lisp/indent.el

   1 ;;; indent.el --- indentation commands for Emacs  -*- lexical-binding:t -*-
   2
   3 ;; Copyright (C) 1985, 1995, 2001-2014 Free Software Foundation, Inc.
   4
   5 ;; Maintainer: emacs-devel@gnu.org
   6 ;; Package: emacs
   7
   8 ;; This file is part of GNU Emacs.
   9
  10 ;; GNU Emacs is free software: you can redistribute it and/or modify
  11 ;; it under the terms of the GNU General Public License as published by
  12 ;; the Free Software Foundation, either version 3 of the License, or
  13 ;; (at your option) any later version.
  14
  15 ;; GNU Emacs is distributed in the hope that it will be useful,
  16 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 ;; GNU General Public License for more details.
  19
  20 ;; You should have received a copy of the GNU General Public License
  21 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  22
  23 ;;; Commentary:
  24
  25 ;; Commands for making and changing indentation in text.  These are
  26 ;; described in the Emacs manual.
  27
  28 ;;; Code:
  29
  30 (defgroup indent nil
  31   "Indentation commands."
  32   :group 'editing)
  33
  34 (defcustom standard-indent 4
  35   "Default number of columns for margin-changing functions to indent."
  36   :group 'indent
  37   :type 'integer)
  38
  39 (defvar indent-line-function 'indent-relative
  40   "Function to indent the current line.
  41 This function will be called with no arguments.
  42 If it is called somewhere where auto-indentation cannot be done
  43 \(e.g. inside a string), the function should simply return `noindent'.
  44 Setting this function is all you need to make TAB indent appropriately.
  45 Don't rebind TAB unless you really need to.")
  46
  47 (defcustom tab-always-indent t
  48   "Controls the operation of the TAB key.
  49 If t, hitting TAB always just indents the current line.
  50 If nil, hitting TAB indents the current line if point is at the left margin
  51 or in the line's indentation, otherwise it inserts a \"real\" TAB character.
  52 If `complete', TAB first tries to indent the current line, and if the line
  53 was already indented, then try to complete the thing at point.
  54
  55 Some programming language modes have their own variable to control this,
  56 e.g., `c-tab-always-indent', and do not respect this variable."
  57   :group 'indent
  58   :type '(choice
  59           (const :tag "Always indent" t)
  60           (const :tag "Indent if inside indentation, else TAB" nil)
  61           (const :tag "Indent, or if already indented complete" complete)))
  62
  63
  64 (defun indent-according-to-mode ()
  65   "Indent line in proper way for current major mode.
  66 Normally, this is done by calling the function specified by the
  67 variable `indent-line-function'.  However, if the value of that
  68 variable is `indent-relative' or `indent-relative-maybe', handle
  69 it specially (since those functions are used for tabbing); in
  70 that case, indent by aligning to the previous non-blank line."
  71   (interactive)
  72   (syntax-propertize (line-end-position))
  73   (if (memq indent-line-function
  74             '(indent-relative indent-relative-maybe))
  75       ;; These functions are used for tabbing, but can't be used for
  76       ;; indenting.  Replace with something ad-hoc.
  77       (let ((column (save-excursion
  78                       (beginning-of-line)
  79                       (if (bobp) 0
  80                         (beginning-of-line 0)
  81                         (if (looking-at "[ \t]*$") 0
  82                           (current-indentation))))))
  83         (if (<= (current-column) (current-indentation))
  84             (indent-line-to column)
  85           (save-excursion (indent-line-to column))))
  86     ;; The normal case.
  87     (funcall indent-line-function)))
  88
  89 (defun indent-for-tab-command (&optional arg)
  90   "Indent the current line or region, or insert a tab, as appropriate.
  91 This function either inserts a tab, or indents the current line,
  92 or performs symbol completion, depending on `tab-always-indent'.
  93 The function called to actually indent the line or insert a tab
  94 is given by the variable `indent-line-function'.
  95
  96 If a prefix argument is given, after this function indents the
  97 current line or inserts a tab, it also rigidly indents the entire
  98 balanced expression which starts at the beginning of the current
  99 line, to reflect the current line's indentation.
