lisp/emacs-lisp/debug.el

   1 ;;; debug.el --- debuggers and related commands for Emacs  -*- lexical-binding: t -*-
   2
   3 ;; Copyright (C) 1985-1986, 1994, 2001-2015 Free Software Foundation,
   4 ;; Inc.
   5
   6 ;; Maintainer: emacs-devel@gnu.org
   7 ;; Keywords: lisp, tools, maint
   8
   9 ;; This file is part of GNU Emacs.
  10
  11 ;; GNU Emacs is free software: you can redistribute it and/or modify
  12 ;; it under the terms of the GNU General Public License as published by
  13 ;; the Free Software Foundation, either version 3 of the License, or
  14 ;; (at your option) any later version.
  15
  16 ;; GNU Emacs is distributed in the hope that it will be useful,
  17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 ;; GNU General Public License for more details.
  20
  21 ;; You should have received a copy of the GNU General Public License
  22 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  23
  24 ;;; Commentary:
  25
  26 ;; This is a major mode documented in the Emacs Lisp manual.
  27
  28 ;;; Code:
  29
  30 (require 'button)
  31
  32 (defgroup debugger nil
  33   "Debuggers and related commands for Emacs."
  34   :prefix "debugger-"
  35   :group 'debug)
  36
  37 (defcustom debugger-mode-hook nil
  38   "Hooks run when `debugger-mode' is turned on."
  39   :type 'hook
  40   :group 'debugger
  41   :version "20.3")
  42
  43 (defcustom debugger-batch-max-lines 40
  44   "Maximum lines to show in debugger buffer in a noninteractive Emacs.
  45 When the debugger is entered and Emacs is running in batch mode,
  46 if the backtrace text has more than this many lines,
  47 the middle is discarded, and just the beginning and end are displayed."
  48   :type 'integer
  49   :group 'debugger
  50   :version "21.1")
  51
  52 (defcustom debugger-bury-or-kill 'bury
  53   "What to do with the debugger buffer when exiting `debug'.
  54 The value affects the behavior of operations on any window
  55 previously showing the debugger buffer.
  56
  57 `nil' means that if its window is not deleted when exiting the
  58   debugger, invoking `switch-to-prev-buffer' will usually show
  59   the debugger buffer again.
  60
  61 `append' means that if the window is not deleted, the debugger
  62   buffer moves to the end of the window's previous buffers so
  63   it's less likely that a future invocation of
  64   `switch-to-prev-buffer' will switch to it.  Also, it moves the
  65   buffer to the end of the frame's buffer list.
  66
  67 `bury' means that if the window is not deleted, its buffer is
  68   removed from the window's list of previous buffers.  Also, it
  69   moves the buffer to the end of the frame's buffer list.  This
  70   value provides the most reliable remedy to not have
  71   `switch-to-prev-buffer' switch to the debugger buffer again
  72   without killing the buffer.
  73
  74 `kill' means to kill the debugger buffer.
  75
  76 The value used here is passed to `quit-restore-window'."
  77   :type '(choice
  78           (const :tag "Keep alive" nil)
  79           (const :tag "Append" append)
  80           (const :tag "Bury" bury)
  81           (const :tag "Kill" kill))
  82   :group 'debugger
  83   :version "24.3")
  84
  85 (defvar debugger-step-after-exit nil
  86   "Non-nil means \"single-step\" after the debugger exits.")
  87
  88 (defvar debugger-value nil
  89   "This is the value for the debugger to return, when it returns.")
  90
  91 (defvar debugger-old-buffer nil
  92   "This is the buffer that was current when the debugger was entered.")
  93
  94 (defvar debugger-previous-window nil
  95   "This is the window last showing the debugger buffer.")
  96
  97 (defvar debugger-previous-window-height nil
  98   "The last recorded height of `debugger-previous-window'.")
  99
 100 (defvar debugger-previous-backtrace nil
 101   "The contents of the previous backtrace (including text properties).
 102 This is to optimize `debugger-make-xrefs'.")
 103
 104 (defvar debugger-outer-match-data)
 105 (defvar debugger-will-be-back nil
 106   "Non-nil if we expect to get back in the debugger soon.")
 107
 108 (defvar inhibit-debug-on-entry nil
 109   "Non-nil means that debug-on-entry is disabled.")
 110
 111 (defvar debugger-jumping-flag nil
 112   "Non-nil means that debug-on-entry is disabled.
 113 This variable is used by `debugger-jump', `debugger-step-through',
 114 and `debugger-reenable' to temporarily disable debug-on-entry.")
 115
 116 (defvar inhibit-trace)                  ;Not yet implemented.
