bug#20385: [PROPOSED PATCH] Support quoting 'like this' in doc strings

[Paul Eggert <eggert@cs.ucla.edu>]

Emacs's traditional doc string style has been to quote symbols
`like this'.  This worked well on older terminals where ` and '
were symmetric quotes, but nowadays this quoting looks odd and
it's better to use apostrophe for single-quoted ASCII text.
Add support for quoting either way, suggesting the newer style.
* doc/lispref/tips.texi (Documentation Tips): Quote symbols
'like-this' as well as `like-this'.  Recommend the former style.
* etc/NEWS: Mention this.
* lisp/cedet/srecode/texi.el (srecode-texi-texify-docstring):
* lisp/emacs-lisp/checkdoc.el (checkdoc-this-string-valid-engine):
* lisp/emacs-lisp/lisp-mode.el (lisp-el-font-lock-keywords-2)
(lisp-cl-font-lock-keywords-2):
* lisp/finder.el (finder-font-lock-keywords):
* lisp/gnus/gnus-art.el (gnus-button-alist):
* lisp/help-mode.el (help-xref-symbol-regexp)
(help-xref-info-regexp, help-xref-url-regexp):
* lisp/international/mule-cmds.el (help-xref-mule-regexp-template):
* lisp/wid-edit.el (widget-documentation-link-regexp):
Parse symbols quoted 'like-this' as well as `like-this'.
---
 doc/lispref/tips.texi           | 27 ++++++++++++++++-----------
 etc/NEWS                        |  4 ++++
 lisp/cedet/srecode/texi.el      |  2 +-
 lisp/emacs-lisp/checkdoc.el     |  4 ++--
 lisp/emacs-lisp/lisp-mode.el    |  8 ++++----
 lisp/finder.el                  |  2 +-
 lisp/gnus/gnus-art.el           |  8 ++++----
 lisp/help-mode.el               |  6 +++---
 lisp/international/mule-cmds.el |  2 +-
 lisp/wid-edit.el                |  2 +-
 10 files changed, 37 insertions(+), 28 deletions(-)

diff --git a/doc/lispref/tips.texi b/doc/lispref/tips.texi
index cc1f0e4..8997249 100644
--- a/doc/lispref/tips.texi
+++ b/doc/lispref/tips.texi
@@ -658,17 +658,22 @@ starting double-quote is not part of the string!
 @anchor{Docstring hyperlinks}
 @item
 When a documentation string refers to a Lisp symbol, write it as it
-would be printed (which usually means in lower case), with a grave
-accent @samp{`} before and apostrophe @samp{'} after it.  There are
+would be printed (which usually means in lower case), with a
+apostrophe @samp{'} before and after it.  There are
 two exceptions: write @code{t} and @code{nil} without surrounding
-punctuation.  For example: @samp{CODE can be `lambda', nil, or t.}
+punctuation.  For example: @samp{CODE can be 'lambda', nil, or t.}
 (In this manual, we use a different convention, with single-quotes
 around symbols.)
 
+Documentation strings can also use an older single-quoting convention,
+which quotes symbols with grave accent @samp{`} and apostrophe, rather
+than with two apostrophes: @samp{`like-this'} rather than
+@samp{'like-this'}.  This older single-quoting convention is not
+recommended for new documentation.
+
 @cindex hyperlinks in documentation strings
 Help mode automatically creates a hyperlink when a documentation string
-uses a symbol name between grave accent and apostrophe, if the symbol
-has either a
+uses a single-quoted symbol name, if the symbol has either a
 function or a variable definition.  You do not need to do anything
 special to make use of this feature.  However, when a symbol has both a
 function definition and a variable definition, and you want to refer to
@@ -710,21 +715,21 @@ followed by the word @samp{face}.  In that case, only the face
 documentation will be shown, even if the symbol is also defined as a
 variable or as a function.
 
