;;; prog-mode.el --- Generic major mode for programming  -*- lexical-binding: t -*-

;; Copyright (C) 2013-2017 Free Software Foundation, Inc.

;; Maintainer: emacs-devel@gnu.org
;; Keywords: internal
;; Package: emacs

;; 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:

;; This major mode is mostly intended as a parent of other programming
;; modes.  All major modes for programming languages should derive from this
;; mode so that users can put generic customization on prog-mode-hook.

;;; Code:

(eval-when-compile (require 'cl-lib)
                   (require 'subr-x))

(defgroup prog-mode nil
  "Generic programming mode, from which others derive."
  :group 'languages)

(defcustom prog-mode-hook nil
  "Normal hook run when entering programming modes."
  :type 'hook
  :options '(flyspell-prog-mode abbrev-mode flymake-mode linum-mode
                                prettify-symbols-mode)
  :group 'prog-mode)

(defvar prog-mode-map
  (let ((map (make-sparse-keymap)))
    (define-key map [?\C-\M-q] 'prog-indent-sexp)
    map)
  "Keymap used for programming modes.")

(defvar prog-indentation-context nil
  "When non-nil, provides context for indenting embedded code chunks.

There are languages where part of the code is actually written in
a sub language, e.g., a Yacc/Bison or ANTLR grammar also consists
of plain C code.  This variable enables the major mode of the
main language to use the indentation engine of the sub-mode for
lines in code chunks written in the sub-mode's language.

When a major mode of such a main language decides to delegate the
indentation of a line/region to the indentation engine of the sub
mode, it should bind this variable to non-nil around the call.

The non-nil value should be a list of the form:

   (FIRST-COLUMN (START . END) PREVIOUS-CHUNKS)

FIRST-COLUMN is the column the indentation engine of the sub-mode
should use for top-level language constructs inside the code
chunk (instead of 0).

START and END specify the region of the code chunk.  END can be
nil, which stands for the value of `point-max'.  The function
`prog-widen' uses this to restore restrictions imposed by the
sub-mode's indentation engine.

PREVIOUS-CHUNKS, if non-nil, provides the indentation engine of
the sub-mode with the virtual context of the code chunk.  Valid
values are:

 - A string containing text which the indentation engine can
   consider as standing in front of the code chunk.  To cache the
   string's calculated syntactic information for repeated calls
   with the same string, the sub-mode can add text-properties to
   the string.

   A typical use case is for grammars with code chunks which are
   to be indented like function bodies -- the string would contain
   the corresponding function preamble.

 - A function, to be called with the start position of the current
   chunk.  It should return either the region of the previous chunk
   as (PREV-START . PREV-END), or nil if there is no previous chunk.

   A typical use case are literate programming sources -- the
   function would successively return the previous code chunks.")

(defvar-local prog-effective-mode-function nil
  "When non-nil, provides the effective mode at point for embedded code chunks.
When non-nil, this is a function that will be called by
`prog-effective-mode' to find the effective major mode at point.
This function should return a symbol naming a major mode, e.g. `css-mode'.
It may return nil to mean the \"outer\" major mode.")

(defun prog-effective-mode ()
  "When non-nil, returns the effective mode at point.

There are languages where part of the code is actually written in
a sub language, e.g., a Yacc/Bison or ANTLR grammar also consists
of plain C code.  This function returns the effective value of
`major-mode' at point."
  (or (if prog-effective-mode-function
          (funcall 'prog-effective-mode-function))
      major-mode))

(defun prog-indent-sexp (&optional defun)
  "Indent the expression after point.
When interactively called with prefix, indent the enclosing defun
instead."
  (interactive "P")
  (save-excursion
    (when defun
      (end-of-line)
      (beginning-of-defun))
    (let ((start (point))
	  (end (progn (forward-sexp 1) (point))))
      (indent-region start end nil))))

(defun prog-first-column ()
  "Return the indentation column normally used for top-level constructs."
  (or (car prog-indentation-context) 0))

(defun prog-widen ()
  "Remove restrictions (narrowing) from current code chunk or buffer.
This function should be used instead of `widen' in any function used
by the indentation engine to make it respect the value of
`prog-indentation-context'.

