path: root/lisp/emacs-lisp/cl-print.el

;;; cl-print.el --- CL-style generic printing  -*- lexical-binding: t; -*-

;; Copyright (C) 2017-2024 Free Software Foundation, Inc.

;; Author: Stefan Monnier <monnier@iro.umontreal.ca>
;; Keywords:
;; Version: 1.0
;; Package-Requires: ((emacs "25"))

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; Customizable print facility.
;;
;; The heart of it is the generic function `cl-print-object' to which you
;; can add any method you like.
;;
;; The main entry point is `cl-prin1'.

;;; Code:

(defvar cl-print-readably nil
  "If non-nil, try and make sure the result can be `read'.")

(defvar cl-print--number-table nil)
(defvar cl-print--currently-printing nil)
(defvar cl-print--depth nil
  "Depth of recursion within cl-print functions.
Compared to `print-level' to determine when to stop recursing.")


;;;###autoload
(cl-defgeneric cl-print-object (object stream)
  "Dispatcher to print OBJECT on STREAM according to its type.
You can add methods to it to customize the output.
But if you just want to print something, don't call this directly:
call other entry points instead, such as `cl-prin1'."
  ;; This delegates to the C printer.  The C printer will not call us back, so
  ;; we should only use it for objects which don't have nesting.
  (prin1 object stream))

(cl-defgeneric cl-print-object-contents (_object _start _stream)
  "Dispatcher to print partial contents of OBJECT on STREAM.
This is used when replacing an ellipsis with the contents it
represents.  OBJECT is the object that has been partially printed
and START represents the place at which the contents were
replaced with an ellipsis.
Print the contents hidden by the ellipsis to STREAM."
  ;; Every cl-print-object method which can print an ellipsis should
  ;; have a matching cl-print-object-contents method to expand an
  ;; ellipsis.
  (error "Missing cl-print-object-contents method"))

(cl-defmethod cl-print-object ((object cons) stream)
  (if (and cl-print--depth (natnump print-level)
           (> cl-print--depth print-level))
      (cl-print-insert-ellipsis object nil stream)
    (let ((car (pop object)))
      (if (and print-quoted
               (memq car '(\, quote function \` \,@ \,.))
               (consp object)
               (null (cdr object)))
          (progn
            (princ (cond
                    ((eq car 'quote) '\')
                    ((eq car 'function) "#'")
                    (t car))
                   stream)
            (cl-print-object (car object) stream))
        (princ "(" stream)
        (cl-print--cons-tail car object stream)
        (princ ")" stream)))))

(defun cl-print--cons-tail (car object stream)
  (let ((count 1))
    (cl-print-object car stream)
    (while (and (consp object)
                (not (cond
                      (cl-print--number-table
                       (numberp (gethash object cl-print--number-table)))
                      ((memq object cl-print--currently-printing))
                      (t (push object cl-print--currently-printing)
                         nil))))
      (princ " " stream)
      (if (or (not (natnump print-length)) (> print-length count))
          (cl-print-object (pop object) stream)
        (cl-print-insert-ellipsis object t stream)
        (setq object nil))
      (cl-incf count))
    (when object
      (princ " . " stream) (cl-print-object object stream))))

(cl-defmethod cl-print-object-contents ((object cons) _start stream)
  (cl-print--cons-tail (car object) (cdr object) stream))

(cl-defmethod cl-print-object ((object vector) stream)
  (if (and cl-print--depth (natnump print-level)
           (> cl-print--depth print-level))
      (cl-print-insert-ellipsis object nil stream)
    (princ "[" stream)
    (cl-print--vector-contents object 0 stream)
    (princ "]" stream)))

(defun cl-print--vector-contents (object start stream)
  (let* ((len (length object))
         (limit (if (natnump print-length)
                    (min (+ start print-length) len) len))
         (i start))
    (while (< i limit)
      (unless (= i start) (princ " " stream))
      (cl-print-object (aref object i) stream)
      (cl-incf i))
    (when (< limit len)
      (princ " " stream)
      (cl-print-insert-ellipsis object limit stream))))

(cl-defmethod cl-print-object-contents ((object vector) start stream)
  (cl-print--vector-contents object start stream)) ;FIXME: η-redex!

