1) It's not a high priority for me to fix white space discrepancies in printing (unless there's a program in the wild that makes use of it) (I would be more worried about a space before the = as it wwould impact the saved environment variable)
2) would you mind adding a test case for this so that we don't lose this use case?
3) I strongly believe SET (and not only SET /P) shall rely on parsing the parameters with the usual helper functions instead of doing their own parsing
4) there's also a more annoying issue like not expanding in SET the potential variables inside quotes (like SET "%foo%=bar", and IIRC Wine doesn't expand %foo%, but it does expand in SET %foo%=bar)
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https://gitlab.winehq.org/wine/wine/-/merge_requests/6170#note_77392