This function (like `widen') is useful inside a
`save-restriction' to make the indentation correctly work when
narrowing is in effect."
  (let ((chunk (cadr prog-indentation-context)))
    (if chunk
        ;; No call to `widen' is necessary here, as narrow-to-region
        ;; changes (not just narrows) the existing restrictions
        (narrow-to-region (car chunk) (or (cdr chunk) (point-max)))
      (widen))))


(defvar-local prettify-symbols-alist nil
  "Alist of symbol prettifications.
Each element looks like (SYMBOL . CHARACTER), where the symbol
matching SYMBOL (a string, not a regexp) will be shown as
CHARACTER instead.

CHARACTER can be a character, or it can be a list or vector, in
which case it will be used to compose the new symbol as per the
third argument of `compose-region'.")

(defun prettify-symbols-default-compose-p (start end _match)
  "Return true iff the symbol MATCH should be composed.
The symbol starts at position START and ends at position END.
This is the default for `prettify-symbols-compose-predicate'
which is suitable for most programming languages such as C or Lisp."
  ;; Check that the chars should really be composed into a symbol.
  (let* ((syntaxes-beg (if (memq (char-syntax (char-after start)) '(?w ?_))
                           '(?w ?_) '(?. ?\\)))
         (syntaxes-end (if (memq (char-syntax (char-before end)) '(?w ?_))
                           '(?w ?_) '(?. ?\\))))
    (not (or (memq (char-syntax (or (char-before start) ?\s)) syntaxes-beg)
             (memq (char-syntax (or (char-after end) ?\s)) syntaxes-end)
             (nth 8 (syntax-ppss))))))

(defvar-local prettify-symbols-compose-predicate
  #'prettify-symbols-default-compose-p
  "A predicate for deciding if the currently matched symbol is to be composed.
The matched symbol is the car of one entry in `prettify-symbols-alist'.
The predicate receives the match's start and end positions as well
as the match-string as arguments.")

(defun prettify-symbols--compose-symbol (alist)
  "Compose a sequence of characters into a symbol.
Regexp match data 0 specifies the characters to be composed."
  ;; Check that the chars should really be composed into a symbol.
  (let ((start (match-beginning 0))
        (end (match-end 0))
        (match (match-string 0)))
    (if (and (not (equal prettify-symbols--current-symbol-bounds (list start end)))
             (funcall prettify-symbols-compose-predicate start end match))
        ;; That's a symbol alright, so add the composition.
        (with-silent-modifications
          (compose-region start end (cdr (assoc match alist)))
          (add-text-properties
           start end
           `(prettify-symbols-start ,start prettify-symbols-end ,end)))
      ;; No composition for you.  Let's actually remove any
      ;; composition we may have added earlier and which is now
      ;; incorrect.
      (remove-text-properties start end '(composition
                                          prettify-symbols-start
                                          prettify-symbols-end))))
  ;; Return nil because we're not adding any face property.
  nil)

(defun prettify-symbols--make-keywords ()
  (if prettify-symbols-alist
      `((,(regexp-opt (mapcar 'car prettify-symbols-alist) t)
         (0 (prettify-symbols--compose-symbol ',prettify-symbols-alist))))
    nil))

(defvar-local prettify-symbols--keywords nil)

(defvar-local prettify-symbols--current-symbol-bounds nil)

(defcustom prettify-symbols-unprettify-at-point nil
  "If non-nil, show the non-prettified version of a symbol when point is on it.
If set to the symbol `right-edge', also unprettify if point
is immediately after the symbol.  The prettification will be
reapplied as soon as point moves away from the symbol.  If
set to nil, the prettification persists even when point is
on the symbol."
  :version "25.1"
  :type '(choice (const :tag "Never unprettify" nil)
                 (const :tag "Unprettify when point is inside" t)
                 (const :tag "Unprettify when point is inside or at right edge" right-edge))
  :group 'prog-mode)

