feat(colorcolchar): make the colorcolumn more flexible

This PR creates the ability to optionally decorate the colorcolumn(s) in
other ways.

Specifically it adds the ability to set:

  * The highlight group to highlight a colorcolumn with
  * A character to draw in a colorcolumn
  * whether the colorcolumn should mix its highlighting with the
    character in the column.

The new syntax for colorcolumn is:

set colorcolumn=[+|-]<num>[/<char>[/<hl_group>[/<flags>]]]

By default the char is ' ', and the hl_group is 'ColorColumn'

This PR does not change the existing semantics, just adds to them.

1 files changed, 16 insertions, 1 deletions

diff --git a/src/nvim/buffer_defs.h b/src/nvim/buffer_defs.h
index f01edd1ad2..dfcbb28c69 100644
--- a/src/nvim/buffer_defs.h
+++ b/src/nvim/buffer_defs.h
@@ -93,6 +93,21 @@ typedef uint64_t disptick_T;  // display tick type
 #include "nvim/syntax_defs.h"
 #include "nvim/terminal.h"
 
+typedef enum {
+  kColorcolBehind = 1
+} colorcol_flags_T;
+
+// Structure to define data associated with a colorcolumn.
+typedef struct {
+  int col;        // The column number to highlight.
+  int ch;         // The character to draw in the column.
+
+  char* syn_name; // The highlight group name. Must be free'd.
+  int syn_attr;   // The attribute. Will be set before a redraw.
+
+  int flags;      // Additional flags
+} colorcol_T;
+
 // The taggy struct is used to store the information about a :tag command.
 typedef struct taggy {
   char *tagname;                // tag name
@@ -1335,7 +1350,7 @@ struct window_S {
   uint32_t w_p_wbr_flags;           // flags for 'winbar'
   uint32_t w_p_fde_flags;           // flags for 'foldexpr'
   uint32_t w_p_fdt_flags;           // flags for 'foldtext'
-  int *w_p_cc_cols;                 // array of columns to highlight or NULL
+  colorcol_T *w_p_cc_cols;          // array of columns to highlight or NULL
   uint8_t w_p_culopt_flags;         // flags for cursorline highlighting
   long w_p_siso;                    // 'sidescrolloff' local value
   long w_p_so;                      // 'scrolloff' local value