fix: preserve panel cursor position when switching tabs (sindrets#457)

Save the file panel cursor position on tab_leave and restore it on
tab_enter. This complements the fold state preservation from sindrets#582.

Author: dlyongemallo

lua/diffview/scene/views/diff/listeners.lua

@@ -19,13 +19,29 @@ return function(view)
         view:set_file(file, false, true)
       end
 
+      -- Restore panel cursor position.
+      if view.panel_cursor and view.panel:is_open() then
+        local winid = view.panel:get_winid()
+        if winid and api.nvim_win_is_valid(winid) then
+          pcall(api.nvim_win_set_cursor, winid, view.panel_cursor)
+        end
+      end
+
       if view.ready then
         view:update_files()
       end
     end,
     tab_leave = function()
       local file = view.panel.cur_file
 
+      -- Save panel cursor position.
+      if view.panel:is_open() then
+        local winid = view.panel:get_winid()
+        if winid and api.nvim_win_is_valid(winid) then
+          view.panel_cursor = api.nvim_win_get_cursor(winid)
+        end
+      end
+
       if file then
         file.layout:detach_files()
       end

lua/diffview/scene/views/file_history/listeners.lua

@@ -8,6 +8,7 @@ local lib = lazy.require("diffview.lib") ---@module "diffview.lib"
 local utils = lazy.require("diffview.utils") ---@module "diffview.utils"
 local vcs_utils = lazy.require("diffview.vcs.utils") ---@module "diffview.vcs.utils"
 
+local api = vim.api
 local await = async.await
 
 ---@param view FileHistoryView
@@ -18,10 +19,26 @@ return function(view)
       if file then
         view:set_file(file)
       end
+
+      -- Restore panel cursor position.
+      if view.panel_cursor and view.panel:is_open() then
+        local winid = view.panel:get_winid()
+        if winid and api.nvim_win_is_valid(winid) then
+          pcall(api.nvim_win_set_cursor, winid, view.panel_cursor)
+        end
+      end
     end,
     tab_leave = function()
       local file = view.panel.cur_item[2]
 
+      -- Save panel cursor position.
+      if view.panel:is_open() then
+        local winid = view.panel:get_winid()
+        if winid and api.nvim_win_is_valid(winid) then
+          view.panel_cursor = api.nvim_win_get_cursor(winid)
+        end
+      end
+
       if file then
         file.layout:detach_files()
       end