fix(api): disallow some more functions during textlock

Problem: nvim_buf_set_text(), nvim_open_term() and termopen() all change buffer
text, which is forbidden during textlock. Additionally, nvim_open_term() and
termopen() may be used to convert the cmdwin buffer into a terminal buffer,
which is weird.

Solution: Allow nvim_buf_set_text() and nvim_open_term() in the cmdwin, but
disallow nvim_open_term() from converting the cmdwin buffer into a terminal
buffer. termopen() is not allowed in the cmdwin (as it always operates on
curbuf), so just check text_locked().

Also happens to improve the error in #21055: nvim_buf_set_text() was callable
during textlock, but happened to check textlock indirectly via u_save();
however, this caused the error to be overwritten by an unhelpful "Failed to
save undo information" message when msg_list == NULL (e.g: an `<expr>` mapping
invoked outside of do_cmdline()).

1 files changed, 21 insertions, 0 deletions

diff --git a/test/functional/vimscript/api_functions_spec.lua b/test/functional/vimscript/api_functions_spec.lua
index 683ae2446c..6548548a9e 100644
--- a/test/functional/vimscript/api_functions_spec.lua
+++ b/test/functional/vimscript/api_functions_spec.lua
@@ -54,11 +54,23 @@ describe('eval-API', function()
     matches('Vim%(call%):E5555: API call: E565: Not allowed to change text or change window$',
        pcall_err(command, "normal! yy"))
 
+    command("autocmd TextYankPost <buffer> ++once call nvim_open_term(0, {})")
+    matches('Vim%(call%):E5555: API call: E565: Not allowed to change text or change window$',
+       pcall_err(command, "normal! yy"))
+
     -- Functions checking textlock should also not be usable from <expr> mappings.
     command("inoremap <expr> <f2> nvim_win_close(0, 1)")
     eq('Vim(normal):E5555: API call: E565: Not allowed to change text or change window',
        pcall_err(command, [[execute "normal i\<f2>"]]))
 
+    -- Text-changing functions gave a "Failed to save undo information" error when called from an
+    -- <expr> mapping outside do_cmdline() (msg_list == NULL), so use feed() to test this.
+    command("inoremap <expr> <f2> nvim_buf_set_text(0, 0, 0, 0, 0, ['hi'])")
+    meths.set_vvar('errmsg', '')
+    feed("i<f2><esc>")
+    eq('E5555: API call: E565: Not allowed to change text or change window',
+       meths.get_vvar('errmsg'))
+
     -- Some functions checking textlock (usually those that may change the current window or buffer)
     -- also ought to not be usable in the cmdwin.
     feed("q:")
@@ -68,6 +80,15 @@ describe('eval-API', function()
     -- But others, like nvim_buf_set_lines(), which just changes text, is OK.
     curbufmeths.set_lines(0, -1, 1, {"wow!"})
     eq({'wow!'}, curbufmeths.get_lines(0, -1, 1))
+
+    -- Turning the cmdwin buffer into a terminal buffer would be pretty weird.
+    eq('E11: Invalid in command-line window; <CR> executes, CTRL-C quits',
+       pcall_err(meths.open_term, 0, {}))
+
+    -- But turning a different buffer into a terminal from the cmdwin is OK.
+    local term_buf = meths.create_buf(false, true)
+    meths.open_term(term_buf, {})
+    eq('terminal', meths.get_option_value("buftype", {buf = term_buf}))
   end)
 
   it("use buffer numbers and windows ids as handles", function()