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.

1 files changed, 31 insertions, 10 deletions

diff --git a/src/nvim/option.c b/src/nvim/option.c
index ad0ccd9f15..0f6408c9d4 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -305,7 +305,10 @@ static char *(p_fcl_values[]) =       { "all", NULL };
 static char *(p_cot_values[]) =       { "menu", "menuone", "longest", "preview",
                                         "noinsert", "noselect", NULL };
 static char *(p_icm_values[]) =       { "nosplit", "split", NULL };
-static char *(p_scl_values[]) =       { "yes", "no", "auto", NULL };
+static char *(p_scl_values[]) =       { "yes", "no", "auto", "auto:1", "auto:2",
+  "auto:3", "auto:4", "auto:5", "auto:6", "auto:7", "auto:8", "auto:9",
+  "yes:1", "yes:2", "yes:3", "yes:4", "yes:5", "yes:6", "yes:7", "yes:8",
+  "yes:9", NULL };
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "option.c.generated.h"
@@ -7091,16 +7094,34 @@ int csh_like_shell(void)
   return strstr((char *)path_tail(p_sh), "csh") != NULL;
 }
 
-/// Return true when window "wp" has a column to draw signs in.
-bool signcolumn_on(win_T *wp)
+/// Return the number of requested sign columns, based on current
+/// buffer signs and on user configuration.
+int win_signcol_count(win_T *wp)
 {
-    if (*wp->w_p_scl == 'n') {
-      return false;
-    }
-    if (*wp->w_p_scl == 'y') {
-      return true;
-    }
-    return wp->w_buffer->b_signlist != NULL;
+  int maximum = 1, needed_signcols;
+  const char *scl = (const char *)wp->w_p_scl;
+
+  if (*scl == 'n') {
+    return 0;
+  }
+  needed_signcols = buf_signcols(wp->w_buffer);
+
+  // yes or yes
+  if (!strncmp(scl, "yes:", 4)) {
+    // Fixed amount of columns
+    return scl[4] - '0';
+  }
+  if (*scl == 'y') {
+    return 1;
+  }
+
+  // auto or auto:<NUM>
+  if (!strncmp(scl, "auto:", 5)) {
+    // Variable depending on a configuration
+    maximum = scl[5] - '0';
+  }
+
+  return MIN(maximum, needed_signcols);
 }
 
 /// Get window or buffer local options