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>

3 files changed, 107 insertions, 11 deletions

diff --git a/lua/telescope/builtin.lua b/lua/telescope/builtin.lua
index 5264ca3..fced93c 100644
--- a/lua/telescope/builtin.lua
+++ b/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?
diff --git a/lua/telescope/make_entry.lua b/lua/telescope/make_entry.lua
index 3ec663b..4db664e 100644
--- a/lua/telescope/make_entry.lua
+++ b/lua/telescope/make_entry.lua
@@ -284,4 +284,53 @@ function make_entry.gen_from_treesitter(opts)
   end
 end
 
+function make_entry.gen_from_tagfile(opts)
+  local help_entry, version
+  local delim = string.char(7)
+
+  local make_display = function(line)
+    help_entry = ""
+    display    = ""
+    version    = ""
+
+    line = line .. delim
+    for section in line:gmatch("(.-)" .. delim) do
+      if section:find("^vim:") == nil then
+        local ver = section:match("^neovim:(.*)")
+        if ver == nil then
+          help_entry = section
+        else
+          version = ver:sub(1, -2)
+        end
+      end
+    end
+
+    result = {}
+    if version ~= "" then -- some Vim only entries are unversioned
+      if opts.show_version then
+        result.display = string.format("%s [%s]", help_entry, version)
+      else
+        result.display = help_entry
+      end
+      result.value = help_entry
+    end
+
+    return result
+  end
+
+  return function(line)
+    local entry = {
+      entry_type = make_entry.types.GENERIC,
+
+    }
+    local d = make_display(line)
+    entry.valid   = next(d) ~= nil
+    entry.display = d.display
+    entry.value   = d.value
+    entry.ordinal = d.value
+
+    return entry
+  end
+end
+
 return make_entry
diff --git a/lua/telescope/previewers.lua b/lua/telescope/previewers.lua
index f3f6261..e28adce 100644
--- a/lua/telescope/previewers.lua
+++ b/lua/telescope/previewers.lua
@@ -58,7 +58,7 @@ end
 local previewer_ns = vim.api.nvim_create_namespace('telescope.previewers')
 
 local with_preview_window = function(status, bufnr, callable)
-  if bufnr and vim.api.nvim_buf_call then
+  if bufnr and vim.api.nvim_buf_call and false then
     vim.api.nvim_buf_call(bufnr, callable)
   else
     return context_manager.with(function()
@@ -365,17 +365,17 @@ previewers.qflist = defaulter(function(opts)
   }
 end, {})
 
--- WIP
 previewers.help = defaulter(function(_)
   return previewers.new {
     preview_fn = function(_, entry, status)
       with_preview_window(status, nil, function()
-        local old_tags = vim.o.tags
-        vim.o.tags = vim.fn.expand("$VIMRUNTIME") .. '/doc/tags'
+        local special_chars = ":~^.?/%[%]%*"
 
-        local taglist = vim.fn.taglist('^' .. entry.value .. '$')
+        local escaped = vim.fn.escape(entry.value, special_chars)
+        local tagfile = vim.fn.expand("$VIMRUNTIME") .. '/doc/tags'
+        local taglist = vim.fn.taglist('^' .. escaped .. '$', tagfile)
         if vim.tbl_isempty(taglist) then
-          taglist = vim.fn.taglist(entry.value)
+          taglist = vim.fn.taglist(escaped, tagfile)
         end
 
         if vim.tbl_isempty(taglist) then
@@ -384,15 +384,23 @@ previewers.help = defaulter(function(_)
 
         local best_entry = taglist[1]
         local new_bufnr = vim.fn.bufnr(best_entry.filename, true)
-
         vim.api.nvim_buf_set_option(new_bufnr, 'filetype', 'help')
         vim.api.nvim_win_set_buf(status.preview_win, new_bufnr)
 
-        vim.cmd [["gg"]]
-        print(best_entry.cmd)
-        vim.cmd(string.format([[execute "%s"]], best_entry.cmd))
+        local search_query = best_entry.cmd
+
+        -- remove leading '/'
+        search_query = search_query:sub(2)
+
+        -- Set the query to "very nomagic".
+        -- This should make it work quite nicely given tags.
+        search_query = [[\V]] .. search_query
+
+        log.trace([[lua vim.fn.search("]], search_query, [[")]])
 
-        vim.o.tags = old_tags
+        vim.cmd "norm! gg"
+        vim.fn.search(search_query, "W")
+        vim.cmd "norm  zt"
       end)
     end
   }