 117
 118 (defvar debugger-args nil
 119   "Arguments with which the debugger was called.
 120 It is a list expected to take the form (CAUSE . REST)
 121 where CAUSE can be:
 122 - debug: called for entry to a flagged function.
 123 - t: called because of debug-on-next-call.
 124 - lambda: same thing but via `funcall'.
 125 - exit: called because of exit of a flagged function.
 126 - error: called because of `debug-on-error'.")
 127
 128 ;;;###autoload
 129 (setq debugger 'debug)
 130 ;;;###autoload
 131 (defun debug (&rest args)
 132   "Enter debugger.  \\<debugger-mode-map>`\\[debugger-continue]' returns from the debugger.
 133 Arguments are mainly for use when this is called from the internals
 134 of the evaluator.
 135
 136 You may call with no args, or you may pass nil as the first arg and
 137 any other args you like.  In that case, the list of args after the
 138 first will be printed into the backtrace buffer."
 139   (interactive)
 140   (if inhibit-redisplay
 141       ;; Don't really try to enter debugger within an eval from redisplay.
 142       debugger-value
 143     (unless noninteractive
 144       (message "Entering debugger..."))
 145     (let (debugger-value
 146           (debugger-previous-state
 147            (if (get-buffer "*Backtrace*")
 148                (with-current-buffer (get-buffer "*Backtrace*")
 149                  (list major-mode (buffer-string)))))
 150           (debugger-args args)
 151           (debugger-buffer (get-buffer-create "*Backtrace*"))
 152           (debugger-old-buffer (current-buffer))
 153           (debugger-window nil)
 154           (debugger-step-after-exit nil)
 155           (debugger-will-be-back nil)
 156           ;; Don't keep reading from an executing kbd macro!
 157           (executing-kbd-macro nil)
 158           ;; Save the outer values of these vars for the `e' command
 159           ;; before we replace the values.
 160           (debugger-outer-match-data (match-data))
 161           (debugger-with-timeout-suspend (with-timeout-suspend)))
 162       ;; Set this instead of binding it, so that `q'
 163       ;; will not restore it.
 164       (setq overriding-terminal-local-map nil)
 165       ;; Don't let these magic variables affect the debugger itself.
 166       (let ((last-command nil) this-command track-mouse
 167             (inhibit-trace t)
 168             (inhibit-debug-on-entry t)
 169             unread-command-events
 170             unread-post-input-method-events
 171             last-input-event last-command-event last-nonmenu-event
 172             last-event-frame
 173             overriding-local-map
 174             load-read-function
 175             ;; If we are inside a minibuffer, allow nesting
 176             ;; so that we don't get an error from the `e' command.
 177             (enable-recursive-minibuffers
 178              (or enable-recursive-minibuffers (> (minibuffer-depth) 0)))
 179             (standard-input t) (standard-output t)
 180             inhibit-redisplay
 181             (cursor-in-echo-area nil)
 182             (window-configuration (current-window-configuration)))
 183         (unwind-protect
 184             (save-excursion
 185               (when (eq (car debugger-args) 'debug)
 186                 ;; Skip the frames for backtrace-debug, byte-code,
 187                 ;; debug--implement-debug-on-entry and the advice's `apply'.
 188                 (backtrace-debug 4 t)
 189                 ;; Place an extra debug-on-exit for macro's.
 190                 (when (eq 'lambda (car-safe (cadr (backtrace-frame 4))))
 191                   (backtrace-debug 5 t)))
 192               (pop-to-buffer
 193                debugger-buffer
 194                `((display-buffer-reuse-window
 195                   display-buffer-in-previous-window)
 196                   . (,(when debugger-previous-window
 197                         `(previous-window . ,debugger-previous-window)))))
 198               (setq debugger-window (selected-window))
 199               (if (eq debugger-previous-window debugger-window)
 200                   (when debugger-jumping-flag
 201                     ;; Try to restore previous height of debugger
 202                     ;; window.
 203                     (condition-case nil
 204                         (window-resize
 205                          debugger-window
 206                          (- debugger-previous-window-height
 207                             (window-total-height debugger-window)))
 208                       (error nil)))
 209                 (setq debugger-previous-window debugger-window))
 210               (debugger-mode)
 211               (debugger-setup-buffer debugger-args)
 212               (when noninteractive
 213                 ;; If the backtrace is long, save the beginning
 214                 ;; and the end, but discard the middle.
