feat(api): set statuscolumn line number in nvim_eval_statusline()

Having the user set `v:lnum` before calling `nvim_eval_statusline()` is
unnecesarily fragile. Redraws inbetween setting `v:lnum` and the
`nvim_eval_statusline()` call will overwrite `v:lnum`.

5 files changed, 50 insertions, 42 deletions

diff --git a/runtime/doc/api.txt b/runtime/doc/api.txt
index 52c3f7fa97..09d260e0cd 100644
--- a/runtime/doc/api.txt
+++ b/runtime/doc/api.txt
@@ -773,8 +773,8 @@ nvim_eval_statusline({str}, {*opts})                  *nvim_eval_statusline()*
                 • use_tabline: (boolean) Evaluate tabline instead of
                   statusline. When true, {winid} is ignored. Mutually
                   exclusive with {use_winbar}.
-                • use_statuscol: (boolean) Evaluate statuscolumn instead of
-                  statusline.
+                • use_statuscol_lnum: (number) Evaluate statuscolumn for this
+                  line number instead of statusline.
 
     Return: ~
         Dictionary containing statusline information, with these keys:
diff --git a/runtime/doc/news.txt b/runtime/doc/news.txt
index 98f3f3f398..12dc4674af 100644
--- a/runtime/doc/news.txt
+++ b/runtime/doc/news.txt
@@ -74,7 +74,7 @@ NEW FEATURES                                                    *news-features*
 The following new APIs or features were added.
 
 • |nvim_eval_statusline()| supports evaluating the |'statuscolumn'| through a
-  new `opts` field: `use_statuscol`.
+  new `opts` field: `use_statuscol_lnum`.
 
 • |nvim_buf_get_extmarks()| now accepts a -1 `ns_id` to request extmarks from
   all namespaces and adds the namespace id to the details array.
diff --git a/src/nvim/api/keysets.lua b/src/nvim/api/keysets.lua
index 26e87bccec..01f5a8b860 100644
--- a/src/nvim/api/keysets.lua
+++ b/src/nvim/api/keysets.lua
@@ -97,7 +97,7 @@ return {
     "highlights";
     "use_winbar";
     "use_tabline";
-    "use_statuscol";
+    "use_statuscol_lnum";
   }};
   { 'option', {
     "scope";
diff --git a/src/nvim/api/vim.c b/src/nvim/api/vim.c
index 383953a676..b62521290d 100644
--- a/src/nvim/api/vim.c
+++ b/src/nvim/api/vim.c
@@ -2056,7 +2056,7 @@ Array nvim_get_mark(String name, Dictionary opts, Error *err)
 ///           - use_winbar: (boolean) Evaluate winbar instead of statusline.
 ///           - use_tabline: (boolean) Evaluate tabline instead of statusline. When true, {winid}
 ///                                    is ignored. Mutually exclusive with {use_winbar}.
-///           - use_statuscol: (boolean) Evaluate statuscolumn instead of statusline.
+///           - use_statuscol_lnum: (number) Evaluate statuscolumn for this line number instead of statusline.
 ///
 /// @param[out] err Error details, if any.
 /// @return Dictionary containing statusline information, with these keys:
@@ -2075,10 +2075,10 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
   int maxwidth;
   int fillchar = 0;
   int use_bools = 0;
+  int statuscol_lnum = 0;
   Window window = 0;
   bool use_winbar = false;
   bool use_tabline = false;
-  bool use_statuscol = false;
   bool highlights = false;
 
