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A user sent a transcript from a curses-based tool 'ncmpc', which carefully disables terminal autowrap when printing a character in the bottom right corner of the display, and then turns it back on again. After that, it expects that sending the backspace character really moves the cursor back a space, instead of clearing the wrapnext flag. But in PuTTY, we set the wrapnext flag even if we're not in wrapping mode - it just doesn't _do_ anything when the next character is sent. But it remains set, and still affects backspace. So the display is corrupted by this change of expectation. (Specifically, ncmpc is printing a time display [m:ss] in the very bottom right, so it disables wrap in order to print the final ']'. Then the next thing it needs to do is to update the low-order digit of the seconds field, so it sends \b as the simplest way to get to that character. The effect on the display is that the updated seconds digit appears where the ] was, instead of overwriting the old seconds digit.) This is a tradeoff in desirable behaviours. The point of having a backspace operation cancel the wrapnext flag and not actually move the cursor is to preserve the invariant that sending 'x', backspace, 'y' causes the y to overprint the x, even if that happens near the end of the terminal's line length. In non-wrapping mode that invariant was bound to break _eventually_, but with this change, it breaks one character earlier than before. However, I think that's less bad than breaking the expectations of curses-based full-screen applications, especially since the _main_ need for that invariant arises from naïve applications that don't want to have to think about the terminal width at all - and those applications generally run in _wrapping_ mode, where it's possible to continue the invariant across multiple lines in any case. |
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| .. | ||
| sclog | ||
| agentmulti.py | ||
| agenttest.py | ||
| agenttestdata.py | ||
| agenttestgen.py | ||
| ca.py | ||
| colours.txt | ||
| cryptsuite.py | ||
| desref.py | ||
| display.txt | ||
| dsa_nonce_recover.py | ||
| eccref.py | ||
| fuzzterm.c | ||
| lattrs.txt | ||
| list-accel.py | ||
| mpu-check.pl | ||
| numbertheory.py | ||
| primegen.py | ||
| scocols.txt | ||
| ssh.py | ||
| test_conf.c | ||
| test_lineedit.c | ||
| test_terminal.c | ||
| testcrypt-enum.h | ||
| testcrypt-func.h | ||
| testcrypt.c | ||
| testcrypt.py | ||
| testsc.c | ||
| testzlib.c | ||
| utf8.txt | ||
| vt100.txt | ||
| windowchange.py | ||