(cl-defmethod cl-print-object ((object hash-table) stream)
  ;; Make sure `pp-fill' can pretty print the result!
  (princ "#<hash-table " stream)
  (princ (hash-table-test object) stream)
  (princ " " stream)
  (princ (hash-table-count object) stream)
  (princ "/" stream)
  (princ (hash-table-size object) stream)
  (princ (format " %#x " (sxhash object)) stream)
  (cl-print-insert-ellipsis object t stream)
  (princ ">" stream))

(cl-defmethod cl-print-object-contents ((object hash-table) _start stream)
  ;; If we want to obey `print-length' here, it's not completely obvious
  ;; what we should use as marker of "where we are" within the hash-table.
  ;; We could use here a simple number or a set of keys already printed,
  ;; but it still breaks down if elements get added/removed.
  ;; Instead here we convert the hash-table to an alist once and for all.
  (let ((alist nil))
    (maphash (lambda (k v) (push (cons k v) alist)) object)
    ;; While the order of elements seen by `maphash' is "arbitrary"
    ;; it tends to be in the order objects have been added, which is
    ;; sometimes handy, so it's nice to preserve this order here.
    (cl-print-object (nreverse alist) stream)))

(define-button-type 'help-byte-code
  'follow-link t
  'action (lambda (button)
            (disassemble (button-get button 'byte-code-function)))
  'help-echo (purecopy "mouse-2, RET: disassemble this function"))

(defvar cl-print-compiled nil
  "Control how to print byte-compiled functions.
Acceptable values include:
- `raw' to print out the full contents of the function using `prin1'.
- `static' to print the vector of constants.
- `disassemble' to print the disassembly of the code.
- nil to skip printing any details about the code.")

(defvar cl-print-compiled-button t
  "Control how to print byte-compiled functions into buffers.
When the stream is a buffer, make the bytecode part of the output
into a button whose action shows the function's disassembly.")

(autoload 'disassemble-1 "disass")

;; FIXME: Don't degenerate to `prin1' for the contents of char-tables
;; and records!

(cl-defmethod cl-print-object ((object compiled-function) stream)
  (unless stream (setq stream standard-output))
  ;; We use "#f(...)" rather than "#<...>" so that pp.el gives better results.
  (princ "#f(compiled-function " stream)
  (let ((args (help-function-arglist object 'preserve-names)))
    (if args
        (prin1 args stream)
      (princ "()" stream)))
  (if (eq cl-print-compiled 'raw)
      (let ((button-start
             (and cl-print-compiled-button
                  (bufferp stream)
                  (with-current-buffer stream (1+ (point))))))
        (princ " " stream)
        (prin1 object stream)
        (when button-start
          (with-current-buffer stream
            (make-text-button button-start (point)
                              :type 'help-byte-code
                              'byte-code-function object))))
    (pcase (help-split-fundoc (documentation object 'raw) object)
      ;; Drop args which `help-function-arglist' already printed.
      (`(,_usage . ,(and doc (guard (stringp doc))))
       (princ " " stream)
       (prin1 doc stream)))
    (let ((inter (interactive-form object)))
      (when inter
        (princ " " stream)
        (cl-print-object
         (if (eq 'byte-code (car-safe (cadr inter)))
             `(interactive ,(make-byte-code nil (nth 1 (cadr inter))
                                            (nth 2 (cadr inter))
                                            (nth 3 (cadr inter))))
           inter)
         stream)))
    (if (eq cl-print-compiled 'disassemble)
        (princ
         (with-temp-buffer
           (insert "\n")
           (disassemble-1 object 0)
           (buffer-string))
         stream)
      (princ " " stream)
      (let ((button-start (and cl-print-compiled-button
                               (bufferp stream)
                               (with-current-buffer stream (point)))))
        (princ (format "#<bytecode %#x>" (sxhash object)) stream)
        (when (eq cl-print-compiled 'static)
          (princ " " stream)
          (cl-print-object (aref object 2) stream))
        (when button-start
          (with-current-buffer stream
            (make-text-button button-start (point)
                              :type 'help-byte-code
                              'byte-code-function object)))))
    (princ ")" stream)))