 100
 101 In most major modes, if point was in the current line's
 102 indentation, it is moved to the first non-whitespace character
 103 after indenting; otherwise it stays at the same position relative
 104 to the text.
 105
 106 If `transient-mark-mode' is turned on and the region is active,
 107 this function instead calls `indent-region'.  In this case, any
 108 prefix argument is ignored."
 109   (interactive "P")
 110   (cond
 111    ;; The region is active, indent it.
 112    ((use-region-p)
 113     (indent-region (region-beginning) (region-end)))
 114    ((or ;; indent-to-left-margin is only meant for indenting,
 115         ;; so we force it to always insert a tab here.
 116         (eq indent-line-function 'indent-to-left-margin)
 117         (and (not tab-always-indent)
 118              (or (> (current-column) (current-indentation))
 119                  (eq this-command last-command))))
 120     (insert-tab arg))
 121    (t
 122     (let ((old-tick (buffer-chars-modified-tick))
 123           (old-point (point))
 124           (old-indent (current-indentation)))
 125
 126       ;; Indent the line.
 127       (funcall indent-line-function)
 128
 129       (cond
 130        ;; If the text was already indented right, try completion.
 131        ((and (eq tab-always-indent 'complete)
 132              (eq old-point (point))
 133              (eq old-tick (buffer-chars-modified-tick)))
 134         (completion-at-point))
 135
 136        ;; If a prefix argument was given, rigidly indent the following
 137        ;; sexp to match the change in the current line's indentation.
 138        (arg
 139         (let ((end-marker
 140                (save-excursion
 141                  (forward-line 0) (forward-sexp) (point-marker)))
 142               (indentation-change (- (current-indentation) old-indent)))
 143           (save-excursion
 144             (forward-line 1)
 145             (when (and (not (zerop indentation-change))
 146                        (< (point) end-marker))
 147               (indent-rigidly (point) end-marker indentation-change))))))))))
 148
 149 (defun insert-tab (&optional arg)
 150   (let ((count (prefix-numeric-value arg)))
 151     (if (and abbrev-mode
 152              (eq (char-syntax (preceding-char)) ?w))
 153         (expand-abbrev))
 154     (if indent-tabs-mode
 155         (insert-char ?\t count)
 156       (indent-to (* tab-width (+ count (/ (current-column) tab-width)))))))
 157
 158 (defun indent-rigidly--current-indentation (beg end)
 159   "Return the smallest indentation in range from BEG to END.
 160 Blank lines are ignored."
 161   (save-excursion
 162     (save-match-data
 163       (let ((beg (progn (goto-char beg) (line-beginning-position)))
 164             indent)
 165         (goto-char beg)
 166         (while (re-search-forward "^\\s-*[[:print:]]" end t)
 167           (setq indent (min (or indent (current-indentation))
 168                             (current-indentation))))
 169         indent))))
 170
 171 (defvar indent-rigidly-map
 172   (let ((map (make-sparse-keymap)))
 173     (define-key map [left]  'indent-rigidly-left)
 174     (define-key map [right] 'indent-rigidly-right)
 175     (define-key map [S-left]  'indent-rigidly-left-to-tab-stop)
 176     (define-key map [S-right] 'indent-rigidly-right-to-tab-stop)
 177     map)
 178   "Transient keymap for adjusting indentation interactively.
 179 It is activated by calling `indent-rigidly' interactively.")
 180
 181 (defun indent-rigidly (start end arg &optional interactive)
 182   "Indent all lines starting in the region.
 183 If called interactively with no prefix argument, activate a
 184 transient mode in which the indentation can be adjusted interactively
 185 by typing \\<indent-rigidly-map>\\[indent-rigidly-left], \\[indent-rigidly-right], \\[indent-rigidly-left-to-tab-stop], or \\[indent-rigidly-right-to-tab-stop].
 186 Typing any other key deactivates the transient mode.
 187
 188 If called from a program, or interactively with prefix ARG,
 189 indent all lines starting in the region forward by ARG columns.
