py: Automatically provide weak links from "foo" to "ufoo" module name.

This commit implements automatic module weak links for all built-in
modules, by searching for "ufoo" in the built-in module list if "foo"
cannot be found.  This means that all modules named "ufoo" are always
available as "foo".  Also, a port can no longer add any other weak links,
which makes strict the definition of a weak link.

It saves some code size (about 100-200 bytes) on ports that previously had
lots of weak links.

Some changes from the previous behaviour:
- It doesn't intern the non-u module names (eg "foo" is not interned),
  which saves code size, but will mean that "import foo" creates a new qstr
  (namely "foo") in RAM (unless the importing module is frozen).
- help('modules') no longer lists non-u module names, only the u-variants;
  this reduces duplication in the help listing.

Weak links are effectively the same as having a set of symbolic links on
the filesystem that is searched last.  So an "import foo" will search
built-in modules first, then all paths in sys.path, then weak links last,
importing "ufoo" if it exists.  Thus a file called "foo.py" somewhere in
sys.path will still have precedence over the weak link of "foo" to "ufoo".

See issues: #1740, #4449, #5229, #5241.

1 files changed, 0 insertions, 4 deletions

diff --git a/py/builtinhelp.c b/py/builtinhelp.c
index a7fede00ac..8f162d8858 100644
--- a/py/builtinhelp.c
+++ b/py/builtinhelp.c
@@ -80,10 +80,6 @@ STATIC void mp_help_print_modules(void) {
 
     mp_help_add_from_map(list, &mp_builtin_module_map);
 
-    #if MICROPY_MODULE_WEAK_LINKS
-    mp_help_add_from_map(list, &mp_builtin_module_weak_links_map);
-    #endif
-
     #if MICROPY_MODULE_FROZEN_STR
     extern const char mp_frozen_str_names[];
     mp_help_add_from_names(list, mp_frozen_str_names);