fix: (terminal) buffer previewer

lua/telescope/actions/init.lua

@@ -787,6 +787,13 @@ end
 actions.delete_buffer = function(prompt_bufnr)
   local current_picker = action_state.get_current_picker(prompt_bufnr)
   current_picker:delete_selection(function(selection)
+    -- avoid preview win from closing by creating tmp buffer
+    local preview_win = state.get_status(prompt_bufnr).preview_win
+    if preview_win ~= nil and vim.api.nvim_win_is_valid(preview_win) then
+      local buf = vim.api.nvim_create_buf(false, true)
+      vim.api.nvim_buf_set_option(buf, "bufhidden", "wipe")
+      vim.api.nvim_win_set_buf(preview_win, buf)
+    end
     vim.api.nvim_buf_delete(selection.bufnr, { force = true })
   end)
 end

lua/telescope/builtin/internal.lua

@@ -637,9 +637,17 @@ internal.buffers = function(opts)
       results = buffers,
       entry_maker = opts.entry_maker or make_entry.gen_from_buffer(opts),
     },
-    previewer = conf.grep_previewer(opts),
+    previewer = previewers.buffers.new(opts),
     sorter = conf.generic_sorter(opts),
     default_selection_index = default_selection_idx,
+    attach_mappings = function(_, _)
+      action_set.select:enhance {
+        post = function()
+          local entry = action_state.get_selected_entry()
+          vim.api.nvim_win_set_cursor(0, { entry.lnum, entry.col or 0 })
+        end,
+      }
+    end,
   }):find()
 end
 

lua/telescope/previewers/buffer_previewer.lua

@@ -81,6 +81,19 @@ local search_teardown = function(self)
   end
 end
 
+local scroll_fn = function(self, direction)
+  if not self.state then
+    return
+  end
+
+  local input = direction > 0 and [[]] or [[]]
+  local count = math.abs(direction)
+
+  vim.api.nvim_win_call(self.state.winid, function()
+    vim.cmd([[normal! ]] .. count .. input)
+  end)
+end
+
 previewers.file_maker = function(filepath, bufnr, opts)
   opts = opts or {}
   if opts.use_ft_detect == nil then
@@ -282,18 +295,7 @@ previewers.new_buffer_previewer = function(opts)
   end
 
   if not opts.scroll_fn then
-    function opts.scroll_fn(self, direction)
-      if not self.state then
-        return
-      end
-
-      local input = direction > 0 and [[]] or [[]]
-      local count = math.abs(direction)
-
-      vim.api.nvim_buf_call(self.state.bufnr, function()
-        vim.cmd([[normal! ]] .. count .. input)
-      end)
-    end
+    opts.scroll_fn = scroll_fn
   end
 
   return Previewer:new(opts)
@@ -370,19 +372,12 @@ previewers.vimgrep = defaulter(function(opts)
         pcall(vim.api.nvim_buf_clear_namespace, self.state.last_set_bufnr, ns_previewer, 0, -1)
       end
 
-      -- Workaround for unnamed buffer when using builtin.buffer
-      if entry.bufnr and (p == "[No Name]" or vim.api.nvim_buf_get_option(entry.bufnr, "buftype") ~= "") then
-        local lines = vim.api.nvim_buf_get_lines(entry.bufnr, 0, -1, false)
-        vim.api.nvim_buf_set_lines(self.state.bufnr, 0, -1, false, lines)
-        jump_to_line(self, self.state.bufnr, entry.lnum)
-      else
-        conf.buffer_previewer_maker(p, self.state.bufnr, {
-          bufname = self.state.bufname,
-          callback = function(bufnr)
-            jump_to_line(self, bufnr, entry.lnum)
-          end,
-        })
-      end
+      conf.buffer_previewer_maker(p, self.state.bufnr, {
+        bufname = self.state.bufname,
+        callback = function(bufnr)
+          jump_to_line(self, bufnr, entry.lnum)
+        end,
+      })
     end,
   }
 end, {})
@@ -872,4 +867,95 @@ previewers.display_content = defaulter(function(_)
   }
 end, {})
 
