Re: A simple solution to "Upcoming loss of usability ..."

[Dmitry Gutov <dgutov@yandex.ru>]

On 06/28/2015 12:09 AM, Paul Eggert wrote:

> How about if you pick a plausible option and give a realistic example
> showing (1) what the source code would be, (2) how the source code would
> be displayed, (3) what the *Help* buffer would be, (4) how the *Help*
> buffer would be displayed normally, and (5) how the *Help* buffer would
> be displayed if the user requests ASCII approximations.

Ok, try this, please. "\\" before a quote keeps it untranslated.

However, it order for us to be able to show an arbitrary number of 
backslashes before a quote (both translated or not), the backslashes 
also escape themselves. I've limited this effect to only before a quote, 
so that we don't have to add them in a lot of places (like 
substitute-command-keys docstring).

> I don't think any single example will illustrate all the gotchas.  But
> how about if we start with the previously-mentioned example, e.g., type
> ‘C-h texinfo-format-verb’ after loading textmodes/texinfmt?

It's good to see how escaping works, but I meant an example of a Help 
buffer where we must not translate quotes in the value.

diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index 4982ee5..aaaf02b 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -746,7 +746,8 @@ it is displayed along with the global value."
  		      (setq from (point))
  		      (pp origval)
  		      (if (< (point) (+ from 20))
-			  (delete-region (1- from) from)))))))
+			  (delete-region (1- from) from)))))
+                (put-text-property val-start-pos (point) 'help-value t)))
  	    (terpri)
  	    (when locus
  	      (cond
diff --git a/lisp/help-mode.el b/lisp/help-mode.el
index f99e916..b5bf618 100644
--- a/lisp/help-mode.el
+++ b/lisp/help-mode.el
@@ -97,6 +97,18 @@ The format is (FUNCTION ARGS...).")
    "Hook run by `help-mode'."
    :type 'hook
    :group 'help)
+
+(defcustom help-quote-translation nil
+  "Style to use for single quotes in help.
+The value is a left single quote character of some style.
+Quote ‘like this’ if the value is ?‘ (left single quotation mark).
+Quote \\'like this\\' if the value is ?\\' (apostrophe).
+Quote \\`like this\\' if the value is ?\\` (grave accent).
+The default value is nil, which means quote with left single quotation mark
+if displayable, and with grave accent otherwise."
+  :type 'character
+  :group 'help)
+
  \f
  ;; Button types used by help

@@ -287,9 +299,37 @@ Commands:
  \\{help-mode-map}"
    (set (make-local-variable 'revert-buffer-function)
         'help-mode-revert-buffer)
+  (setq font-lock-defaults '(nil t))
+  (font-lock-add-keywords
+   nil '(("\\(?:\\=\\|[^\\]\\)\\(\\\\*\\)[`']"
+          (0 (let* ((mbeg (match-beginning 1))
+                    (mend (match-end 1))
+                    (escapes (- mend mbeg)))
+               (unless (get-text-property mend 'help-value)
+                 ;; Collapse all escaped backslashes.
+                 (compose-region mbeg (+ mbeg (- escapes (/ escapes 
2))) "")
+                 ;; If there's an even number of backslashes,
+                 ;; translate the quote.
+                 (when (eq (logand escapes 1) 0)
+                   (help--translate-quote mend)))
+               nil)))))
    (set (make-local-variable 'bookmark-make-record-function)
         'help-bookmark-make-record))

+(defun help--translate-quote (beg)
+  (let* ((char (char-after beg))
+         (replacement
+          (cond
+           ((or (and (null help-quote-translation)
+                     (char-displayable-p ?‘))
+                (eq help-quote-translation ?‘))
+            (cdr (assq char '((?` . ?‘) (?' . ?’)))))
+           ((eq help-quote-translation ?')
+            ?')
+           (t char))))
+    (unless (eq char replacement)
+      (compose-region beg (1+ beg) replacement))))
+
  ;;;###autoload
  (defun help-mode-setup ()
    (help-mode)
diff --git a/lisp/textmodes/texinfmt.el b/lisp/textmodes/texinfmt.el
index e7b6835..392d45b 100644
--- a/lisp/textmodes/texinfmt.el
+++ b/lisp/textmodes/texinfmt.el
@@ -2493,8 +2493,8 @@ surrounded by in angle brackets."
  Enclose the verbatim text, including the delimiters, in braces.  Print
  text exactly as written (but not the delimiters) in a fixed-width.

-For example, @verb\{|@|\} results in @ and
-@verb\{+@'e?`!`+} results in @'e?`!`."
+For example, @verb{|@|} results in @ and
+@verb{+@\\'e?\\`!\\`+} results in @\\'e?\\`!\\`."

    (let ((delimiter (buffer-substring-no-properties
  		    (1+ texinfo-command-end) (+ 2 texinfo-command-end))))