gdb/tui/tui-io.c

   1 /* TUI support I/O functions.
   2
   3    Copyright (C) 1998-2018 Free Software Foundation, Inc.
   4
   5    Contributed by Hewlett-Packard Company.
   6
   7    This file is part of GDB.
   8
   9    This program is free software; you can redistribute it and/or modify
  10    it under the terms of the GNU General Public License as published by
  11    the Free Software Foundation; either version 3 of the License, or
  12    (at your option) any later version.
  13
  14    This program is distributed in the hope that it will be useful,
  15    but WITHOUT ANY WARRANTY; without even the implied warranty of
  16    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17    GNU General Public License for more details.
  18
  19    You should have received a copy of the GNU General Public License
  20    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  21
  22 #include "defs.h"
  23 #include "target.h"
  24 #include "event-loop.h"
  25 #include "event-top.h"
  26 #include "command.h"
  27 #include "top.h"
  28 #include "tui/tui.h"
  29 #include "tui/tui-data.h"
  30 #include "tui/tui-io.h"
  31 #include "tui/tui-command.h"
  32 #include "tui/tui-win.h"
  33 #include "tui/tui-wingeneral.h"
  34 #include "tui/tui-file.h"
  35 #include "tui/tui-out.h"
  36 #include "ui-out.h"
  37 #include "cli-out.h"
  38 #include <fcntl.h>
  39 #include <signal.h>
  40 #include "filestuff.h"
  41 #include "completer.h"
  42 #include "gdb_curses.h"
  43
  44 /* This redefines CTRL if it is not already defined, so it must come
  45    after terminal state releated include files like <term.h> and
  46    "gdb_curses.h".  */
  47 #include "readline/readline.h"
  48
  49 static int tui_getc (FILE *fp);
  50
  51 static int
  52 key_is_start_sequence (int ch)
  53 {
  54   return (ch == 27);
  55 }
  56
  57 /* Use definition from readline 4.3.  */
  58 #undef CTRL_CHAR
  59 #define CTRL_CHAR(c) \
  60      ((c) < control_character_threshold && (((c) & 0x80) == 0))
  61
  62 /* This file controls the IO interactions between gdb and curses.
  63    When the TUI is enabled, gdb has two modes a curses and a standard
  64    mode.
  65
  66    In curses mode, the gdb outputs are made in a curses command
  67    window.  For this, the gdb_stdout and gdb_stderr are redirected to
  68    the specific ui_file implemented by TUI.  The output is handled by
  69    tui_puts().  The input is also controlled by curses with
  70    tui_getc().  The readline library uses this function to get its
  71    input.  Several readline hooks are installed to redirect readline
  72    output to the TUI (see also the note below).
  73
  74    In normal mode, the gdb outputs are restored to their origin, that
  75    is as if TUI is not used.  Readline also uses its original getc()
  76    function with stdin.
  77
  78    Note SCz/2001-07-21: the current readline is not clean in its
  79    management of the output.  Even if we install a redisplay handler,
  80    it sometimes writes on a stdout file.  It is important to redirect
  81    every output produced by readline, otherwise the curses window will
  82    be garbled.  This is implemented with a pipe that TUI reads and
  83    readline writes to.  A gdb input handler is created so that reading
  84    the pipe is handled automatically.  This will probably not work on
  85    non-Unix platforms.  The best fix is to make readline clean enougth
  86    so that is never write on stdout.