 215                 (when (> (count-lines (point-min) (point-max))
 216                          debugger-batch-max-lines)
 217                   (goto-char (point-min))
 218                   (forward-line (/ 2 debugger-batch-max-lines))
 219                   (let ((middlestart (point)))
 220                     (goto-char (point-max))
 221                     (forward-line (- (/ 2 debugger-batch-max-lines)
 222                                      debugger-batch-max-lines))
 223                     (delete-region middlestart (point)))
 224                   (insert "...\n"))
 225                 (goto-char (point-min))
 226                 (message "%s" (buffer-string))
 227                 (kill-emacs -1))
 228               (message "")
 229               (let ((standard-output nil)
 230                     (buffer-read-only t))
 231                 (message "")
 232                 ;; Make sure we unbind buffer-read-only in the right buffer.
 233                 (save-excursion
 234                   (recursive-edit))))
 235           (when (and (window-live-p debugger-window)
 236                      (eq (window-buffer debugger-window) debugger-buffer))
 237             ;; Record height of debugger window.
 238             (setq debugger-previous-window-height
 239                   (window-total-height debugger-window)))
 240           (if debugger-will-be-back
 241               ;; Restore previous window configuration (Bug#12623).
 242               (set-window-configuration window-configuration)
 243             (when (and (window-live-p debugger-window)
 244                        (eq (window-buffer debugger-window) debugger-buffer))
 245               (progn
 246                 ;; Unshow debugger-buffer.
 247                 (quit-restore-window debugger-window debugger-bury-or-kill)
 248                 ;; Restore current buffer (Bug#12502).
 249                 (set-buffer debugger-old-buffer))))
 250           ;; Restore previous state of debugger-buffer in case we were
 251           ;; in a recursive invocation of the debugger, otherwise just
 252           ;; erase the buffer and put it into fundamental mode.
 253           (when (buffer-live-p debugger-buffer)
 254             (with-current-buffer debugger-buffer
 255               (let ((inhibit-read-only t))
 256                 (erase-buffer)
 257                 (if (null debugger-previous-state)
 258                     (fundamental-mode)
 259                   (insert (nth 1 debugger-previous-state))
 260                   (funcall (nth 0 debugger-previous-state))))))
 261           (with-timeout-unsuspend debugger-with-timeout-suspend)
 262           (set-match-data debugger-outer-match-data)))
 263       (setq debug-on-next-call debugger-step-after-exit)
 264       debugger-value)))
 265 \f
 266 (defun debugger-setup-buffer (args)
 267   "Initialize the `*Backtrace*' buffer for entry to the debugger.
 268 That buffer should be current already."
 269   (setq buffer-read-only nil)
 270   (erase-buffer)
 271   (set-buffer-multibyte t)              ;Why was it nil ?  -stef
 272   (setq buffer-undo-list t)
 273   (let ((standard-output (current-buffer))
 274         (print-escape-newlines t)
 275         (print-level 8)
 276         (print-length 50))
 277     (backtrace))
 278   (goto-char (point-min))
 279   (delete-region (point)
 280                  (progn
 281                    (search-forward "\n  debug(")
 282                    (forward-line (if (eq (car args) 'debug)
 283                                      ;; Remove debug--implement-debug-on-entry
 284                                      ;; and the advice's `apply' frame.
 285                                      3
 286                                    1))
 287                    (point)))
 288   (insert "Debugger entered")
 289   ;; lambda is for debug-on-call when a function call is next.
 290   ;; debug is for debug-on-entry function called.
 291   (let ((pos (point)))
 292     (pcase (car args)
 293       ((or `lambda `debug)
 294        (insert "--entering a function:\n")
 295        (setq pos (1- (point))))
 296       ;; Exiting a function.
 297       (`exit
 298        (insert "--returning value: ")
 299        (setq pos (point))
 300        (setq debugger-value (nth 1 args))
 301        (prin1 debugger-value (current-buffer))
 302        (insert ?\n)
 303        (delete-char 1)
 304        (insert ? )
 305        (beginning-of-line))
 306       ;; Debugger entered for an error.
 307       (`error
 308        (insert "--Lisp error: ")
 309        (setq pos (point))
 310        (prin1 (nth 1 args) (current-buffer))
 311        (insert ?\n))
 312       ;; debug-on-call, when the next thing is an eval.
 313       (`t
 314        (insert "--beginning evaluation of function call form:\n")
 315        (setq pos (1- (point))))
 316       ;; User calls debug directly.
 317       (_
 318        (insert ": ")
 319        (setq pos (point))
 320        (prin1 (if (eq (car args) 'nil)
 321                   (cdr args) args)
 322               (current-buffer))
 323        (insert ?\n)))
 324     ;; Place point on "stack frame 0" (bug#15101).
 325     (goto-char pos))
 326   ;; After any frame that uses eval-buffer,
 327   ;; insert a line that states the buffer position it's reading at.
