fix(decoration): don't show signcolumn for non-sign_text extmark (#22135)

Fixes: #22127

src/nvim/buffer_defs.h

@@ -838,6 +838,7 @@ struct file_buffer {
   Map(uint32_t, uint32_t) b_extmark_ns[1];         // extmark namespaces
   size_t b_virt_line_blocks;    // number of virt_line blocks
   size_t b_signs;               // number of sign extmarks
+  size_t b_signs_with_text;     // number of sign extmarks with text
 
   // array of channel_id:s which have asked to receive updates for this
   // buffer.

src/nvim/decoration.c

@@ -100,9 +100,13 @@ void decor_remove(buf_T *buf, int row, int row2, Decoration *decor)
     if (decor_has_sign(decor)) {
       assert(buf->b_signs > 0);
       buf->b_signs--;
-    }
-    if (row2 >= row && decor->sign_text) {
-      buf_signcols_del_check(buf, row + 1, row2 + 1);
+      if (decor->sign_text) {
+        assert(buf->b_signs_with_text > 0);
+        buf->b_signs_with_text--;
+        if (row2 >= row) {
+          buf_signcols_del_check(buf, row + 1, row2 + 1);
+        }
+      }
     }
   }
   decor_free(decor);
@@ -445,11 +449,11 @@ int decor_signcols(buf_T *buf, DecorState *state, int row, int end_row, int max)
   int signcols = 0;      // highest value of count
   int currow = -1;       // current row
 
-  if (max <= 1 && buf->b_signs >= (size_t)max) {
+  if (max <= 1 && buf->b_signs_with_text >= (size_t)max) {
     return max;
   }
 
-  if (buf->b_signs == 0) {
+  if (buf->b_signs_with_text == 0) {
     return 0;
   }
 

src/nvim/extmark.c

@@ -152,6 +152,7 @@ revised:
       buf->b_signs++;
     }
     if (decor->sign_text) {
+      buf->b_signs_with_text++;
       // TODO(lewis6991): smarter invalidation
       buf_signcols_add_check(buf, NULL);
     }

test/functional/ui/decorations_spec.lua

@@ -2109,6 +2109,20 @@ l5
                           |
     ]]}
   end)
+
+  it('does not set signcolumn for signs without text', function()
+    screen:try_resize(20, 3)
+    meths.win_set_option(0, 'signcolumn', 'auto')
+    insert(example_text)
+    feed 'gg'
+    meths.buf_set_extmark(0, ns, 0, -1, {number_hl_group='Error'})
+    screen:expect{grid=[[
+      ^l1                  |
+      l2                  |
+                          |
+    ]]}
+  end)
+
 end)
 
 describe('decorations: virt_text', function()