feature: Vim help-tags picker (#117)

* feature: Vim help-tags picker

* fix: filtered results were wrong because of missing `entry.value`

* fix: filtered (Vim only help) items are listed in results as empty
entries.

* fix: avoid search history pollution by replacing / in cmd returned by taglist() with search()

* fix: improve search() formatting

* fix: escape tilde in search() command

* fix: improve help-preview

* fix: improve search()

* fix: search() string fixes.

* fix: use no magic to do magic

Co-authored-by: TJ DeVries <devries.timothyj@gmail.com>

lua/telescope/builtin.lua

@@ -402,6 +402,45 @@ builtin.command_history = function(opts)
   }):find()
 end
 
+builtin.help_tags = function(opts)
+  opts = opts or {}
+
+  local sourced_file = require('plenary.debug_utils').sourced_filepath()
+  local base_directory = vim.fn.fnamemodify(sourced_file, ":h:h:h")
+  local file = base_directory .. "/data/help/tags"
+
+  local tags = {}
+  local f = assert(io.open(file, "rb"))
+    for line in f:lines() do
+      table.insert(tags, line)
+    end
+  f:close()
+
+  pickers.new(opts, {
+    prompt = 'Help',
+    finder = finders.new_table {
+      results = tags,
+      entry_maker = make_entry.gen_from_tagfile(opts),
+    },
+    -- TODO: previewer for Vim help
+    previewer = previewers.help.new(opts),
+    sorter = sorters.get_generic_fuzzy_sorter(),
+    attach_mappings = function(prompt_bufnr, map)
+      local view_help = function()
+        local selection = actions.get_selected_entry(prompt_bufnr)
+
+        actions.close(prompt_bufnr)
+        vim.cmd("help " .. selection.value)
+      end
+
+      map('i', '<CR>', view_help)
+      map('n', '<CR>', view_help)
+
+      return true
+    end
+  }):find()
+end
+
 -- TODO: What the heck should we do for accepting this.
 --  vim.fn.setreg("+", "nnoremap $TODO :lua require('telescope.builtin').<whatever>()<CR>")
 -- TODO: Can we just do the names instead?