 328   (save-excursion
 329     (let ((tem eval-buffer-list))
 330       (while (and tem
 331                   (re-search-forward "^  eval-\\(buffer\\|region\\)(" nil t))
 332         (end-of-line)
 333         (insert (format "  ; Reading at buffer position %d"
 334                         ;; This will get the wrong result
 335                         ;; if there are two nested eval-region calls
 336                         ;; for the same buffer.  That's not a very useful case.
 337                         (with-current-buffer (car tem)
 338                           (point))))
 339         (pop tem))))
 340   (debugger-make-xrefs))
 341
 342 (defun debugger-make-xrefs (&optional buffer)
 343   "Attach cross-references to function names in the `*Backtrace*' buffer."
 344   (interactive "b")
 345   (with-current-buffer (or buffer (current-buffer))
 346     (save-excursion
 347       (setq buffer (current-buffer))
 348       (let ((inhibit-read-only t)
 349             (old-end (point-min)) (new-end (point-min)))
 350         ;; If we saved an old backtrace, find the common part
 351         ;; between the new and the old.
 352         ;; Compare line by line, starting from the end,
 353         ;; because that's the part that is likely to be unchanged.
 354         (if debugger-previous-backtrace
 355             (let (old-start new-start (all-match t))
 356               (goto-char (point-max))
 357               (with-temp-buffer
 358                 (insert debugger-previous-backtrace)
 359                 (while (and all-match (not (bobp)))
 360                   (setq old-end (point))
 361                   (forward-line -1)
 362                   (setq old-start (point))
 363                   (with-current-buffer buffer
 364                     (setq new-end (point))
 365                     (forward-line -1)
 366                     (setq new-start (point)))
 367                   (if (not (zerop
 368                             (let ((case-fold-search nil))
 369                               (compare-buffer-substrings
 370                                (current-buffer) old-start old-end
 371                                buffer new-start new-end))))
 372                       (setq all-match nil))))
 373               ;; Now new-end is the position of the start of the
 374               ;; unchanged part in the current buffer, and old-end is
 375               ;; the position of that same text in the saved old
 376               ;; backtrace.  But we must subtract (point-min) since strings are
 377               ;; indexed in origin 0.
 378
 379               ;; Replace the unchanged part of the backtrace
 380               ;; with the text from debugger-previous-backtrace,
 381               ;; since that already has the proper xrefs.
 382               ;; With this optimization, we only need to scan
 383               ;; the changed part of the backtrace.
 384               (delete-region new-end (point-max))
 385               (goto-char (point-max))
 386               (insert (substring debugger-previous-backtrace
 387                                  (- old-end (point-min))))
 388               ;; Make the unchanged part of the backtrace inaccessible
 389               ;; so it won't be scanned.
 390               (narrow-to-region (point-min) new-end)))
 391
 392         ;; Scan the new part of the backtrace, inserting xrefs.
 393         (goto-char (point-min))
 394         (while (progn
 395                  (goto-char (+ (point) 2))
 396                  (skip-syntax-forward "^w_")
 397                  (not (eobp)))
 398           (let* ((beg (point))
 399                  (end (progn (skip-syntax-forward "w_") (point)))
 400                  (sym (intern-soft (buffer-substring-no-properties
 401                                     beg end)))
 402                  (file (and sym (symbol-file sym 'defun))))
 403             (when file
 404               (goto-char beg)
 405               ;; help-xref-button needs to operate on something matched
 406               ;; by a regexp, so set that up for it.
 407               (re-search-forward "\\(\\sw\\|\\s_\\)+")
 408               (help-xref-button 0 'help-function-def sym file)))
 409           (forward-line 1))
 410         (widen))
 411       (setq debugger-previous-backtrace (buffer-string)))))
 412 \f
 413 (defun debugger-step-through ()
 414   "Proceed, stepping through subexpressions of this expression.
 415 Enter another debugger on next entry to eval, apply or funcall."
 416   (interactive)
 417   (setq debugger-step-after-exit t)
 418   (setq debugger-jumping-flag t)
 419   (setq debugger-will-be-back t)
 420   (add-hook 'post-command-hook 'debugger-reenable)
 421   (message "Proceeding, will debug on next eval or call.")
 422   (exit-recursive-edit))
 423
 424 (defun debugger-continue ()
 425   "Continue, evaluating this expression without stopping."
 426   (interactive)
 427   (unless debugger-may-continue
 428     (error "Cannot continue"))
 429   (message "Continuing.")
 430   (save-excursion
 431     ;; Check to see if we've flagged some frame for debug-on-exit, in which
 432     ;; case we'll probably come back to the debugger soon.
