decoration: split out "decoration" from "extmark" module

Decorations will only grow more complex. move the to a separate
file, so that extmark.c remains about extmarks.

src/nvim/decoration.h

@@ -0,0 +1,71 @@
+#ifndef NVIM_DECORATION_H
+#define NVIM_DECORATION_H
+
+#include "nvim/pos.h"
+#include "nvim/buffer_defs.h"
+#include "nvim/extmark_defs.h"
+
+// actual Decoration data is in extmark_defs.h
+
+typedef struct {
+  char *text;
+  int hl_id;
+} VirtTextChunk;
+
+typedef kvec_t(VirtTextChunk) VirtText;
+#define VIRTTEXT_EMPTY ((VirtText)KV_INITIAL_VALUE)
+
+struct Decoration
+{
+  int hl_id;  // highlight group
+  VirtText virt_text;
+  // TODO(bfredl): style, signs, etc
+  bool shared;  // shared decoration, don't free
+};
+
+typedef struct {
+  int start_row;
+  int start_col;
+  int end_row;
+  int end_col;
+  int attr_id;
+  VirtText *virt_text;
+  bool virt_text_owned;
+} HlRange;
+
+typedef struct {
+  MarkTreeIter itr[1];
+  kvec_t(HlRange) active;
+  buf_T *buf;
+  int top_row;
+  int row;
+  int col_until;
+  int current;
+  VirtText *virt_text;
+} DecorState;
+
+typedef struct {
+  NS ns_id;
+  bool active;
+  LuaRef redraw_start;
+  LuaRef redraw_buf;
+  LuaRef redraw_win;
+  LuaRef redraw_line;
+  LuaRef redraw_end;
+  LuaRef hl_def;
+  int hl_valid;
+} DecorProvider;
+
+EXTERN kvec_t(DecorProvider) decor_providers INIT(= KV_INITIAL_VALUE);
+EXTERN DecorState decor_state INIT(= { 0 });
+
+#define DECORATION_PROVIDER_INIT(ns_id) (DecorProvider) \
+                                 { ns_id, false, LUA_NOREF, LUA_NOREF, \
+                                   LUA_NOREF, LUA_NOREF, LUA_NOREF, \
+                                   LUA_NOREF, -1 }
+
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "decoration.h.generated.h"
+#endif
+
+#endif  // NVIM_DECORATION_H