decorations: allow nvim_set_hl to break existing links

also add `default` flag to NOT break existing links/defs

src/nvim/api/vim.c

@@ -212,6 +212,9 @@ Dictionary nvim__get_hl_defs(Integer ns_id, Error *err)
 /// @param ns_id number of namespace for this highlight
 /// @param name highlight group name, like ErrorMsg
 /// @param val highlight definiton map, like |nvim_get_hl_by_name|.
+///            in addition the following keys are also recognized:
+///              `default`: don't override existing definition,
+///                         like `hi default`
 /// @param[out] err Error details, if any
 ///
 /// TODO: ns_id = 0, should modify :highlight namespace
@@ -249,7 +252,7 @@ void nvim_set_hl_ns(Integer ns_id, Error *err)
   // event path for redraws caused by "fast" events. This could tie in with
   // better throttling of async events causing redraws, such as non-batched
   // nvim_buf_set_extmark calls from async contexts.
-  if (!updating_screen && !ns_hl_changed) {
+  if (!provider_active && !ns_hl_changed) {
     multiqueue_put(main_loop.events, on_redraw_event, 0);
   }
   ns_hl_changed = true;

src/nvim/decoration.h

@@ -58,6 +58,7 @@ typedef struct {
 
 EXTERN kvec_t(DecorProvider) decor_providers INIT(= KV_INITIAL_VALUE);
 EXTERN DecorState decor_state INIT(= { 0 });
+EXTERN bool provider_active INIT(= false);
 
 #define DECORATION_PROVIDER_INIT(ns_id) (DecorProvider) \
                                  { ns_id, false, LUA_NOREF, LUA_NOREF, \

src/nvim/highlight.c

@@ -149,22 +149,22 @@ int hl_get_syn_attr(int ns_id, int idx, HlAttrs at_en)
   }
 }
 
-static ColorKey colored_key(NS ns_id, int syn_id)
-{
-  return (ColorKey){ .ns_id = (int)ns_id, .syn_id = syn_id };
-}
-
 void ns_hl_def(NS ns_id, int hl_id, HlAttrs attrs, int link_id)
 {
   DecorProvider *p = get_provider(ns_id, true);
+  if ((attrs.rgb_ae_attr & HL_DEFAULT)
+      && map_has(ColorKey, ColorItem)(ns_hl, ColorKey(ns_id, hl_id))) {
+    return;
+  }
   int attr_id = link_id > 0 ? -1 : hl_get_syn_attr(ns_id, hl_id, attrs);
   ColorItem it = { .attr_id = attr_id,
                    .link_id = link_id,
-                   .version = p->hl_valid };
-  map_put(ColorKey, ColorItem)(ns_hl, colored_key(ns_id, hl_id), it);
+                   .version = p->hl_valid,
+                   .is_default = (attrs.rgb_ae_attr & HL_DEFAULT) };
+  map_put(ColorKey, ColorItem)(ns_hl, ColorKey(ns_id, hl_id), it);
 }
 
-int ns_get_hl(NS ns_id, int hl_id, bool link)
+int ns_get_hl(NS ns_id, int hl_id, bool link, bool nodefault)
 {
   static int recursive = 0;
 
@@ -176,7 +176,7 @@ int ns_get_hl(NS ns_id, int hl_id, bool link)
   }
 
   DecorProvider *p = get_provider(ns_id, true);
-  ColorItem it = map_get(ColorKey, ColorItem)(ns_hl, colored_key(ns_id, hl_id));
+  ColorItem it = map_get(ColorKey, ColorItem)(ns_hl, ColorKey(ns_id, hl_id));
   // TODO(bfredl): map_ref true even this?
   bool valid_cache = it.version >= p->hl_valid;
 
