Visual: highlight char-at-cursor

Decide whether to highlight the visual-selected character under the
cursor, depending on 'guicursor' style:

- Highlight if cursor is blinking or non-block (vertical, horiz).
- Do NOT highlight if cursor is non-blinking block.

Traditionally Vim's visual selection does "reverse mode", which perhaps
conflicts with the non-blinking block cursor. But 'guicursor' defaults
to a vertical bar for selection=exclusive, and this confuses users who
expect to see the text highlighted.

closes #8983

5 files changed, 62 insertions, 13 deletions

diff --git a/runtime/doc/vim_diff.txt b/runtime/doc/vim_diff.txt
index 3915763eed..db856ceb65 100644
--- a/runtime/doc/vim_diff.txt
+++ b/runtime/doc/vim_diff.txt
@@ -357,6 +357,9 @@ TUI:
   and has a 'ttybuiltin' setting to control how that combination works.  Nvim
   uses one or the other, it does not attempt to merge the two.
 
+UI/Display:
+  |Visual| selection highlights the character at cursor. |visual-use|
+
 VimL (Vim script) compatibility:
   `count` does not alias to |v:count|
   `errmsg` does not alias to |v:errmsg|
diff --git a/src/nvim/cursor_shape.c b/src/nvim/cursor_shape.c
index cf79005a37..5551576c6d 100644
--- a/src/nvim/cursor_shape.c
+++ b/src/nvim/cursor_shape.c
@@ -254,6 +254,16 @@ char_u *parse_shape_opt(int what)
   return NULL;
 }
 
+/// Returns true if the cursor is non-blinking "block" shape during
+/// visual selection.
+///
+/// @param exclusive If 'selection' option is "exclusive".
+bool cursor_is_block_during_visual(bool exclusive)
+{
+  int mode_idx = exclusive ? SHAPE_IDX_VE : SHAPE_IDX_V;
+  return (SHAPE_BLOCK == shape_table[mode_idx].shape
+          && 0 == shape_table[mode_idx].blinkon);
+}
 
 /// Map cursor mode from string to integer
 ///
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index 8733c6db62..462b476a35 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -2761,9 +2761,9 @@ do_mouse (
   } else if ((mod_mask & MOD_MASK_MULTI_CLICK) && (State & (NORMAL | INSERT))
              && mouse_has(MOUSE_VISUAL)) {
     if (is_click || !VIsual_active) {
-      if (VIsual_active)
+      if (VIsual_active) {
         orig_cursor = VIsual;
-      else {
+      } else {
         VIsual = curwin->w_cursor;
         orig_cursor = VIsual;
         VIsual_active = true;
@@ -6401,8 +6401,8 @@ static void nv_visual(cmdarg_T *cap)
       VIsual_mode = cap->cmdchar;
       showmode();
     }
-    redraw_curbuf_later(INVERTED);          /* update the inversion */
-  } else {                /* start Visual mode */
+    redraw_curbuf_later(INVERTED);          // update the inversion
+  } else {                // start Visual mode
     if (cap->count0 > 0 && resel_VIsual_mode != NUL) {
       /* use previously selected part */
       VIsual = curwin->w_cursor;
diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index 07695031d8..5166bc2e42 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -73,6 +73,7 @@
 #include "nvim/buffer.h"
 #include "nvim/charset.h"
 #include "nvim/cursor.h"
+#include "nvim/cursor_shape.h"
 #include "nvim/diff.h"
 #include "nvim/eval.h"
 #include "nvim/ex_cmds.h"
@@ -679,9 +680,9 @@ static void win_update(win_T *wp)
   int old_botline = wp->w_botline;
   long fold_count;
   // Remember what happened to the previous line.
-#define DID_NONE 1      /* didn't update a line */
-#define DID_LINE 2      /* updated a normal line */
-#define DID_FOLD 3      /* updated a folded line */
+#define DID_NONE 1      // didn't update a line
+#define DID_LINE 2      // updated a normal line
+#define DID_FOLD 3      // updated a folded line
   int did_update = DID_NONE;
   linenr_T syntax_last_parsed = 0;              /* last parsed text line */
   linenr_T mod_top = 0;
@@ -2180,10 +2181,10 @@ win_line (
   int syntax_attr = 0;                  /* attributes desired by syntax */
   int has_syntax = FALSE;               /* this buffer has syntax highl. */
   int save_did_emsg;
-  int eol_hl_off = 0;                   /* 1 if highlighted char after EOL */
-  int draw_color_col = FALSE;           /* highlight colorcolumn */
-  int         *color_cols = NULL;       /* pointer to according columns array */
-  bool has_spell = false;               /* this buffer has spell checking */
+  int eol_hl_off = 0;                   // 1 if highlighted char after EOL
+  int draw_color_col = false;           // highlight colorcolumn
+  int *color_cols = NULL;               // pointer to according columns array
+  bool has_spell = false;               // this buffer has spell checking
 # define SPWORDLEN 150
   char_u nextline[SPWORDLEN * 2];       /* text with start of the next line */
   int nextlinecol = 0;                  /* column where nextline[] starts */
@@ -2389,8 +2390,9 @@ win_line (
         }
       }
 
-      // Check if the character under the cursor should not be inverted
-      if (!highlight_match && lnum == curwin->w_cursor.lnum && wp == curwin) {
+      // Check if the char under the cursor should be inverted (highlighted).
+      if (!highlight_match && lnum == curwin->w_cursor.lnum && wp == curwin
+          && cursor_is_block_during_visual(*p_sel == 'e')) {
         noinvcur = true;
       }
 
diff --git a/test/functional/ui/highlight_spec.lua b/test/functional/ui/highlight_spec.lua
index 96f6b43320..39170337d7 100644
--- a/test/functional/ui/highlight_spec.lua
+++ b/test/functional/ui/highlight_spec.lua
@@ -322,6 +322,40 @@ describe('highlight', function()
     screen:attach()
   end)
 
+  it('visual', function()
+    screen:detach()
+    screen = Screen.new(20,4)
+    screen:attach()
+    screen:set_default_attr_ids({
+      [1] = {background = Screen.colors.LightGrey},
+      [2] = {bold = true, foreground = Screen.colors.Blue1},
+      [3] = {bold = true},
+    })
+    insert([[
+      line1 foo bar
+    ]])
+
+    -- Non-blinking block cursor: does NOT highlight char-at-cursor.
+    command('set guicursor=a:block-blinkon0')
+    feed('gg$vhhh')
+    screen:expect([[
+        line1 foo^ {1:bar}     |
+                          |
+      {2:~                   }|
+      {3:-- VISUAL --}        |
+    ]])
+
+    -- Vertical cursor: highlights char-at-cursor. #8983
+    command('set guicursor=a:block-blinkon175')
+    feed('<esc>gg$vhhh')
+    screen:expect([[
+        line1 foo{1:^ bar}     |
+                          |
+      {2:~                   }|
+      {3:-- VISUAL --}        |
+    ]])
+  end)
+
   it('cterm=standout gui=standout', function()
     screen:detach()
     screen = Screen.new(20,5)