 433     (goto-char (point-min))
 434     (if (re-search-forward "^\\* " nil t)
 435         (setq debugger-will-be-back t)))
 436   (exit-recursive-edit))
 437
 438 (defun debugger-return-value (val)
 439   "Continue, specifying value to return.
 440 This is only useful when the value returned from the debugger
 441 will be used, such as in a debug on exit from a frame."
 442   (interactive "XReturn value (evaluated): ")
 443   (when (memq (car debugger-args) '(t lambda error debug))
 444     (error "Cannot return a value %s"
 445            (if (eq (car debugger-args) 'error)
 446                "from an error" "at function entrance")))
 447   (setq debugger-value val)
 448   (princ "Returning " t)
 449   (prin1 debugger-value)
 450   (save-excursion
 451     ;; Check to see if we've flagged some frame for debug-on-exit, in which
 452     ;; case we'll probably come back to the debugger soon.
 453     (goto-char (point-min))
 454     (if (re-search-forward "^\\* " nil t)
 455         (setq debugger-will-be-back t)))
 456   (exit-recursive-edit))
 457
 458 (defun debugger-jump ()
 459   "Continue to exit from this frame, with all debug-on-entry suspended."
 460   (interactive)
 461   (debugger-frame)
 462   (setq debugger-jumping-flag t)
 463   (add-hook 'post-command-hook 'debugger-reenable)
 464   (message "Continuing through this frame")
 465   (setq debugger-will-be-back t)
 466   (exit-recursive-edit))
 467
 468 (defun debugger-reenable ()
 469   "Turn all debug-on-entry functions back on.
 470 This function is put on `post-command-hook' by `debugger-jump' and
 471 removes itself from that hook."
 472   (setq debugger-jumping-flag nil)
 473   (remove-hook 'post-command-hook 'debugger-reenable))
 474
 475 (defun debugger-frame-number (&optional skip-base)
 476   "Return number of frames in backtrace before the one point points at."
 477   (save-excursion
 478     (beginning-of-line)
 479     (if (looking-at " *;;;\\|[a-z]")
 480         (error "This line is not a function call"))
 481     (let ((opoint (point))
 482           (count 0))
 483       (unless skip-base
 484         (while (not (eq (cadr (backtrace-frame count)) 'debug))
 485           (setq count (1+ count)))
 486         ;; Skip debug--implement-debug-on-entry frame.
 487         (when (eq 'debug--implement-debug-on-entry
 488                   (cadr (backtrace-frame (1+ count))))
 489           (setq count (+ 2 count))))
 490       (goto-char (point-min))
 491       (when (looking-at "Debugger entered--\\(Lisp error\\|returning value\\):")
 492         (goto-char (match-end 0))
 493         (forward-sexp 1))
 494       (forward-line 1)
 495       (while (progn
 496                (forward-char 2)
 497                (cond ((debugger--locals-visible-p)
 498                       (goto-char (next-single-char-property-change
 499                                   (point) 'locals-visible)))
 500                      ((= (following-char) ?\()
 501                       (forward-sexp 1))
 502                      (t
 503                       (forward-sexp 2)))
 504                (forward-line 1)
 505                (<= (point) opoint))
 506         (if (looking-at " *;;;")
 507             (forward-line 1))
 508         (setq count (1+ count)))
 509       count)))
 510
 511 (defun debugger-frame ()
 512   "Request entry to debugger when this frame exits.
 513 Applies to the frame whose line point is on in the backtrace."
 514   (interactive)
 515   (backtrace-debug (debugger-frame-number) t)
 516   (beginning-of-line)
 517   (if (= (following-char) ? )
 518       (let ((inhibit-read-only t))
 519         (delete-char 1)
 520         (insert ?*)))
 521   (beginning-of-line))
 522
 523 (defun debugger-frame-clear ()
 524   "Do not enter debugger when this frame exits.
 525 Applies to the frame whose line point is on in the backtrace."
 526   (interactive)
 527   (backtrace-debug (debugger-frame-number) nil)
 528   (beginning-of-line)
 529   (if (= (following-char) ?*)
 530       (let ((inhibit-read-only t))
 531         (delete-char 1)
 532         (insert ? )))
 533   (beginning-of-line))
 534
 535 (defmacro debugger-env-macro (&rest body)
 536   "Run BODY in original environment."
 537   (declare (indent 0))
 538   `(save-excursion
 539     (if (null (buffer-live-p debugger-old-buffer))
 540         ;; old buffer deleted
 541         (setq debugger-old-buffer (current-buffer)))
 542     (set-buffer debugger-old-buffer)
 543     (set-match-data debugger-outer-match-data)
 544     (prog1
 545         (progn ,@body)
 546       (setq debugger-outer-match-data (match-data)))))
 547
 548 (defun debugger--backtrace-base ()
 549   "Return the function name that marks the top of the backtrace.