;; This belongs in oclosure.el, of course, but some load-ordering issues make it
;; complicated.
(cl-defmethod cl-print-object ((object accessor) stream)
  ;; FIXME: η-reduce!
  (oclosure--accessor-cl-print object stream))

(cl-defmethod cl-print-object ((object cl-structure-object) stream)
  (if (and cl-print--depth (natnump print-level)
           (> cl-print--depth print-level))
      (cl-print-insert-ellipsis object nil stream)
    (princ "#s(" stream)
    (princ (cl--struct-class-name (cl-find-class (type-of object))) stream)
    (cl-print--struct-contents object 0 stream)
    (princ ")" stream)))

(defun cl-print--struct-contents (object start stream)
  (let* ((class (cl-find-class (type-of object)))
         (slots (cl--struct-class-slots class))
         (len (length slots))
         (limit (if (natnump print-length)
                    (min (+ start print-length) len) len))
         (i start))
    (while (< i limit)
      (let ((slot (aref slots i)))
        (unless (and (= i start) (> i 0)) (princ " " stream))
        (princ ":" stream)
        (princ (cl--slot-descriptor-name slot) stream)
        (princ " " stream)
        (cl-print-object (aref object (1+ i)) stream))
      (cl-incf i))
    (when (< limit len)
      (princ " " stream)
      (cl-print-insert-ellipsis object limit stream))))

(cl-defmethod cl-print-object-contents ((object cl-structure-object) start stream)
  (cl-print--struct-contents object start stream)) ;FIXME: η-redex!

(defvar cl-print-string-length nil
  "Maximum length of string to print before abbreviating.
A value of nil means no limit.

When Emacs abbreviates a string, it prints the first
`cl-print-string-length' characters of the string, followed by
\"...\".  You can type RET, or click on this ellipsis to expand
the string.

This variable has effect only in the `cl-prin*' functions, not in
primitives such as `prin1'.")

(cl-defmethod cl-print-object ((object string) stream)
  (unless stream (setq stream standard-output))
  (let* ((has-properties (or (text-properties-at 0 object)
                             (next-property-change 0 object)))
         (len (length object))
         (limit (if (natnump cl-print-string-length)
                    (min cl-print-string-length len)
                  len)))
    (if (and has-properties
             cl-print--depth
             (natnump print-level)
             (> cl-print--depth print-level))
        (cl-print-insert-ellipsis object nil stream)
      ;; Print all or part of the string
      (when has-properties
        (princ "#(" stream))
      (if (= limit len)
          (prin1 (if has-properties (substring-no-properties object) object)
                 stream)
        (let ((part (concat (substring-no-properties object 0 limit) "...")))
          (prin1 part stream)
          (when (bufferp stream)
            (with-current-buffer stream
              (cl-print-propertize-ellipsis object limit
                                            (- (point) 4)
                                            (- (point) 1) stream)))))
      ;; Print the property list.
      (when has-properties
        (cl-print--string-props object 0 stream)
        (princ ")" stream)))))