 190 If called from a program, START and END specify the beginning and
 191 end of the text to act on, in place of the region.
 192
 193 Negative values of ARG indent backward, so you can remove all
 194 indentation by specifying a large negative ARG."
 195   (interactive "r\nP\np")
 196   (if (and (not arg) interactive)
 197       (progn
 198         (message
 199          (substitute-command-keys
 200           "Indent region with \\<indent-rigidly-map>\\[indent-rigidly-left], \\[indent-rigidly-right], \\[indent-rigidly-left-to-tab-stop], or \\[indent-rigidly-right-to-tab-stop]."))
 201         (set-transient-map indent-rigidly-map t))
 202     (save-excursion
 203       (goto-char end)
 204       (setq end (point-marker))
 205       (goto-char start)
 206       (or (bolp) (forward-line 1))
 207       (while (< (point) end)
 208         (let ((indent (current-indentation))
 209               eol-flag)
 210           (save-excursion
 211             (skip-chars-forward " \t")
 212             (setq eol-flag (eolp)))
 213           (or eol-flag
 214               (indent-to (max 0 (+ indent (prefix-numeric-value arg))) 0))
 215           (delete-region (point) (progn (skip-chars-forward " \t") (point))))
 216         (forward-line 1))
 217       (move-marker end nil)
 218       ;; Keep the active region in transient mode.
 219       (when (eq (cadr overriding-terminal-local-map) indent-rigidly-map)
 220         (setq deactivate-mark nil)))))
 221
 222 (defun indent-rigidly--pop-undo ()
 223   (and (memq last-command '(indent-rigidly-left indent-rigidly-right
 224                             indent-rigidly-left-to-tab-stop
 225                             indent-rigidly-right-to-tab-stop))
 226        (consp buffer-undo-list)
 227        (eq (car buffer-undo-list) nil)
 228        (pop buffer-undo-list)))
 229
 230 (defun indent-rigidly-left (beg end)
 231   "Indent all lines between BEG and END leftward by one space."
 232   (interactive "r")
 233   (indent-rigidly--pop-undo)
 234   (indent-rigidly
 235    beg end
 236    (if (eq (current-bidi-paragraph-direction) 'right-to-left) 1 -1)))
 237
 238 (defun indent-rigidly-right (beg end)
 239   "Indent all lines between BEG and END rightward by one space."
 240   (interactive "r")
 241   (indent-rigidly--pop-undo)
 242   (indent-rigidly
 243    beg end
 244    (if (eq (current-bidi-paragraph-direction) 'right-to-left) -1 1)))
 245
 246 (defun indent-rigidly-left-to-tab-stop (beg end)
 247   "Indent all lines between BEG and END leftward to a tab stop."
 248   (interactive "r")
 249   (indent-rigidly--pop-undo)
 250   (let* ((current (indent-rigidly--current-indentation beg end))
 251          (rtl (eq (current-bidi-paragraph-direction) 'right-to-left))
 252          (next (indent--next-tab-stop current (if rtl nil 'prev))))
 253     (indent-rigidly beg end (- next current))))
 254
 255 (defun indent-rigidly-right-to-tab-stop (beg end)
 256   "Indent all lines between BEG and END rightward to a tab stop."
 257   (interactive "r")
 258   (indent-rigidly--pop-undo)
 259   (let* ((current (indent-rigidly--current-indentation beg end))
 260          (rtl (eq (current-bidi-paragraph-direction) 'right-to-left))
 261          (next (indent--next-tab-stop current (if rtl 'prev))))
 262     (indent-rigidly beg end (- next current))))
 263
 264 (defun indent-line-to (column)
 265   "Indent current line to COLUMN.
 266 This function removes or adds spaces and tabs at beginning of line
 267 only if necessary.  It leaves point at end of indentation."
 268   (backward-to-indentation 0)
 269   (let ((cur-col (current-column)))
 270     (cond ((< cur-col column)
 271            (if (>= (- column (* (/ cur-col tab-width) tab-width)) tab-width)
 272                (delete-region (point)
 273                               (progn (skip-chars-backward " ") (point))))
 274            (indent-to column))
 275           ((> cur-col column) ; too far right (after tab?)
