fix: set alternate buffer when inside oil (#60)

lua/oil/init.lua

@@ -709,6 +709,12 @@ M.setup = function(opts)
       local scheme = util.parse_url(bufname)
       if scheme and config.adapters[scheme] then
         require("oil.view").maybe_set_cursor()
+        -- While we are in an oil buffer, set the alternate file to the buffer we were in prior to
+        -- opening oil
+        local has_orig, orig_buffer = pcall(vim.api.nvim_win_get_var, 0, "oil_original_buffer")
+        if has_orig and vim.api.nvim_buf_is_valid(orig_buffer) then
+          vim.fn.setreg("#", orig_buffer)
+        end
       elseif vim.fn.isdirectory(bufname) == 0 then
         -- Only run this logic if we are *not* in an oil buffer (and it's not a directory, which
         -- will be replaced by an oil:// url)

tests/altbuf_spec.lua

@@ -70,6 +70,17 @@ a.describe("Alternate buffer", function()
     assert.equals("foo", vim.fn.expand("#"))
   end)
 
+  a.it("sets previous buffer as alternate when inside oil buffer", function()
+    vim.cmd.edit({ args = { "foo" } })
+    oil.open()
+    test_util.wait_for_autocmd("BufReadPost")
+    assert.equals("foo", vim.fn.expand("#"))
+    vim.cmd.edit({ args = { "bar" } })
+    assert.equals("foo", vim.fn.expand("#"))
+    oil.open()
+    assert.equals("bar", vim.fn.expand("#"))
+  end)
+
   a.describe("floating window", function()
     a.it("sets previous buffer as alternate", function()
       vim.cmd.edit({ args = { "foo" } })