fix(highlight): add create param in nvim_get_hl

runtime/doc/api.txt

@@ -966,6 +966,8 @@ nvim_get_hl({ns_id}, {*opts})                                  *nvim_get_hl()*
                  • id: (integer) Get a highlight definition by id.
                  • link: (boolean, default true) Show linked group name
                    instead of effective definition |:hi-link|.
+                 • create: (boolean, default true) When highlight group
+                   doesn't exist create it.
 
     Return: ~
         Highlight groups as a map from group name to a highlight definition

runtime/lua/vim/_meta/api.lua

@@ -1193,6 +1193,8 @@ function vim.api.nvim_get_current_win() end
 ---              • id: (integer) Get a highlight definition by id.
 ---              • link: (boolean, default true) Show linked group name
 ---                instead of effective definition `:hi-link`.
+---              • create: (boolean, default true) When highlight group
+---                doesn't exist create it.
 --- @return table<string,any>
 function vim.api.nvim_get_hl(ns_id, opts) end
 

runtime/lua/vim/_meta/api_keysets.lua

@@ -126,6 +126,7 @@ error('Cannot require a meta file')
 --- @field id? integer
 --- @field name? string
 --- @field link? boolean
+--- @field create? boolean
 
 --- @class vim.api.keyset.highlight
 --- @field bold? boolean

src/nvim/api/keysets.h

@@ -181,6 +181,7 @@ typedef struct {
   Integer id;
   String name;
   Boolean link;
+  Boolean create;
 } Dict(get_highlight);
 
 typedef struct {

src/nvim/api/vim.c

@@ -96,6 +96,7 @@ Integer nvim_get_hl_id_by_name(String name)
 ///                 - name: (string) Get a highlight definition by name.
 ///                 - id: (integer) Get a highlight definition by id.
 ///                 - link: (boolean, default true) Show linked group name instead of effective definition |:hi-link|.
+///                 - create: (boolean, default true) When highlight group doesn't exist create it.
 ///
 /// @param[out] err Error details, if any.
 /// @return Highlight groups as a map from group name to a highlight definition map as in |nvim_set_hl()|,

src/nvim/highlight_group.c

@@ -1569,7 +1569,13 @@ Dictionary ns_get_hl_defs(NS ns_id, Dict(get_highlight) *opts, Arena *arena, Err
   Boolean link = GET_BOOL_OR_TRUE(opts, get_highlight, link);
   int id = -1;
   if (HAS_KEY(opts, get_highlight, name)) {
-    id = syn_check_group(opts->name.data, opts->name.size);
+    Boolean create = GET_BOOL_OR_TRUE(opts, get_highlight, create);
+    id = create ? syn_check_group(opts->name.data, opts->name.size)
+                : syn_name2id_len(opts->name.data, opts->name.size);
+    if (id == 0 && !create) {
+      Dictionary attrs = ARRAY_DICT_INIT;
+      return attrs;
+    }
   } else if (HAS_KEY(opts, get_highlight, id)) {
     id = (int)opts->id;
   }

test/functional/api/highlight_spec.lua

@@ -439,6 +439,15 @@ describe('API: get highlight', function()
     eq('Highlight id out of bounds', pcall_err(meths.get_hl, 0, { name = 'Test set hl' }))
   end)
 
+  it('nvim_get_hl with create flag', function()
+    eq({}, nvim("get_hl", 0, {name = 'Foo', create = false}))
+    eq(0, funcs.hlexists('Foo'))
+    meths.get_hl(0, {name = 'Bar', create = true})
+    eq(1, funcs.hlexists('Bar'))
+    meths.get_hl(0, {name = 'FooBar'})
+    eq(1, funcs.hlexists('FooBar'))
+  end)
+
   it('can get all highlights in current namespace', function()
     local ns = get_ns()
     meths.set_hl(ns, 'Test_hl', { bg = '#B4BEFE' })