The patch looks pretty good to me. I just have a stylistic suggestion which I've attached as a text file. There are also some outdated comments that are not the responsibility of this patch, but I kind of want to fix them now:
* - Hangul Jamo medial vowels and final consonants (U+1160-U+11FF)
* have a column width of 0.
We got rid of this range in d8594d123c1, which is correct.
* - Other format characters (general category code Cf in the Unicode
* database) and ZERO WIDTH SPACE (U+200B) have a column width of 0.
We don't treat Cf the same as Me or Mn, and I believe that's deliberate. We also no longer have the exception for zero-width space.
It seems the consensus so far is that performance is not an issue, and I'm inclined to agree.
I'm a bit concerned about the build dependencies not working right, but it's not clear it's even due to the patch. I'll spend some time investigating next week.
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