fix(api): expose fg_indexed/bg_indexed in nvim_get_hl #39210

Problem: fg_indexed/bg_indexed were dropped from nvim_get_hl output due
to a wrong short_keys guard. HL_FG_INDEXED also wasn't cleared in
hl_blend_attrs, and HLATTRS_DICT_SIZE was too small.

Solution: Remove the short_keys guard, clear HL_FG_INDEXED in
hl_blend_attrs, bump HLATTRS_DICT_SIZE to 24, and clarify docs that
these flags mean rgb is an approximation of the cterm palette index.

3 files changed, 12 insertions, 13 deletions

diff --git a/src/nvim/api/vim.c b/src/nvim/api/vim.c
index aa3475ad76..9adc4914a8 100644
--- a/src/nvim/api/vim.c
+++ b/src/nvim/api/vim.c
@@ -144,7 +144,8 @@ DictAs(get_hl_info) nvim_get_hl(Integer ns_id, Dict(get_highlight) *opts, Arena
 /// @param val   Highlight definition map, accepts the following keys:
 ///                - altfont: boolean
 ///                - bg: color name or "#RRGGBB", see note.
-///                - bg_indexed: boolean (default false) If true, bg is a terminal palette index (0-255).
+///                - bg_indexed: boolean. If true, `bg` is an RGB approximation of `ctermbg`
+///                  (a palette index). UIs rendering cterm natively may prefer `ctermbg`.
 ///                - blend: integer between 0 and 100
 ///                - blink: boolean
 ///                - bold: boolean
@@ -156,7 +157,7 @@ DictAs(get_hl_info) nvim_get_hl(Integer ns_id, Dict(get_highlight) *opts, Arena
 ///                - default: boolean Don't override existing definition |:hi-default|
 ///                - dim: boolean
 ///                - fg: Color name or "#RRGGBB", see note.
-///                - fg_indexed: boolean (default false) If true, fg is a terminal palette index (0-255).
+///                - fg_indexed: boolean. Same as `bg_indexed`, for `fg` and `ctermfg`.
 ///                - font: GUI font name (string). Sets |highlight-font|. Use "NONE" to clear.
 ///                - force: boolean (default false) Update the highlight group even if it already exists.
 ///                - italic: boolean
diff --git a/src/nvim/highlight.c b/src/nvim/highlight.c
index be58fd9fc4..1d2bb3afd2 100644
--- a/src/nvim/highlight.c
+++ b/src/nvim/highlight.c
@@ -797,7 +797,7 @@ int hl_blend_attrs(int back_attr, int front_attr, bool *through)
       cattrs.rgb_sp_color = -1;
     }
 
-    cattrs.rgb_ae_attr &= ~HL_BG_INDEXED;
+    cattrs.rgb_ae_attr &= ~(HL_FG_INDEXED | HL_BG_INDEXED);
   }
 
   // Check if we should preserve background transparency
@@ -956,8 +956,8 @@ Dict hl_get_attr_by_id(Integer attr_id, Boolean rgb, Arena *arena, Error *err)
 void hlattrs2dict(Dict *hl, Dict *hl_attrs, HlAttrs ae, bool use_rgb, bool short_keys)
 {
   hl_attrs = hl_attrs ? hl_attrs : hl;
-  assert(hl->capacity >= HLATTRS_DICT_SIZE);  // at most 16 items
-  assert(hl_attrs->capacity >= HLATTRS_DICT_SIZE);  // at most 16 items
+  assert(hl->capacity >= HLATTRS_DICT_SIZE);  // at most 24 items
+  assert(hl_attrs->capacity >= HLATTRS_DICT_SIZE);  // at most 24 items
   int mask = use_rgb ? ae.rgb_ae_attr : ae.cterm_ae_attr;
 
   if (mask & HL_INVERSE) {
@@ -1039,14 +1039,12 @@ void hlattrs2dict(Dict *hl, Dict *hl_attrs, HlAttrs ae, bool use_rgb, bool short
       PUT_C(*hl, short_keys ? "sp" : "special", INTEGER_OBJ(ae.rgb_sp_color));
     }
 
-    if (!short_keys) {
-      if (mask & HL_FG_INDEXED) {
-        PUT_C(*hl, "fg_indexed", BOOLEAN_OBJ(true));
-      }
+    if (mask & HL_FG_INDEXED) {
+      PUT_C(*hl, "fg_indexed", BOOLEAN_OBJ(true));
+    }
 
-      if (mask & HL_BG_INDEXED) {
-        PUT_C(*hl, "bg_indexed", BOOLEAN_OBJ(true));
-      }
+    if (mask & HL_BG_INDEXED) {
+      PUT_C(*hl, "bg_indexed", BOOLEAN_OBJ(true));
     }
   } else {
     if (ae.cterm_fg_color != 0) {
diff --git a/src/nvim/highlight_defs.h b/src/nvim/highlight_defs.h
index b682105196..0460fbb829 100644
--- a/src/nvim/highlight_defs.h
+++ b/src/nvim/highlight_defs.h
@@ -181,4 +181,4 @@ typedef struct {
 #define COLOR_ITEM_INITIALIZER { .attr_id = -1, .link_id = -1, .version = -1, \
                                  .is_default = false, .link_global = false }
 
-enum { HLATTRS_DICT_SIZE = 20, };
+enum { HLATTRS_DICT_SIZE = 24, };