     {"site", _Py_M__site, (int)sizeof(_Py_M__site)},
     {"stat", _Py_M__stat, (int)sizeof(_Py_M__stat)},
-
-    /* Test module */
+    {0, 0, 0} /* stdlib sentinel */
+};
+static const struct _frozen test_modules[] = {
     {"__hello__", _Py_M____hello__, (int)sizeof(_Py_M____hello__)},
     {"__hello_alias__", _Py_M____hello__, (int)sizeof(_Py_M____hello__)},
     {"__phello_alias__", _Py_M____hello__, -(int)sizeof(_Py_M____hello__)},
@@ -103,8 +105,11 @@ static const struct _frozen _PyImport_FrozenModules[] = {
     {"__phello__.spam", _Py_M____phello___spam,
         (int)sizeof(_Py_M____phello___spam)},
     {"__hello_only__", _Py_M__frozen_only, (int)sizeof(_Py_M__frozen_only)},
-    {0, 0, 0} /* modules sentinel */
+    {0, 0, 0} /* test sentinel */
 };
+const struct _frozen *_PyImport_FrozenBootstrap = bootstrap_modules;
+const struct _frozen *_PyImport_FrozenStdlib = stdlib_modules;
+const struct _frozen *_PyImport_FrozenTest = test_modules;
 
 static const struct _module_alias aliases[] = {
     {"_frozen_importlib", "importlib._bootstrap"},
@@ -124,4 +129,4 @@ const struct _module_alias *_PyImport_FrozenAliases = aliases;
 /* Embedding apps may change this pointer to point to their favorite
    collection of frozen modules: */
 
-const struct _frozen *PyImport_FrozenModules = _PyImport_FrozenModules;
+const struct _frozen *PyImport_FrozenModules = NULL;