  87
  88    Note SCz/2002-09-01: we now use more readline hooks and it seems
  89    that with them we don't need the pipe anymore (verified by creating
  90    the pipe and closing its end so that write causes a SIGPIPE).  The
  91    old pipe code is still there and can be conditionally removed by
  92    #undef TUI_USE_PIPE_FOR_READLINE.  */
  93
  94 /* For gdb 5.3, prefer to continue the pipe hack as a backup wheel.  */
  95 #ifdef HAVE_PIPE
  96 #define TUI_USE_PIPE_FOR_READLINE
  97 #endif
  98 /* #undef TUI_USE_PIPE_FOR_READLINE */
  99
 100 /* TUI output files.  */
 101 static struct ui_file *tui_stdout;
 102 static struct ui_file *tui_stderr;
 103 struct ui_out *tui_out;
 104
 105 /* GDB output files in non-curses mode.  */
 106 static struct ui_file *tui_old_stdout;
 107 static struct ui_file *tui_old_stderr;
 108 cli_ui_out *tui_old_uiout;
 109
 110 /* Readline previous hooks.  */
 111 static rl_getc_func_t *tui_old_rl_getc_function;
 112 static rl_voidfunc_t *tui_old_rl_redisplay_function;
 113 static rl_vintfunc_t *tui_old_rl_prep_terminal;
 114 static rl_voidfunc_t *tui_old_rl_deprep_terminal;
 115 static rl_compdisp_func_t *tui_old_rl_display_matches_hook;
 116 static int tui_old_rl_echoing_p;
 117
 118 /* Readline output stream.
 119    Should be removed when readline is clean.  */
 120 static FILE *tui_rl_outstream;
 121 static FILE *tui_old_rl_outstream;
 122 #ifdef TUI_USE_PIPE_FOR_READLINE
 123 static int tui_readline_pipe[2];
 124 #endif
 125
 126 /* The last gdb prompt that was registered in readline.
 127    This may be the main gdb prompt or a secondary prompt.  */
 128 static char *tui_rl_saved_prompt;
 129
 130 /* Print a character in the curses command window.  The output is
 131    buffered.  It is up to the caller to refresh the screen if
 132    necessary.  */
 133
 134 static void
 135 do_tui_putc (WINDOW *w, char c)
 136 {
 137   static int tui_skip_line = -1;
 138
 139   /* Catch annotation and discard them.  We need two \032 and discard
 140      until a \n is seen.  */
 141   if (c == '\032')
 142     {
 143       tui_skip_line++;
 144     }
 145   else if (tui_skip_line != 1)
 146     {
 147       tui_skip_line = -1;
 148       /* Expand TABs, since ncurses on MS-Windows doesn't.  */
 149       if (c == '\t')
 150         {
 151           int col;
 152
 153           col = getcurx (w);
 154           do
 155             {
 156               waddch (w, ' ');
 157               col++;
 158             }
 159           while ((col % 8) != 0);
 160         }
 161       else
 162         waddch (w, c);
 163     }
 164   else if (c == '\n')
 165     tui_skip_line = -1;
 166 }
 167
 168 /* Update the cached value of the command window's start line based on
 169    the window's current Y coordinate.  */
 170
 171 static void
 172 update_cmdwin_start_line ()
 173 {
 174   TUI_CMD_WIN->detail.command_info.start_line
 175     = getcury (TUI_CMD_WIN->generic.handle);
 176 }
 177
 178 /* Print a character in the curses command window.  The output is
 179    buffered.  It is up to the caller to refresh the screen if
 180    necessary.  */
 181
 182 static void
 183 tui_putc (char c)
 184 {
 185   WINDOW *w = TUI_CMD_WIN->generic.handle;
 186
 187   do_tui_putc (w, c);
 188   update_cmdwin_start_line ();
 189 }
 190
 191 /* Print LENGTH characters from the buffer pointed to by BUF to the
 192    curses command window.  The output is buffered.  It is up to the
 193    caller to refresh the screen if necessary.  */
 194
 195 void
 196 tui_write (const char *buf, size_t length)
 197 {
 198   WINDOW *w = TUI_CMD_WIN->generic.handle;
 199
 200   for (size_t i = 0; i < length; i++)
 201     do_tui_putc (w, buf[i]);
 202   update_cmdwin_start_line ();
 203 }
 204
 205 /* Print a string in the curses command window.  The output is
 206    buffered.  It is up to the caller to refresh the screen if
 207    necessary.  */
 208
 209 void
 210 tui_puts (const char *string)
 211 {
 212   WINDOW *w = TUI_CMD_WIN->generic.handle;
 213   char c;
 214
 215   while ((c = *string++) != 0)
 216     do_tui_putc (w, c);
 217   update_cmdwin_start_line ();
 218 }
 219
 220 /* Readline callback.
