feat: multi selection. Only integrates with send_selected_to_qflist (#551)

This will not yet work with select actions. More work is needed in that case.

Co-authored-by: Simon Hauser <Simon-Hauser@outlook.de>

lua/telescope/pickers/highlights.lua

@@ -1,4 +1,5 @@
 local a = vim.api
+local log = require('telescope.log')
 
 local highlights = {}
 
@@ -76,25 +77,30 @@ function Highlighter:hi_selection(row, caret)
   )
 end
 
-function Highlighter:hi_multiselect(row, entry)
+function Highlighter:hi_multiselect(row, is_selected)
   local results_bufnr = assert(self.picker.results_bufnr, "Must have a results bufnr")
 
-  if self.picker.multi_select[entry] then
+  if is_selected then
     vim.api.nvim_buf_add_highlight(
-      results_bufnr,
-      ns_telescope_multiselection,
-      "TelescopeMultiSelection",
-      row,
-      0,
-      -1
+      results_bufnr, ns_telescope_multiselection, "TelescopeMultiSelection", row, 0, -1
     )
   else
-    vim.api.nvim_buf_clear_namespace(
-      results_bufnr,
-      ns_telescope_multiselection,
-      row,
-      row + 1
+    local existing_marks = vim.api.nvim_buf_get_extmarks(
+      results_bufnr, ns_telescope_multiselection, {row, 0}, {row, -1}, {}
     )
+
+    -- This is still kind of weird to me, since it seems like I'm erasing stuff
+    -- when i shouldn't... perhaps it's a bout the gravity of the extmark?
+    if #existing_marks > 0 then
+      log.trace("Clearning row: ", row)
+
+      vim.api.nvim_buf_clear_namespace(
+        results_bufnr,
+        ns_telescope_multiselection,
+        row,
+        row + 1
+      )
+    end
   end
 end