importlib._bootstrap._ERR_MSG removed without deprecation

[jmroot]

Bug report

Bug description:

_ERR_MSG was removed by commit 857bdba, which doesn't give any reason for doing so, and it doesn't appear to be related to the bug that that commit was fixing. The removal has broken modulegraph.

While importlib._bootstrap could be considered private and subject to change at any time, 683ab85 says that:

We keep _ERR_MSG and _ERR_MSG_PREFIX as those may be used elsewhere for canonical looking error messages.

That at least suggests that it may be considered an API and thus subject to deprecation periods. If you decide otherwise, that's fine, I just thought I would report this since the removal appears to have been accidental.

CPython versions tested on:

3.14

Operating systems tested on:

macOS

[picnixz]

Those are definitely private APIs IMO and the commit message was likely for internal purposes. I definitely do not think that we need a deprecation period (the removal was likely because the variable was unused) cc @gpshead @colesbury

However if this is really annoying for enf users we can revert the removal but we need to add a comment for the reader.

[gpshead]

I doubt that is worth putting back given we don't use it internally. The rare code that needs it can be updated to carry its own definition.
(1) File a bug against modulegraph and
(2) as a workaround until you can use that, you could monkeypatch the importlib._ERR_MSG constant back into existence before using it.