 221    Redisplay the command line with its prompt after readline has
 222    changed the edited text.  */
 223 void
 224 tui_redisplay_readline (void)
 225 {
 226   int prev_col;
 227   int height;
 228   int col;
 229   int c_pos;
 230   int c_line;
 231   int in;
 232   WINDOW *w;
 233   const char *prompt;
 234   int start_line;
 235
 236   /* Detect when we temporarily left SingleKey and now the readline
 237      edit buffer is empty, automatically restore the SingleKey
 238      mode.  The restore must only be done if the command has finished.
 239      The command could call prompt_for_continue and we must not
 240      restore SingleKey so that the prompt and normal keymap are used.  */
 241   if (tui_current_key_mode == TUI_ONE_COMMAND_MODE && rl_end == 0
 242       && !gdb_in_secondary_prompt_p (current_ui))
 243     tui_set_key_mode (TUI_SINGLE_KEY_MODE);
 244
 245   if (tui_current_key_mode == TUI_SINGLE_KEY_MODE)
 246     prompt = "";
 247   else
 248     prompt = tui_rl_saved_prompt;
 249
 250   c_pos = -1;
 251   c_line = -1;
 252   w = TUI_CMD_WIN->generic.handle;
 253   start_line = TUI_CMD_WIN->detail.command_info.start_line;
 254   wmove (w, start_line, 0);
 255   prev_col = 0;
 256   height = 1;
 257   for (in = 0; prompt && prompt[in]; in++)
 258     {
 259       waddch (w, prompt[in]);
 260       col = getcurx (w);
 261       if (col <= prev_col)
 262         height++;
 263       prev_col = col;
 264     }
 265   for (in = 0; in <= rl_end; in++)
 266     {
 267       unsigned char c;
 268
 269       if (in == rl_point)
 270         {
 271           getyx (w, c_line, c_pos);
 272         }
 273
 274       if (in == rl_end)
 275         break;
 276
 277       c = (unsigned char) rl_line_buffer[in];
 278       if (CTRL_CHAR (c) || c == RUBOUT)
 279         {
 280           waddch (w, '^');
 281           waddch (w, CTRL_CHAR (c) ? UNCTRL (c) : '?');
 282         }
 283       else if (c == '\t')
 284         {
 285           /* Expand TABs, since ncurses on MS-Windows doesn't.  */
 286           col = getcurx (w);
 287           do
 288             {
 289               waddch (w, ' ');
 290               col++;
 291             } while ((col % 8) != 0);
 292         }
 293       else
 294         {
 295           waddch (w, c);
 296         }
 297       if (c == '\n')
 298         TUI_CMD_WIN->detail.command_info.start_line = getcury (w);
 299       col = getcurx (w);
 300       if (col < prev_col)
 301         height++;
 302       prev_col = col;
 303     }
 304   wclrtobot (w);
 305   TUI_CMD_WIN->detail.command_info.start_line = getcury (w);
 306   if (c_line >= 0)
 307     wmove (w, c_line, c_pos);
 308   TUI_CMD_WIN->detail.command_info.start_line -= height - 1;
 309
 310   wrefresh (w);
 311   fflush(stdout);
 312 }
 313
 314 /* Readline callback to prepare the terminal.  It is called once each
 315    time we enter readline.  Terminal is already setup in curses
 316    mode.  */
 317 static void
 318 tui_prep_terminal (int notused1)
 319 {
 320   /* Save the prompt registered in readline to correctly display it.
