UP025 fix introduces a syntax error for an empty string followed by a `u`-prefixed string

[dscorbett]

Summary

The fix for unicode-kind-prefix (UP025) can introduce a syntax error when the prefixed string follows a non-triple-quoted empty string with the same kind of quotation marks without an intervening space. The fix should add a space if necessary.

Playground

$ cat >up025.py <<'# EOF'
""u""
# EOF

$ ruff --isolated check up025.py --select UP025 --diff 2>&1 | grep error:
error: Fix introduced a syntax error. Reverting all changes.

Version

ruff 0.12.0 (87f0feb 2025-06-17)

[lubaskinc0de]

i want to work on this