Add a scrollview_visibility option

This replaces scrollview_always_show. The possible values are:
* always: Always show scrollbars and signs.
* overflow: Show scrollbars and signs only when content overflows the
  window (when there are lines that are not visible).
* info: Show scrollbars and signs when content overflows the window.
  Otherwise, show when there are signs to display (excluding those from
  sign groups included in scrollview_excluded_info_signs).

Author: dstein64

autoload/scrollview.vim

@@ -17,7 +17,6 @@ endfunction
 
 " === General ===
 
-let g:scrollview_always_show = get(g:, 'scrollview_always_show', v:false)
 let g:scrollview_auto_mouse = get(g:, 'scrollview_auto_mouse', v:true)
 let g:scrollview_base = get(g:, 'scrollview_base', 'right')
 " The plugin enters a restricted state when the number of buffer bytes exceeds
@@ -30,6 +29,9 @@ let g:scrollview_consider_border =
 let g:scrollview_current_only = get(g:, 'scrollview_current_only', v:false)
 let g:scrollview_excluded_filetypes =
       \ get(g:, 'scrollview_excluded_filetypes', [])
+let g:scrollview_excluded_info_signs =
+      \ get(g:, 'scrollview_excluded_info_signs',
+      \   ['changelist', 'cursor', 'latestchange'])
 let g:scrollview_floating_windows =
       \ get(g:, 'scrollview_floating_windows', v:false)
 let g:scrollview_signs_hidden_for_insert =
@@ -68,6 +70,12 @@ let g:scrollview_mouse_primary = get(g:, 'scrollview_mouse_primary', 'left')
 let g:scrollview_mouse_secondary =
       \ get(g:, 'scrollview_mouse_secondary', 'right')
 let g:scrollview_on_startup = get(g:, 'scrollview_on_startup', v:true)
+" Use the old option, scrollview_always_show, if it's set.
+if has_key(g:, 'scrollview_always_show')
+      \ && !has_key(g:, 'scrollview_visibility')
+  let g:scrollview_visibility = g:scrollview_always_show ? 'always' : 'overflow'
+endif
+let g:scrollview_visibility = get(g:, 'scrollview_visibility', 'overflow')
 let g:scrollview_winblend = get(g:, 'scrollview_winblend', 50)
 let g:scrollview_winblend_gui = get(g:, 'scrollview_winblend_gui', 0)
 " The default zindex for floating windows is 50. A smaller value is used here

doc/scrollview.txt

@@ -197,10 +197,6 @@ can be set to control when restricted mode is entered.
 4. Configuration                           *scrollview-configuration*
 
 Configuration Variables ~
-                                           *scrollview_always_show*
-scrollview_always_show |Boolean| specifying whether scrollbars and signs are
-                       shown when all lines are visible. Defaults to |v:false|.
-
                                            *scrollview_base*
 scrollview_base        |String| specifying where the scrollbar is anchored.
                        Possible values are `'left'` or `'right'` for corresponding
@@ -244,6 +240,12 @@ scrollview_excluded_filetypes              *scrollview_excluded_filetypes*
                        which scrollbars should not be displayed. Defaults to
                        `[]`.
 
+scrollview_excluded_info_signs             *scrollview_excluded_info_signs*
+                       |List| of |String|s specifying sign groups to exclude from
+                       visibility consideration when |scrollview_visibility| is
+                       set to `'info'` and there is no overflow. Defaults to
+                       `['changelist', 'cursor', 'latestchange']`.
+
 scrollview_floating_windows                *scrollview_floating_windows*
 (experimental)         |Boolean| specifying whether scrollbars and signs are
                        shown in floating windows. Defaults to |v:false|.
@@ -324,6 +326,19 @@ scrollview_on_startup  |Boolean| specifying whether scrollbars are enabled on
                        startup. Defaults to |v:true|. Considered only when the
                        plugin is loaded.
 