(defun cl-print--string-props (object start stream)
  (let* ((first (not (eq start 0)))
         (len (length object))
         (interval-limit (and (natnump print-length)
                              (max 1 (/ print-length 3))))
         (interval-count 0)
         (start-pos (if (text-properties-at start object)
                        start (next-property-change start object)))
         (end-pos (next-property-change start-pos object len)))
    (while (and (or (null interval-limit)
                    (< interval-count interval-limit))
                (< start-pos len))
      (let ((props (text-properties-at start-pos object)))
        (when props
          (if first
              (setq first nil)
            (princ " " stream))
          (princ start-pos stream)
          (princ " " stream) (princ end-pos stream)
          (princ " " stream) (cl-print-object props stream)
          (cl-incf interval-count))
        (setq start-pos end-pos
              end-pos (next-property-change start-pos object len))))
    (when (< start-pos len)
      (princ " " stream)
      (cl-print-insert-ellipsis object (list start-pos) stream))))

(cl-defmethod cl-print-object-contents ((object string) start stream)
  ;; If START is an integer, it is an index into the string, and the
  ;; ellipsis that needs to be expanded is part of the string.  If
  ;; START is a cons, its car is an index into the string, and the
  ;; ellipsis that needs to be expanded is in the property list.
  (let* ((len (length object)))
    (if (atom start)
        ;; Print part of the string.
        (let* ((limit (if (natnump cl-print-string-length)
                          (min (+ start cl-print-string-length) len)
                        len))
               (substr (substring-no-properties object start limit))
               (printed (prin1-to-string substr))
               (trimmed (substring printed 1 -1)))
          (princ trimmed stream)
          (when (< limit len)
            (cl-print-insert-ellipsis object limit stream)))

      ;; Print part of the property list.
      (cl-print--string-props object (car start) stream))))

;;; Circularity and sharing.

;; I don't try to support the `print-continuous-numbering', because
;; I think it's ill defined anyway: if an object appears only once in each call
;; its sharing can't be properly preserved!

(cl-defmethod cl-print-object :around (object stream)
  ;; FIXME: Only put such an :around method on types where it's relevant.
  (let ((cl-print--depth (if cl-print--depth (1+ cl-print--depth) 1)))
    ;; FIXME: Handle print-level here once and forall?
    (cond
     (print-circle
      (let ((n (gethash object cl-print--number-table)))
        (if (not (numberp n))
            (cl-call-next-method)
          (if (> n 0)
              ;; Already printed.  Just print a reference.
              (progn (princ "#" stream) (princ n stream) (princ "#" stream))
            (puthash object (- n) cl-print--number-table)
            (princ "#" stream) (princ (- n) stream) (princ "=" stream)
            (cl-call-next-method)))))
     ((let ((already-printing (memq object cl-print--currently-printing)))
        (when already-printing
          ;; Currently printing, just print reference to avoid endless
          ;; recursion.
          (princ "#" stream)
          (princ (length (cdr already-printing)) stream))))
     (t (let ((cl-print--currently-printing
               (cons object cl-print--currently-printing)))
          (cl-call-next-method))))))

(defvar cl-print--number-index nil)

(defun cl-print--find-sharing (object table)
  ;; Avoid recursion: not only because it's too easy to bump into
  ;; `max-lisp-eval-depth', but also because function calls are fairly slow.
  ;; At first, I thought using a list for our stack would cause too much
  ;; garbage to generated, but I didn't notice any such problem in practice.
  ;; I experimented with using an array instead, but the result was slightly
  ;; slower and the reduction in GC activity was less than 1% on my test.
  (let ((stack (list object)))
    (while stack
      (let ((object (pop stack)))
        (unless
            ;; Skip objects which don't have identity!
            (or (floatp object) (numberp object)
                (null object) (if (symbolp object) (intern-soft object)))
          (let ((n (gethash object table)))
            (cond
             ((numberp n))                   ;All done.
             (n                              ;Already seen, but only once.
              (let ((n (1+ cl-print--number-index)))
                (setq cl-print--number-index n)
                (puthash object (- n) table)))
             (t
              (puthash object t table)
              (pcase object
                (`(,car . ,cdr)
                 (push cdr stack)
                 (push car stack))
                ((pred stringp)
                 (let* ((len (length object))
                        (start (if (text-properties-at 0 object)
                                   0 (next-property-change 0 object)))
                        (end (and start
                                  (next-property-change start object len))))
                   (while (and start (< start len))
                     (let ((props (text-properties-at start object)))
                       (when props
                         (push props stack))
                       (setq start end
                             end (next-property-change start object len))))))
                ((or (pred arrayp) (pred byte-code-function-p))
                 ;; FIXME: Inefficient for char-tables!
                 (dotimes (i (length object))
                   (push (aref object i) stack))))))))))))