+previewers.buffers = defaulter(function(opts)
+  opts = opts or {}
+  local cwd = opts.cwd or vim.loop.cwd()
+  local previewer_active = true -- decouple provider from preview_win
+  return Previewer:new {
+    title = function()
+      return "Buffers"
+    end,
+    setup = function(_, status)
+      local win_id = status.picker.original_win_id
+      -- required because of see `:h local-options` as
+      -- buffers not yet attached to a current window take the options from the `minimal` popup ...
+      local state = {
+        ["previewed_buffers"] = {},
+        ["winid"] = status.preview_win,
+        ["win_options"] = {
+          ["colorcolumn"] = vim.api.nvim_win_get_option(win_id, "colorcolumn"),
+          ["cursorline"] = vim.api.nvim_win_get_option(win_id, "cursorline"),
+          ["foldlevel"] = vim.api.nvim_win_get_option(win_id, "foldlevel"),
+          ["list"] = vim.api.nvim_win_get_option(win_id, "list"),
+          ["number"] = vim.api.nvim_win_get_option(win_id, "number"),
+          ["relativenumber"] = vim.api.nvim_win_get_option(win_id, "relativenumber"),
+          ["signcolumn"] = vim.api.nvim_win_get_option(win_id, "signcolumn"),
+          ["spell"] = vim.api.nvim_win_get_option(win_id, "spell"),
+          ["winhl"] = vim.api.nvim_win_get_option(win_id, "winhl"),
+          ["wrap"] = vim.api.nvim_win_get_option(win_id, "wrap"),
+        },
+      }
+      -- TODO clear explicitly once API should become available
+      -- decoration provider is hierachical on_start -> win
+      vim.api.nvim_set_decoration_provider(ns_previewer, {
+        on_start = function()
+          -- defacto disable provider if status.preview_win does not exist anymore
+          return previewer_active
+        end,
+        on_win = function(_, winid, bufnr, _)
+          if winid ~= status.preview_win then
+            return false -- skip setting extmark for any window other than status.preview_win
+          end
+          local lnum, _ = unpack(vim.api.nvim_win_get_cursor(winid))
+          local line = vim.api.nvim_buf_get_lines(bufnr, lnum - 1, lnum, false)[1]
+          -- only set if winid and rows are matching
+          pcall(vim.api.nvim_buf_set_extmark, bufnr, ns_previewer, lnum - 1, 0, {
+            end_col = #line,
+            virt_text_pos = "overlay",
+            hl_group = "TelescopePreviewLine",
+            ephemeral = true,
+            priority = 101, -- 1 higher than treesitter
+          })
+        end,
+      })
+      return state
+    end,
+    teardown = function(self)
+      -- reapply proper buffer-window options..
+      for opt, value in pairs(self.state.win_options) do
+        vim.api.nvim_win_set_option(self.state.winid, opt, value)
+      end
+      -- TODO precautious clearing of extmark though likely no effect due to ephemeral
+      -- clear extmarks for previewed buffers
+      for buf, _ in pairs(self.state.previewed_buffers) do
+        if vim.api.nvim_buf_is_valid(buf) then
+          vim.api.nvim_buf_clear_namespace(buf, ns_previewer, 0, -1)
+        end
+      end
+      previewer_active = false
+    end,
+    dyn_title = function(_, entry)
+      return Path:new(from_entry.path(entry, true)):normalize(cwd)
+    end,
+    preview_fn = function(self, entry, status)
+      if vim.api.nvim_buf_is_valid(entry.bufnr) then
+        vim.api.nvim_win_set_buf(status.preview_win, entry.bufnr)
+        vim.api.nvim_win_set_option(status.preview_win, "winhl", "Normal:TelescopePreviewNormal")
+        vim.api.nvim_win_set_option(status.preview_win, "signcolumn", "no")
+        vim.api.nvim_win_set_option(status.preview_win, "foldlevel", 100)
+        vim.api.nvim_win_set_option(status.preview_win, "wrap", false)
+        self.state.bufnr = entry.bufnr
+        if not entry.col then
+          local _, col = unpack(vim.api.nvim_win_get_cursor(status.preview_win))
+          entry.col = col + 1
+        end
+        if self.state.previewed_buffers[entry.bufnr] ~= true then
+          self.state.previewed_buffers[entry.bufnr] = true
+        end
+      end
+    end,
+    scroll_fn = scroll_fn,
+  }
+end, {})
+
 return previewers

lua/telescope/previewers/init.lua

@@ -305,6 +305,7 @@ previewers.help = buffer_previewer.help
 previewers.man = buffer_previewer.man
 previewers.autocommands = buffer_previewer.autocommands
 previewers.highlights = buffer_previewer.highlights
+previewers.buffers = buffer_previewer.buffers
 
 --- A deprecated way of displaying content more easily. Was written at a time,
 --- where the buffer_previewer interface wasn't present. Nowadays it's easier

lua/telescope/previewers/previewer.lua

@@ -23,7 +23,7 @@ function Previewer:preview(entry, status)
 
   if not self.state then
     if self._setup_func then
-      self.state = self:_setup_func()
+      self.state = self:_setup_func(status)
     else
       self.state = {}
     end

lua/telescope/previewers/term_previewer.lua

@@ -294,9 +294,6 @@ previewers.vimgrep = defaulter(function(opts)
       if p == nil or p == "" then
         return
       end
-      if entry.bufnr and (p == "[No Name]" or vim.api.nvim_buf_get_option(entry.bufnr, "buftype") ~= "") then
-        return
-      end
 
       local lnum = entry.lnum or 0