[merge] OS/2 table Mixed Versions Crash

[ClintGoss]

Got a crash in pyftmerge when merging several fonts with OS/2 tables that have mixed versions.

If a font with a v5 OS/2 table follows font(s) with v4 OS/2 tables, I get:

File "C:\App\Python37\lib\site-packages\fontTools\misc\loggingTools.py", line 375, in wrapper
return func(*args, **kwds)
File "D:\Kurinto\Bin\Bin_CG\kmerge.py", line 1196, in main
font.save(outfile)
File "C:\App\Python37\lib\site-packages\fontTools\ttLib\ttFont.py", line 173, in save
writer_reordersTables = self._save(tmp)
File "C:\App\Python37\lib\site-packages\fontTools\ttLib\ttFont.py", line 212, in _save
self._writeTable(tag, writer, done, tableCache)
File "C:\App\Python37\lib\site-packages\fontTools\ttLib\ttFont.py", line 633, in _writeTable
tabledata = self.getTableData(tag)
File "C:\App\Python37\lib\site-packages\fontTools\ttLib\ttFont.py", line 651, in getTableData
return self.tables[tag].compile(self)
File "C:\App\Python37\lib\site-packages\fontTools\ttLib\tables\O_S_2f_2.py", line 152, in compile
d['usLowerOpticalPointSize'] = round(self.usLowerOpticalPointSize * 20)
AttributeError: 'table_O_S_2f_2' object has no attribute 'usLowerOpticalPointSize'

Confession: I have not done any serious debugging here. I am hypothesizing the cause of the failure ... but it does seem reasonable given that, when I hacked my one font with a v5 OS/2 table to v4, the issue went away.

[ClintGoss]

Hit this again trying to merge fonts A and B, with A and B having OS/2 table versions of 1 and 3, respectively.

[anthrotype]

I see that OS/2 v5 has a # TODO in fontTools.merge

fonttools/Lib/fontTools/merge.py

Line 298 in c89c948

# TODO version 5

we just need to handle the new attributes.

[anthrotype]

from what I can tell in https://docs.microsoft.com/en-us/typography/opentype/spec/OS2#lps, it should be enough that we take the min() of all the fonts' usLowerOpticalPointSize and the max() of the fonts' usUpperOpticalPointSize.

[anthrotype]

Hit this again trying to merge fonts A and B, with A and B having OS/2 table versions of 1 and 3, respectively.

@ClintGoss that's strange, v1 and v3 are supported and the merger should already take the maximum between the OS/2 versions. Can you provide a test font, the exact command you run and the error you got?

[anthrotype]

Ah I see. The merger is not handling attributes like sxHeight, sCapHeight, usDefaultChar, usBreakChar that were only added in version 2 and are missing from version 1, so when merging v1 with v > 1 you get the AttributeError. I'll fix this

[ClintGoss]

Glad you see the issue ... because it is actually difficult for me to isolate a demonstration case. I've got merge and pyftsubset running hundreds of times in a rather arcane and massive pipeline / build process.