@@ -218,11 +218,16 @@ int ns_get_hl(NS ns_id, int hl_id, bool link)
 
     it.attr_id = fallback ? -1 : hl_get_syn_attr((int)ns_id, hl_id, attrs);
     it.version = p->hl_valid-tmp;
-    map_put(ColorKey, ColorItem)(ns_hl, colored_key(ns_id, hl_id), it);
+    it.is_default = attrs.rgb_ae_attr & HL_DEFAULT;
+    map_put(ColorKey, ColorItem)(ns_hl, ColorKey(ns_id, hl_id), it);
+  }
+
+  if (it.is_default && nodefault) {
+    return -1;
   }
 
   if (link) {
-    return it.attr_id >= 0 ? -1 : it.link_id;
+    return it.attr_id >= 0 ? 0 : it.link_id;
   } else {
     return it.attr_id;
   }
@@ -307,7 +312,7 @@ void update_window_hl(win_T *wp, bool invalid)
   //
   // haha, theme engine go brrr
   int normality = syn_check_group((const char_u *)S_LEN("Normal"));
-  int ns_attr = ns_get_hl(-1, normality, false);
+  int ns_attr = ns_get_hl(-1, normality, false, false);
   if (ns_attr > 0) {
     // TODO(bfredl): hantera NormalNC and so on
     wp->w_hl_attr_normal = ns_attr;
@@ -793,6 +798,8 @@ HlAttrs dict2hlattrs(Dictionary dict, bool use_rgb, int *link_id, Error *err)
       { "undercurl", HL_UNDERCURL },
       { "italic", HL_ITALIC },
       { "reverse", HL_INVERSE },
+      { "default", HL_DEFAULT },
+      { "global", HL_GLOBAL },
       { NULL, 0 },
     };
 

src/nvim/highlight_defs.h

@@ -22,6 +22,8 @@ typedef enum {
   HL_NOCOMBINE       = 0x80,
   HL_BG_INDEXED    = 0x0100,
   HL_FG_INDEXED    = 0x0200,
+  HL_DEFAULT       = 0x0400,
+  HL_GLOBAL        = 0x0800,
 } HlAttrFlags;
 
 /// Stores a complete highlighting entry, including colors and attributes
@@ -188,13 +190,16 @@ typedef struct {
   int ns_id;
   int syn_id;
 } ColorKey;
+#define ColorKey(n, s) (ColorKey) { .ns_id = (int)(n), .syn_id = (s) }
 
 typedef struct {
   int attr_id;
   int link_id;
   int version;
+  bool is_default;
 } ColorItem;
-#define COLOR_ITEM_INITIALIZER { .attr_id = -1, .link_id = -1, .version = -1 }
+#define COLOR_ITEM_INITIALIZER { .attr_id = -1, .link_id = -1, \
+                                 .version = -1, .is_default = false }
 
 
 #endif  // NVIM_HIGHLIGHT_DEFS_H

src/nvim/screen.c

@@ -173,7 +173,9 @@ static bool provider_invoke(NS ns_id, const char *name, LuaRef ref,
   Error err = ERROR_INIT;
 
   textlock++;
+  provider_active = true;
   Object ret = nlua_call_ref(ref, name, args, true, &err);
+  provider_active = false;
   textlock--;
 
   if (!ERROR_SET(&err)

src/nvim/syntax.c

@@ -7563,14 +7563,13 @@ static void syn_unadd_group(void)
 /// @see syn_attr2entry
 int syn_id2attr(int hl_id)
 {
-  struct hl_group     *sgp;
-
   hl_id = syn_get_final_id(hl_id);
-  int attr = ns_get_hl(-1, hl_id, false);
+  struct hl_group *sgp = &HL_TABLE()[hl_id - 1];  // index is ID minus one
+
+  int attr = ns_get_hl(-1, hl_id, false, sgp->sg_set);
   if (attr >= 0) {
     return attr;
   }
-  sgp = &HL_TABLE()[hl_id - 1];  // index is ID minus one
   return sgp->sg_attr;
 }
 
