refactor: only gc oil buffers once all oil bufs are hidden

Previously we were gc-ing all hidden oil buffers 2 seconds after they
were hidden. I think this is a little too magical, and interferes with
some expected vim behavior (ctrl-o/i). If people want the old behavior,
we can expose the "GC hidden buffers" function via the API.

We're also changing the "rerender visible oil buffers" logic, because
previously that would delete hidden oil buffers. Now it simply marks
them as dirty, and they will be rerendered during the next BufEnter.

lua/oil/mutator/init.lua

@@ -511,7 +511,7 @@ M.try_write_changes = function(confirm)
                 vim.split(current_entry.name, "/")[1]
               )
             end
-            view.rerender_visible_and_cleanup({ preserve_undo = M.trash })
+            view.rerender_all_oil_buffers({ preserve_undo = M.trash })
           end
         end)
       )

lua/oil/view.lua

@@ -70,7 +70,7 @@ M.toggle_hidden = function()
     vim.notify("Cannot toggle hidden files when you have unsaved changes", vim.log.levels.WARN)
   else
     config.view_options.show_hidden = not config.view_options.show_hidden
-    view.rerender_visible_and_cleanup({ refetch = false })
+    view.rerender_all_oil_buffers({ refetch = false })
   end
 end
 
@@ -82,7 +82,7 @@ M.set_columns = function(cols)
   else
     config.columns = cols
     -- TODO only refetch if we don't have all the necessary data for the columns
-    view.rerender_visible_and_cleanup({ refetch = true })
+    view.rerender_all_oil_buffers({ refetch = true })
   end
 end
 
@@ -97,7 +97,7 @@ end
 ---@param opts table
 ---@note
 --- This DISCARDS ALL MODIFICATIONS a user has made to oil buffers
-M.rerender_visible_and_cleanup = function(opts)
+M.rerender_all_oil_buffers = function(opts)
   local buffers = M.get_all_buffers()
   local hidden_buffers = {}
   for _, bufnr in ipairs(buffers) do
@@ -110,7 +110,7 @@ M.rerender_visible_and_cleanup = function(opts)
   end
   for _, bufnr in ipairs(buffers) do
     if hidden_buffers[bufnr] then
-      vim.api.nvim_buf_delete(bufnr, { force = true })
+      vim.b[bufnr].oil_dirty = opts
     else
       M.render_buffer_async(bufnr, opts)
     end
@@ -142,8 +142,12 @@ M.restore_win_options = function()
   end
 end
 
----Delete hidden oil buffers and if none remain, clear the cache
-M.cleanup = function()
+---Get a list of visible oil buffers and a list of hidden oil buffers
+---@note
+--- If any buffers are modified, return values are nil
+---@return nil|integer[]
+---@return nil|integer[]
+local function get_visible_hidden_buffers()
   local buffers = M.get_all_buffers()
   local hidden_buffers = {}
   for _, bufnr in ipairs(buffers) do
@@ -157,18 +161,22 @@ M.cleanup = function()
       hidden_buffers[vim.api.nvim_win_get_buf(winid)] = nil
     end
   end
+  local visible_buffers = vim.tbl_filter(function(bufnr)
+    return not hidden_buffers[bufnr]
+  end, buffers)
+  return visible_buffers, vim.tbl_keys(hidden_buffers)
+end
 
-  local any_remaining = false
-  for _, bufnr in ipairs(buffers) do
-    if hidden_buffers[bufnr] then
-      vim.api.nvim_buf_delete(bufnr, { force = true })
-    else
-      any_remaining = true
-    end
+---Delete unmodified, hidden oil buffers and if none remain, clear the cache
+M.delete_hidden_buffers = function()
+  local visible_buffers, hidden_buffers = get_visible_hidden_buffers()
+  if not visible_buffers or not hidden_buffers or not vim.tbl_isempty(visible_buffers) then
+    return
   end
-  if not any_remaining then
-    cache.clear_everything()
+  for _, bufnr in ipairs(hidden_buffers) do
+    vim.api.nvim_buf_delete(bufnr, { force = true })
   end
+  cache.clear_everything()
 end
 
 ---@param bufnr integer
@@ -198,7 +206,16 @@ M.initialize = function(bufnr)
     nested = true,
     buffer = bufnr,
     callback = function()
-      vim.defer_fn(M.cleanup, 2000)
+      -- First wait a short time (10ms) for the buffer change to settle
+      vim.defer_fn(function()
+        local visible_buffers = get_visible_hidden_buffers()
+        -- Only kick off the 2-second timer if we don't have any visible oil buffers
+        if visible_buffers and vim.tbl_isempty(visible_buffers) then
+          vim.defer_fn(function()
+            M.delete_hidden_buffers()
+          end, 2000)
+        end
+      end, 10)
     end,
   })
   vim.api.nvim_create_autocmd("BufDelete", {
@@ -210,6 +227,17 @@ M.initialize = function(bufnr)
       session[bufnr] = nil
     end,
   })
+  vim.api.nvim_create_autocmd("BufEnter", {
+    group = "Oil",
+    buffer = bufnr,
+    callback = function(args)
+      local opts = vim.b[args.buf].oil_dirty
+      if opts then
+        vim.b[args.buf].oil_dirty = nil
+        M.render_buffer_async(args.buf, opts)
+      end
+    end,
+  })
   local timer
   vim.api.nvim_create_autocmd("CursorMoved", {
     desc = "Update oil preview window",