-To make a hyperlink to Info documentation, write the name of the Info
-node (or anchor) between grave accent and apostrophe, preceded by
+To make a hyperlink to Info documentation, write the single-quoted
+name of the Info node (or anchor), preceded by
 @samp{info node}, @samp{Info node}, @samp{info anchor} or @samp{Info
 anchor}.  The Info file name defaults to @samp{emacs}.  For example,
 
 @smallexample
-See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'.
+See Info node 'Font Lock' and Info node '(elisp)Font Lock Basics'.
 @end smallexample
 
-Finally, to create a hyperlink to URLs, write the URL between grave
-accent and apostrophe, preceded by @samp{URL}. For example,
+Finally, to create a hyperlink to URLs, write the single-quoted URL,
+preceded by @samp{URL}. For example,
 
 @smallexample
 The home page for the GNU project has more information (see URL
-`http://www.gnu.org/').
+'http://www.gnu.org/').
 @end smallexample
 
 @item
diff --git a/etc/NEWS b/etc/NEWS
index a9c0d2e..278754e 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -791,6 +791,10 @@ name.  The variable `system-name' is now obsolete.
 *** New macros `thread-first' and `thread-last' allow threading a form
     as the first or last argument of subsequent forms.
 
+** Documentation strings now support single-quoting 'like-this'
+in addition to the older style `like-this'.  The newer style looks
+better on most modern displays, and is recommended for new code.
+
 +++
 ** Time-related changes:
 
diff --git a/lisp/cedet/srecode/texi.el b/lisp/cedet/srecode/texi.el
index 5c3f21c..d03203d 100644
--- a/lisp/cedet/srecode/texi.el
+++ b/lisp/cedet/srecode/texi.el
@@ -253,7 +253,7 @@ that class.
  [ stuff ]  => @code{[ stuff ]}
  Key        => @kbd{Key}     (key is C\\-h, M\\-h, SPC, RET, TAB and the like)
  ...        => @dots{}"
-  (while (string-match "`\\([-a-zA-Z0-9<>.]+\\)'" string)
+  (while (string-match "['`]\\([-a-zA-Z0-9<>.]+\\)'" string)
     (let* ((vs (substring string (match-beginning 1) (match-end 1)))
 	   (v (intern-soft vs)))
       (setq string
diff --git a/lisp/emacs-lisp/checkdoc.el b/lisp/emacs-lisp/checkdoc.el
index 777fed0..d861da9 100644
--- a/lisp/emacs-lisp/checkdoc.el
+++ b/lisp/emacs-lisp/checkdoc.el
@@ -1554,7 +1554,7 @@ mouse-[0-3]\\)\\)\\>"))
      (save-excursion
        (let ((case-fold-search t)
 	     (ret nil) mb me)
-	 (while (and (re-search-forward "`\\(\\sw\\(\\sw\\|\\s_\\)+\\)'" e t)
+	 (while (and (re-search-forward "['`]\\(\\sw\\(\\sw\\|\\s_\\)+\\)'" e t)
 		     (not ret))
 	   (let* ((ms1 (match-string 1))
 		  (sym (intern-soft ms1)))
@@ -1824,7 +1824,7 @@ Replace with \"%s\"? " original replace)
 	   nil)))
      ;; t and nil case
      (save-excursion
-       (if (re-search-forward "\\(`\\(t\\|nil\\)'\\)" e t)
+       (if (re-search-forward "\\(['`]\\(t\\|nil\\)'\\)" e t)
 	   (if (checkdoc-autofix-ask-replace
 		(match-beginning 1) (match-end 1)
 		(format "%s should not appear in quotes.  Remove? "
diff --git a/lisp/emacs-lisp/lisp-mode.el b/lisp/emacs-lisp/lisp-mode.el
index 26a21d5..bfdd41e 100644
--- a/lisp/emacs-lisp/lisp-mode.el
+++ b/lisp/emacs-lisp/lisp-mode.el
@@ -405,8 +405,8 @@
        ;; Words inside \\[] tend to be for `substitute-command-keys'.
        ("\\\\\\\\\\[\\(\\(?:\\sw\\|\\s_\\)+\\)\\]"
         (1 font-lock-constant-face prepend))
-       ;; Words inside `' tend to be symbol names.
-       ("`\\(\\(?:\\sw\\|\\s_\\)\\(?:\\sw\\|\\s_\\)+\\)'"
+       ;; Words inside '' and `' tend to be symbol names.
+       ("['`]\\(\\(?:\\sw\\|\\s_\\)\\(?:\\sw\\|\\s_\\)+\\)'"
         (1 font-lock-constant-face prepend))
        ;; Constant values.
        ("\\_<:\\(?:\\sw\\|\\s_\\)+\\_>" 0 font-lock-builtin-face)
@@ -454,8 +454,8 @@
        ;; Erroneous structures.
        (,(concat "(" cl-errs-re "\\_>")
         (1 font-lock-warning-face))
-       ;; Words inside `' tend to be symbol names.
-       ("`\\(\\(?:\\sw\\|\\s_\\)\\(?:\\sw\\|\\s_\\)+\\)'"
+       ;; Words inside '' and `' tend to be symbol names.
+       ("['`]\\(\\(?:\\sw\\|\\s_\\)\\(?:\\sw\\|\\s_\\)+\\)'"
         (1 font-lock-constant-face prepend))
        ;; Constant values.
        ("\\_<:\\(?:\\sw\\|\\s_\\)+\\_>" 0 font-lock-builtin-face)
diff --git a/lisp/finder.el b/lisp/finder.el
index 47fab3c..847dccc 100644
--- a/lisp/finder.el
+++ b/lisp/finder.el
@@ -115,7 +115,7 @@ Each element has the form (KEYWORD . DESCRIPTION).")
   "Syntax table used while in `finder-mode'.")
 
