Fix zero-width characters and control characters attribute issue. (#1741

)

* Remove unnecessary multiple values return.

* Add Unicode variation selectors to zero-width characters for now.

* Fix the issue of special character attribute.

Previously, if the cursor is at different line than the special
character, Lem will throw out an error.

src/common/character/string-width-utils.lisp

@@ -50,7 +50,7 @@
     table))
 
 (defun control-char (char)
-  (values (gethash char *char-replacement*)))
+  (gethash char *char-replacement*))
 
 (defun wide-char-p (char)
   (declare (character char))

src/display/char-type.lisp

@@ -28,7 +28,9 @@
   (icon-value code :font))
 
 (defun zero-width-char-code-p (code)
-  (or (<= #x200B code #x200D) (= code #xFEFF)))
+  (or (<= #x200B code #x200D)
+      (<= #xFE00 code #xFE0F)
+      (= code #xFEFF)))
 
 (defun char-type (char)
   (let ((code (char-code char)))

src/display/physical-line.lisp

@@ -141,10 +141,11 @@
                               string))
                    :attribute (case type
                                 ((:control :zero-width)
-                                 (merge-attribute attribute
-                                                  (ensure-attribute 'special-char-attribute nil)))
-                                (otherwise
-                                 attribute))
+                                 (let ((attr (ensure-attribute 'special-char-attribute nil)))
+                                   (if attribute
+                                       (merge-attribute attribute attr)
+                                       attr)))
+                                (otherwise attribute))
                    :type type
                    :within-cursor (and attribute
                                        (cursor-attribute-p attribute)))))