 321      (we can't use gdb_prompt() due to secondary prompts and can't use
 322      rl_prompt because it points to an alloca buffer).  */
 323   xfree (tui_rl_saved_prompt);
 324   tui_rl_saved_prompt = rl_prompt != NULL ? xstrdup (rl_prompt) : NULL;
 325 }
 326
 327 /* Readline callback to restore the terminal.  It is called once each
 328    time we leave readline.  There is nothing to do in curses mode.  */
 329 static void
 330 tui_deprep_terminal (void)
 331 {
 332 }
 333
 334 #ifdef TUI_USE_PIPE_FOR_READLINE
 335 /* Read readline output pipe and feed the command window with it.
 336    Should be removed when readline is clean.  */
 337 static void
 338 tui_readline_output (int error, gdb_client_data data)
 339 {
 340   int size;
 341   char buf[256];
 342
 343   size = read (tui_readline_pipe[0], buf, sizeof (buf) - 1);
 344   if (size > 0 && tui_active)
 345     {
 346       buf[size] = 0;
 347       tui_puts (buf);
 348     }
 349 }
 350 #endif
 351
 352 /* TUI version of displayer.crlf.  */
 353
 354 static void
 355 tui_mld_crlf (const struct match_list_displayer *displayer)
 356 {
 357   tui_putc ('\n');
 358 }
 359
 360 /* TUI version of displayer.putch.  */
 361
 362 static void
 363 tui_mld_putch (const struct match_list_displayer *displayer, int ch)
 364 {
 365   tui_putc (ch);
 366 }
 367
 368 /* TUI version of displayer.puts.  */
 369
 370 static void
 371 tui_mld_puts (const struct match_list_displayer *displayer, const char *s)
 372 {
 373   tui_puts (s);
 374 }
 375
 376 /* TUI version of displayer.flush.  */
 377
 378 static void
 379 tui_mld_flush (const struct match_list_displayer *displayer)
 380 {
 381   wrefresh (TUI_CMD_WIN->generic.handle);
 382 }
 383
 384 /* TUI version of displayer.erase_entire_line.  */
 385
 386 static void
 387 tui_mld_erase_entire_line (const struct match_list_displayer *displayer)
 388 {
 389   WINDOW *w = TUI_CMD_WIN->generic.handle;
 390   int cur_y = getcury (w);
 391
 392   wmove (w, cur_y, 0);
 393   wclrtoeol (w);
 394   wmove (w, cur_y, 0);
 395 }
 396
 397 /* TUI version of displayer.beep.  */
 398
 399 static void
 400 tui_mld_beep (const struct match_list_displayer *displayer)
 401 {
 402   beep ();
 403 }
 404
 405 /* A wrapper for wgetch that enters nonl mode.  We We normally want
 406   curses' "nl" mode, but when reading from the user, we'd like to
 407   differentiate between C-j and C-m, because some users bind these
 408   keys differently in their .inputrc.  So, put curses into nonl mode
 409   just when reading from the user.  See PR tui/20819.  */
 410
 411 static int
 412 gdb_wgetch (WINDOW *win)
 413 {
 414   nonl ();
 415   int r = wgetch (win);
 416   nl ();
 417   return r;
 418 }
 419
 420 /* Helper function for tui_mld_read_key.
 421    This temporarily replaces tui_getc for use during tab-completion
 422    match list display.  */
 423
 424 static int
 425 tui_mld_getc (FILE *fp)
 426 {
 427   WINDOW *w = TUI_CMD_WIN->generic.handle;
 428   int c = gdb_wgetch (w);
 429
 430   return c;
 431 }
 432
 433 /* TUI version of displayer.read_key.  */
 434
 435 static int
 436 tui_mld_read_key (const struct match_list_displayer *displayer)
 437 {
 438   rl_getc_func_t *prev = rl_getc_function;
 439   int c;
 440
 441   /* We can't use tui_getc as we need NEWLINE to not get emitted.  */
 442   rl_getc_function = tui_mld_getc;
 443   c = rl_read_key ();
 444   rl_getc_function = prev;
 445   return c;
 446 }
 447
 448 /* TUI version of rl_completion_display_matches_hook.