 276            (delete-region (progn (move-to-column column t) (point))
 277                           (progn (backward-to-indentation 0) (point)))))))
 278
 279 (defun current-left-margin ()
 280   "Return the left margin to use for this line.
 281 This is the value of the buffer-local variable `left-margin' plus the value
 282 of the `left-margin' text-property at the start of the line."
 283   (save-excursion
 284     (back-to-indentation)
 285     (max 0
 286          (+ left-margin (or (get-text-property
 287                              (if (and (eobp) (not (bobp)))
 288                                  (1- (point)) (point))
 289                              'left-margin) 0)))))
 290
 291 (defun move-to-left-margin (&optional n force)
 292   "Move to the left margin of the current line.
 293 With optional argument, move forward N-1 lines first.
 294 The column moved to is the one given by the `current-left-margin' function.
 295 If the line's indentation appears to be wrong, and this command is called
 296 interactively or with optional argument FORCE, it will be fixed."
 297   (interactive (list (prefix-numeric-value current-prefix-arg) t))
 298   (beginning-of-line n)
 299   (skip-chars-forward " \t")
 300   (if (minibufferp (current-buffer))
 301       (if (save-excursion (beginning-of-line) (bobp))
 302           (goto-char (minibuffer-prompt-end))
 303         (beginning-of-line))
 304     (let ((lm (current-left-margin))
 305           (cc (current-column)))
 306       (cond ((> cc lm)
 307              (if (> (move-to-column lm force) lm)
 308                  ;; If lm is in a tab and we are not forcing, move before tab
 309                  (backward-char 1)))
 310             ((and force (< cc lm))
 311              (indent-to-left-margin))))))
 312
 313 ;; This used to be the default indent-line-function,
 314 ;; used in Fundamental Mode, Text Mode, etc.
 315 (defun indent-to-left-margin ()
 316   "Indent current line to the column given by `current-left-margin'."
 317   (save-excursion (indent-line-to (current-left-margin)))
 318   ;; If we are within the indentation, move past it.
 319   (when (save-excursion
 320           (skip-chars-backward " \t")
 321           (bolp))
 322     (skip-chars-forward " \t")))
 323
 324 (defun delete-to-left-margin (&optional from to)
 325   "Remove left margin indentation from a region.
 326 This deletes to the column given by `current-left-margin'.
 327 In no case will it delete non-whitespace.
 328 Args FROM and TO are optional; default is the whole buffer."
 329   (save-excursion
 330     (goto-char (or to (point-max)))
 331     (setq to (point-marker))
 332     (goto-char (or from (point-min)))
 333     (or (bolp) (forward-line 1))
 334     (while (< (point) to)
 335       (delete-region (point) (progn (move-to-left-margin nil t) (point)))
 336       (forward-line 1))
 337     (move-marker to nil)))
 338
 339 (defun set-left-margin (from to width)
 340   "Set the left margin of the region to WIDTH.
 341 If `auto-fill-mode' is active, re-fill the region to fit the new margin.
 342
 343 Interactively, WIDTH is the prefix argument, if specified.
 344 Without prefix argument, the command prompts for WIDTH."
 345   (interactive "r\nNSet left margin to column: ")
 346   (save-excursion
 347     ;; If inside indentation, start from BOL.
 348     (goto-char from)
 349     (skip-chars-backward " \t")
 350     (if (bolp) (setq from (point)))
 351     ;; Place end after whitespace
 352     (goto-char to)
 353     (skip-chars-forward " \t")
 354     (setq to (point-marker)))
 355   ;; Delete margin indentation first, but keep paragraph indentation.
 356   (delete-to-left-margin from to)
 357   (put-text-property from to 'left-margin width)
 358   (indent-rigidly from to width)
 359   (if auto-fill-function (save-excursion (fill-region from to nil t t)))
 360   (move-marker to nil))
 361
 362 (defun set-right-margin (from to width)
 363   "Set the right margin of the region to WIDTH.
