Problem solved. In case anyone else has something similar, it looks like Xcode 16 has become more strict in verifying ascii files. The same ascii import has been running on the same text file in my app for years, but now it seems that if there's even a single non-ascii character it gives the "Can't open the file" error. Previously it would just strip out any non-ascii characters and continue to load the file.
I got chatgpt to write me a clever little macro that checks for non-ascii characters in excel and highlights the cells they're in. Turns out there was an eclipse, a smart quote and a few invisible NBSP's which had been copied in from another source many years ago. Replacing those allowed the file to be read again.
Topic:
Programming Languages
SubTopic:
Swift
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