 449    See gdb_display_match_list for a description of the arguments.  */
 450
 451 static void
 452 tui_rl_display_match_list (char **matches, int len, int max)
 453 {
 454   struct match_list_displayer displayer;
 455
 456   rl_get_screen_size (&displayer.height, &displayer.width);
 457   displayer.crlf = tui_mld_crlf;
 458   displayer.putch = tui_mld_putch;
 459   displayer.puts = tui_mld_puts;
 460   displayer.flush = tui_mld_flush;
 461   displayer.erase_entire_line = tui_mld_erase_entire_line;
 462   displayer.beep = tui_mld_beep;
 463   displayer.read_key = tui_mld_read_key;
 464
 465   gdb_display_match_list (matches, len, max, &displayer);
 466 }
 467
 468 /* Setup the IO for curses or non-curses mode.
 469    - In non-curses mode, readline and gdb use the standard input and
 470    standard output/error directly.
 471    - In curses mode, the standard output/error is controlled by TUI
 472    with the tui_stdout and tui_stderr.  The output is redirected in
 473    the curses command window.  Several readline callbacks are installed
 474    so that readline asks for its input to the curses command window
 475    with wgetch().  */
 476 void
 477 tui_setup_io (int mode)
 478 {
 479   extern int _rl_echoing_p;
 480
 481   if (mode)
 482     {
 483       /* Redirect readline to TUI.  */
 484       tui_old_rl_redisplay_function = rl_redisplay_function;
 485       tui_old_rl_deprep_terminal = rl_deprep_term_function;
 486       tui_old_rl_prep_terminal = rl_prep_term_function;
 487       tui_old_rl_getc_function = rl_getc_function;
 488       tui_old_rl_display_matches_hook = rl_completion_display_matches_hook;
 489       tui_old_rl_outstream = rl_outstream;
 490       tui_old_rl_echoing_p = _rl_echoing_p;
 491       rl_redisplay_function = tui_redisplay_readline;
 492       rl_deprep_term_function = tui_deprep_terminal;
 493       rl_prep_term_function = tui_prep_terminal;
 494       rl_getc_function = tui_getc;
 495       _rl_echoing_p = 0;
 496       rl_outstream = tui_rl_outstream;
 497       rl_prompt = 0;
 498       rl_completion_display_matches_hook = tui_rl_display_match_list;
 499       rl_already_prompted = 0;
 500
 501       /* Keep track of previous gdb output.  */
 502       tui_old_stdout = gdb_stdout;
 503       tui_old_stderr = gdb_stderr;
 504       tui_old_uiout = dynamic_cast<cli_ui_out *> (current_uiout);
 505       gdb_assert (tui_old_uiout != nullptr);
 506
 507       /* Reconfigure gdb output.  */
 508       gdb_stdout = tui_stdout;
 509       gdb_stderr = tui_stderr;
 510       gdb_stdlog = gdb_stdout;  /* for moment */
 511       gdb_stdtarg = gdb_stderr; /* for moment */
 512       gdb_stdtargerr = gdb_stderr;      /* for moment */
 513       current_uiout = tui_out;
 514
 515       /* Save tty for SIGCONT.  */
 516       savetty ();
 517     }
 518   else
 519     {
 520       /* Restore gdb output.  */
 521       gdb_stdout = tui_old_stdout;
 522       gdb_stderr = tui_old_stderr;
 523       gdb_stdlog = gdb_stdout;  /* for moment */
 524       gdb_stdtarg = gdb_stderr; /* for moment */
 525       gdb_stdtargerr = gdb_stderr;      /* for moment */
 526       current_uiout = tui_old_uiout;
 527
 528       /* Restore readline.  */
 529       rl_redisplay_function = tui_old_rl_redisplay_function;
 530       rl_deprep_term_function = tui_old_rl_deprep_terminal;
 531       rl_prep_term_function = tui_old_rl_prep_terminal;
 532       rl_getc_function = tui_old_rl_getc_function;