+                                           *scrollview_visibility*
+scrollview_visibility  |String| specifying the visibility level of scrollbars
+                       and signs. Possible values are `'always'`, `'overflow'`,
+                       and `'info'`. Defaults to `'overflow'`.
+                       * `always` Always show scrollbars and signs.
+                       * `overflow` Show scrollbars and signs only when content
+                         overflows the window (when there are lines that are
+                         not visible).
+                       * `info` Show scrollbars and signs when content overflows
+                         the window. Otherwise, show when there are signs to
+                         display (excluding those from sign groups included in
+                         |scrollview_excluded_info_signs|).
+
                                            *scrollview_winblend*
 scrollview_winblend    |Number| specifying the level of transparency for
                        scrollbars when a GUI is not running and 'termguicolors'
@@ -972,8 +987,8 @@ register_sign_spec({spec})                 *scrollview.register_sign_spec()*
                   `false`.
                 + extend (boolean): Show each sign on all corresponding rows
                   of the scrollview column, instead of just a single row. This
-                  is relevant when |scrollview_always_show| is on and all lines
-                  and at least one filler line are visible.
+                  is relevant when the window is not scrollable (see
+                  |scrollview_visibility|).
                 + group (string): Defaults to `'other'`.
                 + highlight (string): Defaults to `'Pmenu'`.
                 + priority (integer): Defaults to `50`.

doc/tags

@@ -44,7 +44,6 @@ scrollview.set_sign_group_callback()	scrollview.txt	/*scrollview.set_sign_group_
 scrollview.set_sign_group_state()	scrollview.txt	/*scrollview.set_sign_group_state()*
 scrollview.setup()	scrollview.txt	/*scrollview.setup()*
 scrollview.txt	scrollview.txt	/*scrollview.txt*
-scrollview_always_show	scrollview.txt	/*scrollview_always_show*
 scrollview_base	scrollview.txt	/*scrollview_base*
 scrollview_byte_limit	scrollview.txt	/*scrollview_byte_limit*
 scrollview_changelist_current_priority	scrollview.txt	/*scrollview_changelist_current_priority*
@@ -76,6 +75,7 @@ scrollview_diagnostics_warn_priority	scrollview.txt	/*scrollview_diagnostics_war
 scrollview_diagnostics_warn_symbol	scrollview.txt	/*scrollview_diagnostics_warn_symbol*
 scrollview_enabled	scrollview.txt	/*scrollview_enabled*
 scrollview_excluded_filetypes	scrollview.txt	/*scrollview_excluded_filetypes*
+scrollview_excluded_info_signs	scrollview.txt	/*scrollview_excluded_info_signs*
 scrollview_floating_windows	scrollview.txt	/*scrollview_floating_windows*
 scrollview_folds_priority	scrollview.txt	/*scrollview_folds_priority*
 scrollview_folds_symbol	scrollview.txt	/*scrollview_folds_symbol*
@@ -130,6 +130,7 @@ scrollview_textwidth_priority	scrollview.txt	/*scrollview_textwidth_priority*
 scrollview_textwidth_symbol	scrollview.txt	/*scrollview_textwidth_symbol*
 scrollview_trail_priority	scrollview.txt	/*scrollview_trail_priority*
 scrollview_trail_symbol	scrollview.txt	/*scrollview_trail_symbol*
+scrollview_visibility	scrollview.txt	/*scrollview_visibility*
 scrollview_winblend	scrollview.txt	/*scrollview_winblend*
 scrollview_winblend_gui	scrollview.txt	/*scrollview_winblend_gui*
 scrollview_zindex	scrollview.txt	/*scrollview_zindex*

lua/scrollview.lua

@@ -8,6 +8,8 @@ local binary_search = utils.binary_search
 local concat = utils.concat
 local copy = utils.copy
 local echo = utils.echo
+local extend = utils.extend
+local mapify = utils.mapify
 local preceding = utils.preceding
 local remove_duplicates = utils.remove_duplicates
 local round = utils.round
@@ -1172,6 +1174,14 @@ local is_scrollview_window = function(winid)
   return bufnr == bar_bufnr or bufnr == sign_bufnr
 end
 
