Electric quote mode: Conditionally replace " (Bug#24710)

* lisp/electric.el (electric-quote-replace-double): New user option.
(electric-quote-post-self-insert-function): Use it.

* test/lisp/electric-tests.el (electric-quote-replace-double-disabled)
(electric-quote-replace-double-bob)
(electric-quote-replace-double-bol)
(electric-quote-replace-double-after-space)
(electric-quote-replace-double-after-letter)
(electric-quote-replace-double-after-paren): New unit tests.

* doc/emacs/text.texi (Quotation Marks): Document
'electric-quote-replace-double'.

4 files changed, 74 insertions, 4 deletions

diff --git a/doc/emacs/text.texi b/doc/emacs/text.texi
index 496b43ce1e3..5aa0c77d34c 100644
--- a/doc/emacs/text.texi
+++ b/doc/emacs/text.texi
@@ -443,6 +443,13 @@ non-@code{nil}, and in programming-language strings if
 @code{nil} for @code{electric-quote-string} and @code{t} for the other
 variables.
 
+@vindex electric-quote-replace-double
+  You can also set the option @code{electric-quote-replace-double} to
+a non-@code{nil} value.  Then, typing @t{"} insert an appropriate
+curved double quote depending on context: @t{“} at the beginning of
+the buffer or after a line break, whitespace, opening parenthesis, or
+quote character, and @t{”} otherwise.
+
   Electric Quote mode is disabled by default.  To toggle it, type
 @kbd{M-x electric-quote-mode}.  To toggle it in a single buffer, use
 @kbd{M-x electric-quote-local-mode}.  To suppress it for a single use,
diff --git a/etc/NEWS b/etc/NEWS
index 8fbc354fc06..42c1b048169 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -42,6 +42,11 @@ When you add a new item, use the appropriate mark if you are sure it applies,
 This controls how long Emacs will wait for updates to the graphical
 state to take effect (making a frame visible, for example).
 
++++
+** The new user option 'electric-quote-replace-double' controls
+whether " is also replaced in 'electric-quote-mode'.  If non-nil, " is
+replaced by a double typographic quote.
+
 
 * Changes in Specialized Modes and Packages in Emacs 27.1
 
diff --git a/lisp/electric.el b/lisp/electric.el
index d7929945db2..65e36b7a63f 100644
--- a/lisp/electric.el
+++ b/lisp/electric.el
@@ -451,6 +451,14 @@ whitespace, opening parenthesis, or quote and leaves \\=` alone."
   :version "26.1"
   :type 'boolean :safe #'booleanp :group 'electricity)
 
+(defcustom electric-quote-replace-double nil
+  "Non-nil means to replace \" with an electric double quote.
+Emacs replaces \" with an opening double quote after a line
+break, whitespace, opening parenthesis, or quote, and with a
+closing double quote otherwise."
+  :version "26.1"
+  :type 'boolean :safe #'booleanp :group 'electricity)
+
 (defvar electric-quote-inhibit-functions ()
   "List of functions that should inhibit electric quoting.
 When the variable `electric-quote-mode' is non-nil, Emacs will
@@ -467,7 +475,9 @@ This requotes when a quoting key is typed."
   (when (and electric-quote-mode
              (or (eq last-command-event ?\')
                  (and (not electric-quote-context-sensitive)
-                      (eq last-command-event ?\`)))
+                      (eq last-command-event ?\`))
+                 (and electric-quote-replace-double
+                      (eq last-command-event ?\")))
              (not (run-hook-with-args-until-success
                    'electric-quote-inhibit-functions))
              (if (derived-mode-p 'text-mode)
@@ -488,7 +498,8 @@ This requotes when a quoting key is typed."
        (save-excursion
          (let ((backtick ?\`))
            (if (or (eq last-command-event ?\`)
-                   (and electric-quote-context-sensitive
+                   (and (or electric-quote-context-sensitive
+                            electric-quote-replace-double)
                         (save-excursion
                           (backward-char)
                           (or (bobp) (bolp)
@@ -506,13 +517,19 @@ This requotes when a quoting key is typed."
                       (setq last-command-event q<<))
                      ((search-backward (string backtick) (1- (point)) t)
                       (replace-match (string q<))
-                      (setq last-command-event q<)))
+                      (setq last-command-event q<))
+                     ((search-backward "\"" (1- (point)) t)
+                      (replace-match (string q<<))
+                      (setq last-command-event q<<)))
              (cond ((search-backward (string q> ?') (- (point) 2) t)
                     (replace-match (string q>>))
                     (setq last-command-event q>>))
                    ((search-backward "'" (1- (point)) t)
                     (replace-match (string q>))
-                    (setq last-command-event q>))))))))))
+                    (setq last-command-event q>))
+                   ((search-backward "\"" (1- (point)) t)
+                    (replace-match (string q>>))
+                    (setq last-command-event q>>))))))))))
 