   if (str.size < 2 || memcmp(str.data, "%!", 2) != 0) {
@@ -2116,47 +2116,48 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
   }
   if (HAS_KEY(opts->use_winbar)) {
     use_winbar = api_object_to_bool(opts->use_winbar, "use_winbar", false, err);
-    use_bools++;
     if (ERROR_SET(err)) {
       return result;
     }
+    use_bools++;
   }
   if (HAS_KEY(opts->use_tabline)) {
     use_tabline = api_object_to_bool(opts->use_tabline, "use_tabline", false, err);
-    use_bools++;
     if (ERROR_SET(err)) {
       return result;
     }
-  }
-  if (HAS_KEY(opts->use_statuscol)) {
-    use_statuscol = api_object_to_bool(opts->use_statuscol, "use_statuscol", false, err);
     use_bools++;
-    if (ERROR_SET(err)) {
+  }
+
+  win_T *wp = use_tabline ? curwin : find_window_by_handle(window, err);
+  if (wp == NULL) {
+    api_set_error(err, kErrorTypeException, "unknown winid %d", window);
+    return result;
+  }
+
+  if (HAS_KEY(opts->use_statuscol_lnum)) {
+    VALIDATE_T("use_statuscol_lnum", kObjectTypeInteger, opts->use_statuscol_lnum.type, {
       return result;
-    }
+    });
+    statuscol_lnum = (int)opts->use_statuscol_lnum.data.integer;
+    VALIDATE_RANGE(statuscol_lnum > 0 && statuscol_lnum <= wp->w_buffer->b_ml.ml_line_count,
+                   "use_statuscol_lnum", {
+      return result;
+    });
+    use_bools++;
   }
   VALIDATE(use_bools <= 1, "%s",
-           "Can only use one of 'use_winbar', 'use_tabline' and 'use_statuscol'", {
+           "Can only use one of 'use_winbar', 'use_tabline' and 'use_statuscol_lnum'", {
     return result;
   });
 
-  win_T *wp, *ewp;
   int stc_hl_id = 0;
   statuscol_T statuscol = { 0 };
   SignTextAttrs sattrs[SIGN_SHOW_MAX] = { 0 };
 
   if (use_tabline) {
-    wp = NULL;
-    ewp = curwin;
     fillchar = ' ';
   } else {
-    wp = find_window_by_handle(window, err);
-    if (wp == NULL) {
-      api_set_error(err, kErrorTypeException, "unknown winid %d", window);
-      return result;
-    }
-    ewp = wp;
-
     if (fillchar == 0) {
       if (use_winbar) {
         fillchar = wp->w_p_fcs_chars.wbr;
@@ -2165,18 +2166,25 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
         fillchar = fillchar_status(&attr, wp);
       }
     }
-    if (use_statuscol) {
+    if (statuscol_lnum) {
       HlPriId line = { 0 };
       HlPriId cul  = { 0 };
       HlPriId num  = { 0 };
-      linenr_T lnum = (linenr_T)get_vim_var_nr(VV_LNUM);
+      linenr_T lnum = statuscol_lnum;
       int num_signs = buf_get_signattrs(wp->w_buffer, lnum, sattrs, &num, &line, &cul);
       decor_redraw_signs(wp->w_buffer, lnum - 1, &num_signs, sattrs, &num, &line, &cul);
 
       statuscol.sattrs = sattrs;
       statuscol.foldinfo = fold_info(wp, lnum);
-      statuscol.use_cul = wp->w_p_cul && lnum == wp->w_cursorline
-                          && (wp->w_p_culopt_flags & CULOPT_NBR);
+      wp->w_cursorline = win_cursorline_standout(wp) ? wp->w_cursor.lnum : 0;
+
+      if (wp->w_p_cul) {
+        if (statuscol.foldinfo.fi_level > 0 && statuscol.foldinfo.fi_lines > 0) {
+          wp->w_cursorline = statuscol.foldinfo.fi_lnum;
+        }
+        statuscol.use_cul = lnum == wp->w_cursorline && (wp->w_p_culopt_flags & CULOPT_NBR);
+      }
+
       statuscol.sign_cul_id = statuscol.use_cul ? cul.hl_id : 0;
       if (num.hl_id) {
         stc_hl_id = num.hl_id;
@@ -2187,6 +2195,8 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
       } else {
         stc_hl_id = HLF_N + 1;
       }
+
+      set_vim_var_nr(VV_LNUM, lnum);
       set_vim_var_nr(VV_RELNUM, labs(get_cursor_rel_lnum(wp, lnum)));
       set_vim_var_nr(VV_VIRTNUM, 0);
     }
@@ -2199,7 +2209,7 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
 
     maxwidth = (int)opts->maxwidth.data.integer;
   } else {
-    maxwidth = use_statuscol ? win_col_off(wp)
+    maxwidth = statuscol_lnum ? win_col_off(wp)
                : (use_tabline || (!use_winbar && global_stl_height() > 0)) ? Columns : wp->w_width;
   }
 
