feat: Better border configuration.

Started adding `resolve` which will allow you to do some really nice
stuff easily with options to get the window options from a variety of
inputs.

You can see how we do it in pickers.lua for borders & borderchars
currently.

lua/telescope/config/resolve.lua

@@ -79,8 +79,12 @@ That's the next step to scrolling.
     width = ...
 }
 
+
+
 --]]
 
+local get_default = require('telescope.utils').get_default
+
 local resolver = {}
 
 local percentage_resolver = function(selector, percentage)
@@ -100,4 +104,52 @@ resolver.resolve_percentage_width = function(percentage)
   return percentage_resolver(2, percentage)
 end
 
+--- Win option always returns a table with preview, results, and prompt.
+--- It handles many different ways. Some examples are as follows:
+--
+-- -- Disable
+-- borderschars = false
+--
+-- -- All three windows share the same
+-- borderchars = { '─', '│', '─', '│', '┌', '┐', '┘', '└'},
+--
+-- -- Each window gets it's own configuration
+-- borderchars = {
+--   preview = {...},
+--   results = {...},
+--   prompt = {...},
+-- }
+--
+-- -- Default to [1] but override with specific items
+-- borderchars = {
+--   {...}
+--   prompt = {...},
+-- }
+resolver.win_option = function(val, default)
+  if type(val) ~= 'table' or vim.tbl_islist(val) then
+    if val == nil then
+      val = default
+    end
+
+    return {
+      preview = val,
+      results = val,
+      prompt = val,
+    }
+  elseif type(val) == 'table' then
+    assert(not vim.tbl_islist(val))
+
+    local val_to_set = val[1]
+    if val_to_set == nil then
+      val_to_set = default
+    end
+
+    return {
+      preview = get_default(val.preview, val_to_set),
+      results = get_default(val.results, val_to_set),
+      prompt = get_default(val.prompt, val_to_set),
+    }
+  end
+end
+
 return resolver

lua/telescope/pickers.lua

@@ -3,6 +3,7 @@ local popup = require('popup')
 
 local actions = require('telescope.actions')
 local config = require('telescope.config')
+local resolve = require('telescope.config.resolve')
 local layout_strategies = require('telescope.pickers.layout_strategies')
 local log = require('telescope.log')
 local mappings = require('telescope.mappings')
@@ -134,28 +135,28 @@ function Picker:new(opts)
 end
 
 function Picker:_get_initial_window_options(prompt_title)
-  local popup_border = self.window.border
-  local popup_borderchars = self.window.borderchars
+  local popup_border = resolve.win_option(self.window.border)
+  local popup_borderchars = resolve.win_option(self.window.borderchars)
 
   local preview = {
     title = 'Preview',
-    border = popup_border,
-    borderchars = popup_borderchars,
+    border = popup_border.preview,
+    borderchars = popup_borderchars.preview,
     enter = false,
     highlight = false
   }
 
   local results = {
     title = 'Results',
-    border = popup_border,
-    borderchars = popup_borderchars,
+    border = popup_border.results,
+    borderchars = popup_borderchars.results,
     enter = false,
   }
 
   local prompt = {
     title = prompt_title,
-    border = popup_border,
-    borderchars = popup_borderchars,
+    border = popup_border.prompt,
+    borderchars = popup_borderchars.prompt,
     enter = true
   }