 (put 'electric-quote-post-self-insert-function 'priority 10)
 
diff --git a/test/lisp/electric-tests.el b/test/lisp/electric-tests.el
index fc69919fbe1..7df2449b9eb 100644
--- a/test/lisp/electric-tests.el
+++ b/test/lisp/electric-tests.el
@@ -617,6 +617,12 @@ baz\"\""
   :fixture-fn #'electric-quote-local-mode
   :test-in-comments nil :test-in-strings nil)
 
+(define-electric-pair-test electric-quote-replace-double-disabled
+  "" "\"" :expected-string "\"" :expected-point 2
+  :modes '(text-mode)
+  :fixture-fn #'electric-quote-local-mode
+  :test-in-comments nil :test-in-strings nil)
+
 (define-electric-pair-test electric-quote-context-sensitive-backtick
   "" "`" :expected-string "`" :expected-point 2
   :modes '(text-mode)
@@ -638,6 +644,13 @@ baz\"\""
   :bindings '((electric-quote-context-sensitive . t))
   :test-in-comments nil :test-in-strings nil)
 
+(define-electric-pair-test electric-quote-replace-double-bob
+  "" "\"" :expected-string "“" :expected-point 2
+  :modes '(text-mode)
+  :fixture-fn #'electric-quote-local-mode
+  :bindings '((electric-quote-replace-double . t))
+  :test-in-comments nil :test-in-strings nil)
+
 (define-electric-pair-test electric-quote-context-sensitive-bol-single
   "a\n" "--'" :expected-string "a\n‘" :expected-point 4
   :modes '(text-mode)
@@ -652,6 +665,13 @@ baz\"\""
   :bindings '((electric-quote-context-sensitive . t))
   :test-in-comments nil :test-in-strings nil)
 
+(define-electric-pair-test electric-quote-replace-double-bol
+  "a\n" "--\"" :expected-string "a\n“" :expected-point 4
+  :modes '(text-mode)
+  :fixture-fn #'electric-quote-local-mode
+  :bindings '((electric-quote-replace-double . t))
+  :test-in-comments nil :test-in-strings nil)
+
 (define-electric-pair-test electric-quote-context-sensitive-after-space-single
   " " "-'" :expected-string " ‘" :expected-point 3
   :modes '(text-mode)
@@ -666,6 +686,13 @@ baz\"\""
   :bindings '((electric-quote-context-sensitive . t))
   :test-in-comments nil :test-in-strings nil)
 
+(define-electric-pair-test electric-quote-replace-double-after-space
+  " " "-\"" :expected-string " “" :expected-point 3
+  :modes '(text-mode)
+  :fixture-fn #'electric-quote-local-mode
+  :bindings '((electric-quote-replace-double . t))
+  :test-in-comments nil :test-in-strings nil)
+
 (define-electric-pair-test electric-quote-context-sensitive-after-letter-single
   "a" "-'" :expected-string "a’" :expected-point 3
   :modes '(text-mode)
@@ -680,6 +707,13 @@ baz\"\""
   :bindings '((electric-quote-context-sensitive . t))
   :test-in-comments nil :test-in-strings nil)
 
+(define-electric-pair-test electric-quote-replace-double-after-letter
+  "a" "-\"" :expected-string "a”" :expected-point 3
+  :modes '(text-mode)
+  :fixture-fn #'electric-quote-local-mode
+  :bindings '((electric-quote-replace-double . t))
+  :test-in-comments nil :test-in-strings nil)
+
 (define-electric-pair-test electric-quote-context-sensitive-after-paren-single
   "(" "-'" :expected-string "(‘" :expected-point 3
   :modes '(text-mode)
@@ -694,6 +728,13 @@ baz\"\""
   :bindings '((electric-quote-context-sensitive . t))
   :test-in-comments nil :test-in-strings nil)
 
+(define-electric-pair-test electric-quote-replace-double-after-paren
+  "(" "-\"" :expected-string "(“" :expected-point 3
+  :modes '(text-mode)
+  :fixture-fn #'electric-quote-local-mode
+  :bindings '((electric-quote-replace-double . t))
+  :test-in-comments nil :test-in-strings nil)
+
 ;; Simulate ‘markdown-mode’: it sets both ‘comment-start’ and
 ;; ‘comment-use-syntax’, but derives from ‘text-mode’.
 (define-electric-pair-test electric-quote-markdown-in-text