@@ -7583,7 +7582,6 @@ int syn_id2attr(int hl_id)
 int syn_get_final_id(int hl_id)
 {
   int count;
-  struct hl_group     *sgp;
 
   if (hl_id > highlight_ga.ga_len || hl_id < 1)
     return 0;                           /* Can be called from eval!! */
@@ -7593,19 +7591,20 @@ int syn_get_final_id(int hl_id)
    * Look out for loops!  Break after 100 links.
    */
   for (count = 100; --count >= 0; ) {
+    struct hl_group *sgp = &HL_TABLE()[hl_id - 1];  // index is ID minus one
+
     // ACHTUNG: when using "tmp" attribute (no link) the function might be
     // called twice. it needs be smart enough to remember attr only to
     // syn_id2attr time
-    int check = ns_get_hl(-1, hl_id, true);
+    int check = ns_get_hl(-1, hl_id, true, sgp->sg_set);
     if (check == 0) {
-      return 0;  // how dare! it broke the link!
+      return hl_id;  // how dare! it broke the link!
     } else if (check > 0) {
       hl_id = check;
       continue;
     }
 
 
-    sgp = &HL_TABLE()[hl_id - 1];  // index is ID minus one
     if (sgp->sg_link == 0 || sgp->sg_link > highlight_ga.ga_len) {
       break;
     }

src/nvim/types.h

@@ -2,6 +2,7 @@
 #define NVIM_TYPES_H
 
 #include <stdint.h>
+#include <stdbool.h>
 
 // dummy to pass an ACL to a function
 typedef void *vim_acl_T;

test/functional/ui/decorations_spec.lua

@@ -27,6 +27,7 @@ describe('decorations providers', function()
       [9] = {reverse = true};
       [10] = {italic = true, background = Screen.colors.Magenta};
       [11] = {foreground = Screen.colors.Red, background = tonumber('0x005028')};
+      [12] = {foreground = tonumber('0x990000')};
     }
   end)
 
@@ -227,4 +228,77 @@ describe('decorations providers', function()
     ]]}
 
   end)
+
+  it('can break an existing link', function()
+    insert(mulholland)
+    local ns1 = setup_provider()
+
+    exec [[
+      highlight OriginalGroup guifg='#990000'
+      highlight link LinkGroup OriginalGroup
+    ]]
+
+    meths.buf_set_virtual_text(0, 0, 2, {{'- not red', 'LinkGroup'}}, {})
+    screen:expect{grid=[[
+      // just to see if there was an accident |
+      // on Mulholland Drive                  |
+      try_start(); {12:- not red}                  |
+      bufref_T save_buf;                      |
+      switch_buffer(&save_buf, buf);          |
+      posp = getmark(mark, false);            |
+      restore_buffer(&save_buf);^              |
+                                              |
+    ]]}
+
+    meths.set_hl(ns1, 'LinkGroup', {fg = 'Blue'})
+    meths.set_hl_ns(ns1)
+
+    screen:expect{grid=[[
+      // just to see if there was an accident |
+      // on Mulholland Drive                  |
+      try_start(); {4:- not red}                  |
+      bufref_T save_buf;                      |
+      switch_buffer(&save_buf, buf);          |
+      posp = getmark(mark, false);            |
+      restore_buffer(&save_buf);^              |
+                                              |
+    ]]}
+  end)
+
+  it("with 'default': do not break an existing link", function()
+    insert(mulholland)
+    local ns1 = setup_provider()
+
+    exec [[
+      highlight OriginalGroup guifg='#990000'
+      highlight link LinkGroup OriginalGroup
+    ]]
+
+    meths.buf_set_virtual_text(0, 0, 2, {{'- not red', 'LinkGroup'}}, {})
+    screen:expect{grid=[[
+      // just to see if there was an accident |
+      // on Mulholland Drive                  |
+      try_start(); {12:- not red}                  |
+      bufref_T save_buf;                      |
+      switch_buffer(&save_buf, buf);          |
+      posp = getmark(mark, false);            |
+      restore_buffer(&save_buf);^              |
+                                              |
+    ]]}
+
+    meths.set_hl(ns1, 'LinkGroup', {fg = 'Blue', default=true})
+    meths.set_hl_ns(ns1)
+    feed 'k'
+
+    screen:expect{grid=[[
+      // just to see if there was an accident |
+      // on Mulholland Drive                  |
+      try_start(); {12:- not red}                  |
+      bufref_T save_buf;                      |
+      switch_buffer(&save_buf, buf);          |
+      posp = getmark(mark, false^);            |
+      restore_buffer(&save_buf);              |
+                                              |
+    ]]}
+  end)
 end)