 (defvar finder-font-lock-keywords
-  '(("`\\([^'`]+\\)'" 1 font-lock-constant-face prepend))
+  '(("['`]\\([^'`]+\\)'" 1 font-lock-constant-face prepend))
   "Font-lock keywords for Finder mode.")
 
 (defvar finder-headmark nil
diff --git a/lisp/gnus/gnus-art.el b/lisp/gnus/gnus-art.el
index 14f9adc..4560a0e 100644
--- a/lisp/gnus/gnus-art.el
+++ b/lisp/gnus/gnus-art.el
@@ -7828,11 +7828,11 @@ positives are possible."
     ("/\\([a-z][-a-z0-9]+\\.el\\)\\>[^.?]"
      ;; Exclude [.?] for URLs in gmane.emacs.cvs
      1 (>= gnus-button-emacs-level 8) gnus-button-handle-library 1)
-    ("`\\([a-z][-a-z0-9]+\\.el\\)'"
+    ("['`]\\([a-z][-a-z0-9]+\\.el\\)'"
      1 (>= gnus-button-emacs-level 8) gnus-button-handle-library 1)
-    ("`\\([a-z][a-z0-9]+-[a-z0-9]+-[-a-z0-9]*[a-z]\\|\\(gnus\\|message\\)-[-a-z]+\\)'"
+    ("['`]\\([a-z][a-z0-9]+-[a-z0-9]+-[-a-z0-9]*[a-z]\\|\\(gnus\\|message\\)-[-a-z]+\\)'"
      0 (>= gnus-button-emacs-level 8) gnus-button-handle-symbol 1)
-    ("`\\([a-z][a-z0-9]+-[a-z]+\\)'"
+    ("['`]\\([a-z][a-z0-9]+-[a-z]+\\)'"
      0 (>= gnus-button-emacs-level 9) gnus-button-handle-symbol 1)
     ("(setq[ \t\n]+\\([a-z][a-z0-9]+-[-a-z0-9]+\\)[ \t\n]+.+)"
      1 (>= gnus-button-emacs-level 7) gnus-button-handle-describe-variable 1)
@@ -7842,7 +7842,7 @@ positives are possible."
      0 (>= gnus-button-emacs-level 1) gnus-button-handle-describe-function 2)
     ("\\b\\(C-h\\|<?[Ff]1>?\\)[ \t\n]+v[ \t\n]+\\([^ \t\n]+\\)[ \t\n]+RET\\>"
      0 (>= gnus-button-emacs-level 1) gnus-button-handle-describe-variable 2)
-    ("`\\(\\(C-h\\|<?[Ff]1>?\\)[ \t\n]+k[ \t\n]+\\([^']+\\)\\)'"
+    ("['`]\\(\\(C-h\\|<?[Ff]1>?\\)[ \t\n]+k[ \t\n]+\\([^']+\\)\\)'"
      ;; Unlike the other regexps we really have to require quoting
      ;; here to determine where it ends.
      1 (>= gnus-button-emacs-level 1) gnus-button-handle-describe-key 3)
diff --git a/lisp/help-mode.el b/lisp/help-mode.el
index d6679e9..13e5ed4 100644
--- a/lisp/help-mode.el
+++ b/lisp/help-mode.el
@@ -322,7 +322,7 @@ Commands:
 		    "\\(source \\(?:code \\)?\\(?:of\\|for\\)\\)\\)"
 		    "[ \t\n]+\\)?"
 		    ;; Note starting with word-syntax character:
-		    "`\\(\\sw\\(\\sw\\|\\s_\\)+\\)'"))
+		    "['`]\\(\\sw\\(\\sw\\|\\s_\\)+\\)'"))
   "Regexp matching doc string references to symbols.
 
