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Don't set term->wrapnext when not in auto-wrapping mode.

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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.
This commit is contained in:
Simon Tatham 2024-08-10 10:38:02 +01:00
parent 22f8122b13
commit 3c3c179237
2 changed files with 40 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

36
terminal/terminal.c
View File

@ -1796,8 +1796,13 @@ void term_reconfig(Terminal *term, Conf *conf)
conf_free(term->conf);
term->conf = conf_copy(conf);
if (reset_wrap)
if (reset_wrap) {
term->alt_wrap = term->wrap = conf_get_bool(term->conf, CONF_wrap_mode);
if (!term->wrap)
term->wrapnext = false;
if (!term->alt_wrap)
term->alt_wnext = false;
}
if (reset_decom)
term->alt_om = term->dec_om = conf_get_bool(term->conf, CONF_dec_om);
if (reset_bce) {
@ -3093,6 +3098,8 @@ static void toggle_mode(Terminal *term, int mode, int query, bool state)
break;
case 7: /* DECAWM: auto wrap */
term->wrap = state;
if (!term->wrap)
term->wrapnext = false;
break;
case 8: /* DECARM: auto key repeat */
term->repeat_off = !state;
@ -3425,15 +3432,23 @@ static void term_display_graphic_char(Terminal *term, unsigned long c)
term->curs.x++;
if (term->curs.x >= linecols) {
term->curs.x = linecols - 1;
term->wrapnext = true;
if (term->wrap && term->vt52_mode) {
cline->lattr |= LATTR_WRAPPED;
if (term->curs.y == term->marg_b)
scroll(term, term->marg_t, term->marg_b, 1, true);
else if (term->curs.y < term->rows - 1)
term->curs.y++;
term->curs.x = 0;
term->wrapnext = false;
if (term->wrap) {
if (!term->vt52_mode) {
/* Set the wrapnext flag, so that the next character
* wraps, but this one doesn't. */
term->wrapnext = true;
} else {
/* VT52 mode expects simpler handling, and we just
* wrap straight away. */
cline->lattr |= LATTR_WRAPPED;
if (term->curs.y == term->marg_b)
scroll(term, term->marg_t, term->marg_b, 1, true);
else if (term->curs.y < term->rows - 1)
term->curs.y++;
term->curs.x = 0;
term->wrapnext = false;
}
}
}
seen_disp_event(term);
@ -5655,6 +5670,7 @@ static void term_out(Terminal *term, bool called_from_term_data)
case 'w': /* Autowrap off */
/* compatibility(ATARI) */
term->wrap = false;
term->wrapnext = false;
break;
case 'R':

