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py/builtinimport: Handle empty sys.path correctly. 

If sys.path is enabled, but empty, this will now no longer search the
filesystem. Previously an empty sys.path was equivalent to having
`sys.path=[""]`. This is a breaking change, but this behavior now matches
CPython.

This also provides an alternative mechanism to the u-prefix to force an
import of a builtin module:

```
import sys
_path = sys.path[:]
sys.path.clear()
import foo  # Forces the built-in foo.
sys.path.extend(_path)
del _path
```

Code size diff is -32 bytes on PYBV11.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
This commit is contained in:
Jim Mussared 2023-05-10 13:02:09 +10:00 committed by Damien George
parent 69dd013919
commit 42f3f66431
1 changed files with 26 additions and 23 deletions
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49
py/builtinimport.c
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@ -117,8 +117,9 @@ STATIC mp_import_stat_t stat_dir_or_file(vstr_t *path) {
return stat_file_py_or_mpy(path);
}
// Given a top-level module, try and find it in each of the sys.path entries
// via stat_dir_or_file.
// Given a top-level module name, try and find it in each of the sys.path
// entries. Note: On success, the dest argument will be updated to the matching
// path (i.e. "<entry>/mod_name(.py)").
STATIC mp_import_stat_t stat_top_level_dir_or_file(qstr mod_name, vstr_t *dest) {
DEBUG_printf("stat_top_level_dir_or_file: '%s'\n", qstr_str(mod_name));
#if MICROPY_PY_SYS
@ -126,32 +127,34 @@ STATIC mp_import_stat_t stat_top_level_dir_or_file(qstr mod_name, vstr_t *dest)
mp_obj_t *path_items;
mp_obj_list_get(mp_sys_path, &path_num, &path_items);
if (path_num > 0) {
// go through each path looking for a directory or file
for (size_t i = 0; i < path_num; i++) {
vstr_reset(dest);
size_t p_len;
const char *p = mp_obj_str_get_data(path_items[i], &p_len);
if (p_len > 0) {
vstr_add_strn(dest, p, p_len);
vstr_add_char(dest, PATH_SEP_CHAR[0]);
}
vstr_add_str(dest, qstr_str(mod_name));
mp_import_stat_t stat = stat_dir_or_file(dest);
if (stat != MP_IMPORT_STAT_NO_EXIST) {
return stat;
}
// go through each sys.path entry, trying to import "<entry>/<mod_name>".
for (size_t i = 0; i < path_num; i++) {
vstr_reset(dest);
size_t p_len;
const char *p = mp_obj_str_get_data(path_items[i], &p_len);
if (p_len > 0) {
// Add the path separator (unless the entry is "", i.e. cwd).
vstr_add_strn(dest, p, p_len);
vstr_add_char(dest, PATH_SEP_CHAR[0]);
}
vstr_add_str(dest, qstr_str(mod_name));
mp_import_stat_t stat = stat_dir_or_file(dest);
if (stat != MP_IMPORT_STAT_NO_EXIST) {
return stat;
}
// could not find a directory or file
return MP_IMPORT_STAT_NO_EXIST;
}
#endif
// mp_sys_path is empty (or not enabled), so just stat the given path
// directly.
// sys.path was empty or no matches, do not search the filesystem or
// frozen code.
return MP_IMPORT_STAT_NO_EXIST;
#else
// mp_sys_path is not enabled, so just stat the given path directly.
vstr_add_str(dest, qstr_str(mod_name));
return stat_dir_or_file(dest);
#endif
}
#if MICROPY_MODULE_FROZEN_STR || MICROPY_ENABLE_COMPILER