 550 See `backtrace-frame'."
 551   (cond ((eq 'debug--implement-debug-on-entry
 552              (cadr (backtrace-frame 1 'debug)))
 553          'debug--implement-debug-on-entry)
 554         (t 'debug)))
 555
 556 (defun debugger-eval-expression (exp &optional nframe)
 557   "Eval an expression, in an environment like that outside the debugger.
 558 The environment used is the one when entering the activation frame at point."
 559   (interactive
 560    (list (read--expression "Eval in stack frame: ")))
 561   (let ((nframe (or nframe
 562                     (condition-case nil (1+ (debugger-frame-number 'skip-base))
 563                       (error 0)))) ;; If on first line.
 564         (base (debugger--backtrace-base)))
 565     (debugger-env-macro
 566       (let ((val (backtrace-eval exp nframe base)))
 567         (prog1
 568             (prin1 val t)
 569           (let ((str (eval-expression-print-format val)))
 570             (if str (princ str t))))))))
 571
 572 (defun debugger--locals-visible-p ()
 573   "Are the local variables of the current stack frame visible?"
 574   (save-excursion
 575     (move-to-column 2)
 576     (get-text-property (point) 'locals-visible)))
 577
 578 (defun debugger--insert-locals (locals)
 579   "Insert the local variables LOCALS at point."
 580   (cond ((null locals)
 581          (insert "\n    [no locals]"))
 582         (t
 583          (let ((print-escape-newlines t))
 584            (dolist (s+v locals)
 585              (let ((symbol (car s+v))
 586                    (value (cdr s+v)))
 587                (insert "\n    ")
 588                (prin1 symbol (current-buffer))
 589                (insert " = ")
 590                (prin1 value (current-buffer))))))))
 591
 592 (defun debugger--show-locals ()
 593   "For the frame at point, insert locals and add text properties."
 594   (let* ((nframe (1+ (debugger-frame-number 'skip-base)))
 595          (base (debugger--backtrace-base))
 596          (locals (backtrace--locals nframe base))
 597          (inhibit-read-only t))
 598     (save-excursion
 599       (let ((start (progn
 600                      (move-to-column 2)
 601                      (point))))
 602         (end-of-line)
 603         (debugger--insert-locals locals)
 604         (add-text-properties start (point) '(locals-visible t))))))
 605
 606 (defun debugger--hide-locals ()
 607   "Delete local variables and remove the text property."
 608   (let* ((col (current-column))
 609          (end (progn
 610                 (move-to-column 2)
 611                 (next-single-char-property-change (point) 'locals-visible)))
 612          (start (previous-single-char-property-change end 'locals-visible))
 613          (inhibit-read-only t))
 614     (remove-text-properties start end '(locals-visible))
 615     (goto-char start)
 616     (end-of-line)
 617     (delete-region (point) end)
 618     (move-to-column col)))
 619
 620 (defun debugger-toggle-locals ()
 621   "Show or hide local variables of the current stack frame."
 622   (interactive)
 623   (cond ((debugger--locals-visible-p)
 624          (debugger--hide-locals))
 625         (t
 626          (debugger--show-locals))))
 627
 628 \f
 629 (defvar debugger-mode-map
 630   (let ((map (make-keymap))
 631         (menu-map (make-sparse-keymap)))
 632     (set-keymap-parent map button-buffer-map)
 633     (suppress-keymap map)
 634     (define-key map "-" 'negative-argument)
 635     (define-key map "b" 'debugger-frame)
 636     (define-key map "c" 'debugger-continue)
 637     (define-key map "j" 'debugger-jump)
 638     (define-key map "r" 'debugger-return-value)
 639     (define-key map "u" 'debugger-frame-clear)
 640     (define-key map "d" 'debugger-step-through)
 641     (define-key map "l" 'debugger-list-functions)
 642     (define-key map "h" 'describe-mode)
 643     (define-key map "q" 'top-level)
 644     (define-key map "e" 'debugger-eval-expression)
 645     (define-key map "v" 'debugger-toggle-locals) ; "v" is for "variables".
