vim-patch:8.0.0677: setting 'filetype' may switch buffers

Problem:    Setting 'filetype' internally may cause the current buffer and
            window to change unexpectedly.
Solution:   Set curbuf_lock. (closes vim/vim#1734)
https://github.com/vim/vim/commit/1814183b865059679f6ee526ec23fc575e536e66

4 files changed, 25 insertions, 2 deletions

diff --git a/src/nvim/ex_cmds.c b/src/nvim/ex_cmds.c
index 15b49b69ce..0b30132eb8 100644
--- a/src/nvim/ex_cmds.c
+++ b/src/nvim/ex_cmds.c
@@ -4906,7 +4906,9 @@ void fix_help_buffer(void)
 
   // Set filetype to "help".
   if (STRCMP(curbuf->b_p_ft, "help") != 0) {
+    curbuf_lock++;
     set_option_value("ft", 0L, "help", OPT_LOCAL);
+    curbuf_lock--;
   }
 
   if (!syntax_present(curwin)) {
diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index d152dfa271..4b9ef5d819 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -6057,8 +6057,10 @@ static int open_cmdwin(void)
   curbuf->b_p_ma = true;
   curwin->w_p_fen = false;
 
-  /* Do execute autocommands for setting the filetype (load syntax). */
+  // Do execute autocommands for setting the filetype (load syntax).
   unblock_autocmds();
+  // But don't allow switching to another buffer.
+  curbuf_lock++;
 
   /* Showing the prompt may have set need_wait_return, reset it. */
   need_wait_return = FALSE;
@@ -6071,6 +6073,7 @@ static int open_cmdwin(void)
     }
     set_option_value("ft", 0L, "vim", OPT_LOCAL);
   }
+  curbuf_lock--;
 
   /* Reset 'textwidth' after setting 'filetype' (the Vim filetype plugin
    * sets 'textwidth' to 78). */
diff --git a/src/nvim/quickfix.c b/src/nvim/quickfix.c
index aeb27a5cac..47760e1e70 100644
--- a/src/nvim/quickfix.c
+++ b/src/nvim/quickfix.c
@@ -3008,6 +3008,7 @@ static void qf_fill_buffer(qf_info_T *qi, buf_T *buf, qfline_T *old_last)
     // Set the 'filetype' to "qf" each time after filling the buffer.  This
     // resembles reading a file into a buffer, it's more logical when using
     // autocommands.
+    curbuf_lock++;
     set_option_value("ft", 0L, "qf", OPT_LOCAL);
     curbuf->b_p_ma = false;
 
@@ -3017,6 +3018,7 @@ static void qf_fill_buffer(qf_info_T *qi, buf_T *buf, qfline_T *old_last)
     apply_autocmds(EVENT_BUFWINENTER, (char_u *)"quickfix", NULL,
                    false, curbuf);
     keep_filetype = false;
+    curbuf_lock--;
 
     // make sure it will be redrawn
     redraw_curbuf_later(NOT_VALID);
diff --git a/src/nvim/testdir/test_quickfix.vim b/src/nvim/testdir/test_quickfix.vim
index 85f93cf3da..646245f857 100644
--- a/src/nvim/testdir/test_quickfix.vim
+++ b/src/nvim/testdir/test_quickfix.vim
@@ -2172,7 +2172,7 @@ endfunc
 func Test_cclose_from_copen()
     augroup QF_Test
 	au!
-	au FileType qf :cclose
+        au FileType qf :call assert_fails(':cclose', 'E788')
     augroup END
     copen
     augroup QF_Test
@@ -2209,3 +2209,19 @@ func Test_Qf_Size()
   call XsizeTests('c')
   call XsizeTests('l')
 endfunc
+
+func Test_cclose_in_autocmd()
+  " Problem is only triggered if "starting" is zero, so that the OptionsSet
+  " event will be triggered.
+  " call test_override('starting', 1)
+  augroup QF_Test
+    au!
+    au FileType qf :call assert_fails(':cclose', 'E788')
+  augroup END
+  copen
+  augroup QF_Test
+    au!
+  augroup END
+  augroup! QF_Test
+  " call test_override('starting', 0)
+endfunc