32
test/test_terminal.c
View File

@ -384,7 +384,8 @@ static void test_wrap(Mock *mk)
static void test_nonwrap(Mock *mk)
{
/* Test behaviour when printing characters hit end of line without wrap */
/* Test behaviour when printing characters hit end of line without wrap.
* The wrapnext flag is never set in this mode. */
mk->ucsdata->line_codepage = CP_UTF8;
/* Print 'abc' without enough space for the c */
@ -398,27 +399,22 @@ static void test_nonwrap(Mock *mk)
IEQUAL(mk->term->curs.y, 0);
IEQUAL(mk->term->wrapnext, 0);
IEQUAL(get_termchar(mk->term, 78, 0).chr, CSET_ASCII | 'a');
/* The 'b' prints, leaving the cursor where it is with wrapnext set */
/* The 'b' prints, leaving the cursor where it is */
term_datapl(mk->term, PTRLEN_LITERAL("b"));
IEQUAL(mk->term->curs.x, 79);
IEQUAL(mk->term->curs.y, 0);
IEQUAL(mk->term->wrapnext, 1);
IEQUAL(mk->term->wrapnext, 0);
IEQUAL(get_lineattr(mk->term, 0), 0);
IEQUAL(get_termchar(mk->term, 79, 0).chr, CSET_ASCII | 'b');
/* The 'c' overwrites the b, leaving wrapnext still set */
/* The 'c' overwrites the b */
term_datapl(mk->term, PTRLEN_LITERAL("c"));
IEQUAL(mk->term->curs.x, 79);
IEQUAL(mk->term->curs.y, 0);
IEQUAL(mk->term->wrapnext, 1);
IEQUAL(mk->term->wrapnext, 0);
IEQUAL(get_lineattr(mk->term, 0), 0);
IEQUAL(get_termchar(mk->term, 78, 0).chr, CSET_ASCII | 'a');
IEQUAL(get_termchar(mk->term, 79, 0).chr, CSET_ASCII | 'c');
/* So backspacing clears wrapnext, leaving us on the c */
term_datapl(mk->term, PTRLEN_LITERAL("\b"));
IEQUAL(mk->term->curs.x, 79);
IEQUAL(mk->term->curs.y, 0);
IEQUAL(mk->term->wrapnext, 0);
/* And backspacing again returns the cursor to the a */
/* Since wrapnext was never set, backspacing returns us to the a */
term_datapl(mk->term, PTRLEN_LITERAL("\b"));
IEQUAL(mk->term->curs.x, 78);
IEQUAL(mk->term->curs.y, 0);
@ -428,18 +424,18 @@ static void test_nonwrap(Mock *mk)
mk->term->curs.x = 78;
mk->term->curs.y = 0;
mk->term->wrap = false;
/* The DW character goes directly to the wrapnext state */
/* The DW character occupies the rightmost two columns */
term_datapl(mk->term, PTRLEN_LITERAL("\xEA\xB0\x80"));
IEQUAL(mk->term->curs.x, 79);
IEQUAL(mk->term->curs.y, 0);
IEQUAL(mk->term->wrapnext, 1);
IEQUAL(mk->term->wrapnext, 0);
IEQUAL(get_termchar(mk->term, 78, 0).chr, 0xAC00);
IEQUAL(get_termchar(mk->term, 79, 0).chr, UCSWIDE);
/* The 'c' must overprint the RHS of the DW char, clearing the LHS */
term_datapl(mk->term, PTRLEN_LITERAL("c"));
IEQUAL(mk->term->curs.x, 79);
IEQUAL(mk->term->curs.y, 0);
IEQUAL(mk->term->wrapnext, 1);
IEQUAL(mk->term->wrapnext, 0);
IEQUAL(get_lineattr(mk->term, 0), 0);
IEQUAL(get_termchar(mk->term, 78, 0).chr, CSET_ASCII | ' ');
IEQUAL(get_termchar(mk->term, 79, 0).chr, CSET_ASCII | 'c');
@ -459,7 +455,7 @@ static void test_nonwrap(Mock *mk)
term_datapl(mk->term, PTRLEN_LITERAL("\xEA\xB0\x80"));
IEQUAL(mk->term->curs.x, 79);
IEQUAL(mk->term->curs.y, 0);
IEQUAL(mk->term->wrapnext, 1);
IEQUAL(mk->term->wrapnext, 0);
IEQUAL(get_lineattr(mk->term, 0), 0);
IEQUAL(get_termchar(mk->term, 78, 0).chr, CSET_ASCII | 'a');
IEQUAL(get_termchar(mk->term, 79, 0).chr, 0xFFFD);
@ -469,18 +465,18 @@ static void test_nonwrap(Mock *mk)
mk->term->curs.x = 78;
mk->term->curs.y = 0;
mk->term->wrap = false;
/* First DW character goes directly to the wrapnext state */
/* First DW character occupies the rightmost columns */
term_datapl(mk->term, PTRLEN_LITERAL("\xEA\xB0\x80"));
IEQUAL(mk->term->curs.x, 79);
IEQUAL(mk->term->curs.y, 0);
IEQUAL(mk->term->wrapnext, 1);
IEQUAL(mk->term->wrapnext, 0);
IEQUAL(get_termchar(mk->term, 78, 0).chr, 0xAC00);
IEQUAL(get_termchar(mk->term, 79, 0).chr, UCSWIDE);
/* Second DW char becomes U+FFFD, overwriting RHS of the first one */
term_datapl(mk->term, PTRLEN_LITERAL("\xEA\xB0\x81"));
IEQUAL(mk->term->curs.x, 79);
IEQUAL(mk->term->curs.y, 0);
IEQUAL(mk->term->wrapnext, 1);
IEQUAL(mk->term->wrapnext, 0);
IEQUAL(get_lineattr(mk->term, 0), 0);
IEQUAL(get_termchar(mk->term, 78, 0).chr, CSET_ASCII | ' ');
IEQUAL(get_termchar(mk->term, 79, 0).chr, 0xFFFD);