fix(lua): make vim._with() work with buf=0 and win=0 context #39151

Problem: Using `buf=0`/`win=0` context in `vim._with` should be
  equivalent to using explicit buffer/window identifier respectively.

Solution: Explicitly adjust context in case of `buf=0` or `win=0`.
(cherry picked from commit 3a4cc5db0b)

runtime/lua/vim/_core/shared.lua

@@ -1609,6 +1609,7 @@ function vim._with(context, f)
     if not vim.api.nvim_buf_is_valid(context.buf) then
       error('Invalid buffer id: ' .. context.buf)
     end
+    context.buf = context.buf == 0 and vim.api.nvim_get_current_buf() or context.buf
   end
 
   -- Check window exists
@@ -1620,6 +1621,7 @@ function vim._with(context, f)
     if context.buf and vim.api.nvim_win_get_buf(context.win) ~= context.buf then
       error('Can not set both `buf` and `win` context.')
     end
+    context.win = context.win == 0 and vim.api.nvim_get_current_win() or context.win
   end
 
   -- Decorate so that save-set-restore options is done in correct window-buffer

test/functional/lua/with_spec.lua

@@ -267,6 +267,12 @@ describe('vim._with', function()
         -- Current
         assert_buf(api.nvim_get_current_buf())
 
+        local buf = api.nvim_get_current_buf()
+        vim._with({ buf = 0 }, function()
+          assert(api.nvim_get_current_buf() == buf)
+        end)
+        assert(api.nvim_get_current_buf() == buf)
+
         -- Hidden listed
         local listed = api.nvim_create_buf(true, true)
         assert_buf(listed)
@@ -1161,6 +1167,14 @@ describe('vim._with', function()
         -- Current
         assert_win(api.nvim_get_current_win())
 
+        local win = api.nvim_get_current_win()
+        vim._with({ win = 0 }, function()
+          assert(api.nvim_get_current_win() == win)
+          -- Should restore context window if that changed
+          vim.cmd.tabnew()
+        end)
+        assert(api.nvim_get_current_win() == win)
+
         -- Not visible
         local other_win, cur_win = setup_windows()
         vim.cmd.tabnew()