 533       rl_completion_display_matches_hook = tui_old_rl_display_matches_hook;
 534       rl_outstream = tui_old_rl_outstream;
 535       _rl_echoing_p = tui_old_rl_echoing_p;
 536       rl_already_prompted = 0;
 537
 538       /* Save tty for SIGCONT.  */
 539       savetty ();
 540     }
 541 }
 542
 543 #ifdef SIGCONT
 544 /* Catch SIGCONT to restore the terminal and refresh the screen.  */
 545 static void
 546 tui_cont_sig (int sig)
 547 {
 548   if (tui_active)
 549     {
 550       /* Restore the terminal setting because another process (shell)
 551          might have changed it.  */
 552       resetty ();
 553
 554       /* Force a refresh of the screen.  */
 555       tui_refresh_all_win ();
 556
 557       wrefresh (TUI_CMD_WIN->generic.handle);
 558     }
 559   signal (sig, tui_cont_sig);
 560 }
 561 #endif
 562
 563 /* Initialize the IO for gdb in curses mode.  */
 564 void
 565 tui_initialize_io (void)
 566 {
 567 #ifdef SIGCONT
 568   signal (SIGCONT, tui_cont_sig);
 569 #endif
 570
 571   /* Create tui output streams.  */
 572   tui_stdout = new tui_file (stdout);
 573   tui_stderr = new tui_file (stderr);
 574   tui_out = tui_out_new (tui_stdout);
 575
 576   /* Create the default UI.  */
 577   tui_old_uiout = cli_out_new (gdb_stdout);
 578
 579 #ifdef TUI_USE_PIPE_FOR_READLINE
 580   /* Temporary solution for readline writing to stdout: redirect
 581      readline output in a pipe, read that pipe and output the content
 582      in the curses command window.  */
 583   if (gdb_pipe_cloexec (tui_readline_pipe) != 0)
 584     error (_("Cannot create pipe for readline"));
 585
 586   tui_rl_outstream = fdopen (tui_readline_pipe[1], "w");
 587   if (tui_rl_outstream == 0)
 588     error (_("Cannot redirect readline output"));
 589
 590   setvbuf (tui_rl_outstream, (char*) NULL, _IOLBF, 0);
 591
 592 #ifdef O_NONBLOCK
 593   (void) fcntl (tui_readline_pipe[0], F_SETFL, O_NONBLOCK);
 594 #else
 595 #ifdef O_NDELAY
 596   (void) fcntl (tui_readline_pipe[0], F_SETFL, O_NDELAY);
 597 #endif
 598 #endif
 599   add_file_handler (tui_readline_pipe[0], tui_readline_output, 0);
 600 #else
 601   tui_rl_outstream = stdout;
 602 #endif
 603 }
 604
 605 /* Get a character from the command window.  This is called from the
 606    readline package.  */
 607 static int
 608 tui_getc (FILE *fp)
 609 {
 610   int ch;
 611   WINDOW *w;
 612
 613   w = TUI_CMD_WIN->generic.handle;
 614
 615 #ifdef TUI_USE_PIPE_FOR_READLINE
 616   /* Flush readline output.  */
 617   tui_readline_output (0, 0);
 618 #endif
 619
 620   ch = gdb_wgetch (w);
 621
 622   /* The \n must be echoed because it will not be printed by
 623      readline.  */
 624   if (ch == '\n')
 625     {
 626       /* When hitting return with an empty input, gdb executes the last
 627          command.  If we emit a newline, this fills up the command window
 628          with empty lines with gdb prompt at beginning.  Instead of that,
 629          stay on the same line but provide a visual effect to show the
 630          user we recognized the command.  */
 631       if (rl_end == 0 && !gdb_in_secondary_prompt_p (current_ui))
 632         {
 633           wmove (w, getcury (w), 0);
 634
 635           /* Clear the line.  This will blink the gdb prompt since
 636              it will be redrawn at the same line.  */
 637           wclrtoeol (w);
 638           wrefresh (w);
 639           napms (20);
 640         }
 641       else