+-- Indicates whether content overflows the window.
+local has_overflow = function(winid)
+  local bufnr = api.nvim_win_get_buf(winid)
+  local topline, botline = line_range(winid)
+  local line_count = api.nvim_buf_line_count(bufnr)
+  return botline - topline + 1 ~= line_count
+end
+
 -- Whether scrollbar and signs should be shown. This is the first check; it
 -- only checks for conditions that apply to both the position bar and signs.
 local should_show = function(winid)
@@ -1215,14 +1225,8 @@ local should_show = function(winid)
   if winheight == 0 or winwidth == 0 then
     return false
   end
-  local always_show = to_bool(vim.g.scrollview_always_show)
-  if not always_show then
-    -- Don't show when all lines are on screen.
-    local topline, botline = line_range(winid)
-    local line_count = api.nvim_buf_line_count(bufnr)
-    if botline - topline + 1 == line_count then
-      return false
-    end
+  if vim.g.scrollview_visibility == 'overflow' and not has_overflow(winid) then
+    return false
   end
   return true
 end
@@ -1679,9 +1683,10 @@ end
 -- removed from the list. The bar_winid is necessary so that signs can be
 -- properly highlighted when intersecting a scrollbar.
 local show_signs = function(winid, sign_winids, bar_winid)
+  local shown = {}  -- a list winids for the signs created
   -- Neovim 0.8 has an issue with matchaddpos highlighting (similar type of
   -- issue reported in Neovim #22906).
-  if not to_bool(fn.has('nvim-0.9')) then return end
+  if not to_bool(fn.has('nvim-0.9')) then return shown end
   local bar_props
   if bar_winid ~= -1 then
     bar_props = api.nvim_win_get_var(bar_winid, PROPS_VAR)
@@ -1690,7 +1695,7 @@ local show_signs = function(winid, sign_winids, bar_winid)
   local wininfo = fn.getwininfo(winid)[1]
   local config = api.nvim_win_get_config(winid)
   local is_float = tbl_get(config, 'relative', '') ~= ''
-  if is_restricted(winid) then return end
+  if is_restricted(winid) then return shown end
   local bufnr = api.nvim_win_get_buf(winid)
   local line_count = api.nvim_buf_line_count(bufnr)
   local topline_lookup = nil  -- only set when needed
@@ -1939,6 +1944,7 @@ local show_signs = function(winid, sign_winids, bar_winid)
           sign_winid = table.remove(sign_winids)
           api.nvim_win_set_config(sign_winid, sign_config)
         end
+        table.insert(shown, sign_winid)
         local over_scrollbar = bar_props ~= nil
           and bar_props.col >= col
           and bar_props.col <= col + sign_width - 1
@@ -2046,6 +2052,7 @@ local show_signs = function(winid, sign_winids, bar_winid)
       end
     end
   end
+  return shown
 end
 
 -- Given a scrollbar properties dictionary and a target window row, the
@@ -2464,6 +2471,7 @@ local refresh_bars = function()
         sign_bufnr, 0, api.nvim_buf_line_count(sign_bufnr), true, {})
       api.nvim_buf_set_option(sign_bufnr, 'modifiable', false)
     end
+    local excluded_info_signs = mapify(vim.g.scrollview_excluded_info_signs)
     for _, winid in ipairs(target_wins) do
       if should_show(winid) then
         local existing_winid = -1
@@ -2484,7 +2492,25 @@ local refresh_bars = function()
           table.remove(existing_barids)
         end
         -- Repeat a similar process for signs.
-        show_signs(winid, existing_signids, bar_winid)
+        local sign_winids = show_signs(winid, existing_signids, bar_winid)
+        -- If scrollview_visibility is info, there's no overflow, and there are
+        -- no info signs, make the bar_winid and the sign_winids available for
+        -- potential re-use.
+        if vim.g.scrollview_visibility == 'info' and not has_overflow(winid) then
+          local has_info_signs = false
+          for _, sign_winid in ipairs(sign_winids) do
+            local sign_props = api.nvim_win_get_var(sign_winid, PROPS_VAR)
+            local group = sign_specs[sign_props.sign_spec_id].group
+            if excluded_info_signs[group] == nil then
+              has_info_signs = true
+              break
+            end
+          end
+          if not has_info_signs then
+            table.insert(existing_barids, bar_winid)
+            extend(existing_signids, sign_winids)
+          end
+        end
       end
     end
     local existing_wins = concat(existing_barids, existing_signids)

lua/scrollview/utils.lua

@@ -56,6 +56,27 @@ function M.echo(echo_list)
   vim.cmd('echohl None')
 end
 
+-- Given array-like tables a and b, add all elements from b to a.
+function M.extend(a, b)
+  for _, item in ipairs(b) do
+    table.insert(a, item)
+  end
+end
+
+-- Convert a list-like table to a map-like table. The output's keys are the
+-- elements of the input, and the corresponding values are the indices where
+-- the element is in the list.
+function M.mapify(l)
+  local result = {}
+  for idx, item in ipairs(l) do
+    if result[item] == nil then
+      result[item] = {}
+    end
+    table.insert(result[item], idx)
+  end
+  return result
+end
+
 -- For sorted list l with no duplicates, return the previous item before the
 -- specified item (wraps around).
 function M.preceding(l, item, count, wrapscan)