fix(api): nvim_create_buf assert fails if autocmds set &swapfile

Problem: assertion failure in nvim_create_buf if buflist_new autocommands open
a swapfile when "scratch" is set.

Solution: block autocommands when setting up the buffer; fire them later
instead.

Note that, unlike buflist_new, I don't check if autocommands aborted script
processing; the buffer is already created and configured at that point, so might
as well return the handle anyway.

Rather than repeat try_{start,end} and {un}block_autocmds for each relevant
operation, just do it at the start and near the end. This means that, if
TermResponse fires from unblock_autocmds for whatever reason, it can see the
buffer in an already configured state if we didn't bail due to an error (plus
it's probably a bit cleaner this way).

1 files changed, 41 insertions, 0 deletions

diff --git a/test/functional/api/vim_spec.lua b/test/functional/api/vim_spec.lua
index a3f70efcea..ef602b3a51 100644
--- a/test/functional/api/vim_spec.lua
+++ b/test/functional/api/vim_spec.lua
@@ -3144,6 +3144,47 @@ describe('API', function()
       api.nvim_create_buf(false, true)
       eq(1, eval('g:loaded'))
     end)
+
+    it('creating scratch buffer where autocommands set &swapfile works', function()
+      exec([[
+        autocmd BufNew * ++once execute expand("<abuf>") "buffer"
+                             \| file foobar
+                             \| setlocal swapfile
+      ]])
+      local new_buf = api.nvim_create_buf(false, true)
+      neq('', fn.swapname(new_buf))
+    end)
+
+    it('fires expected autocommands', function()
+      exec([=[
+        " Append the &buftype to check autocommands trigger *after* the buffer was configured to be
+        " scratch, if applicable.
+        autocmd BufNew * let fired += [["BufNew", expand("<abuf>")->str2nr(),
+                                      \ getbufvar(expand("<abuf>")->str2nr(), "&buftype")]]
+        autocmd BufAdd * let fired += [["BufAdd", expand("<abuf>")->str2nr(),
+                                      \ getbufvar(expand("<abuf>")->str2nr(), "&buftype")]]
+
+        " Don't want to see OptionSet; buffer options set from passing true for "scratch", etc.
+        " should be configured invisibly, and before autocommands.
+        autocmd OptionSet * let fired += [["OptionSet", expand("<amatch>")]]
+
+        let fired = []
+      ]=])
+      local new_buf = api.nvim_create_buf(false, false)
+      eq({ { 'BufNew', new_buf, '' } }, eval('g:fired'))
+
+      command('let fired = []')
+      new_buf = api.nvim_create_buf(false, true)
+      eq({ { 'BufNew', new_buf, 'nofile' } }, eval('g:fired'))
+
+      command('let fired = []')
+      new_buf = api.nvim_create_buf(true, false)
+      eq({ { 'BufNew', new_buf, '' }, { 'BufAdd', new_buf, '' } }, eval('g:fired'))
+
+      command('let fired = []')
+      new_buf = api.nvim_create_buf(true, true)
+      eq({ { 'BufNew', new_buf, 'nofile' }, { 'BufAdd', new_buf, 'nofile' } }, eval('g:fired'))
+    end)
   end)
 
   describe('nvim_get_runtime_file', function()