feat(columns): per-character permission column highlights (#375) (#146)

Problem: the permissions column rendered as a monolithic unstyled
string, making it hard to scan `rwx` bits at a glance.

Solution: add per-character highlight groups for permission characters
following the `eza`/`lsd` convention. All groups link to standard
Neovim highlights so every colorscheme works out of the box.

doc/oil.txt

@@ -868,6 +868,24 @@ OilExecutable                                                   *hl-OilExecutabl
 OilExecutableHidden                                       *hl-OilExecutableHidden*
     Hidden executable files in an oil buffer
 
+OilPermissionRead                                           *hl-OilPermissionRead*
+    Read permission character in the permissions column
+
+OilPermissionWrite                                         *hl-OilPermissionWrite*
+    Write permission character in the permissions column
+
+OilPermissionExec                                           *hl-OilPermissionExec*
+    Execute permission character in the permissions column
+
+OilPermissionSetuid                                       *hl-OilPermissionSetuid*
+    Setuid/setgid permission character in the permissions column
+
+OilPermissionSticky                                       *hl-OilPermissionSticky*
+    Sticky bit permission character in the permissions column
+
+OilPermissionNone                                           *hl-OilPermissionNone*
+    No permission character in the permissions column
+
 OilCreate                                                           *hl-OilCreate*
     Create action in the oil preview window
 

doc/upstream.md

@@ -66,7 +66,7 @@ issues against this fork.
 | [#363](https://github.com/stevearc/oil.nvim/issues/363) | `prompt_save_on_select_new_entry` wrong prompt             | fixed                                                                                                                                                                                     |
 | [#371](https://github.com/stevearc/oil.nvim/issues/371) | Constrain cursor in insert mode                            | fixed ([#93](https://github.com/barrettruth/canola.nvim/pull/93))                                                                                                                         |
 | [#373](https://github.com/stevearc/oil.nvim/issues/373) | Dir from quickfix with bqf/trouble broken                  | open                                                                                                                                                                                      |
-| [#375](https://github.com/stevearc/oil.nvim/issues/375) | Highlights for file types and permissions                  | open                                                                                                                                                                                      |
+| [#375](https://github.com/stevearc/oil.nvim/issues/375) | Highlights for file types and permissions                  | fixed — per-character permission column highlights                                                                                                                                        |
 | [#380](https://github.com/stevearc/oil.nvim/issues/380) | Silently overriding `show_hidden`                          | not actionable — counter to config intent                                                                                                                                                 |
 | [#382](https://github.com/stevearc/oil.nvim/issues/382) | Relative path in window title                              | not actionable — solved by `get_win_title` callback ([#482](https://github.com/stevearc/oil.nvim/pull/482))                                                                               |
 | [#392](https://github.com/stevearc/oil.nvim/issues/392) | Option to skip delete prompt                               | fixed                                                                                                                                                                                     |

lua/oil/adapters/files.lua

@@ -100,7 +100,8 @@ if not fs.is_windows then
       if not stat then
         return columns.EMPTY
       end
-      return permissions.mode_to_str(stat.mode)
+      local str = permissions.mode_to_str(stat.mode)
+      return { str, permissions.mode_to_highlights(str) }
     end,
 
     parse = function(line, conf)

lua/oil/adapters/files/permissions.lua

@@ -25,6 +25,31 @@ M.mode_to_str = function(mode)
     .. perm_to_str(bit.band(extra, 1) ~= 0 and 't', mode)
 end
 
+local char_hl = {
+  r = 'OilPermissionRead',
+  w = 'OilPermissionWrite',
+  x = 'OilPermissionExec',
+  s = 'OilPermissionSetuid',
+  S = 'OilPermissionSetuid',
+  t = 'OilPermissionSticky',
+  T = 'OilPermissionSticky',
+  ['-'] = 'OilPermissionNone',
+}
+
+---@param str string
+---@return table[]
+M.mode_to_highlights = function(str)
+  local highlights = {}
+  for i = 1, #str do
+    local c = str:sub(i, i)
+    local hl = char_hl[c]
+    if hl then
+      table.insert(highlights, { hl, i - 1, i })
+    end
+  end
+  return highlights
+end
+
 ---@param mode integer
 ---@return string
 M.mode_to_octal_str = function(mode)

lua/oil/adapters/ssh.lua

@@ -118,7 +118,11 @@ local ssh_columns = {}
 ssh_columns.permissions = {
   render = function(entry, conf)
     local meta = entry[FIELD_META]
-    return meta and permissions.mode_to_str(meta.mode)
+    if not meta then
+      return
+    end
+    local str = permissions.mode_to_str(meta.mode)
+    return { str, permissions.mode_to_highlights(str) }
   end,
 
   parse = function(line, conf)

lua/oil/init.lua

@@ -1066,6 +1066,36 @@ M._get_highlights = function()
       link = 'OilHidden',
       desc = 'Hidden executable files in an oil buffer',
     },
+    {
+      name = 'OilPermissionRead',
+      link = 'DiagnosticWarn',
+      desc = 'Read permission character in the permissions column',
+    },
+    {
+      name = 'OilPermissionWrite',
+      link = 'DiagnosticError',
+      desc = 'Write permission character in the permissions column',
+    },
+    {
+      name = 'OilPermissionExec',
+      link = 'DiagnosticOk',
+      desc = 'Execute permission character in the permissions column',
+    },
+    {
+      name = 'OilPermissionSetuid',
+      link = 'DiagnosticError',
+      desc = 'Setuid/setgid permission character in the permissions column',
+    },
+    {
+      name = 'OilPermissionSticky',
+      link = 'DiagnosticInfo',
+      desc = 'Sticky bit permission character in the permissions column',
+    },
+    {
+      name = 'OilPermissionNone',
+      link = 'NonText',
+      desc = 'No permission character in the permissions column',
+    },
     {
       name = 'OilCreate',
       link = 'DiagnosticInfo',