Handle 'orphaned signs' on line deletion for signcolumn >= 2

runtime/doc/options.txt

@@ -5555,6 +5555,12 @@ A jump table for the options with a short description can be found at |Q_op|.
 	   "number"	display signs in the 'number' column. If the number
 			column is not present, then behaves like 'auto'.
 
+	Note regarding 'orphaned signs': with signcolumn numbers higher than
+	1, deleting lines will also remove the associated signs automatically,
+	in contrast to the default Vim behavior of keeping and grouping them.
+	This is done in order for the signcolumn appearence not appear weird
+	during line deletion.
+
 
 			*'smartcase'* *'scs'* *'nosmartcase'* *'noscs'*
 'smartcase' 'scs'	boolean	(default off)

src/nvim/option.c

@@ -7582,10 +7582,20 @@ int csh_like_shell(void)
 /// Return the number of requested sign columns, based on current
 /// buffer signs and on user configuration.
 int win_signcol_count(win_T *wp)
+{
+  return win_signcol_configured(wp, NULL);
+}
+
+/// Return the number of requested sign columns, based on user / configuration.
+int win_signcol_configured(win_T *wp, int *is_fixed)
 {
   int minimum = 0, maximum = 1, needed_signcols;
   const char *scl = (const char *)wp->w_p_scl;
 
+  if (is_fixed) {
+    *is_fixed = 1;
+  }
+
   // Note: It checks "no" or "number" in 'signcolumn' option
   if (*scl == 'n'
       && (*(scl + 1) == 'o' || (*(scl + 1) == 'u'
@@ -7603,7 +7613,11 @@ int win_signcol_count(win_T *wp)
     return 1;
   }
 
+  if (is_fixed) {
     // auto or auto:<NUM>
+    *is_fixed = 0;
+  }
+
   if (!strncmp(scl, "auto:", 5)) {
     // Variable depending on a configuration
     maximum = scl[5] - '0';

src/nvim/sign.c

@@ -18,6 +18,7 @@
 #include "nvim/move.h"
 #include "nvim/screen.h"
 #include "nvim/syntax.h"
+#include "nvim/option.h"
 
 /// Struct to hold the sign properties.
 typedef struct sign sign_T;
@@ -727,14 +728,28 @@ void sign_mark_adjust(
 )
 {
   sign_entry_T *sign;           // a sign in a b_signlist
+  sign_entry_T *next;           // the next sign in a b_signlist
+  sign_entry_T *last = NULL;    // pointer to pointer to current sign
+  sign_entry_T **lastp = NULL;  // pointer to pointer to current sign
   linenr_T new_lnum;            // new line number to assign to sign
+  int is_fixed = 0;
+  int signcol = win_signcol_configured(curwin, &is_fixed);
 
   curbuf->b_signcols_max = -1;
+  lastp = &curbuf->b_signlist;
 
-  FOR_ALL_SIGNS_IN_BUF(curbuf, sign) {
+  for (sign = curbuf->b_signlist; sign != NULL; sign = next) {
+    next = sign->se_next;
     new_lnum = sign->se_lnum;
     if (sign->se_lnum >= line1 && sign->se_lnum <= line2) {
-      if (amount != MAXLNUM) {
+      if (amount == MAXLNUM && (!is_fixed || signcol >= 2)) {
+        *lastp = next;
+        if (next) {
+          next->se_prev = last;
+        }
+        xfree(sign);
+        continue;
+      } else {
         new_lnum += amount;
       }
     } else if (sign->se_lnum > line2) {
@@ -746,6 +761,9 @@ void sign_mark_adjust(
     if (sign->se_lnum >= line1 && new_lnum <= curbuf->b_ml.ml_line_count) {
       sign->se_lnum = new_lnum;
     }
+
+    last = sign;
+    lastp = &sign->se_next;
   }
 }
 

test/functional/ui/sign_spec.lua

@@ -264,6 +264,24 @@ describe('Signs', function()
         {0:~                                                    }|
                                                              |
       ]]}
+      -- line deletion deletes signs.
+      command('2d')
+      screen:expect([[
+        {1:>>}XX{2:  }{6:  1 }a                                          |
+        XX{1:>>}WW{6:  2 }^c                                          |
+        {2:      }{6:  3 }                                           |
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+                                                             |
+      ]])
     end)
 
     it('auto-resize sign column with minimum size (#13783)', function()