 364 If `auto-fill-mode' is active, re-fill the region to fit the new margin.
 365
 366 Interactively, WIDTH is the prefix argument, if specified.
 367 Without prefix argument, the command prompts for WIDTH."
 368   (interactive "r\nNSet right margin to width: ")
 369   (save-excursion
 370     (goto-char from)
 371     (skip-chars-backward " \t")
 372     (if (bolp) (setq from (point))))
 373   (put-text-property from to 'right-margin width)
 374   (if auto-fill-function (save-excursion (fill-region from to nil t t))))
 375
 376 (defun alter-text-property (from to prop func &optional object)
 377   "Programmatically change value of a text-property.
 378 For each region between FROM and TO that has a single value for PROPERTY,
 379 apply FUNCTION to that value and sets the property to the function's result.
 380 Optional fifth argument OBJECT specifies the string or buffer to operate on."
 381   (let ((begin from)
 382         end val)
 383     (while (setq val (get-text-property begin prop object)
 384                  end (text-property-not-all begin to prop val object))
 385       (put-text-property begin end prop (funcall func val) object)
 386       (setq begin end))
 387     (if (< begin to)
 388         (put-text-property begin to prop (funcall func val) object))))
 389
 390 (defun increase-left-margin (from to inc)
 391   "Increase or decrease the left-margin of the region.
 392 With no prefix argument, this adds `standard-indent' of indentation.
 393 A prefix arg (optional third arg INC noninteractively) specifies the amount
 394 to change the margin by, in characters.
 395 If `auto-fill-mode' is active, re-fill the region to fit the new margin."
 396   (interactive "*r\nP")
 397   (setq inc (if inc (prefix-numeric-value inc) standard-indent))
 398   (save-excursion
 399     (goto-char from)
 400     (skip-chars-backward " \t")
 401     (if (bolp) (setq from (point)))
 402     (goto-char to)
 403     (setq to (point-marker)))
 404   (alter-text-property from to 'left-margin
 405                        (lambda (v) (max (- left-margin) (+ inc (or v 0)))))
 406   (indent-rigidly from to inc)
 407   (if auto-fill-function (save-excursion (fill-region from to nil t t)))
 408   (move-marker to nil))
 409
 410 (defun decrease-left-margin (from to inc)
 411   "Make the left margin of the region smaller.
 412 With no prefix argument, decrease the indentation by `standard-indent'.
 413 A prefix arg (optional third arg INC noninteractively) specifies the amount
 414 to change the margin by, in characters.
 415 If `auto-fill-mode' is active, re-fill the region to fit the new margin."
 416   (interactive "*r\nP")
 417   (setq inc (if inc (prefix-numeric-value inc) standard-indent))
 418   (increase-left-margin from to (- inc)))
 419
 420 (defun increase-right-margin (from to inc)
 421   "Increase the right-margin of the region.
 422 With no prefix argument, increase the right margin by `standard-indent'.
 423 A prefix arg (optional third arg INC noninteractively) specifies the amount
 424 to change the margin by, in characters.  A negative argument decreases
 425 the right margin width.
 426 If `auto-fill-mode' is active, re-fill the region to fit the new margin."
 427   (interactive "r\nP")
 428   (setq inc (if inc (prefix-numeric-value inc) standard-indent))
 429   (save-excursion
 430     (alter-text-property from to 'right-margin
 431                          (lambda (v) (+ inc (or v 0))))
 432     (if auto-fill-function
 433         (fill-region from to nil t t))))
 434
 435 (defun decrease-right-margin (from to inc)
 436   "Make the right margin of the region smaller.
 437 With no prefix argument, decrease the right margin by `standard-indent'.
 438 A prefix arg (optional third arg INC noninteractively) specifies the amount
 439 of width to remove, in characters.  A negative argument increases
 440 the right margin width.
 441 If `auto-fill-mode' is active, re-fills region to fit in new margin."
 442   (interactive "*r\nP")
 443   (setq inc (if inc (prefix-numeric-value inc) standard-indent))
 444   (increase-right-margin from to (- inc)))
 445
 446 (defun beginning-of-line-text (&optional n)
 447   "Move to the beginning of the text on this line.