 The words preceding the quoted symbol can be used in doc strings to
@@ -337,11 +337,11 @@ when help commands related to multilingual environment (e.g.,
 
 
 (defconst help-xref-info-regexp
-  (purecopy "\\<[Ii]nfo[ \t\n]+\\(node\\|anchor\\)[ \t\n]+`\\([^']+\\)'")
+  (purecopy "\\<[Ii]nfo[ \t\n]+\\(node\\|anchor\\)[ \t\n]+['`]\\([^']+\\)'")
   "Regexp matching doc string references to an Info node.")
 
 (defconst help-xref-url-regexp
-  (purecopy "\\<[Uu][Rr][Ll][ \t\n]+`\\([^']+\\)'")
+  (purecopy "\\<[Uu][Rr][Ll][ \t\n]+['`]\\([^']+\\)'")
   "Regexp matching doc string references to a URL.")
 
 ;;;###autoload
diff --git a/lisp/international/mule-cmds.el b/lisp/international/mule-cmds.el
index cca659f..0856995 100644
--- a/lisp/international/mule-cmds.el
+++ b/lisp/international/mule-cmds.el
@@ -177,7 +177,7 @@
 		    "\\(charset\\)"
 		    "\\)\\s-+\\)?"
 		    ;; Note starting with word-syntax character:
-		    "`\\(\\sw\\(\\sw\\|\\s_\\)+\\)'")))
+		    "['`]\\(\\sw\\(\\sw\\|\\s_\\)+\\)'")))
 
 (defun coding-system-change-eol-conversion (coding-system eol-type)
   "Return a coding system which differs from CODING-SYSTEM in EOL conversion.
diff --git a/lisp/wid-edit.el b/lisp/wid-edit.el
index 04a900f..9e1c895 100644
--- a/lisp/wid-edit.el
+++ b/lisp/wid-edit.el
@@ -2855,7 +2855,7 @@ The following properties have special meanings for this widget:
   :type 'boolean
   :group 'widget-documentation)
 
-(defcustom widget-documentation-link-regexp "`\\([^\n`' ]+\\)'"
+(defcustom widget-documentation-link-regexp "['`]\\([^\n`' ]+\\)'"
   "Regexp for matching potential links in documentation strings.
 The first group should be the link itself."
   :type 'regexp
-- 
2.1.0