Implements horizontal scrolling in previewer & results. (#2437)

* Implements horizontal scrolling in previewer & results.

* docs: update wrt. horizontal scrolling in previewer &  results

lua/telescope/previewers/buffer_previewer.lua

@@ -189,6 +189,19 @@ local scroll_fn = function(self, direction)
   end)
 end
 
+local scroll_horizontal_fn = function(self, direction)
+  if not self.state then
+    return
+  end
+
+  local input = direction > 0 and [[zl]] or [[zh]]
+  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 = vim.F.if_nil(opts, {})
   -- TODO(conni2461): here shouldn't be any hardcoded magic numbers ...
@@ -462,6 +475,10 @@ previewers.new_buffer_previewer = function(opts)
     opts.scroll_fn = scroll_fn
   end
 
+  if not opts.scroll_horizontal_fn then
+    opts.scroll_horizontal_fn = scroll_horizontal_fn
+  end
+
   return Previewer:new(opts)
 end
 

lua/telescope/previewers/init.lua

@@ -47,6 +47,7 @@ local previewers = {}
 --- - `:teardown()`
 --- - `:send_input(input)`
 --- - `:scroll_fn(direction)`
+--- - `:scroll_horizontal_fn(direction)`
 ---
 --- `Previewer:new()` expects a table as input with following keys:
 ---   - `setup` function(self): Will be called the first time preview will be
@@ -64,6 +65,8 @@ local previewers = {}
 ---                                         used to send input to the terminal
 ---                                         application, like less.
 ---   - `scroll_fn` function(self, direction): Used to make scrolling work.
+---   - `scroll_horizontal_fn` function(self, direction): Used to make
+---                                                       horizontal scrolling work.
 previewers.Previewer = Previewer
 
 --- A shorthand for creating a new Previewer.

lua/telescope/previewers/previewer.lua

@@ -26,6 +26,7 @@ function Previewer:new(opts)
     _teardown_func = opts.teardown,
     _send_input = opts.send_input,
     _scroll_fn = opts.scroll_fn,
+    _scroll_horizontal_fn = opts.scroll_horizontal_fn,
     preview_fn = opts.preview_fn,
     _empty_bufnr = nil,
   }, Previewer)
@@ -95,4 +96,12 @@ function Previewer:scroll_fn(direction)
   end
 end
 
+function Previewer:scroll_horizontal_fn(direction)
+  if self._scroll_horizontal_fn then
+    self:_scroll_horizontal_fn(direction)
+  else
+    vim.api.nvim_err_writeln "scroll_horizontal_fn is not defined for this previewer"
+  end
+end
+
 return Previewer