(defun cl-print--preprocess (object)
  (let ((print-number-table (make-hash-table :test 'eq :rehash-size 2.0)))
    (if (fboundp 'print--preprocess)    ;Emacs≥26
        ;; Use the predefined C version if available.
        (print--preprocess object)           ;Fill print-number-table!
      (let ((cl-print--number-index 0))
        (cl-print--find-sharing object print-number-table)))
    print-number-table))

(define-button-type 'cl-print-ellipsis
  'skip t 'action #'cl-print-expand-ellipsis
  'help-echo "mouse-2, RET: expand this ellipsis")

(defvar cl-print-expand-ellipsis-function
  #'cl-print--default-expand-ellipsis
  "Function to tweak the way ellipses are expanded.
The function is called with 3 arguments, BEG, END, and FUNC.
BEG and END delimit the ellipsis that will be replaced.
FUNC is the function that will do the expansion.
It should be called with a single argument specifying the desired
limit of the expansion's length, as used in `cl-print-to-string-with-limit'.
FUNC will return the position of the end of the newly printed text.")

(defun cl-print--default-expand-ellipsis (begin end value line-length)
  (delete-region begin end)
  (insert (cl-print-to-string-with-limit
           #'cl-print--expand-ellipsis value line-length))
  (point))


(defun cl-print-expand-ellipsis (&optional button)
  "Expand display of the elided form at BUTTON.
BUTTON can also be a buffer position or nil (to mean point)."
  (interactive)
  (goto-char (cond
              ((null button) (point))
              (t (button-start button))))
  (unless (get-text-property (point) 'cl-print-ellipsis)
    (if (and (> (point) (point-min))
             (get-text-property (1- (point)) 'cl-print-ellipsis))
        (backward-char)
      (user-error "No ellipsis to expand here")))
  (let* ((end (next-single-property-change (point) 'cl-print-ellipsis))
         (begin (previous-single-property-change end 'cl-print-ellipsis))
         (value (get-text-property begin 'cl-print-ellipsis)))
    ;; FIXME: Rather than `t' (i.e. reuse the print-length/level unchanged),
    ;; I think it would make sense to increase the level by 1 and to
    ;; double the length at each expansion step.
    (funcall cl-print-expand-ellipsis-function
             begin end value t)
    (goto-char begin)))

(defun cl-print-insert-ellipsis (object start stream)
  "Print \"...\" to STREAM with the `cl-print-ellipsis' text property.
Save state in the text property in order to print the elided part
of OBJECT later.  START should be nil if the whole OBJECT is being
elided, otherwise it should be an index or other pointer into the
internals of OBJECT which can be passed to
`cl-print-object-contents' at a future time."
  (unless stream (setq stream standard-output))
  (let ((ellipsis-start (and (bufferp stream)
                             (with-current-buffer stream (point)))))
    (princ "..." stream)
    (when ellipsis-start
      (with-current-buffer stream
        (cl-print-propertize-ellipsis object start ellipsis-start (point)
                                      stream)))))

(defun cl-print-propertize-ellipsis (object start beg end stream)
  "Add the `cl-print-ellipsis' property between BEG and END.
STREAM should be a buffer.  OBJECT and START are as described in
`cl-print-insert-ellipsis'."
  (let ((value (list object start cl-print--number-table
                     cl-print--currently-printing)))
    (with-current-buffer stream
      (put-text-property beg end 'cl-print-ellipsis value stream)
      (make-text-button beg end :type 'cl-print-ellipsis))))

