4 files changed, 89 insertions, 2 deletions
diff --git a/src/nvim/option.c b/src/nvim/option.c
index 4157d28894..97f31b4754 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -3183,6 +3183,13 @@ ambw_end:
     if (check_opt_strings(*varp, p_scl_values, false) != OK) {
       errmsg = e_invarg;
     }
+    // When changing the 'signcolumn' to or from 'number', recompute the
+    // width of the number column if 'number' or 'relativenumber' is set.
+    if (((*oldval == 'n' && *(oldval + 1) == 'u')
+         || (*curwin->w_p_scl == 'n' && *(curwin->w_p_scl + 1) =='u'))
+        && (curwin->w_p_nu || curwin->w_p_rnu)) {
+      curwin->w_nrwidth_line_count = 0;
+    }
   } else if (varp == &curwin->w_p_fdc || varp == &curwin->w_allbuf_opt.wo_fdc) {
     // 'foldcolumn'
     if (check_opt_strings(*varp, p_fdc_values, false) != OK) {
diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index e9df68f657..92a34dfc42 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -7400,9 +7400,17 @@ int number_width(win_T *wp)
     ++n;
   } while (lnum > 0);
 
-  /* 'numberwidth' gives the minimal width plus one */
-  if (n < wp->w_p_nuw - 1)
+  // 'numberwidth' gives the minimal width plus one
+  if (n < wp->w_p_nuw - 1) {
     n = wp->w_p_nuw - 1;
+  }
+
+  // If 'signcolumn' is set to 'number' and there is a sign to display, then
+  // the minimal width for the number column is 2.
+  if (n < 2 && (wp->w_buffer->b_signlist != NULL)
+      && (*wp->w_p_scl == 'n' && *(wp->w_p_scl + 1) == 'u')) {
+    n = 2;
+  }
 
   wp->w_nrwidth_width = n;
   return n;
diff --git a/src/nvim/sign.c b/src/nvim/sign.c
index ab5d04d39b..ffe51287c5 100644
--- a/src/nvim/sign.c
+++ b/src/nvim/sign.c
@@ -881,6 +881,17 @@ int sign_undefine_by_name(const char_u *name)
   return OK;
 }
 
+static void may_force_numberwidth_recompute(buf_T *buf, int unplace)
+{
+  FOR_ALL_TAB_WINDOWS(tp, wp)
+    if (wp->w_buffer == buf
+        && (wp->w_p_nu || wp->w_p_rnu)
+        && (unplace || wp->w_nrwidth_width < 2)
+        && (*wp->w_p_scl == 'n' && *(wp->w_p_scl + 1) == 'u')) {
+      wp->w_nrwidth_line_count = 0;
+    }
+}
+
 /// List the signs matching 'name'
 static void sign_list_by_name(char_u *name)
 {
@@ -935,6 +946,10 @@ int sign_place(
   }
   if (lnum > 0) {
     redraw_buf_line_later(buf, lnum);
+
+    // When displaying signs in the 'number' column, if the width of the
+    // number column is less than 2, then force recomputing the width.
+    may_force_numberwidth_recompute(buf, false);
   } else {
     EMSG2(_("E885: Not possible to change sign %s"), sign_name);
     return FAIL;
@@ -964,6 +979,13 @@ int sign_unplace(int sign_id, char_u *sign_group, buf_T *buf, linenr_T atlnum)
     redraw_buf_line_later(buf, lnum);
   }
 
+  // When all the signs in a buffer are removed, force recomputing the
+  // number column width (if enabled) in all the windows displaying the
+  // buffer if 'signcolumn' is set to 'number' in that window.
+  if (buf->b_signlist == NULL) {
+    may_force_numberwidth_recompute(buf, true);
+  }
+
   return OK;
 }
 
diff --git a/src/nvim/testdir/test_signs.vim b/src/nvim/testdir/test_signs.vim
index f89095ec5d..9d1146453a 100644
--- a/src/nvim/testdir/test_signs.vim
+++ b/src/nvim/testdir/test_signs.vim
@@ -1796,6 +1796,56 @@ func Test_sign_numcol()
   redraw!
   call assert_equal("=>  1 01234", s:ScreenLine(1, 1, 11))
 
+  " Test displaying signs in the number column with width 1
+  call sign_unplace('*')
+  call append(1, "abcde")
+  call append(2, "01234")
+  " Enable number column with width 1
+  set number numberwidth=1 signcolumn=auto
+  redraw!
+  call assert_equal("3 01234", s:ScreenLine(3, 1, 7))
+  " Place a sign and make sure number column width remains the same
+  sign place 20 line=2 name=sign1
+  redraw!
+  call assert_equal("=>2 abcde", s:ScreenLine(2, 1, 9))
+  call assert_equal("  3 01234", s:ScreenLine(3, 1, 9))
+  " Set 'signcolumn' to 'number', make sure the number column width increases
+  set signcolumn=number
+  redraw!
+  call assert_equal("=> abcde", s:ScreenLine(2, 1, 8))
+  call assert_equal(" 3 01234", s:ScreenLine(3, 1, 8))
+  " Set 'signcolumn' to 'auto', make sure the number column width is 1.
+  set signcolumn=auto
+  redraw!
+  call assert_equal("=>2 abcde", s:ScreenLine(2, 1, 9))
+  call assert_equal("  3 01234", s:ScreenLine(3, 1, 9))
+  " Set 'signcolumn' to 'number', make sure the number column width is 2.
+  set signcolumn=number
+  redraw!
+  call assert_equal("=> abcde", s:ScreenLine(2, 1, 8))
+  call assert_equal(" 3 01234", s:ScreenLine(3, 1, 8))
+  " Disable 'number' column
+  set nonumber
+  redraw!
+  call assert_equal("=>abcde", s:ScreenLine(2, 1, 7))
+  call assert_equal("  01234", s:ScreenLine(3, 1, 7))
+  " Enable 'number' column
+  set number
+  redraw!
+  call assert_equal("=> abcde", s:ScreenLine(2, 1, 8))
+  call assert_equal(" 3 01234", s:ScreenLine(3, 1, 8))
+  " Remove the sign and make sure the width of the number column is 1.
+  call sign_unplace('', {'id' : 20})
+  redraw!
+  call assert_equal("3 01234", s:ScreenLine(3, 1, 7))
+  " When the first sign is placed with 'signcolumn' set to number, verify that
+  " the number column width increases
+  sign place 30 line=1 name=sign1
+  redraw!
+  call assert_equal("=> 01234", s:ScreenLine(1, 1, 8))
+  call assert_equal(" 2 abcde", s:ScreenLine(2, 1, 8))
+
+  sign unplace * group=*
   sign undefine sign1
   set signcolumn&
   set number&