(defun prettify-symbols--post-command-hook ()
  (cl-labels ((get-prop-as-list
               (prop)
               (remove nil
                       (list (get-text-property (point) prop)
                             (when (and (eq prettify-symbols-unprettify-at-point 'right-edge)
                                        (not (bobp)))
                               (get-text-property (1- (point)) prop))))))
    ;; Re-apply prettification to the previous symbol.
    (when (and prettify-symbols--current-symbol-bounds
	       (or (< (point) (car prettify-symbols--current-symbol-bounds))
		   (> (point) (cadr prettify-symbols--current-symbol-bounds))
		   (and (not (eq prettify-symbols-unprettify-at-point 'right-edge))
			(= (point) (cadr prettify-symbols--current-symbol-bounds)))))
      (apply #'font-lock-flush prettify-symbols--current-symbol-bounds)
      (setq prettify-symbols--current-symbol-bounds nil))
    ;; Unprettify the current symbol.
    (when-let* ((c (get-prop-as-list 'composition))
	        (s (get-prop-as-list 'prettify-symbols-start))
	        (e (get-prop-as-list 'prettify-symbols-end))
	        (s (apply #'min s))
	        (e (apply #'max e)))
      (with-silent-modifications
	(setq prettify-symbols--current-symbol-bounds (list s e))
	(remove-text-properties s e '(composition))))))

;;;###autoload
(define-minor-mode prettify-symbols-mode
  "Toggle Prettify Symbols mode.
With a prefix argument ARG, enable Prettify Symbols mode if ARG is
positive, and disable it otherwise.  If called from Lisp, enable
the mode if ARG is omitted or nil.

When Prettify Symbols mode and font-locking are enabled, symbols are
prettified (displayed as composed characters) according to the rules
in `prettify-symbols-alist' (which see), which are locally defined
by major modes supporting prettifying.  To add further customizations
for a given major mode, you can modify `prettify-symbols-alist' thus:

  (add-hook \\='emacs-lisp-mode-hook
            (lambda ()
              (push \\='(\"<=\" . ?≤) prettify-symbols-alist)))

You can enable this mode locally in desired buffers, or use
`global-prettify-symbols-mode' to enable it for all modes that
support it."
  :init-value nil
  (if prettify-symbols-mode
      ;; Turn on
      (when (setq prettify-symbols--keywords (prettify-symbols--make-keywords))
        (font-lock-add-keywords nil prettify-symbols--keywords)
        (setq-local font-lock-extra-managed-props
                    (append font-lock-extra-managed-props
                            '(composition
                              prettify-symbols-start
                              prettify-symbols-end)))
        (when prettify-symbols-unprettify-at-point
          (add-hook 'post-command-hook
                    #'prettify-symbols--post-command-hook nil t))
        (font-lock-flush))
    ;; Turn off
    (remove-hook 'post-command-hook #'prettify-symbols--post-command-hook t)
    (when prettify-symbols--keywords
      (font-lock-remove-keywords nil prettify-symbols--keywords)
      (setq prettify-symbols--keywords nil))
    (when (memq 'composition font-lock-extra-managed-props)
      (setq font-lock-extra-managed-props (delq 'composition
                                                font-lock-extra-managed-props))
      (with-silent-modifications
        (remove-text-properties (point-min) (point-max) '(composition nil))))))

(defun turn-on-prettify-symbols-mode ()
  (when (and (not prettify-symbols-mode)
             (local-variable-p 'prettify-symbols-alist))
    (prettify-symbols-mode 1)))

;;;###autoload
(define-globalized-minor-mode global-prettify-symbols-mode
  prettify-symbols-mode turn-on-prettify-symbols-mode)

;;;###autoload
(define-derived-mode prog-mode fundamental-mode "Prog"
  "Major mode for editing programming language source code."
  (setq-local require-final-newline mode-require-final-newline)
  (setq-local parse-sexp-ignore-comments t)
  ;; Any programming language is always written left to right.
  (setq bidi-paragraph-direction 'left-to-right))

(provide 'prog-mode)

;;; prog-mode.el ends here