lineedit: fix moving backwards across lines with wide chars

function                                             old     new   delta
input_backward                                       212     208      -4

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index bc089ab1cf5861da94123a2a304e6e87220839bf..836fc0089b62121fc13644304a9ae54572b45575 100644 (file)
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -413,12 +413,22 @@ static void beep(void)
        bb_putchar('\007');
 }
 
+static void put_prompt(void)
+{
+       unsigned w;
+
+       out1str(cmdedit_prompt);
+       fflush_all();
+       cursor = 0;
+       w = cmdedit_termw; /* read volatile var once */
+       cmdedit_y = cmdedit_prmt_len / w; /* new quasireal y */
+       cmdedit_x = cmdedit_prmt_len % w;
+}
+
 /* Move back one character */
 /* (optimized for slow terminals) */
 static void input_backward(unsigned num)
 {
-       int count_y;
-
        if (num > cursor)
                num = cursor;
        if (num == 0)
@@ -456,29 +466,44 @@ static void input_backward(unsigned num)
        }
 
        /* Need to go one or more lines up */
-//FIXME: this does not work correctly if prev line has one "unfilled" screen position
-//caused by wide unicode char not fitting in that one screen position.
-       num -= cmdedit_x;
-       {
-               unsigned w = cmdedit_termw; /* volatile var */
+       if (ENABLE_UNICODE_WIDE_WCHARS) {
+               /* With wide chars, it is hard to "backtrack"
+                * and reliably figure out where to put cursor.
+                * Example (<> is a wide char; # is an ordinary char, _ cursor):
+                * |prompt: <><> |
+                * |<><><><><><> |
+                * |_            |
+                * and user presses left arrow. num = 1, cmdedit_x = 0,
+                * We need to go up one line, and then - how do we know that
+                * we need to go *10* positions to the right? Because
+                * |prompt: <>#<>|
+                * |<><><>#<><><>|
+                * |_            |
+                * in this situation we need to go *11* positions to the right.
+                *
+                * A simpler thing to do is to redraw everything from the start
+                * up to new cursor position (which is already known):
+                */
+               unsigned sv_cursor;
+               if (cmdedit_y > 0)  /* up to start y */
+                       printf("\033[%uA", cmdedit_y);
+               bb_putchar('\r');
+               cmdedit_y = 0;
+               sv_cursor = cursor;
+               put_prompt(); /* sets cursor to 0 */
+               while (cursor < sv_cursor)
+                       put_cur_glyph_and_inc_cursor();
+       } else {
+               int count_y;
+               unsigned w;
+               num -= cmdedit_x;
+               w = cmdedit_termw; /* read volatile var once */
                count_y = 1 + (num / w);
                cmdedit_y -= count_y;
                cmdedit_x = w * count_y - num;
+               /* go to 1st column; go up; go to correct column */
+               printf("\r" "\033[%uA" "\033[%uC", count_y, cmdedit_x);
        }
-       /* go to 1st column; go up; go to correct column */
-       printf("\r" "\033[%uA" "\033[%uC", count_y, cmdedit_x);
-}
-
-static void put_prompt(void)
-{
-       unsigned w;
-
-       out1str(cmdedit_prompt);
-       fflush_all();
-       cursor = 0;
-       w = cmdedit_termw; /* read volatile var once */
-       cmdedit_y = cmdedit_prmt_len / w; /* new quasireal y */
-       cmdedit_x = cmdedit_prmt_len % w;
 }
 
 /* draw prompt, editor line, and clear tail */