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

2 files changed, 15 insertions, 23 deletions

diff --git a/Programs/_freeze_module.c b/Programs/_freeze_module.c
index 316c70d2c7..e3f6c11c8b 100644
--- a/Programs/_freeze_module.c
+++ b/Programs/_freeze_module.c
@@ -23,13 +23,16 @@
    of frozen modules instead, left deliberately blank so as to avoid
    unintentional import of a stale version of _frozen_importlib. */
 
-static const struct _frozen _PyImport_FrozenModules[] = {
+static const struct _frozen no_modules[] = {
     {0, 0, 0} /* sentinel */
 };
 static const struct _module_alias aliases[] = {
     {0, 0} /* sentinel */
 };
 
+const struct _frozen *_PyImport_FrozenBootstrap;
+const struct _frozen *_PyImport_FrozenStdlib;
+const struct _frozen *_PyImport_FrozenTest;
 const struct _frozen *PyImport_FrozenModules;
 const struct _module_alias *_PyImport_FrozenAliases;
 
@@ -188,7 +191,10 @@ main(int argc, char *argv[])
 {
     const char *name, *inpath, *outpath;
 
-    PyImport_FrozenModules = _PyImport_FrozenModules;
+    _PyImport_FrozenBootstrap = no_modules;
+    _PyImport_FrozenStdlib = no_modules;
+    _PyImport_FrozenTest = no_modules;
+    PyImport_FrozenModules = NULL;
     _PyImport_FrozenAliases = aliases;
 
     if (argc != 4) {
diff --git a/Programs/_testembed.c b/Programs/_testembed.c
index 773c6c3e99..6fe18d93a7 100644
--- a/Programs/_testembed.c
+++ b/Programs/_testembed.c
@@ -8,6 +8,7 @@
 #include <Python.h>
 #include "pycore_initconfig.h"    // _PyConfig_InitCompatConfig()
 #include "pycore_runtime.h"       // _PyRuntime
+#include "pycore_import.h"        // _PyImport_FrozenBootstrap
 #include <Python.h>
 #include <inttypes.h>
 #include <stdio.h>
@@ -1804,30 +1805,10 @@ static int test_unicode_id_init(void)
 
 static int test_frozenmain(void)
 {
-    // Get "_frozen_importlib" and "_frozen_importlib_external"
-    // from PyImport_FrozenModules
-    const struct _frozen *importlib = NULL, *importlib_external = NULL;
-    for (const struct _frozen *mod = PyImport_FrozenModules; mod->name != NULL; mod++) {
-        if (strcmp(mod->name, "_frozen_importlib") == 0) {
-            importlib = mod;
-        }
-        else if (strcmp(mod->name, "_frozen_importlib_external") == 0) {
-            importlib_external = mod;
-        }
-    }
-    if (importlib == NULL || importlib_external == NULL) {
-        error("cannot find frozen importlib and importlib_external");
-        return 1;
-    }
-
     static struct _frozen frozen_modules[4] = {
-        {0, 0, 0},  // importlib
-        {0, 0, 0},  // importlib_external
         {"__main__", M_test_frozenmain, sizeof(M_test_frozenmain)},
         {0, 0, 0}   // sentinel
     };
-    frozen_modules[0] = *importlib;
-    frozen_modules[1] = *importlib_external;
 
     char* argv[] = {
         "./argv0",
@@ -1846,7 +1827,12 @@ static int test_frozenmain(void)
 static int list_frozen(void)
 {
     const struct _frozen *p;
-    for (p = PyImport_FrozenModules; ; p++) {
+    for (p = _PyImport_FrozenBootstrap; ; p++) {
+        if (p->name == NULL)
+            break;
+        printf("%s\n", p->name);
+    }
+    for (p = _PyImport_FrozenStdlib; ; p++) {
         if (p->name == NULL)
             break;
         printf("%s\n", p->name);