signs: support multiple columns #9295

closes #990
closes #9295

- Support for multiple auto-adjusted sign columns.
  With this change, having more than one sign on a line, and with the
  'auto' setting on 'signcolumn', extra columns will shown automatically
  to accomodate all the existing signs.

  For example, suppose we have this view:

   5147             }
   5148
   5149             return sign->typenr;
   5150         }
   5151     }
   5152     return 0;
   5153 }
   5154

  We have GitGutter installed, so it tells us about modified lines that
  are not commmited. So let's change line 5152:

     5147             }
     5148
     5149             return sign->typenr;
     5150         }
     5151     }
   ~ 5152     return 0;
     5153 }
     5154

  Now we add a mark over line 5152 using 'ma' in normal mode:

      5147             }
      5148
      5149             return sign->typenr;
      5150         }
      5151     }
  a ~ 5152     return 0;
      5153 }
      5154

  Previously, Vim/Nvim would have picked only one of the signs,
  because there was no support for having multiple signs in a line.

- Remove signs from deleted lines.
  Suppose we have highlights on a group of lines and we delete them:

   +     6 use std::ops::Deref;
   --+   7 use std::borrow::Cow;
   --+   8 use std::io::{Cursor};
         9 use proc_macro2::TokenStream;
        10 use syn::export::ToTokens;
   --+  11 use std::io::Write;
   >>   12 use std::ops::Deref;

  Without this change, these signs will momentarily accumulate in
  the sign column until the plugins wake up to refresh them.

  + --+ --+ --+ >>  6

  Discussion: It may be better to extend the API a bit and allow this
  to happen for only certain types of signs. For example, VIM marks
  and vim-gitgutter removal signs may want to be presreved, unlike
  line additions and linter highlights.

- 'signcolumn': support 'auto:NUM' and 'yes:NUM' settings
- sort signs according to id, from lowest to highest. If you have
  git-gutter, vim-signature, and ALE, it would appear in this order:
  git-gutter - vim-signature - ALE.
- recalculate size before screen update
- If no space for all signs, prefer the higher ids (while keeping the
  rendering order from low to high).
- Prevent duplicate signs. Duplicate signs were invisible to the user,
  before using our extended non-standard signcolumn settings.
- multi signcols: fix bug related to wrapped lines.
  In wrapped lines, the wrapped parts of a line did not include the extra
  columns if they existed. The result was a misdrawing of the wrapped
  parts. Fix the issue by:
    1. initializing the signcol counter to 0 when we are on a wrap boundary
    2. allowing for the draw of spaces in that case.

3 files changed, 10 insertions, 2 deletions

diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index c7e247133c..361cb3da5c 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -5403,10 +5403,14 @@ A jump table for the options with a short description can be found at |Q_op|.
 						*'signcolumn'* *'scl'*
 'signcolumn' 'scl'	string	(default "auto")
 			local to window
-	Whether or not to draw the signcolumn. Valid values are:
+	When and how to draw the signcolumn. Valid values are:
 	   "auto"   	only when there is a sign to display
+	   "auto:[1-9]" resize to accommodate multiple signs up to the
+	                given number (maximum 9), e.g. "auto:4"
 	   "no"	    	never
 	   "yes"    	always
+	   "yes:[1-9]"  always, with fixed space for signs up to the given
+	                number (maximum 9), e.g. "yes:3"
 
 
 			*'smartcase'* *'scs'* *'nosmartcase'* *'noscs'*
diff --git a/runtime/doc/quickref.txt b/runtime/doc/quickref.txt
index da064ab89b..d3d9303d3c 100644
--- a/runtime/doc/quickref.txt
+++ b/runtime/doc/quickref.txt
@@ -857,7 +857,7 @@ Short explanation of each option:		*option-list*
 'showtabline'	  'stal'    tells when the tab pages line is displayed
 'sidescroll'	  'ss'	    minimum number of columns to scroll horizontal
 'sidescrolloff'   'siso'    min. nr. of columns to left and right of cursor
-'signcolumn'	  'scl'	    when to display the sign column
+'signcolumn'	  'scl'	    when and how to display the sign column
 'smartcase'	  'scs'     no ignore case when pattern has uppercase
 'smartindent'	  'si'	    smart autoindenting for C programs
 'smarttab'	  'sta'     use 'shiftwidth' when inserting <Tab>
diff --git a/runtime/doc/vim_diff.txt b/runtime/doc/vim_diff.txt
index d3ac0ba613..30d7e972c3 100644
--- a/runtime/doc/vim_diff.txt
+++ b/runtime/doc/vim_diff.txt
@@ -193,11 +193,15 @@ Options:
   'listchars' local to window
   'pumblend' pseudo-transparent popupmenu
   'scrollback'
+  'signcolumn' supports up to 9 dynamic/fixed columns
   'statusline' supports unlimited alignment sections
   'tabline' %@Func@foo%X can call any function on mouse-click
   'wildoptions' `pum` flag to use popupmenu for wildmode completion
   'winhighlight' window-local highlights
 
+Signs:
+  Signs are removed if the associated line is deleted.
+
 Variables:
   |v:event|
   |v:exiting|