 448 With optional argument, move forward N-1 lines first.
 449 From the beginning of the line, moves past the left-margin indentation, the
 450 fill-prefix, and any indentation used for centering or right-justifying the
 451 line, but does not move past any whitespace that was explicitly inserted
 452 \(such as a tab used to indent the first line of a paragraph)."
 453   (interactive "p")
 454   (beginning-of-line n)
 455   (skip-chars-forward " \t")
 456   ;; Skip over fill-prefix.
 457   (if (and fill-prefix
 458            (not (string-equal fill-prefix "")))
 459       (if (equal fill-prefix
 460                  (buffer-substring
 461                   (point) (min (point-max) (+ (length fill-prefix) (point)))))
 462           (forward-char (length fill-prefix)))
 463     (if (and adaptive-fill-mode adaptive-fill-regexp
 464              (looking-at adaptive-fill-regexp))
 465         (goto-char (match-end 0))))
 466   ;; Skip centering or flushright indentation
 467   (if (memq (current-justification) '(center right))
 468       (skip-chars-forward " \t")))
 469
 470 (defvar indent-region-function nil
 471   "Short cut function to indent region using `indent-according-to-mode'.
 472 A value of nil means really run `indent-according-to-mode' on each line.")
 473
 474 (defun indent-region (start end &optional column)
 475   "Indent each nonblank line in the region.
 476 A numeric prefix argument specifies a column: indent each line to that column.
 477
 478 With no prefix argument, the command chooses one of these methods and
 479 indents all the lines with it:
 480
 481   1) If `fill-prefix' is non-nil, insert `fill-prefix' at the
 482      beginning of each line in the region that does not already begin
 483      with it.
 484   2) If `indent-region-function' is non-nil, call that function
 485      to indent the region.
 486   3) Indent each line via `indent-according-to-mode'.
 487
 488 Called from a program, START and END specify the region to indent.
 489 If the third argument COLUMN is an integer, it specifies the
 490 column to indent to; if it is nil, use one of the three methods above."
 491   (interactive "r\nP")
 492   (cond
 493    ;; If a numeric prefix is given, indent to that column.
 494    (column
 495     (setq column (prefix-numeric-value column))
 496     (save-excursion
 497       (goto-char end)
 498       (setq end (point-marker))
 499       (goto-char start)
 500       (or (bolp) (forward-line 1))
 501       (while (< (point) end)
 502         (delete-region (point) (progn (skip-chars-forward " \t") (point)))
 503         (or (eolp)
 504             (indent-to column 0))
 505         (forward-line 1))
 506       (move-marker end nil)))
 507    ;; If a fill-prefix is specified, use it.
 508    (fill-prefix
 509     (save-excursion
 510       (goto-char end)
 511       (setq end (point-marker))
 512       (goto-char start)
 513       (let ((regexp (regexp-quote fill-prefix)))
 514         (while (< (point) end)
 515           (or (looking-at regexp)
 516               (and (bolp) (eolp))
 517               (insert fill-prefix))
 518           (forward-line 1)))))
 519    ;; Use indent-region-function is available.
 520    (indent-region-function
 521     (funcall indent-region-function start end))
 522    ;; Else, use a default implementation that calls indent-line-function on
 523    ;; each line.
 524    (t
 525     (save-excursion
 526       (setq end (copy-marker end))
 527       (goto-char start)
 528       (let ((pr (unless (minibufferp)
 529                   (make-progress-reporter "Indenting region..." (point) end))))
 530         (while (< (point) end)
 531           (or (and (bolp) (eolp))
 532               (indent-according-to-mode))
 533           (forward-line 1)
 534           (and pr (progress-reporter-update pr (point))))
 535         (and pr (progress-reporter-done pr))
 536         (move-marker end nil)))))
 537   ;; In most cases, reindenting modifies the buffer, but it may also
 538   ;; leave it unmodified, in which case we have to deactivate the mark
 539   ;; by hand.