 642         {
 643           /* Move cursor to the end of the command line before emitting the
 644              newline.  We need to do so because when ncurses outputs a newline
 645              it truncates any text that appears past the end of the cursor.  */
 646           int px, py;
 647           getyx (w, py, px);
 648           px += rl_end - rl_point;
 649           py += px / TUI_CMD_WIN->generic.width;
 650           px %= TUI_CMD_WIN->generic.width;
 651           wmove (w, py, px);
 652           tui_putc ('\n');
 653         }
 654     }
 655
 656   /* Handle prev/next/up/down here.  */
 657   ch = tui_dispatch_ctrl_char (ch);
 658
 659   if (ch == KEY_BACKSPACE)
 660     return '\b';
 661
 662   if (current_ui->command_editing && key_is_start_sequence (ch))
 663     {
 664       int ch_pending;
 665
 666       nodelay (w, TRUE);
 667       ch_pending = gdb_wgetch (w);
 668       nodelay (w, FALSE);
 669
 670       /* If we have pending input following a start sequence, call the stdin
 671          event handler again because ncurses may have already read and stored
 672          the input into its internal buffer, meaning that we won't get an stdin
 673          event for it.  If we don't compensate for this missed stdin event, key
 674          sequences as Alt_F (^[f) will not behave promptly.
 675
 676          (We only compensates for the missed 2nd byte of a key sequence because
 677          2-byte sequences are by far the most commonly used. ncurses may have
 678          buffered a larger, 3+-byte key sequence though it remains to be seen
 679          whether it is useful to compensate for all the bytes of such
 680          sequences.)  */
 681       if (ch_pending != ERR)
 682         {
 683           ungetch (ch_pending);
 684           call_stdin_event_handler_again_p = 1;
 685         }
 686     }
 687
 688   return ch;
 689 }
 690
 691 /* Utility function to expand TABs in a STRING into spaces.  STRING
 692    will be displayed starting at column COL, and is assumed to include
 693    no newlines.  The returned expanded string is malloc'ed.  */
 694
 695 char *
 696 tui_expand_tabs (const char *string, int col)
 697 {
 698   int n_adjust, ncol;
 699   const char *s;
 700   char *ret, *q;
 701
 702   /* 1. How many additional characters do we need?  */
 703   for (ncol = col, n_adjust = 0, s = string; s; )
 704     {
 705       s = strpbrk (s, "\t");
 706       if (s)
 707         {
 708           ncol += (s - string) + n_adjust;
 709           /* Adjustment for the next tab stop, minus one for the TAB
 710              we replace with spaces.  */
 711           n_adjust += 8 - (ncol % 8) - 1;
 712           s++;
 713         }
 714     }
 715
 716   /* Allocate the copy.  */
 717   ret = q = (char *) xmalloc (strlen (string) + n_adjust + 1);
 718
 719   /* 2. Copy the original string while replacing TABs with spaces.  */
 720   for (ncol = col, s = string; s; )
 721     {
 722       const char *s1 = strpbrk (s, "\t");
 723       if (s1)
 724         {
 725           if (s1 > s)
 726             {
 727               strncpy (q, s, s1 - s);
 728               q += s1 - s;
 729               ncol += s1 - s;
 730             }
 731           do {
 732             *q++ = ' ';
 733             ncol++;
 734           } while ((ncol % 8) != 0);
 735           s1++;
 736         }
 737       else
 738         strcpy (q, s);
 739       s = s1;
 740     }
 741
 742   return ret;
 743 }