tree-widget with unicode box chars

[JD Smith <jdtsmith@gmail.com>]

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tree-widget.el provides both xpm icons and crude plain-text versions of the tree glyphs.  Most fixed-space fonts have unicode box-drawing characters, which can be used to draw high quality text-only trees.  Such unicode trees look identical in graphical or terminal Emacs (see attached for an example).  

This works just fine, but one small change is needed to accommodate this style.  `tree-widget-guide’ specifies a single vertical bar “guide” widget.  In the unicode tree, two separate vertical bars are needed — one “plain” (│), and one which connects to the horizontal “handle” preceding the node (├). A patch is attached implementing this.  For the default graphical-icon version to continue working, linking from nohandle-guide.* -> guide.* in etc/images/tree-widget/* would be necessary.


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--- -	2022-06-04 22:15:22.000000000 -0400
+++ tree-widget.el	2022-06-04 22:15:20.000000000 -0400
@@ -319,6 +319,7 @@
   '(
     ("guide"     . arrow)
     ("no-guide"  . arrow)
+    ("nohandle-guide" . arrow)
     ("end-guide" . arrow)
     ("handle"    . arrow)
     ("no-handle" . arrow)
@@ -440,6 +441,13 @@
   :format    "%t"
   )
 
+(define-widget 'tree-widget-nohandle-guide 'item
+  "Vertical guide line, when there is no handle."
+  :tag       " |"
+  ;;:tag-glyph (tree-widget-find-image "nohandle-guide")
+  :format    "%t" 
+  )
+
 (define-widget 'tree-widget-end-guide 'item
   "End of a vertical guide line."
   :tag       " \\=`"
@@ -483,6 +491,7 @@
   :empty-icon     'tree-widget-empty-icon
   :leaf-icon      'tree-widget-leaf-icon
   :guide          'tree-widget-guide
+  :nohandle-guide 'tree-widget-nohandle-guide
   :end-guide      'tree-widget-end-guide
   :no-guide       'tree-widget-no-guide
   :handle         'tree-widget-handle
@@ -612,11 +621,13 @@
 ;;;; Expanded node.
         (let ((args     (widget-get tree :args))
               (guide    (widget-get tree :guide))
+              (nohandle-guide (widget-get tree :nohandle-guide))
               (noguide  (widget-get tree :no-guide))
               (endguide (widget-get tree :end-guide))
               (handle   (widget-get tree :handle))
               (nohandle (widget-get tree :no-handle))
               (guidi    (tree-widget-find-image "guide"))
+              (nohandle-guidi (tree-widget-find-image "nohandle-guide"))
               (noguidi  (tree-widget-find-image "no-guide"))
               (endguidi (tree-widget-find-image "end-guide"))
               (handli   (tree-widget-find-image "handle"))
@@ -648,8 +659,8 @@
             ;; Insert guide lines elements from previous levels.
             (dolist (f (reverse flags))
               (widget-create-child-and-convert
-               tree (if f guide noguide)
-               :tag-glyph (if f guidi noguidi))
+               tree (if f nohandle-guide noguide)
+               :tag-glyph (if f nohandle-guidi noguidi))
               (widget-create-child-and-convert
                tree nohandle :tag-glyph nohandli))
             ;; Insert guide line element for this level.

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