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, 2 insertions, 7 deletions

diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index 969023b70d..f77822cec6 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -236,7 +236,7 @@ static bool do_incsearch_highlighting(int firstc, int *search_delim, incsearch_s
   bool delim_optional = false;
   int delim;
   char *end;
-  char *dummy;
+  const char *dummy;
   pos_T save_cursor;
   bool use_last_pat;
   bool retval = false;
@@ -261,7 +261,6 @@ static bool do_incsearch_highlighting(int firstc, int *search_delim, incsearch_s
     return false;
   }
 
-  emsg_off++;
   exarg_T ea = {
     .line1 = 1,
     .line2 = 1,
@@ -369,7 +368,6 @@ static bool do_incsearch_highlighting(int firstc, int *search_delim, incsearch_s
   curwin->w_cursor = save_cursor;
   retval = true;
 theend:
-  emsg_off--;
   return retval;
 }
 
@@ -2428,13 +2426,10 @@ static bool cmdpreview_may_show(CommandLineState *s)
   // Copy the command line so we can modify it.
   int cmdpreview_type = 0;
   char *cmdline = xstrdup(ccline.cmdbuff);
-  char *errormsg = NULL;
-  emsg_off++;  // Block errors when parsing the command line, and don't update v:errmsg
+  const char *errormsg = NULL;
   if (!parse_cmdline(cmdline, &ea, &cmdinfo, &errormsg)) {
-    emsg_off--;
     goto end;
   }
-  emsg_off--;
 
   // Check if command is previewable, if not, don't attempt to show preview
   if (!(ea.argt & EX_PREVIEW)) {