@@ -2207,10 +2217,10 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
   stl_hlrec_t *hltab;
 
   // Temporarily reset 'cursorbind' to prevent side effects from moving the cursor away and back.
-  int p_crb_save = ewp->w_p_crb;
-  ewp->w_p_crb = false;
+  int p_crb_save = wp->w_p_crb;
+  wp->w_p_crb = false;
 
-  int width = build_stl_str_hl(ewp,
+  int width = build_stl_str_hl(wp,
                                buf,
                                sizeof(buf),
                                str.data,
@@ -2220,12 +2230,12 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
                                maxwidth,
                                highlights ? &hltab : NULL,
                                NULL,
-                               use_statuscol ? &statuscol : NULL);
+                               statuscol_lnum ? &statuscol : NULL);
 
   PUT(result, "width", INTEGER_OBJ(width));
 
   // Restore original value of 'cursorbind'
-  ewp->w_p_crb = p_crb_save;
+  wp->w_p_crb = p_crb_save;
 
   if (highlights) {
     Array hl_values = ARRAY_DICT_INIT;
@@ -2236,7 +2246,7 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
     // add the default highlight at the beginning of the highlight list
     if (hltab->start == NULL || (hltab->start - buf) != 0) {
       Dictionary hl_info = ARRAY_DICT_INIT;
-      grpname = get_default_stl_hl(wp, use_winbar, stc_hl_id);
+      grpname = get_default_stl_hl(use_tabline ? NULL : wp, use_winbar, stc_hl_id);
 
       PUT(hl_info, "start", INTEGER_OBJ(0));
       PUT(hl_info, "group", CSTR_TO_OBJ(grpname));
@@ -2250,7 +2260,7 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
       PUT(hl_info, "start", INTEGER_OBJ(sp->start - buf));
 
       if (sp->userhl == 0) {
-        grpname = get_default_stl_hl(wp, use_winbar, stc_hl_id);
+        grpname = get_default_stl_hl(use_tabline ? NULL : wp, use_winbar, stc_hl_id);
       } else if (sp->userhl < 0) {
         grpname = syn_id2name(-sp->userhl);
       } else {
diff --git a/test/functional/api/vim_spec.lua b/test/functional/api/vim_spec.lua
index cddea48a76..af6fbf092a 100644
--- a/test/functional/api/vim_spec.lua
+++ b/test/functional/api/vim_spec.lua
@@ -3422,7 +3422,7 @@ describe('API', function()
             { use_winbar = true, highlights = true }))
       end)
       it('works with statuscolumn', function()
-        command([[
+        exec([[
           let &stc='%C%s%=%l '
           set cul nu nuw=3 scl=yes:2 fdc=2
           call setline(1, repeat(['aaaaa'], 5))
@@ -3431,9 +3431,8 @@ describe('API', function()
           call sign_place(2, 1, 'a', bufnr(), {'lnum':4})
           call nvim_buf_set_extmark(0, g:ns, 3, 1, { 'sign_text':'bb', 'sign_hl_group':'ErrorMsg' })
           1,5fold | 1,5 fold | foldopen!
+          norm 4G
         ]])
-        command('norm 4G')
-        command('let v:lnum=4')
         eq({
           str = '││aabb 4 ',
           width = 9,
@@ -3444,8 +3443,7 @@ describe('API', function()
             { group = 'ErrorMsg', start = 8 },
             { group = 'Normal', start = 10 }
           }
-        }, meths.eval_statusline('%C%s%=%l ', { use_statuscol = true, highlights = true }))
-        command('let v:lnum=3')
+        }, meths.eval_statusline('%C%s%=%l ', { use_statuscol_lnum = 4, highlights = true }))
         eq({
           str = '3 ' ,
           width = 2,
@@ -3453,7 +3451,7 @@ describe('API', function()
             { group = 'LineNr', start = 0 },
             { group = 'ErrorMsg', start = 1 }
           }
-        }, meths.eval_statusline('%l%#ErrorMsg# ', { use_statuscol = true, highlights = true }))
+        }, meths.eval_statusline('%l%#ErrorMsg# ', { use_statuscol_lnum = 3, highlights = true }))
       end)
       it('no memory leak with click functions', function()
         meths.eval_statusline('%@ClickFunc@StatusLineStringWithClickFunc%T', {})