 646     (define-key map " " 'next-line)
 647     (define-key map "R" 'debugger-record-expression)
 648     (define-key map "\C-m" 'debug-help-follow)
 649     (define-key map [mouse-2] 'push-button)
 650     (define-key map [menu-bar debugger] (cons "Debugger" menu-map))
 651     (define-key menu-map [deb-top]
 652       '(menu-item "Quit" top-level
 653                   :help "Quit debugging and return to top level"))
 654     (define-key menu-map [deb-s0] '("--"))
 655     (define-key menu-map [deb-descr]
 656       '(menu-item "Describe Debugger Mode" describe-mode
 657                   :help "Display documentation for debugger-mode"))
 658     (define-key menu-map [deb-hfol]
 659       '(menu-item "Help Follow" debug-help-follow
 660                   :help "Follow cross-reference"))
 661     (define-key menu-map [deb-nxt]
 662       '(menu-item "Next Line" next-line
 663                   :help "Move cursor down"))
 664     (define-key menu-map [deb-s1] '("--"))
 665     (define-key menu-map [deb-lfunc]
 666       '(menu-item "List debug on entry functions" debugger-list-functions
 667                   :help "Display a list of all the functions now set to debug on entry"))
 668     (define-key menu-map [deb-fclear]
 669       '(menu-item "Cancel debug frame" debugger-frame-clear
 670                   :help "Do not enter debugger when this frame exits"))
 671     (define-key menu-map [deb-frame]
 672       '(menu-item "Debug frame" debugger-frame
 673                   :help "Request entry to debugger when this frame exits"))
 674     (define-key menu-map [deb-s2] '("--"))
 675     (define-key menu-map [deb-ret]
 676       '(menu-item "Return value..." debugger-return-value
 677                   :help "Continue, specifying value to return."))
 678     (define-key menu-map [deb-rec]
 679       '(menu-item "Display and Record Expression" debugger-record-expression
 680                   :help "Display a variable's value and record it in `*Backtrace-record*' buffer"))
 681     (define-key menu-map [deb-eval]
 682       '(menu-item "Eval Expression..." debugger-eval-expression
 683                   :help "Eval an expression, in an environment like that outside the debugger"))
 684     (define-key menu-map [deb-jump]
 685       '(menu-item "Jump" debugger-jump
 686                   :help "Continue to exit from this frame, with all debug-on-entry suspended"))
 687     (define-key menu-map [deb-cont]
 688       '(menu-item "Continue" debugger-continue
 689         :help "Continue, evaluating this expression without stopping"))
 690     (define-key menu-map [deb-step]
 691       '(menu-item "Step through" debugger-step-through
 692         :help "Proceed, stepping through subexpressions of this expression"))
 693     map))
 694
 695 (put 'debugger-mode 'mode-class 'special)
 696
 697 (define-derived-mode debugger-mode fundamental-mode "Debugger"
 698   "Mode for backtrace buffers, selected in debugger.
 699 \\<debugger-mode-map>
 700 A line starts with `*' if exiting that frame will call the debugger.
 701 Type \\[debugger-frame] or \\[debugger-frame-clear] to set or remove the `*'.
 702
 703 When in debugger due to frame being exited,
 704 use the \\[debugger-return-value] command to override the value
 705 being returned from that frame.
 706
 707 Use \\[debug-on-entry] and \\[cancel-debug-on-entry] to control
 708 which functions will enter the debugger when called.
 709
 710 Complete list of commands:
 711 \\{debugger-mode-map}"
 712   (setq truncate-lines t)
 713   (set-syntax-table emacs-lisp-mode-syntax-table)
 714   (use-local-map debugger-mode-map))
 715 \f
 716 (defcustom debugger-record-buffer "*Debugger-record*"
 717   "Buffer name for expression values, for \\[debugger-record-expression]."
 718   :type 'string
 719   :group 'debugger
 720   :version "20.3")
 721
 722 (defun debugger-record-expression  (exp)
 723   "Display a variable's value and record it in `*Backtrace-record*' buffer."
 724   (interactive
 725    (list (read--expression "Record Eval: ")))
 726   (let* ((buffer (get-buffer-create debugger-record-buffer))
 727          (standard-output buffer))
 728     (princ (format "Debugger Eval (%s): " exp))
 729     (princ (debugger-eval-expression exp))
 730     (terpri))
 731
 732   (with-current-buffer (get-buffer debugger-record-buffer)
 733     (message "%s"
 734              (buffer-substring (line-beginning-position 0)
 735                                (line-end-position 0)))))
 736
 737 (declare-function help-xref-interned "help-mode" (symbol))
 738
 739 (defun debug-help-follow (&optional pos)
 740   "Follow cross-reference at POS, defaulting to point.
 741
 742 For the cross-reference format, see `help-make-xrefs'."
 743   (interactive "d")
 744   (require 'help-mode)
 745   ;; Ideally we'd just do (call-interactively 'help-follow) except that this
 746   ;; assumes we're already in a *Help* buffer and reuses it, so it ends up
 747   ;; incorrectly "reusing" the *Backtrace* buffer to show the help info.
