feat: add highlight group for orphaned links (#502)

* feat: add highlight for orphan links

Closes #501

* feat: add OilOrphanLinkTarget highlight group

---------

Co-authored-by: Steven Arcangeli <stevearc@stevearc.com>

doc/oil.txt

@@ -619,9 +619,15 @@ OilSocket                                                           *hl-OilSocke
 OilLink                                                               *hl-OilLink*
     Soft links in an oil buffer
 
+OilOrphanLink                                                   *hl-OilOrphanLink*
+    Orphaned soft links in an oil buffer
+
 OilLinkTarget                                                   *hl-OilLinkTarget*
     The target of a soft link
 
+OilOrphanLinkTarget                                       *hl-OilOrphanLinkTarget*
+    The target of an orphaned soft link
+
 OilFile                                                               *hl-OilFile*
     Normal files in an oil buffer
 

lua/oil/init.lua

@@ -816,11 +816,21 @@ M._get_highlights = function()
       link = nil,
       desc = "Soft links in an oil buffer",
     },
+    {
+      name = "OilOrphanLink",
+      link = nil,
+      desc = "Orphaned soft links in an oil buffer",
+    },
     {
       name = "OilLinkTarget",
       link = "Comment",
       desc = "The target of a soft link",
     },
+    {
+      name = "OilOrphanLinkTarget",
+      link = "DiagnosticError",
+      desc = "The target of an orphaned soft link",
+    },
     {
       name = "OilFile",
       link = nil,

lua/oil/view.lua

@@ -728,10 +728,11 @@ M.format_entry_cols = function(entry, column_defs, col_width, adapter)
         end
       end
     end
+    local is_orphan = not (meta and meta.link_stat)
 
-    table.insert(cols, { name, "OilLink" })
+    table.insert(cols, { name, is_orphan and "OilOrphanLink" or "OilLink" })
     if link_text then
-      table.insert(cols, { link_text, "OilLinkTarget" })
+      table.insert(cols, { link_text, is_orphan and "OilOrphanLinkTarget" or "OilLinkTarget" })
     end
   else
     table.insert(cols, { name, "OilFile" })