 540   (deactivate-mark))
 541
 542 (defun indent-relative-maybe ()
 543   "Indent a new line like previous nonblank line.
 544 If the previous nonblank line has no indent points beyond the
 545 column point starts at, this command does nothing.
 546
 547 See also `indent-relative'."
 548   (interactive)
 549   (indent-relative t))
 550
 551 (defun indent-relative (&optional unindented-ok)
 552   "Space out to under next indent point in previous nonblank line.
 553 An indent point is a non-whitespace character following whitespace.
 554 The following line shows the indentation points in this line.
 555     ^         ^    ^     ^   ^           ^      ^  ^    ^
 556 If the previous nonblank line has no indent points beyond the
 557 column point starts at, `tab-to-tab-stop' is done instead, unless
 558 this command is invoked with a numeric argument, in which case it
 559 does nothing.
 560
 561 See also `indent-relative-maybe'."
 562   (interactive "P")
 563   (if (and abbrev-mode
 564            (eq (char-syntax (preceding-char)) ?w))
 565       (expand-abbrev))
 566   (let ((start-column (current-column))
 567         indent)
 568     (save-excursion
 569       (beginning-of-line)
 570       (if (re-search-backward "^[^\n]" nil t)
 571           (let ((end (save-excursion (forward-line 1) (point))))
 572             (move-to-column start-column)
 573             ;; Is start-column inside a tab on this line?
 574             (if (> (current-column) start-column)
 575                 (backward-char 1))
 576             (or (looking-at "[ \t]")
 577                 unindented-ok
 578                 (skip-chars-forward "^ \t" end))
 579             (skip-chars-forward " \t" end)
 580             (or (= (point) end) (setq indent (current-column))))))
 581     (if indent
 582         (let ((opoint (point-marker)))
 583           (indent-to indent 0)
 584           (if (> opoint (point))
 585               (goto-char opoint))
 586           (move-marker opoint nil))
 587       (tab-to-tab-stop))))
 588
 589 (defcustom tab-stop-list nil
 590   "List of tab stop positions used by `tab-to-tab-stop'.
 591 This should be nil, or a list of integers, ordered from smallest to largest.
 592 It implicitly extends to infinity through repetition of the last step.
 593 For example, '(1 2 5) is equivalent to '(1 2 5 8 11 ...).  If the list has
 594 fewer than 2 elements, `tab-width' is used as the \"last step\".
 595 A value of nil means a tab stop every `tab-width' columns."
 596   :group 'indent
 597   :version "24.4"                       ; from explicit list to nil
 598   :safe 'listp
 599   :type '(repeat integer))
 600
 601 (defvar edit-tab-stops-map
 602   (let ((map (make-sparse-keymap)))
 603     (define-key map "\C-x\C-s" 'edit-tab-stops-note-changes)
 604     (define-key map "\C-c\C-c" 'edit-tab-stops-note-changes)
 605     map)
 606   "Keymap used in `edit-tab-stops'.")
 607
 608 (defvar edit-tab-stops-buffer nil
 609   "Buffer whose tab stops are being edited.
 610 This matters if the variable `tab-stop-list' is local in that buffer.")
 611
 612 (defun edit-tab-stops ()
 613   "Edit the tab stops used by `tab-to-tab-stop'.
 614 Creates a buffer *Tab Stops* containing text describing the tab stops.
 615 A colon indicates a column where there is a tab stop.
 616 You can add or remove colons and then do \\<edit-tab-stops-map>\\[edit-tab-stops-note-changes] to make changes take effect."