 748   (unless pos
 749     (setq pos (point)))
 750   (unless (push-button pos)
 751     ;; check if the symbol under point is a function or variable
 752     (let ((sym
 753            (intern
 754             (save-excursion
 755               (goto-char pos) (skip-syntax-backward "w_")
 756               (buffer-substring (point)
 757                                 (progn (skip-syntax-forward "w_")
 758                                        (point)))))))
 759       (when (or (boundp sym) (fboundp sym) (facep sym))
 760         (help-xref-interned sym)))))
 761 \f
 762 ;; When you change this, you may also need to change the number of
 763 ;; frames that the debugger skips.
 764 (defun debug--implement-debug-on-entry (&rest _ignore)
 765   "Conditionally call the debugger.
 766 A call to this function is inserted by `debug-on-entry' to cause
 767 functions to break on entry."
 768   (if (or inhibit-debug-on-entry debugger-jumping-flag)
 769       nil
 770     (funcall debugger 'debug)))
 771
 772 ;;;###autoload
 773 (defun debug-on-entry (function)
 774   "Request FUNCTION to invoke debugger each time it is called.
 775
 776 When called interactively, prompt for FUNCTION in the minibuffer.
 777
 778 This works by modifying the definition of FUNCTION.  If you tell the
 779 debugger to continue, FUNCTION's execution proceeds.  If FUNCTION is a
 780 normal function or a macro written in Lisp, you can also step through
 781 its execution.  FUNCTION can also be a primitive that is not a special
 782 form, in which case stepping is not possible.  Break-on-entry for
 783 primitive functions only works when that function is called from Lisp.
 784
 785 Use \\[cancel-debug-on-entry] to cancel the effect of this command.
 786 Redefining FUNCTION also cancels it."
 787   (interactive
 788    (let ((fn (function-called-at-point)) val)
 789      (when (special-form-p fn)
 790        (setq fn nil))
 791      (setq val (completing-read
 792                 (if fn
 793                     (format "Debug on entry to function (default %s): " fn)
 794                   "Debug on entry to function: ")
 795                 obarray
 796                 #'(lambda (symbol)
 797                     (and (fboundp symbol)
 798                          (not (special-form-p symbol))))
 799                 t nil nil (symbol-name fn)))
 800      (list (if (equal val "") fn (intern val)))))
 801   (advice-add function :before #'debug--implement-debug-on-entry
 802               '((depth . -100)))
 803   function)
 804
 805 (defun debug--function-list ()
 806   "List of functions currently set for debug on entry."
 807   (let ((funs '()))
 808     (mapatoms
 809      (lambda (s)
 810        (when (advice-member-p #'debug--implement-debug-on-entry s)
 811          (push s funs))))
 812     funs))
 813
 814 ;;;###autoload
 815 (defun cancel-debug-on-entry (&optional function)
 816   "Undo effect of \\[debug-on-entry] on FUNCTION.
 817 If FUNCTION is nil, cancel debug-on-entry for all functions.
 818 When called interactively, prompt for FUNCTION in the minibuffer.
 819 To specify a nil argument interactively, exit with an empty minibuffer."
 820   (interactive
 821    (list (let ((name
 822                 (completing-read
 823                  "Cancel debug on entry to function (default all functions): "
 824                  (mapcar #'symbol-name (debug--function-list)) nil t)))
 825            (when name
 826              (unless (string= name "")
 827                (intern name))))))
 828   (if function
 829       (progn
 830         (advice-remove function #'debug--implement-debug-on-entry)
 831         function)
 832     (message "Canceling debug-on-entry for all functions")
 833     (mapcar #'cancel-debug-on-entry (debug--function-list))))
 834
 835 (defun debugger-list-functions ()
 836   "Display a list of all the functions now set to debug on entry."
 837   (interactive)
 838   (require 'help-mode)
 839   (help-setup-xref '(debugger-list-functions)
 840                    (called-interactively-p 'interactive))
 841   (with-output-to-temp-buffer (help-buffer)
 842     (with-current-buffer standard-output
 843       (let ((funs (debug--function-list)))
 844         (if (null funs)
 845             (princ "No debug-on-entry functions now\n")
 846           (princ "Functions set to debug on entry:\n\n")
 847           (dolist (fun funs)
 848             (make-text-button (point) (progn (prin1 fun) (point))
 849                               'type 'help-function
 850                               'help-args (list fun))
 851             (terpri))
 852           (terpri)
 853           (princ "Note: if you have redefined a function, then it may no longer\n")
 854           (princ "be set to debug on entry, even if it is in the list."))))))
 855
 856 (provide 'debug)
 857
 858 ;;; debug.el ends here