tinput hits assertion failure if prompt runs off the screen

[Jiri Svoboda]

tinput_read[_i]() will hit an assertion failure if we call it while the cursor is within str_length(prompt) characters from the end of the screen.

tinput_display() performs the following calculation, using current cursor coordinates col0, row0:

ti->prompt_coord = row0 * ti->con_cols + col0;
ti->text_coord = ti->prompt_coord + str_length(ti->prompt);

where ti→text_coord will be ≥ cols*rows and then in tinput_console_set_lpos():

       unsigned col = LIN_TO_COL(ti, lpos);
       unsigned row = LIN_TO_ROW(ti, lpos);
        
        assert(col < ti->con_cols);
        assert(row < ti->con_rows);

here we will have row ≥ ti→con_rows and hence the assert will fail.

An example of how to reproduce this is to create a program that purposefully puts the cursor to the bottom-right corner of the screen and then exists - at which point bdsh will try to print the prompt and it will abort.

[Jiri Svoboda]

The problem was that we did not account for scrolling while (initially) printing the prompt or the text. We computed the linear coordinate of text to be beyond the end of the screen and then assertion that the coordinate is within the screen failed.

Fixed in changeset ​f7a80521b3314c77b61a3a2ce80b11347ea69ce0.