fix(api): nvim_parse_cmd error message in pcall() #23297

Problem:
nvim_parse_cmd() in pcall() may show an error message (side-effect):

    :lua pcall(vim.api.nvim_parse_cmd, vim.fn.getcmdline(), {})
    E16: Invalid range

Solution:
Avoid emsg() in the nvim_parse_cmd() codepath.

- refactor(api): add error message output parameter to get_address()
- fix: null check emsg() parameter
- refactor: remove emsg_off workaround from do_incsearch_highlighting()
- refactor: remove emsg_off workaround from cmdpreview_may_show()
- refactor: remove remaining calls to emsg() from parse_cmd_address() and get_address()
- (refactor): lint set_cmd_dflall_range()
- refactor: addr_error() - move output parameter to return value

Fix #20339

TODO:

These are the functions called by `get_address()`:

```
nvim_parse_cmd() -> parse_cmdline() -> parse_cmd_address() -> get_address()
    skipwhite()
    addr_error()
    qf_get_cur_idx()
    qf_get_cur_valid_idx()
    qf_get_size()
    qf_get_valid_size()
    mark_get()
    mark_check()
    assert()
    skip_regexp()
    magic_isset()
>   do_search()
>   searchit()
    ascii_isdigit()
    getdigits()
    getdigits_int32()
    compute_buffer_local_count()
    hasFolding()
```

From these functions, I found at least two that call emsg directly:
- do_search()
  - seems to be simple to refactor
- searchit()
  - will be more challenging because it may generate multiple error messages,
    which can't be handled by the current `errormsg` out-parameter.
    For example, it makes multiple calls to `vim_regexec_multi()` in a loop that
    possibly generate error messages, and later `searchit()` itself may generate
    another one:
    - https://github.com/neovim/neovim/blob/c194acbfc479d8e5839fa629363f93f6550d035c/src/nvim/search.c#L631-L647
    - https://github.com/neovim/neovim/blob/c194acbfc479d8e5839fa629363f93f6550d035c/src/nvim/search.c#L939-L954

---------

Co-authored-by: Justin M. Keyes <justinkz@gmail.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/test/functional/api/vim_spec.lua b/test/functional/api/vim_spec.lua
index 1ac732b128..c4f89318e0 100644
--- a/test/functional/api/vim_spec.lua
+++ b/test/functional/api/vim_spec.lua
@@ -3467,6 +3467,7 @@ describe('API', function()
       end)
     end)
   end)
+
   describe('nvim_parse_cmd', function()
     it('works', function()
       eq({
@@ -4048,7 +4049,13 @@ describe('API', function()
       meths.cmd(meths.parse_cmd("set cursorline", {}), {})
       eq(true, meths.get_option_value("cursorline", {}))
     end)
+    it('no side-effects (error messages) in pcall() #20339', function()
+      eq({ false, 'Error while parsing command line: E16: Invalid range' },
+        exec_lua([=[return {pcall(vim.api.nvim_parse_cmd, "'<,'>n", {})}]=]))
+      eq('', eval('v:errmsg'))
+    end)
   end)
+
   describe('nvim_cmd', function()
     it('works', function ()
       meths.cmd({ cmd = "set", args = { "cursorline" } }, {})