Default all G-sets to ASCII unless ISO-2022 is requested #11658
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## Summary of the Pull Request There is a non-zero subset of applications that randomly output _Locking Shift_ escape sequences which will invoke a character set from G2 or G3 into the left half of the code table. If those G-sets are mapped to Latin1, that can result in the terminal producing output that appears to be broken. This PR now defaults all G-sets to ASCII, to prevent an unintentional _Locking Shift_ from having any effect. ## PR Checklist * [x] Closes #10408 * [x] CLA signed. * [ ] Tests added/passed * [ ] Documentation updated. * [ ] Schema updated. * [x] I've discussed this with core contributors already. Issue number where discussion took place: #10408 ## Detailed Description of the Pull Request / Additional comments Most other modern terminals also default to ASCII in all G-sets, so this shouldn't break any modern applications. Legacy 8-bit applications may still expect the G2 and G3 sets mapped to Latin1, but they would also need to have the ISO-2022 encoding enabled, so we can keep them happy by setting G2 and G3 correctly when the ISO-2022 encoding is requested. ## Validation Steps Performed I've manually confirmed that `echo -e "\en"` and `echo -e "\eo"` no longer have any visible effect on the output (at least without first invoking another character set into G2 or G3). I've also confirmed that they do still work as expected (i.e. selecting Latin1) after enabling the ISO-2022 encoding. (cherry picked from commit 27e042b)
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## Summary of the Pull Request There is a non-zero subset of applications that randomly output _Locking Shift_ escape sequences which will invoke a character set from G2 or G3 into the left half of the code table. If those G-sets are mapped to Latin1, that can result in the terminal producing output that appears to be broken. This PR now defaults all G-sets to ASCII, to prevent an unintentional _Locking Shift_ from having any effect. ## PR Checklist * [x] Closes #10408 * [x] CLA signed. * [ ] Tests added/passed * [ ] Documentation updated. * [ ] Schema updated. * [x] I've discussed this with core contributors already. Issue number where discussion took place: #10408 ## Detailed Description of the Pull Request / Additional comments Most other modern terminals also default to ASCII in all G-sets, so this shouldn't break any modern applications. Legacy 8-bit applications may still expect the G2 and G3 sets mapped to Latin1, but they would also need to have the ISO-2022 encoding enabled, so we can keep them happy by setting G2 and G3 correctly when the ISO-2022 encoding is requested. ## Validation Steps Performed I've manually confirmed that `echo -e "\en"` and `echo -e "\eo"` no longer have any visible effect on the output (at least without first invoking another character set into G2 or G3). I've also confirmed that they do still work as expected (i.e. selecting Latin1) after enabling the ISO-2022 encoding. (cherry picked from commit 27e042b)
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Summary of the Pull Request
There is a non-zero subset of applications that randomly output Locking Shift escape sequences which will invoke a character set from G2 or G3 into the left half of the code table. If those G-sets are mapped to Latin1, that can result in the terminal producing output that appears to be broken. This PR now defaults all G-sets to ASCII, to prevent an unintentional Locking Shift from having any effect.
PR Checklist
Detailed Description of the Pull Request / Additional comments
Most other modern terminals also default to ASCII in all G-sets, so this shouldn't break any modern applications. Legacy 8-bit applications may still expect the G2 and G3 sets mapped to Latin1, but they would also need to have the ISO-2022 encoding enabled, so we can keep them happy by setting G2 and G3 correctly when the ISO-2022 encoding is requested.
Validation Steps Performed
I've manually confirmed that
echo -e "\en"andecho -e "\eo"no longer have any visible effect on the output (at least without first invoking another character set into G2 or G3). I've also confirmed that they do still work as expected (i.e. selecting Latin1) after enabling the ISO-2022 encoding.