Remove IsGlyphFullWidth from InputBuffer #17680
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DHowett
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Aug 7, 2024
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YAY. I love getting rid of a big comment that says "this is broke and has been forever"
carlos-zamora
approved these changes
Aug 7, 2024
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In several places the old conhost codebase appears to assume that any
wide glyph is represented by two codepoints. This is probably an
artifact of the ASCII/DBCS split that conhost used to have.
When conhost got merged into a single UCS2-aware application,
this artifact was apparently never properly resolved.
To my knowledge there are at least two places where this assumption
exists: The clipboard code which translates non-wide non-ascii
characters to Alt-numpad sequences, and this code. Both are wrong.
This is because in a Unicode-context there's no correlation between
the number of codepoints and the width of the glyph, even with UCS2.
In a post-UCS2-world the correct check is for surrogate pairs,
as they must be avoided for the same reason DBCS were avoided.
One could consider this a breaking change of the API,
as this can now result in repeat counts >1 for wide glyphs.
If someone complained about this change in behavior, I'd probably
not change it back, as narrow complex Unicode characters exist too.