(defun cl-print--expand-ellipsis (value stream)
  "Print the expansion of an ellipsis to STREAM.
VALUE should be the value of the `cl-print-ellipsis' text property
which was attached to the ellipsis by `cl-prin1'."
  (let ((cl-print--depth 1)
        (object (nth 0 value))
        (start (nth 1 value))
        (cl-print--number-table (nth 2 value))
        (print-number-table (nth 2 value))
        (cl-print--currently-printing (nth 3 value)))
    (when (eq object (car cl-print--currently-printing))
      (pop cl-print--currently-printing))
    (if (memq start '(0 nil))
        (cl-print-object object stream)
      (cl-print-object-contents object start stream))))

;;;###autoload
(defun cl-prin1 (object &optional stream)
  "Print OBJECT on STREAM according to its type.
Output is further controlled by the variables
`cl-print-readably', `cl-print-compiled', along with output
variables for the standard printing functions.  See Info
node `(elisp)Output Variables'."
  (if cl-print-readably
      (prin1 object stream)
    (with-demoted-errors "cl-prin1: %S"
      (if (not print-circle)
          (cl-print-object object stream)
        (let ((cl-print--number-table (cl-print--preprocess object)))
          (cl-print-object object stream))))))

;;;###autoload
(defun cl-prin1-to-string (object)
  "Return a string containing the `cl-prin1'-printed representation of OBJECT."
  (with-temp-buffer
    (cl-prin1 object (current-buffer))
    (buffer-string)))

;;;###autoload
(defun cl-print-to-string-with-limit (print-function value limit)
  "Return a string containing a printed representation of VALUE.
Attempt to get the length of the returned string under LIMIT
characters with appropriate settings of `print-level',
`print-length', and `cl-print-string-length'.  Use
PRINT-FUNCTION to print, which should take the arguments VALUE
and STREAM and which should respect `print-length',
`print-level', and `cl-print-string-length'.  LIMIT may be nil or
zero in which case PRINT-FUNCTION will be called with these
settings bound to nil, and it can also be t in which case
PRINT-FUNCTION will be called with their current values.

Use this function with `cl-prin1' to print an object,
abbreviating it with ellipses to fit within a size limit."
  (setq limit (and (not (eq limit 0)) limit))
  ;; Since this is used by the debugger when stack space may be
  ;; limited, if you increase print-level here, add more depth in
  ;; call_debugger (bug#31919).
  (let* ((print-length (cond
                        ((eq limit t) print-length)
                        ((or (null limit) (zerop limit)) nil)
                        (t (min limit 50))))
         (print-level (cond
                        ((eq limit t) print-level)
                        ((or (null limit) (zerop limit)) nil)
                        (t (min 8 (truncate (log limit))))))
         (cl-print-string-length
          (cond
           ((eq limit t) cl-print-string-length)
           ((or (null limit) (zerop limit)) nil)
           (t (max 0 (- limit 3)))))
         (delta-length (when (natnump limit)
                         (max 1 (truncate (/ print-length print-level))))))
    (with-temp-buffer
      (catch 'done
        (while t
          (erase-buffer)
          (funcall print-function value (current-buffer))
          (let ((result (- (point-max) (point-min))))
            ;; Stop when either print-level is too low or the value is
            ;; successfully printed in the space allowed.
            (when (or (not (natnump limit)) (< result limit) (<= print-level 2))
              (throw 'done (buffer-string)))
            (let* ((ratio (/ result limit))
                   (delta-level (max 1 (min (- print-level 2) ratio))))
              (cl-decf print-level delta-level)
              (cl-decf print-length (* delta-length delta-level))
              (when cl-print-string-length
                (cl-decf cl-print-string-length
                         (ceiling cl-print-string-length 4.0))))))))))

(provide 'cl-print)
;;; cl-print.el ends here