 617   (interactive)
 618   (setq edit-tab-stops-buffer (current-buffer))
 619   (switch-to-buffer (get-buffer-create "*Tab Stops*"))
 620   (use-local-map edit-tab-stops-map)
 621   (setq-local indent-tabs-mode nil)
 622   (overwrite-mode 1)
 623   (setq truncate-lines t)
 624   (erase-buffer)
 625   (let ((tabs tab-stop-list))
 626     (while tabs
 627       (indent-to (car tabs) 0)
 628       (insert ?:)
 629       (setq tabs (cdr tabs))))
 630   (let ((count 0))
 631     (insert ?\n)
 632     (while (< count 8)
 633       (insert (+ count ?0))
 634     (insert "         ")
 635       (setq count (1+ count)))
 636     (insert ?\n)
 637     (while (> count 0)
 638       (insert "0123456789")
 639       (setq count (1- count))))
 640   (insert "\nTo install changes, type C-c C-c")
 641   (goto-char (point-min)))
 642
 643 (defun edit-tab-stops-note-changes ()
 644   "Put edited tab stops into effect."
 645   (interactive)
 646     (let (tabs)
 647       (save-excursion
 648         (goto-char 1)
 649         (end-of-line)
 650         (while (search-backward ":" nil t)
 651           (setq tabs (cons (current-column) tabs))))
 652       (bury-buffer (prog1 (current-buffer)
 653                           (switch-to-buffer edit-tab-stops-buffer)))
 654       (setq tab-stop-list tabs))
 655   (message "Tab stops installed"))
 656
 657 (defun indent--next-tab-stop (column &optional prev)
 658   "Return the next tab stop after COLUMN.
 659 If PREV is non-nil, return the previous one instead."
 660   (let ((tabs tab-stop-list))
 661     (while (and tabs (>= column (car tabs)))
 662       (setq tabs (cdr tabs)))
 663     (if tabs
 664         (if (not prev)
 665             (car tabs)
 666           (let ((prevtabs (cdr (memq (car tabs) (reverse tab-stop-list)))))
 667             (if (null prevtabs) 0
 668               (if (= column (car prevtabs))
 669                   (or (nth 1 prevtabs) 0)
 670                 (car prevtabs)))))
 671       ;; We passed the end of tab-stop-list: guess a continuation.
 672       (let* ((last2 (last tab-stop-list 2))
 673              (step (if (cdr last2) (- (cadr last2) (car last2)) tab-width))
 674              (last (or (cadr last2) (car last2) 0)))
 675         ;; Repeat the last tab's length.
 676         (+ last (* step (if prev
 677                             (if (<= column last) -1 (/ (- column last 1) step))
 678                           (1+ (/ (- column last) step)))))))))
 679
 680 (defun tab-to-tab-stop ()
 681   "Insert spaces or tabs to next defined tab-stop column.
 682 The variable `tab-stop-list' is a list of columns at which there are tab stops.
 683 Use \\[edit-tab-stops] to edit them interactively."
 684   (interactive)
 685   (and abbrev-mode (= (char-syntax (preceding-char)) ?w)
 686        (expand-abbrev))
 687   (let ((nexttab (indent--next-tab-stop (current-column))))
 688     (delete-horizontal-space t)
 689     (indent-to nexttab)))
 690
 691 (defun move-to-tab-stop ()
 692   "Move point to next defined tab-stop column.
 693 The variable `tab-stop-list' is a list of columns at which there are tab stops.
 694 Use \\[edit-tab-stops] to edit them interactively."
 695   (interactive)
 696   (let ((nexttab (indent--next-tab-stop (current-column))))
 697     (let ((before (point)))
 698       (move-to-column nexttab t)
 699       (save-excursion
 700         (goto-char before)
 701         ;; If we just added a tab, or moved over one,
 702         ;; delete any superfluous spaces before the old point.
 703         (if (and (eq (preceding-char) ?\s)
 704                  (eq (following-char) ?\t))
 705             (let ((tabend (* (/ (current-column) tab-width) tab-width)))
 706               (while (and (> (current-column) tabend)
 707                           (eq (preceding-char) ?\s))
 708                 (forward-char -1))
 709               (delete-region (point) before)))))))
 710
 711 (define-key global-map "\t" 'indent-for-tab-command)
 712 (define-key esc-map "\C-\\" 'indent-region)
 713 (define-key ctl-x-map "\t" 'indent-rigidly)
 714 (define-key esc-map "i" 'tab-to-tab-stop)
 715
 716 ;;; indent.el ends here